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Until today, more than 100 years after its first description in Italy, the highly pathogenic avian influenza virus (HPAIV) has not lost its fearsome character for wild birds, poultry and humans. On the contrary, the number of outbreaks with high casualty rates in wild birds and poultry has multiplied in recent years and cases of zoonotic infections are also increasingly reported from HPAI endemic areas. The epidemiology of these infections is complex and also involves surface water and possibly sediments of shallow standing waters, which could play a role as a vector medium and/or virus reservoir. The goal of this project was to expand current knowledge of the influence of water on the spread of AIV. As part of this project, we were able to ...
1. ...improve AIV detection methods using real time RT-PCR in terms of sensitivity and breadth of viruses detected. In addition, we succeeded in economizing the procedure so that fewer resources are required and results are obtained faster (publication I: [173]).
2. ...develop an ultrafiltration-based enrichment method for AIV from surface water and evaluate it with field samples from HPAI outbreak areas in wild bird habitats (Wadden Sea coast of Schleswig-Holstein) and previously unaffected regions (Antarctic Weddell Sea) (publication II: [174]). Furthermore, protocols for testing different environmental sample matrices for AIV screening were tested and compared to results of passive monitoring by dabbing diseased or dead wild birds. AIV was detected in more than half (61%) of 44 water samples. We received additional sediment samples from 36 of the 44 water samples. In 18 of 36 of the sediments tested, as well as in 4.16% of 1705 fecal samples tested AIV was detected. However, the studies of the environmental samples mostly yielded only generic AIV detections, with viral loads in the range of the detection limit. This massively hampered further investigations for sub- and pathotyping. In contrast, 79.41% of 68 samples from passive monitoring showed high to very high HPAIV viral loads which also allowed sub- and pathotyping.
3. ...demonstrate in animal experiments that even very low titers (0.1 TCID50 ml-1) of HPAI viral infectivity in water can induce productive infection in susceptible but clinically largely resistant mallard ducks (publication III: [175]). Furthermore, we were able to develop evidence that there is a difference in virus spread that depends on the type of (contaminated) water source. This means that infections on poultry farms with inverted or nipple drinkers may follow a different course than infections in the wild, which are mediated via larger surface waters.
Overall, the results of this project highlight the important role of surface and drinking water, as well as aquatic sediments, in the spread of AIV. The methods developed here for AIV detection extend the possibilities for surveillance of AIV infections; however, passive remains superior to active surveillance of HPAIV infections in several aspects. Examination of various environmental samples did not yield a significant advantage in terms of an early warning system that would indicate the presence or spread of HPAIV in wild bird habitats prior to the occurrence of lethal infections in wild birds.
Bacillus subtilis has been extensively used as a microbial cell factory for industrial enzymes due to its excellent capacities for protein secretion and large-scale fermentation. This bacterium is also an attractive host for biopharmaceutical production. However, the secretion potential of this organism is not fully utilized yet, mostly due to a limited understanding of critical rearrangements in the membrane proteome upon high-level protein secretion. Recently, it was shown that bottlenecks in heterologous protein secretion can be resolved by genome minimization. Here, we present for the first time absolute membrane protein concentrations of a genome-reduced B. subtilis strain (“midiBacillus”) expressing the immunodominant Staphylococcus aureus antigen A (IsaA). We quantitatively characterize the membrane proteome adaptation of midiBacillus during production stress on the level of molecules per cell for more than 400 membrane proteins, including determination of protein concentrations for ∼61% of the predicted transporters. We demonstrate that ∼30% of proteins with unknown functions display a significant increase in abundance, confirming the crucial role of membrane proteins in vital biological processes. In addition, our results show an increase of proteins dedicated to translational processes in response to IsaA induction. For the first time reported, we provide accumulation rates of a heterologous protein, demonstrating that midiBacillus secretes 2.41 molecules of IsaA per minute. Despite the successful secretion of this protein, it was found that there is still some IsaA accumulation occurring in the cytosol and membrane fraction, leading to a severe secretion stress response, and a clear adjustment of the cell’s array of transporters. This quantitative dataset offers unprecedented insights into bioproduction stress responses in a synthetic microbial cell.
Orthohantaviruses are rodent-borne pathogens distributed all over the world, which do not cause visible disease in their reservoir host. Puumala orthohantavirus (PUUV) causes most human hantavirus disease cases in Europe and is transmitted by the bank vole (Clethrionomys glareolus). Hantaviruses have a tri-segmented genome consisting of the large (L) segment, coding for the RNA-dependent RNA polymerase (RdRP), the medium (M) segment, encoding the glycoproteins, and the small (S) segment. The S-segment contains two major overlapping open reading frames (ORF) coding for the nucleocapsid (N) protein and a non-structural (NSs) protein, a putative type I interferon (IFN-I) antagonist. To date, pathogenesis and reservoir host adaptation of hantaviruses are poorly understood due to missing adequate cell culture and animal models.
In contrast to previous studies, in this work, data from spring and summer 2019 indicated a high vole abundance, a high PUUV prevalence in voles and high human incidence for some endemic regions in Germany, but elsewhere values were low to moderate. Regional and local human health institutions need to be aware about the heterogeneous distribution of human PUUV infection risk.
