title: Comparison of cellular and biomass specific activities of dominant bacterioplankton groups in stratified waters of the Celtic Sea.
abstract: A flow-sorting technique was developed to determine unperturbed metabolic activities of phylogenetically characterized bacterioplankton groups with incorporation rates of [(35)S]methionine tracer. According to fluorescence in situ hybridization with rRNA targeted oligonucleotide probes, a clade of alpha-proteobacteria, related to Roseobacter spp., and a Cytophaga-Flavobacterium cluster dominated the different groups. Cytometric characterization revealed both these groups to have high DNA (HNA) content, while the alpha-proteobacteria exhibited high light scatter (hs) and the Cytophaga-Flavobacterium cluster exhibited low light scatter (ls). A third abundant group with low DNA (LNA) content contained cells from a SAR86 cluster of gamma-proteobacteria. Cellular specific activities of the HNA-hs group were 4- and 1.7-fold higher than the activities in the HNA-ls and LNA groups, respectively. However, the higher cellular protein synthesis by the HNA-hs could simply be explained by their maintenance of a larger cellular protein biomass. Similar biomass specific activities of the different groups strongly support the main assumption that underlies the determination of bacterial production: different bacteria in a complex community incorporate amino acids at a rate proportional to their protein synthesis. The fact that the highest growth-specific rates were determined for the smallest cells of the LNA group can explain the dominance of this group in nutrient-limited waters. The metabolic activities of the three groups accounted for almost the total bacterioplankton activity, indicating their key biogeochemical role in the planktonic ecosystem of the Celtic Sea.
authors.affiliation: Plymouth Marine Laboratory, Plymouth PL1 3DH, United Kingdom. mvz@pml.ac.uk
authors.forename: M V
authors.initials: MV
authors.lastname: Zubkov
authors.forename: B M
authors.initials: BM
authors.lastname: Fuchs
authors.forename: P H
authors.initials: PH
authors.lastname: Burkill
authors.forename: R
authors.initials: R
authors.lastname: Amann
mesh_terms: D000818:Animals; D001419:Bacteria / Q000145:classification* / Q000235:genetics / Q000378:metabolism*; D018533:Biomass; D005434:Flow Cytometry / Q000379:methods*; D017404:In Situ Hybridization, Fluorescence; D008715:Methionine / Q000378:metabolism; D010802:Phylogeny; D010933:Plankton / Q000145:classification* / Q000235:genetics / Q000378:metabolism*; D012335:RNA, Ribosomal / Q000235:genetics; D012623:Seawater / Q000382:microbiology*; D013462:Sulfur Radioisotopes / Q000378:metabolism
chemical_list: D012335:RNA, Ribosomal; D013462:Sulfur Radioisotopes; D008715:Methionine