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ACETOGENIC BACTERIA ASSOCIATED WITH SEAGRASS ROOTS
Citation:
Devereux, R D., K. Kusel, T. Trinkwalter, AND H. L. Drake. ACETOGENIC BACTERIA ASSOCIATED WITH SEAGRASS ROOTS. Presented at 2000 Annual Meeting of the American Society for Microbiology, Los Angeles, CA, May 21-25, 2000.
Description:
Seagrasses are adapted to being rooted in reduced, anoxic sediments with high rates of sulfate reduction. During the day, an oxygen gradient is generated around the roots, becoming anoxic at night. Thus, obligate anaerobic bacteria in the rhizosphere have to tolerate elevated oxygen tension. Microautoradiography of root thin sections hybridized with 33 P-labeled probes reveal the presence of acetogenic and sulfate-reducing bacteria in the rhizoplane and deep cortex cells [1]. In this study, MPN analyses demonstrated that H2-utilizing acetogens were enriched in the seagrass root and rhizosphere sediment compared to unvegetated sediment. In contrast, sulfate reducers, which dominated the anaerobic microflora, were not enriched in the root and rhizosphere sediment. An H2-utilizing acetogen (RD1) was isolated from the highest growth-positive MPN dilution of the seagrass root and characterized. Acetate, the sole end product of H2 utilization, was produced in stoichiometries indicative of an actyl-CoA pathway-dependent metabolism. During the fermentation of sugars, small amounts of ethanol were also produced. The 16S rRNA gene sequence of RD1 was closely related to that of Clostridium glycolicum (99.7%), which is not known to be an acetogen. DNA-DNA relatedness between both strains was 91.4%. Carbon monoxide dehydrogenase, formate dehydrogenase, and hydrogenase activities were present in both strains. These collective results indicate that (i) the seagrass root is colonized by acetogenic clostridia that are heretofore unrecognized as acetogens, and (ii) the biogeochemistry of this sulfate-reducing habitat promotes the colonization of the rhizosphere by acetogens.