Microorganisms are of great importance for the large scale elemental cycles and overallfunctioning of most natural ecosystems, and this also includes the ecology and maintenance offreshwater resources. Anthropogenic actions as well as climate change has greatly affectedfreshwaters and it is therefore important to understand how microorganisms react to suchenvironmental changes. I investigated how one such pressure, increased nutrient levels,influenced freshwater microbial communities and their potential to degrade the globallyabundant biopolymer chitin. To assess the effects of changed nutrient levels on functionalsubcommunities within the natural microbiota, I established a collection of mixed culturesoriginating from Lake Erken and two mesocosms from the same lake subjected to either highor low nutrient amendments. I observed that higher nutrient addition greatly increasedbacterial cell numbers in the source community. However, for the emerging mixed culturesgrowing on chitin as a substrate, those originating from the “Low” nutrient amendmentmesocosm treatment featured higher cell growth potential compared to cultures originatingfrom the “High” ones or inoculated with the natural lake water. Moreover, mixed culturesfrom the mesocosms presented higher chitinase extracellular enzymatic activity compared tothe lake cultures. Interestingly, “High” and “Low” mesocosm cultures were quite constrainedin bacterial growth response (low variance for the respective treatment) while the growthpotential in cultures from the lake were much more diverse, indicating a higher degree ofpatchiness and subcommunities with variable ability to profit from chitin as a substrate.Ongoing work will assess how individual microbial lineages react to variable nutrient levelsand how the composition of less diverse but fully functional subcommunities profiting fromchitin will change under such conditions.