For a better understanding of virus-host associations, two novel cell lines from bank voles and common voles each were generated and their susceptibility and replication capacities for a variety of zoonotic and non-zoonotic viruses were analyzed. The PUUV strain Vranica/Hällnäs showed efficient replication in a new bank vole kidney cell line, but not in four other cell lines of bank and common voles. Vice versa, Tula orthohantavirus (TULV) replicated in the kidney cell line of common voles, but was hampered in its replication in other cell lines. Several viruses, such as Cowpox virus, Vaccinia virus, Rift Valley fever virus, and Encephalomyocarditis virus 1 replicated in all four cell lines. West Nile virus, Usutu virus, Sindbis virus and Tick-borne encephalitis virus replicated only in a part of the cell lines. These results indicate a tissue or species specific tropism for many of the tested viruses and the potential value of vole cell lines to address such questions in detail.
Using one of these new cell lines, the first German PUUV strains were isolated from bank voles caught in the highly endemic region around Osnabrück. Complete genomes were determined by target-enrichment-mediated high-throughput sequencing from original lung tissue, after isolation and after additional passaging in VeroE6 cells and a bank vole-derived kidney cell line. Different single amino acid substitutions were observed in the RdRP of the two stable PUUV isolates. The PUUV strain isolated on VeroE6 cells showed a lower titer when propagated on bank vole cells compared to VeroE6 cells. Additionally, glycoprotein precursor (GPC)-derived virus-like particles of a German PUUV strain from the same region allowed the generation of monoclonal antibodies that reacted with the isolated PUUV strains.
To investigate the role of PUUV and other vole-borne hantavirus NSs proteins, the evolution of the NSs and N encoding sequences was investigated by a field study in bank voles and the NSs sequences were characterized in vitro for their inhibitory effect on the human interferon-β promoter. Analysis of blood and lung samples of 851 bank voles trapped during 2010-2014 in Baden-Wuerttemberg and North Rhine-Westphalia resulted in detection of 27.8% PUUV-specific antibody positive bank voles, whereas in 22.3% PUUV-specific RNA was detected. In the hantavirus outbreak years 2010 and 2012 PUUV prevalence in bank voles was higher compared to 2011, 2013 and 2014. Sequences of the S segment of all positive bank voles showed amino acid and nucleotide sequence types of the NSs-ORF with temporal and/or local variation, whereas the N-ORF was highly conserved. One sequence type persisted over the whole observation period in both regions. The NSs coding sequence was highly divergent among regional bank vole populations in the outbreak year 2012.
Transfection experiments resulted in the detection of different products of the NSs-ORF of PUUV, TULV, Prospect Hill and Khabarovsk orthohantaviruses, due to translation initiation at different methionine codons along the coding sequence. Using luciferase reporter assays, the NSs proteins of PUUV, TULV, Prospect Hill and Khabarovsk orthohantaviruses showed inhibition of IFN-I induction of up to 70%, whereas Sin Nombre and Andes orthohantavirus NSs proteins showed a reduced effect compared to the other NSs proteins. The first 20 amino acids of the N-terminal region of PUUV NSs were found to be crucial for IFN-I promoter inhibition.
In conclusion, the newly established cell lines, antibodies, reporter assays and PUUV isolates are highly valuable tools for future hantavirus research. The activity of PUUV NSs protein in human cells contributes to our understanding of virus-host interactions and highlights the importance of corresponding future reservoir host studies. Hantavirus surveillance studies showed the necessity for timely information of the potential human PUUV infection risk to public health institutions in endemic areas to initiate appropriate actions.
LPAIV H9N2 and HPAIV H5N8 clade 2.3.4.4 viruses have been frequently isolated from domestic and wild birds in Germany and they are endemic in poultry worldwide. H9N2 is known to donate gene segments to other AIV with high case fatality rate in humans (e.g. H5N1, H7N9). Similarly, H5N8 devastated poultry worldwide since 2014 and has been recently isolated from humans. Therefore, it is important to understand the genetic predisposition for adaptation of H9N2 and H5N8 AIV in poultry and mammals. In the first publication, we focused on the variable hemagglutinin cleavage site (HACS) of European and Non-European H9N2 viruses, since the HACS is a main virulence determinant of AIV in birds. We found a preferential substitution of non-basic amino acids (G, A, N, S, D, K) in the HACS at position 319 of European H9N2 viruses compared to non-European H9N2 viruses. Recombinant viruses carrying different non-basic amino acids in the HACS modulated replication in vitro. While these non-basic amino acids did not affect virulence or transmission in chickens, they modulated virulence and replication in turkeys. Moreover, H9N2 viruses with non-basic amino acids in the HACS were able to replicate in mammalian brain cells for multiple cycles even without trypsin. In the second publication, we addressed the question whether reassortment between two recent German H9N2 and H5N8 clade 2.3.4.4. B viruses is possible and analysed the impact on virus fitness in mammals and birds. We found that H9N2 PB1 and NP segments were not compatible to generate infectious H5N8 viruses and this incompatibility was due to mutations outside the packaging region. However, H9N2 NS alone or in combination with PB2 and PA significantly increased replication of H5N8 in human cells. Moreover, H9N2 PB2, PA and/or NS segments increased virulence of H5N8 in mice. Interestingly, in chickens, reassortment with H9N2 gene segments, particularly NS, partially or fully impaired chicken-to-chicken transmission. These results indicate that the evolution of H9N2/H5N8 reassortants showing high virulence for mammals is unlikely to occur in chickens. In the third publication, we focused on