Vol. 43: 233–241, 2006
AQUATIC MICROBIAL ECOLOGY Aquat Microb Ecol
Published July 19
Contribution of major bacterial groups to bacterial biomass production along a salinity gradient in the South China Sea
Yao Zhang1, Nianzhi Jiao1,*, Matthew T. Cottrell2, David L. Kirchman2
State Key Laboratory for Marine Environmental Sciences, Xiamen University, 422 Siming Nan Road, Xiamen 361005, PR China 2 College of Marine and Earth Studies, University of Delaware, 700 Pilottown Road, Lewes, Delaware 19958, USA
1
ABSTRACT: Bacterial abundance and assimilation of 3H-leucine were examined using a combination of microautoradiography and fluorescent in situ hybridization (Micro-FISH) to determine the bacterioplankton community structure and estimate the contribution of major bacterial groups to total bacterial biomass production (leucine incorporation) from the Pearl River mouth to the open water area in the South China Sea. Alpha-, beta-, gamma-proteobacteria and the Cytophaga-Flavobacterium cluster differed substantially in their relative abundance and contribution to leucine assimilation along the salinity gradient. The contribution of major bacterial groups to leucine assimilation was closely associated with their relative abundance in the communities. Alpha-proteobacteria were the dominant group in the high-salinity water in terms of abundance and 3H-leucine assimilation, whereas beta-proteobacteria were more important in fresh water. At all stations, gamma-proteobacteria were a minor component, but the Cytophaga-Flavobacterium cluster was always a significant component in both marine and freshwater systems. The relative abundance of bacterial groups explained the variation in 3H-leucine assimilation by the major bacterial groups to a great extent. At the singlebacterial group level, a statistically significant correlation between abundance and leucineuptake activity was observed for beta-proteobacteria, suggesting that the relative abundance of betaproteobacteria in bacterioplankton communities was controlled by growth-related processes. In general, the numerical dominance of the major phylogenetic groups and their contribution to total bacterial biomass production varied consistently along the salinity gradient in the South China Sea. KEY WORDS: Proteobacteria Cytophaga-Flavobacterium Community Leucine assimilation Bacterial biomass production Microautoradiography Fluorescent in situ hybridization

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