Interactions in phototroph-heterotroph microbial communities

Investigator: Sinikka Lennartz

Carbon fixation by phytoplankton and organic matter remineralization by heterotrophic bacteria are two of the most fundamental processes in marine ecosystems. The phototrophic and heterotrophic microbes involved in these processes interact in various ways, from competition for inorganic nutrients to growth promotion or inhibition by releasing metabolites into seawater. While occurring at the cellular level, such systematic feedbacks on growth and nutrient uptake scale up to affect large-scale ecosystem processes. Current biogeochemical models mainly focus on competition alone, and neglect the widespread experimental evidence for active interactions mediated by secondary metabolites. The overall goal of this project is to characterize systematic impacts of metabolite-mediated interactions between phototrophic and heterotrophic microbes on carbon and nutrient turnover. We develop the Microbial COmmunity Model (MCOM) as a scalable framework, in which microbial community structure is modelled as the topology of an interaction network. A focus lies on assessing links between community composition, i.e. the underlying topology of the interaction network, and resilience against environmental perturbations. We are combining numerical modelling with aspects of network theory and microbiology to assess the influences of competition and cooperation in diverse microbial communities, and their impact on elemental cycles of carbon and nutrients.