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

Chair

Prof. , Dr.

Inside-out: Remodeling of gonococcal microcolonies due to changing pili interaction network

Microbial communities

Neisseria gonorrhoeae, the causative agent of one of the most common sexually transmitted diseases in humans, rapidly aggregates from single cells to microcolonies with thousands of cells. This process is facilitated by its type 4 pili (T4P). Driven by a tug-of-war between the T4P of neighboring cells, the bacteria are motile within the microcolony and from an interaction network. In the colony center this motility is highly restricted.In this study, we investigate how changes in the T4P interaction network lead to a global reconstruction of the whole microcolony and the dispersal of cells.To do so, we combine flow chamber-based microscopy and single-cell tracking with an agent-based dissipative-particle-dynamics model that allows the simulation and prediction of bacterial microcolony behaviour. In addition, we apply a direct cysteine-maleimide-based pili visualization protocol to investigate the piliation level of single cells with fluorescent microscopy.We show that after several hours of microcolony maturation, the inner motility-restricted core can become motile again. Like in a jet, highly motile cells flow from the center to the periphery and cause an eversion of the entire colony from the inside to the outside. Theoretical modeling predicts such spatio-temporal dynamics when the cell-cell interactions in the core are lower than interactions in the outer envelope of the colony. We argue that reduced growth resources in the center of the colony could result in fewer interactions between the cells. Indeed, direct visualization of T4P, shows that piliation is decreased in response to oxygen limitation, resulting in reduced T4P-mediated cell-cell interaction. Additionally, we find that dead cells that have accumulated in the center of the colony are expelled during the eversion and that large amounts of live and dead cells are shed throughout the eversion process into the environment.Overall, this study shows how small changes in the active pili interaction network of microcolonies can trigger global colony remodeling and the dispersal of cells.

Short lecture

Prof.

Prof., Dr.

The periodontal pathogen Tannerella forsythia thrives in the oral microbial community by means of peptidoglycan salvage

Periodontitis is an inflammatory disease leading to the destruction of the teeth-supporting tissue, ultimately causing tooth loss. Tannerella forsythia, an anaerobic, Gram-negative oral pathogen of the Bacteroidota phylum, is part of the red complex consortium of periodontal pathogens, strongly associated with the late stages of periodontitis progression. T. forsythia critically depends on co-habiting bacteria in the oral biofilm for the provision of nutrients [1]. Earlier axenic culturing studies revealed that the organism is auxotroph for N-acetylmuramic acid (MurNAc), which is an essential component of the bacterial peptidoglycan (PGN) cell walls. Later, whole genome sequencing revealed that the bacterium lacks the generally essential genes encoding the canonical MurA/MurB enzymes, required for the de novo synthesis of PGN precursors, thus rationalizing MurNAc auxotrophy. We showed that T. forsythia accepts soluble PGN-derived fragments as well as polymeric PGN as sources of exogenous MurNAc [2]. We discovered two, presumably periplasmic, unique exolytic β-N-acetylmuramidases (NamZ1 and NamZ2), which cleave exogenous PGN glycan sugar strands at the non-reducing ends, generating N-acetylglucosamine (GlcNAc)-MurNAc disaccharides and MurNAc, respectively [3]. Further, we identified two inner membrane transporters: AmpG, importing disaccharides generated by NamZ1 [3] and MurT, importing MurNAc generated by NamZ2 [4]. Metabolism of these sugars involves two intracellular MurNAc kinases, that were characterized and their crystal structures solved [5,6]. Our study unraveled a complex PGN salvage metabolism that is crucial for the oral pathogen T. forsythia to survive within the oral microbial community.Hottmann, I, Borisova, M, Schäffer, C, Mayer, C (2021) Microb Physiol 31(2):123-134.Mayer VMT, Tomek MB, Figl R, Borisova M, Hottmann I, Blaukopf M, Altmann F, Mayer C, Schäffer C (2020): BMC Microbiol. 20(1):352.Borisova M, Balbuchta K, Lovering A, Titz A, Mayer C (2022) J Bacteriol. 204(3):e0059721.Ruscitto A, Hottmann I, Stafford GP, Schaffer C, Mayer C, Sharma A (2016) J Bacteriol. 198(22):3119-3125.Hottmann I, Mayer VMT, Tomek MB, Friedrich V, Calvert MB, Titz A, Schäffer C, Mayer C (2018) Front Microbiol. 9:19.Stasiak AC, Gogler K, Borisova M, Fink P, Mayer C, Stehle T, Zocher, G (2023) J. Biol. Chem. 299:105076.

