Ecophysiology of Vacuolate Marine Sulfur Bacteria

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Large, vacuolate, nitrate-accumulating bacteria such as Beggiatoa can oxidize a majority of the sulfide produced in a variety of marine niches. Closely related sulfur bacteria (vacuolated attached filaments or VAF) that do not accumulate nitrate are abundant on surfaces at marine sulfidic vents. Collectively, these phylogenetically coherent organisms are the only Proteobacteria known to contain vacuoles and it is clear that they play a significant role in the nitrogen and sulfur cycles of a variety of marine environments. Beggiatoa species are also members of the bacterial consortium known as "black band disease" that constitutes a widespread and lethal disease of corals. The principal investigator has isolated a stable culture of a 7-micron diameter vacuolate Beggiatoa from black band disease (strain BBD) that accumulates nitrate and seems to be capable of dinitrogen fixation. This cultured strain and a number of natural populations of VAF and nitrate-accumulating Beggiatoa are the focus of this project. The investigator will use microelectrode and molecular analyses to understand the relative importance of nitrate- vs. oxygen-based respiration of sulfide in subgroups of vacuolate sulfur bacteria. The investigator will survey the vertical distribution and abundance of vacuolate Beggiatoa spp. and determine how vacuolar nitrate affects nitrogen fixation, and will derive and use probes of important nitrogen cycle genes (nifD, nifH and a nrfA homologue). In addition to training a graduate student, the project will specifically target disadvantaged and underrepresented undergraduates through interaction with the Biology Undergraduate Scholars Program at UC-Davis.