Heterotrophic bacteria play a central role in the carbon cycle of the oceans, consuming organic matter equivalent to 30?60% of phytoplankton primary production. Although we have learned much about the diversity of bacteria in the ocean, there is little information on the metabolic function of specific bacterial groups in natural assemblages as few culture?independent studies have linked bacterial community structure and function. In particular, there is little information on dissolved organic matter (DOM) consumption by different phylogenetic groups of bacteria, an important ecological and biogeochemical role of bacteria in the ocean.
This study will determine the role of one group of bacteria in DOM consumption, the Cytophaga?Flavobacter group. Our hypothesis is that the Cytophaga?Flavobacter group plays a central role in DOM consumption in the ocean. We will address the following questions: (1) Does the Cytophaga?Flavobacter group comprise a large fraction of marine bacterioplankton abundance and biovolume? (2) Does the Cytophaga?Flavobacter group consume DOM compounds that support a large fraction of bacterial production and comprise much of the DOM input? and (3) Is the Cytophaga?Flavobacter group responsible for a large fraction of the measured bacterial production?
Culture?independent approaches will be used to assay communities in estuarine and upwelling environments having a range of DOM input and consumption by bacteria. The relative abundance of the Cytophaga?Flavobacter group will be determined using fluorescence in situ hybridization (FISH). Uptake of DOM compounds by the Cytophaga?Flavobacter group will be determined using radiolabeled DOM compounds and microautoradiography coupled with FISH (MICRO?FISH). The contribution of the Cytophaga?Flavobacter group to bacterial production will be compared to other groups by determining which bacterial groups take up 'H?thymidine and 'H?leucine. DOM uptake is an important aspect of carbon cycling in the ocean, so determining which types of bacteria are responsible for the bulk of bacterial production and DOM consumption is a key step in developing a better understanding of the marine carbon cycle.