Annual Conference 2025 of the Association for General and Applied Microbiology - Jahrestagung 2025 der Vereinigung für Allgemeine und Angewandte Mikrobiologie

Prof. Dr.

Heme-degrading bacteria from blood-sucking organisms

Open topics

Many ectoparasites that frequently change hosts, especially hematophagous parasites, often serve as vectors for pathogenic microorganisms and thus contribute to their transport and spread. The microbiome of these parasites can also contain pathogenic bacteria that can be transmitted on contact with the host. Especially in times of progressive climate change, which favors the spread of such parasitic vectors for pathogens, the precise research and associated prevention of such vector-borne infectious diseases and their bacteria is essential.Since heme is a major component of the blood meal of these hematophagous parasites, the aim of this work is to investigate the different microbiomes of such parasites for heme-degrading bacteria, since these bacteria have to survive in an environment with a lot of, partly also toxic, free heme. The degradation and thus the potential utilization of heme also plays an important role for these pathogens in the case of infectious transmission into the bloodstream of a host.The microbiome was extracted from leeches, ticks, mosquitoes and other bloodsuckers using various methods and individual bacterial strains were isolated and analyzed using Maldi Tof. Subsequently, these bacterial strains were examined for their ability to grow in heme-containing M9 medium with heme as the only carbon source.Some bacteria showed no growth at all in this medium, others showed slightly increased growth with a slight but significant difference to the control without heme, which could indicate the utilization of heme. Genomic and proteomic studies of these strains will follow in the future to better elucidate the degradation and utilization pathway.

Poster

Prof

Proteomics analysis of biofilm matrix of Stenotrophomonas maltophilia in single and mixed species biofiolms

Introduction : Stenotrophomonas maltophilia is a gram-negative bacterium constitutively occurring in man but has drawn more concern due to its notable adaptability and opportunistic nosocomial infections especially in immunocompromised patients. As an opportunistic pathogen, this organism has the propensity to form biofilms rendering it highly resilient to antibacterial measures and host immune system. Biofilms are three-dimensional structures of multicellular aggregates encased in a self-made matrix of biofilm associated EPS (extracellular polymeric substances) wherein understanding the protein content is imperative in the study of biofilm"s pathobiology.Objectives: So far little is known what peptides are secreted by the pathogen S. maltophilia in single and mixed species biofilms and what they paly role in biofilm formation and pathogenicity.Materials and methods:This study focuses on the identification of proteins secreted into the biofilm matrix by S. maltophilia in single or mixed species biofilms. Biofilms were grown under static conditions for 48 hours. Biofilm matrix was isolated using the NaCl method as proposed in ref: Pan, Xiangliang, et al. (2010). After a purification step using the C18 spin Columns, a liquid chromatography (LC) mass spectrometry (MS) tandem system was employed for protein identification[IA1] .Results: Our results showed that the majority of proteins identified were exported hypothetical protein, secreted proteases, ton B receptors and adhesins. Most of the ton b receptors have been associated with iron acquisition and the some of the identified proteases have been inked to virulence. Conclusion: We have successfully established a method for the isolation and identification of peptides from the biofilm matrix of S. maltophilia. Our Proteomics data showed that the majority of identified proteins are extracellular proteases, receptors involved in iron acquisition , adhesins for cell adhesion and exported hypotheitical proteins.We are currently analyzing the proteomics profile of S. maltophilia planctonic cultures and S. maltophilia in a mixed species biofilm with P. aeruginosa.

Prof.