the NS1 protein of different HPAIV H5N8 clade 2.3.4.4 viruses from 2013 to 2019 and studied the impact of its C-terminus (CTE) variation on virus fitness in chickens and ducks. Our findings revealed a preferential selection for a certain NS1 CTE length in 2.3.4.4. H5N8 clade A (237 aa) and B (217 aa) viruses over the common length of 230 aa. Indeed, the NS1 CTE can affect virus virulence and pathogenesis in a species and virus clade dependent manner. In chickens, although there was no impact on virulence, NS1 CTE of H5N8-A and H5N8-B, regardless of the length, have evolved towards higher efficiency to block the IFN response. In ducks, NS1 CTE contributed to efficient transmission, replication and high virulence of H5N8-B. In the fourth publication, we assessed the impact of variable length of NS1 on H5N8 virus replication in human cells and virulence in mice. We showed that NS1 of H5N8-B virus unlike the vast majority of NS1 of AIV, shared preferences for short NS1 similar to human and zoonotic influenza viruses. This virus (i) was able to efficiently block IFN and apoptosis induction which might be the first steps for efficient adaptation to human cells and (ii) without prior adaptation replicated at higher levels and was more virulent in mice than H5N8-A. The virulence of the latter virus increased after shortening the NS1 similar to H5N8-B virus. Therefore, it is conceivable that truncation in NS1 is a determinant for adaptation of H5N8 in mammals irrespective of its impact on virus fitness in poultry. Findings in this dissertation indicated that HA mutations in the European H9N2 and NS1 variations in H5N8 viruses play a role in virus fitness in poultry and/or mammals. These results improve our current understanding for AIV adaptation and are useful to assess the potential of these viruses to infect mammals.
Responses of bovine and human neutrophils to members of the Mycobacterium tuberculosis complex
(2023)
PMN are one of the most important cells of the innate immune system and are responsible for fast clearance of invading pathogens in most circumstances. The role of human PMN during mycobacterial infection have been widely studied. Nevertheless, there are contradicting results regarding their role in protection or pathology during TB. Similar studies focusing on bovine PMN and their role in M. bovis infection remain understudied. Also, not much is known about attenuation of M. tb in cattle and responses of PMN to this MTBC member.
The major aims of this study were to i) gain insights into bovine PMN biology and the cellular processes triggered by challenge with virulent mycobacteria and to ii) find out whether interspecies differences result in different outcomes upon in vitro challenge. In the first part of the work, a new isolation method for bovine PMN from whole blood was developed. Human and bovine PMN have different buoyant properties and hence need to be isolated using different procedures. The magnetic isolation method developed within this thesis is robust and results in very good yields of highly pure, viable bovine PMN populations. This is extremely advantageous and indispensable for downstream functional assays that are required to be performed on a single day.
The second goal of this study was to compare and contrast the functional differences between bovine and human PMN upon BCG infection. The findings reveal for the first time that human PMN phagocytose more BCG in comparison to bovine counterparts. Non-opsonized bacteria were internalized via the lectin-like C-domain, require cholesterol and an active cytoskeleton in human PMN, whereas opsonized bacteria entered cells via the CR3 and, in particular, CD11b. It remains unresolved why bovine PMN reacted differently, notably phagocytosis remained unaltered, to various treatments, including blocking monoclonal antibodies to CD11b and chemical inhibitors altering the cell membrane. Nonetheless, the increased uptake of BCG by human PMN correlates to more potent response of these cells in functional assays in comparison to bovine PMN. No PMN intrinsic differences were found in the basal cholesterol content. Comparative assays with the virulent strains would be essential in order to generalize these observations.
The third aim was to investigate the responses of bovine PMN to BCG, M. tb and M. bovis. While there was no difference in uptake between BCG and M. tb, serum opsonized BCG was taken up at a higher amount. This finding suggests differential binding of bacterial epitopes to host cell receptors which modulates mycobacteria uptake. However, between the virulent strains M. tb and M. bovis, the human-adapted bacillus was phagocytosed at a higher rate which hints towards the possibility of rapid recognition and clearance of M. tb in bovine host thereby possibly preventing pathology. The release of selective cytokines by PMN post infection with the virulent strains offers baseline information relevant for processes that probably occur in vivo. This work for the first time provides insights into responses of bovine PMN to mycobacteria in a two-tier approach: by cross-species analysis of PMN responses to selected mycobacterium and by head-to-head analysis of bovine PMN to animal-adapted and human-adapted mycobacteria.
As a prospect for future research in bovine PMN biology in the context of mycobacterial infection, it would be highly advantageous to compare the subcellular localization of M. tb and M. bovis in bovine PMN using confocal and/or electron microscopy. This analysis would confer proof on attachment or internalization of mycobacteria by PMN and identify the features of the mycobacteria-containing compartments. Also, in-depth investigations of additional entry pathways for the pathogen in bovine cells would be informative for unlocking downstream cell signaling events. In addition, PMN viability studies will be meaningful particularly in bovine PMN challenged with M. bovis and M. tb, given the impact of death patterns on tissue pathology. Current results and follow up studies will contribute to the understanding of the roles of PMN in controlling elimination or growth of M. bovis and M. tb in cattle.
