Functional similarity of attached and free-living bacteria during freshwater phytoplankton blooms

Phytoplankton blooms were created in freshwater enclosures to study the fun ctional succession and diversification for attached (>10 mum size fraction) and free-living (<10 <mu>m size fraction) assemblages of bacteria, Bacteri al dynamics in abundance, production and enzyme activity was monitored by s tandard methods. The functional diversity with respect to sole carbon sourc e utilization was assessed with Biolog GN plates inoculated with bacteria f rom the 2 size fractions. Moreover, bacterial isolates were screened for en zyme activity involved in the degradation of carbohydrates, chitin, protein and lipid. As the bloom proceeded, the functional diversity of attached an d free-living bacteria appeared to be very similar. Most functional groups present in the free-living bacterial assemblage were also recovered attache d to particulate matter. Additionally, the distribution of bacterial isolat es with enzyme expression was similar with respect to 6 enzymes (p > 0.07), whereas 3 glucoside-bond cleaving enzymes were more frequent among the fre e-living isolates (p < 0.02). These results indicate that attached and free -living bacteria were functionally closely related and that their successio n tended to converge during the phytoplankton bloom. Hence, bacteria attach ed to particulate matter are not necessarily functionally distinct and spec ialized for polymer hydrolysis relative to the free-living assemblage, thou gh they are often anticipated to be different due to their close associatio n with particulate polymers.