Modulations of the microbiome from Atlantic salmon epidermal mucus after changes in diet and stressing conditions

The development of sustainable aquaculture is a prerequisite to minimize environmental impacts associated to aquaculture industry [1]. The replacement of fishmeal for plant-based diets is a key element to improve sustainability and fish welfare [2]. A balanced diet is important to counteract environmental changing circumstances that cause stress to fish [3]. The interpretation of the bacterial communities residing in the mucosal surfaces has been very poorly studied, and could act as a promising tool to use as welfare indicator during the fish production cycle [4, 5], since the epithelial mucus acts as a barrier against external stressors.The first aim of the study is to determine whereas environmental stressors cause changes in the microbiome from the mucosal surfaces of the fish. The second aim investigates whereas a microalgae-based diet modulates the microbiome from the epidermal mucus, and promotes a positive health condition during stressing conditions.Each tank from the Recirculating Aquaculture System contained 20 Atlantic salmon. Water parameters were constant over the trial period. Swabs were collected before the start of the trial (T0) and after eight weeks of feeding the experimental diets (T1). Three different diets were formulated: Group A was fed with commercial feed; Group B feed contained cortisol (100 mg kg-1) as a stressor factor; Group C feed contained Schizochytrium sp. and cortisol. Eight fish were sampled per tank to collect one swabs from the epithelial mucus. Sample DNA was extracted and sent for the amplification of the V3-V4 16S rRNA gene region. Illumina MiSeq sequencing produced a total of 19,339,640 reads. DADA2 workflow for Amplicon Sequence Variants (ASV) prediction was used for data processing and analysis [6]. Relative abundances, diversity index and PERMANOVA were calculated.The microbiome from the mucosal surface of the fish from all treatments was composed mainly by Proteobacteria, Bacteroidetes, Actinobacteria and Verrucomicrobia. Shannon diversity index was significantly different between T0 and T1 from the control group A. At T1, diversity was significantly different between group A and C, and between group B and C. Microbial diversity was significantly higher when fish was fed with microalgae, even under stressful conditions. The microbial diversity decreased after feeding the fish for 8 weeks with a commercial feed.We observed a positive response from the fish and its external mucosal microbiome to the diet with microalgae during stress conditions

Extraintestinal Escherichia coli employ the membrane protein RcrB to protect against reactive chlorine species

Members of the Escherichia coli species are remarkably diverse and comprise commensal, probiotic and pathogenic strains. While some pathogenic E. coli cause intestinal diseases, extraintestinal E. coli (ExPEC) can colonize and infect environments outside the gut, including the urinary tract. Upon entry of the urinary tract, ExPEC must counter a multitude of bactericidal host defense strategies, which require specialized genetic adaption for survival from this E. coli pathotype. For instance, ExPEC must defend highly antimicrobial oxidnts such as hypochlorous acid (HOCl), a potent reactive chlorine species (RCS) generated during neutrophil-mediated phagocytosis and by enzymes in uroepithelial cells to control bacterial colonization. The increasing rate of ExPEC infections in humans due to changing infection dynamics demonstrate the critical need for a better understanding of ExPEC pathogenesis, which is desperately needed to improve approaches for infection prevention and treatment given the rise in antibiotic resistance spreading among E. coli. Our lab has reported that members of the ExPEC pathotype are more resistant to RCS in vitro and to neutrophil-mediated phagocytosis when compared to non-pathogenic and enteropathogenic E. coli. We identified the defense system responsible for these phenotypes and characterized its regulation during RCS stress: the RcrR regulon consisting of the rcrARB genes is controlled by the RCS-sensing transcriptional repressor RcrR, which reversibly loses its repressor activity upon oxidation by RCS, resulting in de-repression of its downstream targets. Induced expression of RcrB, which we identified as a membrane protein, contributes significantly to ExPEC"s increased RCS resistance. We show that ExPEC cells that lack RcrB are characterized by elevated protein and DNA damage, indicating increased RCS influx into the cell. Moreover, RcrB quenches RCS in the media, which it does through select redox-active amino acids located on its periplasmic side. Overall, our data indicate that RcrB works as an RCS reductase, which is novel in the field. Thus, RcrB plays a crucial role for ExPEC in maintaining bacterial redox homeostasis in RCS-rich environments.

Open topics 1

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