Coding constraints imposed by the very small genome sizes of negative-strand RNA viruses (NSVs) have led to the development of numerous strategies that increase viral protein diversity, enabling the virus to both establish a productive viral replication cycle and effectively control the host antiviral response. Arenaviruses are no exception to this, and previous findings have demonstrated that the nucleoprotein (NP) of the highly pathogenic Junín virus (JUNV) exists as three additional N-terminally truncated isoforms of 53 kD (NP53kD), 47 kD (NP47kD), and 40 kD (NP40kD). The two smaller isoforms (i.e. NP47kD and NP40kD) have been characterized as products of caspase cleavage, which appears to serve a decoy function to inhibit apoptosis induction. However, whether they have additional functions in the viral replication cycle remains unknown. Further, the origin and function of NP53kD has not yet been described.
In order to first identify the mechanism responsible for production of the NP53kD variant, a possible role of additional caspase cleavage sites was first excluded using a site mutagenesis approach. Subsequently, alanine mutagenesis was then used to identify a region responsible for NP53kD production. As a result, three methionine residues were identified within the characterized sequence segment of NP, linking the production of NP53kD to an alternative in-frame translation initiation. Further site-directed mutagenesis of the previously identified putative in-frame methionine codons (i.e. M78, M80 and M100) finally led to the identification of translation initiation at M80 as being predominantly responsible for the production of NP53kD. Once the identity of all three NP isoforms was known, it was then of further interest to more deeply characterize their functional roles. Consistent with the N-terminal domain containing RNA binding and homotrimerization motifs that are relevant for the viral RNA synthesis process, it could be demonstrated that all three truncated NP isoforms lost the ability to support viral RNA synthesis in a minigenome assay. However, they also did not interfere with viral RNA synthesis by full-length NP, nor did they affect the ability of the matrix protein Z to inhibit viral RNA synthesis. Moreover, it was observed that loss of the oligomerization motifs in the N-terminus also affected the subcellular localization of all three NP isoforms, which were no longer localized in discrete perinuclear inclusion bodies, but rather showed a diffuse distribution throughout the cytoplasm, with the smallest isoform NP40kD also being able to enter the nucleus. Surprisingly, the 3'-5' exonuclease function of NP, which is associated with the C-terminal domain and plays a role in inhibiting interferon induction by digestion of double-stranded RNAs, was found to be retained only by the NP40kD isoform, despite that all three isoforms retained the associated domain. Finally, previous studies using transfected NP and chemical induction of apoptosis have suggested that cleavage of NP at the caspase motifs responsible for generating NP47kD and NP40kD plays a role in controlling activation of the apoptosis pathway. Therefore, to further characterize the connection between the generation of NP isoforms and the regulation of apoptosis in a viral context, recombinant JUNVs deficient in the respective isoforms were generated. Unlike infections with wild-type JUNV, mutations of the caspase cleavage sites resulted in the induction of caspases activation. Surprisingly, however, this was also the case for mutation of the alternate start codon responsible for NP53kD generation.
Taken together, the data from this study suggest a model whereby JUNV generates a pool of smaller NP isoforms with a predominantly cytoplasmic distribution. As a result of this altered localization, NP53kD appears to be able to serve as the substrate for further generation of NP47kD and NP40kD by caspase cleavage. Not only does this cleavage inhibit apoptosis induction during JUNV infection, it also results in a cytoplasmic isoform of NP that retains strong 3'-5' exonuclease activity (i.e. NP40kD) and thus may play an important role in preventing viral double-stranded RNA accumulation in the cytoplasm, where it can lead to activation of IFN signaling. Overall, such results emphasize the relevance of alternative protein isoforms in virus biology, and particularly in regulation of the host response to infection.
Ebolaviruses are zoonotic pathogens causing severe hemorrhagic fevers in humans
and non-human primates with high case fatality rates. In recent years, the number and
scope of outbreaks has increased, highlighting the importance of better understanding
the molecular aspects of ebolaviral infection and host cell interactions in order to be able to better control this virus.
To facilitate virus genome replication, transcription and protein expression,
ebolaviruses recruit and interact with specific host factors. These interactions play a key role in viral infection and influence virus survival and disease outcome. Based on a genome-wide siRNA screen, the three host factors CAD, NXF1 and UAP56 were
recently identified to be involved in ebolavirus genome replication and/or transcription
and/or mRNA-translation. However, mechanistical details of how these host factors
affect the ebolavirus lifecycle remained elusive.
