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SULFATE-REDUCING BACTERIA IN THE SEAGRASS RHIZOSPHERE
Citation:
Devereux, R D., S S. Wilkinson, D F. Yates, A. Goldfinch, AND J. E. Kostka. SULFATE-REDUCING BACTERIA IN THE SEAGRASS RHIZOSPHERE. Presented at 2002 Ocean Sciences Meeting, Honolulu, HI, Feb 11-15, 2002.
Description:
Seagrasses are rooted in anoxic sediments that support high levels of microbial activity including utilization of sulfate as a terminal electron acceptor which is reduced to sulfide. Sulfate reduction in seagrass bed sediments is stimulated by input of organic carbon through the deposition of periphyton from the leaves and exudation of organic acids from the roots. Release of oxygen from the roots establishes a redox gradient and prevents sulfide from approaching levels that could otherwise be toxic to the plants. Bacteria considered to be
obligate anaerobes (sulfate reducers, methanogens and acetogens) internally colonize roots of the submerged macrophyte Halodule wrightii. The distribution of these bacteria observed in root cross sections suggests their alignment along a redox gradient emanating from the center of the root. The in situ activities of these obligately anaerobic endorhizobacteria, and whether their association with the roots may be beneficial or harmful to the plant, are not known. In order to begin to address these questions, a sulfate-reducing bacterium, Summer lac-1, was isolated from H. wrightii roots by selecteive enrichment with lactate. The isolate has
physiological characteristics typical of Desulfovibrio strains, yet a 16S rRNA sequence that is only 90% similar to sequences from other Desulfovibrionaceae. The sequence of the bisulfite reductase gene, dsr, from Summer lac 1 has been determined and used to develop PCR primers. RT-PCRs with the dsr-specific primers and RNA extracted from Summer lac-1 cells grown under sulfate reducing conditions yield a band of the expected size whereas RT-PCRs with RNA from Summer lac-1 cells grown fermentatively do not yield the expected band. In situ RT-PCR for the dsr mRNA can differentiate Summer lac-1 cells grown with sulfate from those grown without sulfate. This method is being further developed to determine whether sulfate reduction occurs within seagrass roots.