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Chapter 39 : Bacterial Organic Carbon Cycling in Aquatic Environments
This chapter introduces some of the important aspects of bacterial organic carbon cycling and to provides an update on the molecular biological approaches currently in use for examining carbon cycling by bacteria without cultivation. Such investigations by microbial ecologists are motivated by the desire to understand how the composition of microbial communities dictates the way that food webs and carbon cycling function in the oceans and other aquatic environments. The goal of one study by Cottrell and Kirchman was to determine whether the relative contributions of various types of bacteria to DOM consumption depend solely on the relative abundance of these types of bacteria in the community. This study used microautoradiography and fluorescent in situ hybridization (FISH) to test the hypothesis that low-molecular-weight compounds are used by all bacteria and high-molecular-weight compounds are used by a smaller, less diverse group of bacteria. In another study, Brennan et al. examined microbial xylanases in insect guts. Although the study did not include aquatic bacteria, the approach used in this study should be applicable to aquatic microbes with appropriate modification by using a DNA extraction method for aquatic microbial DNA. The great phylogenetic distance between the novel xylanases and the known xylanases suggests that microbes in the insect gut have evolved in isolation from other microbes that have been successfully cultivated.