In this thesis I analyzed the functional interactions between EBOV and these newly
identified host proteins in order to better understand the virus-host interface. To this
end I used siRNA knockdown as well as overexpression of these host proteins in
combination with different reverse-genetics based lifecycle modelling assays to
investigate the influence of CAD, NXF1 and UAP56 on individual aspects of the EBOV
lifecycle. Using these systems in relation with a host factor knockdown I was able to
show that the provision of pyrimidines by CAD plays an important role for both EBOV
genome replication and transcription, whereas NXF1 is predominantly required for
mRNA transport. I furthermore used immunofluorescence analysis to examine whether
these host factors are recruited by one or more EBOV proteins to inclusion bodies,
which represent physical sites of ebolavirus genome replication. During these
experiments, I was able to show that CAD and NXF1, and possibly also UAP56, are
recruited to EBOV inclusion bodies in order to fulfill their individual function for EBOV RNA synthesis or later steps in protein expression. Additionally, I was able to show that the uptake of NXF1 into NP-induced inclusion bodies is most likely mediated via the C-terminal domain of NP, and that the FG-repeat interaction domains of NXF1 are sufficient for recruitment. Further, my data indicate that RNA interaction of both NXF1 and NP is not required for this process, but rather important for exit of NXF1 from inclusion bodies. I therefore suggest that the viral mRNA is transferred in inclusionbodies from NP to NXF1, which leads to a rapid export of the NXF1 packed viral mRNA into the cytosol for mRNA translation.
The exact mechanism of how these host factors are recruited into inclusion bodies and whether they have similar functions in the lifecycle of other negative-sense RNA viruses still needs to be investigated. Nevertheless, this study increases our understanding of virus-host interaction of ebolaviruses, and thus helps to identify targets for the development of novel therapeutics against these viruses.
Abstract
DNA extraction and preservation bias is a recurring topic in DNA sequencing‐based microbial ecology. The different methodologies can lead to distinct outcomes, which has been demonstrated especially in studies investigating prokaryotic community composition. Eukaryotic microbes are ubiquitous, diverse, and increasingly a subject of investigation in addition to bacteria and archaea. However, little is known about how the choice of DNA preservation and extraction methodology impacts perceived eukaryotic community composition. In this study, we compared the effect of two DNA preservation methods and six DNA extraction methods on the community profiles of both eukaryotes and prokaryotes in phototrophic biofilms on seagrass (Zostera marina) leaves from the Baltic Sea. We found that, whereas both DNA preservation and extraction method caused significant bias in perceived community composition for both eukaryotes and prokaryotes, extraction bias was more pronounced for eukaryotes than for prokaryotes. In particular, soft‐bodied and hard‐shelled eukaryotes like nematodes and diatoms, respectively, were differentially abundant depending on the extraction method. We conclude that careful consideration of DNA preservation and extraction methodology is crucial to achieving representative community profiles of eukaryotes in marine biofilms and likely all other habitats containing diverse eukaryotic microbial communities.
Clostridioides difficile is the leading cause of antibiotic-associated diarrhea referring to infections of the gastrointestinal tract in the course of (broad-spectrum)antibiotic therapy. While antibiotic therapy, preferentially with fidaxomicin or vancomycin, often stops the acute infection, recurrence events due to remaining spores and biofilm-associated cells are observed in up to 20% of cases. Therefore, new antibiotics, which spare the intestinal microbiota and eventually clear infections with C. difficile are urgently required. In this light, the presented work aimed at the evaluation and characterization of three natural product classes, namely chlorotonils, myxopyronins and chelocardins, with respect to their antimicrobial activity spectrum under anaerobic conditions and their potential for the therapy of C. difficile infections. Briefly, compounds of all three classes were screened for their activity against a panel of anaerobic bacteria. Subsequently, the systemic effects of selected derivatives of each compound class were analyzed in C. difficile using a proteomics approach. Finally, appropriate downstream experiments were performed to follow up on hypotheses drawn from the proteomics datasets. Thereby, all three compound classes demonstrated significant activity against C. difficile. However, chelocardins similarly inhibited the growth of other anaerobes excluding chelocardins as antibiotic candidates for C. difficile infection therapy. In contrast, chlorotonils demonstrated significantly higher in vitro activity against C. difficile and close relatives compared to a small panel of other anaerobes. In addition, it could be shown that chlorotonils affect intracellular metal homeostasis as demonstrated in a multi-omics approach. The data led to speculate that chlorotonils eventually affect cobalt and selenate availability in particular. Moreover, a metaproteomics approach verified that oral chlorotonil treatment only marginally affected the intestinal microbiota of piglets on taxonomic and functional level. Furthermore, the proteome stress response of C. difficile 630 to myxopyronin B, which similarly showed elevated activity against C. difficile compared to a few other anaerobes, indicated that the antibiotic inhibited early toxin synthesis comparatively to fidaxomicin. Finally, evidence is provided that C. difficile 630 responds to dissipation of its membrane potential by production and accumulation of aromatic metabolites.
The anaerobic, gastrointestinal pathogen Clostridioides difficile can cause severe forms of enterocolitis which is mainly mediated by the toxins it produces. The RNA polymerase inhibitor Fidaxomicin is the current gold standard for the therapy of C. difficile infections due to several beneficial features including its ability to suppress toxin synthesis in C. difficile. In contrast to the Rifamycins, Fidaxomicin binds to the RNA polymerase switch region, which is also the binding site for Myxopyronin B. Here, serial broth dilution assays were performed to test the susceptibility of C. difficile and other anaerobes to Myxopyronin B, proving that the natural product is considerably active against C. difficile and that there is no cross-resistance between Fidaxomicin and Myxopyronin B in a Fidaxomicin-resistant C. difficile strain. Moreover, mass spectrometry analysis indicated that Myxopyronin B is able to suppress early phase toxin synthesis in C. difficile to the same degree as Fidaxomicin. Conclusively, Myxopyronin B is proposed as a new lead structure for the design of novel antibiotics for the therapy of C. difficile infections.
