AME 25:103-111 (2001)  -  doi:10.3354/ame025103

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

Jakob Worm1,*, Kim Gustavson2, Kristine Garde2, Niels Henrik Borch3, Morten Søndergaard3

1Department of Ecology, Royal Veterinary and Agricultural University, Thorvaldsensvej 40, 1871 Frederiksberg (Copenhagen), Denmark
2DHI Water and Environment, Agern allé 11, 2970 Hørsholm, Denmark
3Freshwater Biological Laboratory, University of Copenhagen, Helsingørsgade 51, 3400 Hillerød, Denmark

ABSTRACT: Phytoplankton blooms were created in freshwater enclosures to study the functional succession and diversification for attached (>10 μm size fraction) and free-living (<10 μm size fraction) assemblages of bacteria. Bacterial dynamics in abundance, production and enzyme activity was monitored by standard methods. The functional diversity with respect to sole carbon source utilization was assessed with Biolog GN plates inoculated with bacteria from the 2 size fractions. Moreover, bacterial isolates were screened for enzyme activity involved in the degradation of carbohydrates, chitin, protein and lipid. As the bloom proceeded, the functional diversity of attached and free-living bacteria appeared to be very similar. Most functional groups present in the free-living bacterial assemblage were also recovered attached to particulate matter. Additionally, the distribution of bacterial isolates with enzyme expression was similar with respect to 6 enzymes (p > 0.07), whereas 3 glucoside-bond cleaving enzymes were more frequent among the free-living isolates (p < 0.02). These results indicate that attached and free-living bacteria were functionally closely related and that their succession tended to converge during the phytoplankton bloom. Hence, bacteria attached to particulate matter are not necessarily functionally distinct and specialized for polymer hydrolysis relative to the free-living assemblage, though they are often anticipated to be different due to their close association with particulate polymers.

KEY WORDS: Attached bacteria · Particles · Phytoplankton bloom · Enzyme activity · Sole carbon source utilization · Functional diversity

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