Temporal changes of major bacterial groups and bacterial heterotrophic activity during a Phaeocystis globosa bloom in the eastern English Channel

摘要

The temporal changes in major bacterial groups and bulk heterotrophic activity were determined during the growth, senescence and post-bloom phases of a Phaeocystis globosa bloom, at a coastal site in the eastern English Channel. Cell-specific exoenzymatic activities were highest during the growth period of P. globosa, while bacterial abundance and bacterial heterotrophic production peaked during the senescence of the P. globosa bloom. Bacteroidetes and Gammaproteobacteria were the most important bacterial groups during the growth period of P. globosa, contributing between 13 and 47% of bulk bacterial abundance and leucine incorporation. At the end of the phytoplankton growth period, Gammaproteobacteria were the most important contributors to bacterial heterotrophic production, accounting for 68% of bulk leucine incorporation. During the senescent phase, 36 and 29% of bulk leucine incorporation were attributable to Bacteroidetes and Alphaproteobacteria, respectively. Finally, after the disappearance of the bloom, Gamma- and Alphaproteobacteria dominated by the Roseobacter clade were responsible for 33 and 43% of bulk leucine incorporation, respectively. The relative abundance of the bacterial groups showed little variability between consecutive dates during most of the study period. The contributions of different bacterial groups to bulk abundance and leucine incorporation were correlated with exo-proteolytic and -glucosidic activities and with particulate organic carbon, suggesting at least some specificity of these bacterial groups with respect to their metabolic properties in the environment.