The anaerobic pathogen Clostridioides difficile is perfectly equipped to survive and persist inside the mammalian intestine. When facing unfavorable conditions C. difficile is able to form highly resistant endospores. Likewise, biofilms are currently discussed as form of persistence. Here a comprehensive proteomics approach was applied to investigate the molecular processes of C. difficile strain 630Δerm underlying biofilm formation. The comparison of the proteome from two different forms of biofilm-like growth, namely aggregate biofilms and colonies on agar plates, revealed major differences in the formation of cell surface proteins, as well as enzymes of its energy and stress metabolism. For instance, while the obtained data suggest that aggregate biofilm cells express both flagella, type IV pili and enzymes required for biosynthesis of cell-surface polysaccharides, the S-layer protein SlpA and most cell wall proteins (CWPs) encoded adjacent to SlpA were detected in significantly lower amounts in aggregate biofilm cells than in colony biofilms. Moreover, the obtained data suggested that aggregate biofilm cells are rather actively growing cells while colony biofilm cells most likely severely suffer from a lack of reductive equivalents what requires induction of the Wood-Ljungdahl pathway and C. difficile’s V-type ATPase to maintain cell homeostasis. In agreement with this, aggregate biofilm cells, in contrast to colony biofilm cells, neither induced toxin nor spore production. Finally, the data revealed that the sigma factor SigL/RpoN and its dependent regulators are noticeably induced in aggregate biofilms suggesting an important role of SigL/RpoN in aggregate biofilm formation.
Mussel farming, compared to marine finfish aquaculture, represents an environmentally friendly alternative for a high quality protein source and can at the same time be a measure to remove excess nutrients in eutrophic areas. As such, it is considered as a promising “blue growth” potential and promoted within the European Union. To expand mussel aquaculture, new regions have to be considered because there are multiple marine usages, and spatial limitations occur in coastal areas. The brackish Baltic Sea might be considered for expansion of mussel aquaculture. This study focusses on estimated production potential, economic profitability and nutrient remediation potential of mussel farming at different salinities. Four experimental mussel farms were set up along the German Baltic coast at salinities ranging from 7 to 17 psu. Collected growth data was used to calibrate and validate a Dynamic Energy Budget model and to predict the potential mussel production at 12 sites along the German coast. The estimated production and nutrient removal was used to assess economic profitability, assuming two usages of the harvest: human consumption and mussel meal production. Measured mussel specific growth rates increased with salinity from 0.05 mm d–1 in Greifswald Bay to 0.11 mm d–1 in Kiel Fjord. Within 6 months, a 1-ha farm could produce from 1 t (Darss-Zingst-Bodden-Chain) to 51 t (Flensburg) fresh mussels and remove 1.1 to 27.7 kg P and 24.7 to 612.7 kg N, respectively. Mussel farms at sites west of Rostock at salinities >10 psu could produce 5 cm mussels within 18 months, but only farms at Flensburg, Eckernförde and Kiel Fjord became profitable at a farm size of 4 ha (160,000 m3) at current market prices of 2.2 € kg–1. Regardless of the farm size, none of the farm sites could operate profitable if fresh mussels were sold for animal feeding at sales price of 0.06 € kg–1. Yearly nutrient removal costs at a small-scale farm (1 ha) ranged between 162 € (Flensburg) and 4,018 € (Darss-Zingst-Bodden-Chain) kg–1 nitrogen, and 3,580 € and 88,750 € kg–1 phosphorus, respectively.
Reactive oxygen species (ROS) can damage all cellular macromolecules and also produce secondary reactive intermediates, like reactive electrophilic species (RES) that include quinones or aldehydes. Low molecular weight (LMW) thiols are small thiol-containing compounds that play essential roles in the defense against ROS and RES in all organisms. The best studied LMW thiol is the tripeptide glutathione (GSH). Firmicutes bacteria including Bacillus und Staphylococcus species have been recently discovered to utilize the redox buffer bacillithiol (BSH). LMW thiols function as redox buffers to maintain the reduced state of the cytoplasm. Under conditions of oxidative stress, LMW thiols also react with protein thiols to form mixed LMW thiol – protein disulfides, termed S-thiolations, as major protection mechanism. Investigating the role of BSH in oxidative stress response and ROS-induced S-thiolations in Firmicutes bacteria was one subject of this PhD thesis. Specifically, the regulatory mechanisms and post-translational thiol-modifications in response to NaOCl stress were studied in the model bacterium for low-GC Gram-positive bacteria Bacillus subtilis. The transcriptome profile after NaOCl stress was indicative of disulfide stress and overlapped strongly with the response to diamide. NaOCl stress caused induction of the thiol- and oxidative stress-specific Spx, CtsR, PerR and OhrR regulons. Thiol redox proteomics identified only few NaOCl-sensitive proteins with reversible thiol-oxidations. Using mass spectrometry, eleven proteins were identified that were oxidized to mixed BSH protein disulfides (S-bacillithiolated) in B. subtilis cells after NaOCl-exposure. Methionine synthase MetE is the most abundant S-bacillithiolated protein in B. subtilis and other Bacillus species after NaOCl exposure. S-bacillithiolation of OhrR repressor leads to upregulation of the OhrA peroxiredoxin that confers together with BSH specific protection against NaOCl. S-bacillithiolation of MetE, YxjG, PpaC, and SerA causes hypochlorite-induced methionine starvation as supported by the induction of the S-box regulon. To further assess the conservation of targets for S-bacillithiolations in other Firmicutes bacteria, we studied the