Growth and grazing mortality rates of phylogenetic groups of bacterioplankton in coastal marine environments.

Dilution culture experiments were conducted in western North Pacific coastal regions to determine growth and grazing mortality rates of bacterial phylogenetic groups (alpha-, beta-, and gamma-proteobacteria and the Cytophaga-Flavobacter cluster) detected by fluorescent in situ hybridization. Growth rates varied greatly (1.2- to 4.0-fold) among different groups, and they were related to environmental variables (chlorophyll a concentrations and temperature) in a group-specific fashion. Growth rates of alpha-proteobacteria, the most abundant group in all the samples examined, were generally lower than those of less abundant groups, including the Cytophaga-Flavobacter cluster and gamma-proteobacteria. Grazing mortality rates and mean cell volumes varied little among different groups. These results provide insights into factors that affect distributions of different groups, but growth and grazing mortality alone did not fully explain bacterial community compositions at a broad phylogenetic level.