Algicidal Bacteria in Plankton Communities: Resistance, Lysis and Heterotrophy

Organisms in the plankton form complex communities that contribute substantially to global primary production and fuel the marine food web. This project focuses on the role of secondary metabolites as mediators of the complex plankton community structure. We focus on the lytic bacterium Kordia algicida that is capable of lysing bloom forming algae and investigate its influence on plankton dynamics. The regulation of algal / bacterial interaction and the cascading effects on the marine food web will be addressed in lab and field experiments.

Are Plant Defenses Chemicals Commonly Sequestered and Metabolized by their Herbivores to Function as Infochemicals in Higher Trophic Level Interactions in Nature?

Plants integrate responses between two spatially separated habitats: air and soil, with different communities of heterotrophs depending on the same host. Little is known about the chemical mediators of interactions between aboveground herbivores and root colonizers. Using metabo-lomics and transcriptomics, we will characterize spatiotemporal changes in roots of herbivore-damaged plants and identify underlying signalling pathways. We will genetically modify identified traits to determine their ecological function in interactions with soil bacteria and mycorrhizal fungi and the consequences for herbivore resistance and plant fitness in field experiments.

Thiopeptide Signals in Actinomycete Communities

Microbial consortia are structured by antibiotics such as thiopeptides (TP) and by environmental factors such as heavy metals (HM). In this project the signaling of sublethal TP doses via the TP-activated TipA receptor and its interaction with HM-stress and resistance mechanisms will be investigated on the molecular, genomic and interspecies level. Ligand function, target genes, and HM-dependence will be clarified in model organisms and microcosms by using targeted mutants, tool compounds, and HM-contaminated soil media.

Metallophores as Mediators for Metal Cycling: Profiling and Ecological Evaluation of Ligands Involved in the Microbial Cycling of Iron in Complex Systems

Iron in complexed form is central to the microbial iron cycle. In this project, we identify and characterize metallophores formed and excreted by bacteria and compare them with the diverse compounds found in nature. The goal is to elucidate the chemical communication of bacteria that use iron in very different forms for energy production. Co-cultivations have shown that biofilm formation plays a key role in the interaction. We want to clarify whether synchronization of lifestyles drives these interactions.

Metallophores as Mediators for Metal Cycling: Development of Libraries for Metal Ion Buffering and as Redox Carriers as well as Profiling of Metallophores

This project aims to identify novel metallophores based on recently developed LC/MS analytical techniques and to unravel their multiple functions particularly in nitrogen-fixing and microbial iron-cycling systems. To mimic natural sources of molybdenum, which is an essential cofactor of nitrogenases, we will develop libraries of synthetic chelating agents for this metal. The resulting complexes serve as “Mo-buffers” to control the availability of molybdenum species in aqueous cultures. To model redox shuttle systems in communities of Fe(II) oxidizers and Fe(III) reducers appropriate ligands as well as metal complexes will be developed.

Complex Ecological Phenomena Arising from Enzymatic Modification of Chemical Effectors

Identification of common patterns across different microbial communities can lead to powerful fundamental insights. Current work in ChemBioSys has identified enzymatic modification of secreted chemical effectors as one such common theme. We propose to investigate the complex temporal and spatial dynamics that can emerge in such systems. Specifically, we will investigate systems where one organism secretes a chemical effector to impact a second organism, while a third organism secretes an enzyme that modifies that effector, changing the ecological outcome. Our project will combine theoretical and experimental methodologies.

Chemical Mediators of Microbiota Composition and Functionality in a Multipartite Defensive Symbiosis

Beneficial microbes are fundamental for plant and animal health, but the molecular factors shaping the composition of symbiotic microbiomes remain poorly understood. Using an experimentally tractable defensive symbiosis in beetles, this project will characterize the secondary metabolites produced by the bacterial community members and elucidate their impact on community structure and on the protective benefit for the host. Through a combination of in vitro assays and manipulative experiments in the host, the results will shed light on the dynamics of competition and facilitation among symbiont strains and thereby provide insights into the processes guiding the assembly of host-associated microbiomes.

Probing the Role of Chemical Signalling in the Interplay of Gut Commensals, Pathogens, and their Phages

When colonizing the human gut, Vibrio cholerae interacts with dozens of commensal microorganisms, their secreted molecules, and numerous phages. In this project, we will investigate the interplay of V. cholerae with microbial competitors in the gut, as well as how phages play into this process. We will focus our investigations on key mediators of collective behavior in V. cholerae and pinpoint their roles in other organisms. We expect that this project will allow us to better understand how microbial commensals and phages influence collective behaviours, such as virulence gene expression and biofilm formation, in the major human pathogen V. cholerae.

Chemical Signaling in Algae-Parasites Communities

Single-cell parasites thrive in aquatic ecosystems and contribute to algal blooms termination, yet the molecular mechanism supporting parasitism is poorly understood. We will explore parasite-induced diseases in diatoms and dinoflagellates and identify the chemical signaling that mediates pathogenesis, host defense and multipartite interactions with the plankton microbiome. The CRC project will provide insights into the fundamental mechanism of alga-parasite interactions that balance the aquatic food web.