S-bacillithiolomes of Bacillus megaterium, Bacillus pumilus, Bacillus amyloliquefaciens, and Staphylococcus carnosus under NaOCl stress conditions. In total, 54 S-bacillithiolated proteins were identified, including 29 unique proteins and 8 conserved proteins involved in amino acid and cofactor biosynthesis, nucleotide metabolism, translation, protein quality control, redox and antioxidant functions. Together our data support a major role of BSH redox buffer in redox control and thiol protection of conserved and essential proteins against irreversible oxidation by S-bacillithiolations in Firmicutes bacteria. In response to ROS and RES, bacteria also activate the expression of antioxidant and detoxification enzymes, such as catalases, peroxidases, thiol-dependent peroxiredoxins and other specific oxidoreductases to detoxify ROS and RES. These defense mechanisms are often controlled by redox-sensitive transcription factors. B. subtilis encodes redox-sensing MarR-type regulators belonging to the OhrR and DUF24-families that are conserved among bacteria. Hence, we were further interested in this PhD thesis to study at the molecular and structural level the redox-sensing mechanisms of novel redox-sensing MarR/DUF24-type regulators in B. subtilis. We have characterized the regulatory mechanisms of HypR, YodB and CatR that sense and respond to hypochlorite, diamide and quinones stress. HypR is the first DUF24-family regulator whose crystal structure was resolved. HypR senses specifically disulfide stress and controls positively expression of the flavin oxidoreductase HypO after NaOCl and diamide stress. HypR resembles a 2-Cys-type regulator with a reactive nucleophilic N-terminal Cys14 and a second C-terminal Cys49. Besides HypR, B. subtilis encodes further MarR/DUF24-family members including the paralogous YodB and CatR repressors that sense quinones and diamide. YodB controls the azoreductase AzoR1, the nitroreductase YodC, and the Spx regulator. YodB resembles a 2-Cys-type MarR/DUF24-family regulator with three Cys residues (Cys6, Cys101, and Cys108) that form intermolecular disulfides in vivo under oxidative stress. YodB and its paralog CatR were further identified as repressors of the catDE operon encoding a catechol-2,3-dioxygenase that also contributes to quinone resistance. Although CatR is a 1-Cys-type regulator, our data showed that CatR also forms intermolecular disulfide in response to diamide and quinones in vitro. Thus, HypR, YodB and CatR are controlled by 2-Cys-type thiol-disulfide redox switches to sense disulfide and RES stress conditions, and to control specific RES detoxification enzymes.
This work focuses the glycoprotein H of PrV which was analysed by structure-based functional analyses by targeted site-directed mutagenesis. Disulfid bridges were introduced at specific sites and the effects on the fusion mechanism investigated. A revertant was obtained and characterised during the studies, as well as chimeric glycoprotein H proteins were constructed, combining the different domains of the glycoproteins Hs of PrV and HSV1.
Lyssaviruses, the causative agents of rabies, are a long-known threat for animals and humans. To date, terrestrial rabies still accounts for tens of thousands of human deaths annually, notwithstanding ambitious vaccination campaigns targeting susceptible dog and wildlife populations that act as reservoirs for the prototypic rabies virus. Moreover, the continuing discovery of newly emerging virus species in hitherto unconcerned chiropteran hosts and geographic regions drive the expansion of the Lyssavirus genus by unveiling its actual variety, host range and distribution.In this work, the genetic diversity of three distinct lyssaviruses, namely EBLV-1, KBLV and RABV, was elucidated by in-depth genomic analyses to provide further insight into lyssavirus evolution. The generation of full-genome sequences from primarily bat-associated Danish EBLV-1 samples significantly increased the number of available Danish EBLV-1 genome sequences while phylogenetic and phylogeographic analysis revealed a stronger phylogeographic structure for the cluster A1 of the sublineage EBLV-1a than it was postulated in previous studies. In addition, the acquisition of a nearly complete genome sequence for the Kotalahti bat lyssavirus provided the basis for the classification of this putative new lyssavirus species as a recognized member of the genus. Furthermore, phylogenetic analysis revealed the affiliation of KBLV to a group of Myotis-associated lyssaviruses giving a deeper insight into the shared evolutionary history of lyssaviruses co-evolving with particular bat species. Moreover, a deep-sequencing approach was utilized to assess the high genetic diversity of vaccine virus populations, uncovering three independent patterns of single nucleotide variants (SNVs) that became selected in ERA-related vaccine-induced cases. However, no apparent influence of the genetic diversity of vaccine viruses on microevolutionary processes like a potential reversion to virulence or a species-specific adaptation of the vaccine virus strains could be detected, leaving the question for the cause of rabies induction in the affected animals unanswered. Lastly, the successful implementation of a hybridization capturing system for the generation of full-genome sequences and deep-sequencing variant analyses of RABV and KBLV samples was demonstrated for a diagnostic bait set, highlighting the versatility and consistency of this approach to assess the genetic spectrum of known and novel lyssavirus species while setting the basis for its application and optimization in upcoming projects.In conclusion, as shown by the studies in this work, the investigation of lyssavirus genomes at the sub-consensus, full-genome and population level remains crucial to assess the complexity of lyssavirus evolution, as it provides an indispensable source of information to cover the diversity of the genus and understand evolutionary dynamics on a long-term and microevolutionary scale.
