UC Irvine

Bacteria are key drivers of global biogeochemical cycling. By producing extracellular enzymes they are able to turnover organic matter so that it can be assimilated for new biomass or energy production. However, enzymes are metabolically expensive, resulting in decreased fitness with their production. How bacteria allocate their resources determines not only the rate at which carbon is cycled, but its fate in an ecosystem. Therefore, the central role that enzymes play in this process makes them an important research target. Understanding the mechanisms that impact the expression of extracellular enzymes is fundamental to predicting ecosystem carbon and nutrient cycling. In this dissertation, we began with a literature review that explores the role that microbial interactions play in soil carbon cycling dynamics through phenotypic plasticity and evolutionary processes. Next, to determine the physiological limitation of extracellular enzyme production and how bacteria allocate resources, we assessed the trade-offs between extracellular enzyme production and growth rate relative to resources across several strains of bacteria. Bacteria do trade off these traits, though selectively, and with a stronger effect in nutrient-poor media. Finally, we examined the functional capacity in a river system to determine if enzyme expression is determined by community structure, nutrients, or environmental parameters. Enzyme expression was most strongly determined by biofilm productivity, and had no relationship to alpha or beta diversity. While there is some evidence to suggest a phylogenetic signal of extracellular enzyme production, from the empirical results presented here, bacterial expression of extracellular enzymes, in both populations and communities, appears to be predominantly determined by nutrient parameters.