Differential freshwater flagellate community response to bacterial food quality with a focus on Limnohabitans bacteria

Different bacterial strains can have different value as food for heterotrophic nanoflagellates (HNF),thus modulating HNF growth and community composition. We examined the influence of prey foodquality using four Limnohabitans strains, one Polynucleobacter strain and one freshwateractinobacterial strain on growth (growth rate, length of lag phase and growth efficiency) andcommunity composition of a natural HNF community from a freshwater reservoir. Pyrosequencingof eukaryotic small subunit rRNA amplicons was used to assess time-course changes in HNFcommunity composition. All four Limnohabitans strains and the Polynucleobacter strain yieldedsignificant HNF community growth while the actinobacterial strain did not although it was detectedin HNF food vacuoles. Notably, even within the Limnohabitans strains we found significant prey-related differences in HNF growth parameters, which could not be related only to size of the bacterialprey. Sequence data characterizing the HNF communities showed also that different bacterial preyitems induced highly significant differences in community composition of flagellates. Generally,Stramenopiles dominated the communities and phylotypes closely related to Pedospumella(Chrysophyceae) were most abundant bacterivorous flagellates rapidly reacting to addition of thebacterial prey of high food quality.