The following work is describing the development of two innovative biosensors for the detection of biologically relevant molecules in the field of ecology and medical diagnostics. Biosensors have the particularity to possess a biological partner which recognizes the target molecule and a physical detection method responsible for the transformation of this biological interaction into measurable information. In the present case, both biosensors are designed following the same strategy and use a recombinant produced human receptor as biological partner and the surface plasmon resonance (SPR) technique to transform the biological interaction in quantitative information. The progesterone biosensor is aimed to detect and quantify substances with affinity to the human progesterone receptor. The recent discoveries that some chemicals present in low quantities in the ecosystem called endocrine disrupting chemicals (EDCs) have a negative impact on the aquatic life fitness raised concerns about the effects of these same molecules to the human health. In order to assess the effects of these EDCs, the use of classical analytical detection methods like high performance liquid chromatography (HPLC) or gas chromatography (GC) is not sufficient as these techniques only quantify a defined molecule without giving information about its biological activity. By integrating a recombinant human progesterone receptor, the progesterone biosensor can determine the biological activity of an unknown molecule or of a mixture of molecules in a real sample. In this work, two different yeasts – one methylotrophic (Hansenula polymorpha) and one non-methylotrophic (Arxula adeninivorans) - were selected as host for the recombinant protein production and their performances were compared. Different purification strategies were assayed and the binding activity of the purified progesterone receptor was then confirmed by enzyme like receptor assay (ELRA) and SPR. This led to the design of a first version of the biosensor with the immobilization of a progesterone-BSA ligand to the surface of a SPR chip and the use of a progesterone receptor mixed with the target molecule as sample. This competitive assay format was successfully utilized with a commercial progesterone-BSA ligand as target molecule and the next step will be the adaptation of this biosensor for real samples measurements. The HER-2 biosensor was developed as an answer for one of the most critical issue in the field of breast cancer diagnostics. In approximately 30 % of cancer cases, the transmembrane protein HER-2 can be found in large amount at the surface of the carcinoma cells and these cases are known to be particularly aggressive. Based on the amount of HER-2 protein at the surface of the cells, the pathologists established a scale with four levels to adapt the treatment to each patient. Although effective therapies have been developed to treat the HER-2 positive breast cancer, one of the major challenges remains the classification of breast sample in this scale as the only accepted determination methods are immunohistochemistry (IHC) and fluorescent in situ hybridization (FISH) which are only qualitative. In this work, a biosensor has been designed to quantify the amount of the HER-2 protein in a crude cell extract from a breast cancer tissue sample. To achieve this, the strategy is to utilize an antibody specifically targeted against the HER-2 protein and bound to a SPR chip. As the development of this biosensor necessitated the use of large amount of purified HER-2 protein, it was decided to produce recombinant full-length HER-2 in two different yeasts and to purify it by chromatography. This recombinant protein production required particular attention due to the membrane localization of HER-2. The structural integrity of the recombinant protein was confirmed by Western Blot and ELISA and different antibodies were bound to SPR chips in order to detect the HER-2 protein. After finding the conditions giving an optimal SPR signal, a protocol was developed to extract native HER-2 from breast tissue sample and the biosensor was assayed with this crude cell extract.
Hepatitis E virus (HEV) is emerging worldwide as a zoonotic pathogen that has remained largely undetected for decades, if not centuries. Its enormous success can be attributed to the wide range of host species, which can transmit the virus to humans, depending on the viral genotype. As a result, HEV is likely to remain a challenge even when the remaining hepatitis viruses (HAV, HBV, HCV), which are transmitted exclusively between humans, are under control. Although millions of HEV infections occur each year, little is known about this puzzling pathogen. One major issue in HEV research is the lack of reliable model systems. Established animal models are inefficient, expensive, or simply not representative of human HEV. On the other hand, cell culture systems are limited by the slow growth of the virus and inefficient replication and infection. The aim of this work is to with deepen the understanding of zoonotic HEV in animal hosts in Germany. For this purpose, a molecular and phylogenetic characterization of HEV sequences from rabbits and swine was conducted. A novel subtype of the zoonotic genotype HEV-3 was identified in a rabbit sample, further emphasizing the role of rabbits as HEV host species and possible reservoir of zoonotic HEV infections in Germany. On the other hand, a molecular biological screening of pigs and wild boars in Mecklenburg-Western Pomerania indicates a wide range of HEV-3 subtypes circulating in swine in north-east Germany. Furthermore, an optimized replicon system was established in order to enable characterization of various HEV sequences by reverse genetics. As a proof of concept, two rabbit HEV derived replicons were compared with two established, cell culture adapted HEV strains. The influence of different regions of the nonstructural protein on HEV replication was determined and quantified. In particular, a system was established, to reproducibly compare different strains and genotypes. This refined replicon system will enable the characterization of further HEV sequences and thus expand the knowledge on the determinants of the viral life cycle.