Sequencing of the human lung microbiome – Methodical challenges, controls and first metagenome assembled genomes from a nearly sterile habitat

Question: Microbial populations are usually present within many sites of the human body and in the past, it became increasingly clear that they play key roles in maintaining health, as well as causing diseases, when its natural composition is disrupted. While the healthy lung was considered traditionally sterile, an increasing number of studies, culture dependent and independent, indicate otherwise. A better understanding of the lung microbiome is therefore needed to assess its potential role in disease development and prevention. However, due to the low bacterial biomass nature of the lung, molecular research has remained challenging and to date was mostly restricted on 16S rRNA-gene amplicon analysis. In our study, we aimed to overcome these limitations and conduct a first metagenomic analysis of bacterial communities of the human lung.Methods: By performing bronchoscopy on healthy individuals of smokers and non-smokers, bronchoalveolar lavage was collected and subjected to metagenomic analysis. To enable bacterial metagenomic analyses, samples had to be subjected to extensive clean up procedures, depleting human background DNA, while preserving the original microbial community.Results & Conclusions: In the end, a robust method could be developed to create the first metagenome assembled genomes from this habitat characterized by very low microbial abundances. This represents a key step forward in understanding of the human lung microbiome and provides the baseline for future microbiome analyses.

Bacterial degradation of plasticizers on the example of diethyl phthalate (DEP)

Environmental microbiology & ecology

The continuing reports of plastic pollution in various ecosystems highlight the threat posed by the ever-increasing consumption of synthetic polymers. Plastics are frequently associated with additives such as phthalic acid esters. Such compounds are used as plasticizers to provide flexibility to plastic products and as common additives in various consumer products, and suspect to cause endocrine disruption in animals.The bacterial degradation of diethyl phthalate (DEP) as a model compound for plasticizers was studied. In order to isolate bacterial DEP degraders, a biofilm present on a polyurethane tubing was scratched off. From this biofilm, a microbial consortium containing two strains Microbacterium ginsengisoli and Pseudomonas canadensis was isolated. These strains were further characterized and found to be capable to grow in mineral medium with DEP as sole carbon energy source. The complete degradation of up to 4 mM DEP was confirmed by UPLC analysis. Furthermore, the substrate spectrum of the microbial consortium was assessed by testing different carbon sources like phthalic acid, 3,4-Dihydroxybenzoic acid, and other phthalate esters. Based on that and on the metagenome of the bacterial consortium, a degradation pathway of DEP was suggested.

Natural oil slicks serve as microbial seedbank for accelerated hydrocarbon degradation in anthropogenic oil slick

Crude oil can naturally seep to the Earth's surface, releasing oil into various ecosystems and forming oil slicks. Although oil is toxic to most life, some bacteria can use oil as carbon source and degrade it. Natural and anthropogenic oil slicks differ in their biological, chemical, and physical properties, yet natural seeps remain understudied from a microbiological perspective. Oil spills contribute largely to global hydrocarbon pollution and natural weathering is often the best choice for oil spill countermeasures in sensitive ecosystems like marshes and coral reefs, where physical cleanup could cause more damage. Accelerating weathering of anthropogenic oil spills before they reach vulnerable habitats could ultimately minimize ecosystem damages.We hypothesized, that oil degradation is faster in natural oil films compared to recently introduced oil films and that adapted microorganisms, isolated from natural oil seeps, can accelerate anthropogenic oil slick weathering.To study our hypotheses, water and heavy oil from a natural oil seep in Germany and from oil-unaffected river water were sampled, microorganisms are considered as adapted and naïve, respectively. Microcosm experiments were conducted to compare oil degradation rates between adapted, naïve and mixed microbes, treated with light and heavy oil. Oil biodegradation was monitored over 153 days by pH-measurements, cell counting, CO2-deveolopment by reverse stable isotope labeling (RSIL) and changes in the microbial community composition via 16S rRNA gene amplicon sequencing. A pH decrease was observed for all test conditions and aligned with the amount of produced CO2. Adapted microbes demonstrated up to 5x faster degradation rates of light oil compared to the naïve microbes. In mixed oil incubations, simulating the application of adapted microbes to anthropogenic spills, degradation rates were 0.26 ± 0.01 mM/day with microbes from the adapted water and 0.15 ± 0.02 mM/day in naïve water microcosms, resulting in 58% higher degradation rates.Natural oil seeps can serve as a valuable source of oil degrading microbial communities that can be used as seedbanks for accelerated hydrocarbon degradation, especially in anthropogenic oil spill scenarios where oxygen is not a limiting factor.

Prof.Dr

Race for iron: An exploiter's perspective on siderophore-mediated networking in bacterial communities

The trace element iron is a physiological requirement of almost every living organism as it plays important roles in numerous biological processes. Nevertheless, due to the extreme low solubility of Fe3+ in aerobic environments, microbes need to employ sophisticated strategies to manage homeostasis of this valuable resource. One strategy is the production and secretion of Fe3+-complexing siderophores. Within this project, we assess competitive and cooperative strategies for the acquisition of iron through siderophores as public goods in defined microbial communities.Corynebacterial species have been reported as frequently occurring natural siderophore exploiter in natural microbiomes, such as the nasal microbiome (1). Within this project, we investigate Corynebacterium glutamicum as model to explore the exploiter"s perspective on siderophore-mediated networking. To establish defined microbial communities, we screened for different siderophore producers allowing C. glutamicum to overcome iron-limitation. These result indicated that C. glutamicum is capable of utilizing a chemically diverse set of xenosiderophores including Escherichia coli enterobactin, Bacillus subtilis bacillibactin and Ustilago maydis ferrichrome. Adaptive laboratory evolution experiments with C. glutamicum and spent medium from different siderophore producers resulted in the isolation of C. glutamicum strains with superior xenosiderophore utilization capabilities. Establishment of synthetic co-cultures grown in microfluidic devices confirmed the dependency of C. glutamicum on enterobactin production of E. coli under iron limiting conditions. With this set-ups we are able to examine the impact of iron management strategies on the structure and dynamics of microbial communities, uncovering spatial variations and dynamics.(1) Zhao et al. (2024): The ISME Journal.

