"Substrate complexity shapes the interactions within microbial consortia: a theoretical study"Guseva, KseniaMicrobes play crucial roles in biogeochemical cycles across all ecosystems, forming complex communities with both positive and negative interactions. Cooperation within these communities is often driven by the necessity of microorganisms to decompose complex polysaccharides. To process these large molecules, microorganisms invest in costly secretions such as hydrolytic enzymes, which function as public goods. However, even for a single substrate type, a variety of extracellular enzymes catalyzing different steps of polymer degradation are required, which may promote division of labor and species coexistence even on a single nutrient source. In this work we highlight two enzyme types with different kinetic strategies: exo-enzymes that cleave the ends of polysaccharide chains, thereby releasing mono- or dimers, and endo-enzymes that act on all intermittent bonds, thereby generating oligosaccharides of various sizes. We theoretically analyzing the consequences of different depolymerization dynamics on microbial growth and interactions within consortia. To explore how enzyme production strategies affect organic matter degradation in microbial populations, we integrate polymer degradation into a spatially explicit microbial model using population balance equations. This approach enables tracking of biopolymer molecule distribution over space and time. Our findings indicate that microorganisms are limited by both carbon quantity and form (biopolymer size). We show that the different pathways in the degradation dynamics can have fundamentally distinct outcomes for microbes. Our analysis demonstrates that bacteria can excel either at low substrate concentrations (producing endo-enzymes) or high concentrations (producing exo-enzymes). As a consequence we show that bacteria would have to optimize the two ratios to survive in both conditions. Furthermore, we illustrate how microbial consortia can emerge from the degradation of complex substrates by splitting the production of these two enzymes. Finally, we also show how interactions within such consortia can change from positive to negative depending on substrate availability. |
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