Stress response of ISS and school isolates for assessment of survival mechanisms across different habitats

Microorganisms exposed to space-relevant stressors, such as microgravity, high levels of ionizing radiation, and desiccation, face distinctive survival challenges. These stressors have the potential to induce physiological and genetic adaptations, which can impact microbial behavior, growth rates, and pathogenicity. For example, a compromised immune system in microgravity environments may facilitate certain microorganisms to become more virulent, thereby posing health risks for astronauts on long-duration missions. Furthermore, space radiation can cause DNA damage, potentially driving the evolution of more resilient strains that could influence microbial communities in spacecraft habitats. Understanding these adaptive responses is critical for developing effective microbial control strategies and ensuring the safety of space missions, especially as humanity plans for prolonged space travel and habitation on extraterrestrial surfaces. Moreover, these insights could inform biotechnology applications on Earth, such as the engineering of stress-resistant microorganisms for industrial or medical use.Within the study "Touching Surfaces", which tested antimicrobial surfaces in space and on Earth, several microbial isolates were retrieved. The isolates will be tested for their tolerance to key environmental stressors relevant to spaceflight. Stress resistance assays involve exposing microbial samples to X-ray doses simulating cosmic radiation, followed by assessment of cell viability. Desiccation resistance is evaluated by drying the samples under controlled conditions and monitoring recovery upon rehydration. Additionally, the susceptibility of the isolates to antibiotics will be tested.This study focuses on microbial isolates collected in the "Touching Surfaces" project in both confined environments such as the International Space Station, and everyday settings like German schools. The project aims to evaluate whether these distinct environments yield microbial isolates with differing stress resistance profiles. The central hypothesis being tested is whether isolates from confined and extreme habitats display enhanced resistance towards spaceflight relevant stressors compared to those from everyday environments such as schools.

Prof. Dr.

Sterol-degrading actinobacteria function as an unexpected sterol source for sterol-auxotrophic Caenorhabditis nematodes

During evolution the nematode Caenorhabditis elegans has lost the ability to synthesize steroids de novo, making its survival dependent on exogenous sterols for reproduction and life stage development. Strikingly, C. elegans feeds almost exclusively on bacteria, which typically do not synthesize steroids, raising the question of how C. elegans acquires sterols in nature. We recently found that sterol-degrading Rhodococcus and Mycobacterium bacteria accumulate sterols in intracellular lipid droplets under stress conditions such as nitrogen limitation and hypothesized that these bacteria may constitute an important sterol source for C. elegans in oligotrophic habitats.To test this hypothesis, we compared C. elegans brood sizes with different sterol-accumulating and sterol-free bacteria as food sources on sterol-free medium. While C. elegans was not able to produce offspring with sterol-free E. coli, M. smegmatis or M. aurum, around 250 offspring were produced per worm when M. smegmatis and M. aurum had accumulated intracellular sterols or with sterol-free bacteria when cholesterol was supplied in the growth medium. To differentiate bacteria- and medium-derived sterol uptake in C. elegans, we performed feeding assays with fluorescently labelled cholesterol. Confocal microscopy showed that bacteria-derived cholesterol was taken up via the pharynx into the gut and across the gut wall. In contrast, medium-derived cholesterol localized primarily in the nerve ring and sensory dendrites but was almost absent from the intestine, indicating differences in sterol uptake and transport. Feeding assays with C. elegans sterol uptake mutants showed that the intestinal cholesterol transporter CHUP-1 was required for uptake of bacteria-derived cholesterol into the worm body, while deletion of the sphingomyelin synthase SMS-5, which is involved in cholesterol absorption in the pharynx, had no significant effect. Proteomic analyses are currently underway to further investigate different physiological responses in C. elegans to bacteria- and medium-derived sterols.Our results show that the sterol-auxotrophic C. elegans can use intracellular bacterial sterol storage compounds to maintain its reproductive cycle, suggesting that sterol-degrading actinobacteria represent a natural and previously unstudied sterol source for bacterivorous animals in oligotrophic habitats. This opens a new field of research into sterol-dependent regulation and developmental processes in C. elegans

Microbial communities I
Microbes associated with humans, animal and anthropogenic sites

Appointment

Chair

Topic

Programme

Microbial communities IMicrobes associated with humans, animal and anthropogenic sites

Appointment

Chair

Topic

Programme

Microbial communities I
Microbes associated with humans, animal and anthropogenic sites