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Benthic processes

Ecophysiology and genetics of Monterey Canyon Beggiatoa species
Project Manager/Lead Scientist: Douglas Nelson

This proposal is a continuation of studies first begun under this title in 2001. A renewed three-year NSF award to Doug Nelson (Ecophysiology and Phylogeny of Vacuolate, Nitrate-Accumulating Sulfur Bacteria) has a major focus on populations of Beggiatoa sp. that occur as dense sediment mats at various seeps in Monterey Canyon. Numerous sediment cores obtained from this site have yielded several different width classes of very large Beggiatoa filaments (120 and 80 micrometers in diameter for the widest cells) that have been shown to accumulate nitrate in their central vacuoles to concentrations that are typically ten thousand-fold above ambient levels. We have further shown, through studies of sediment porewater profiles and microbial enzyme activities, that this Beggiatoa strain appears to be able to generate energy via respiration of hydrogen sulfide to sulfate while reducing nitrate to ammonia. This unusual mode of lithoautotrophic metabolism is only known to extend to the close relatives Thioploca spp. and Thiomargarita namibiansis

Emerging differences in the ability of various sediment Beggiatoa mats to tolerate or consume oxygen will be investigated along with a characterization of differences in their internal nitrate pools. The 16S rRNA affinity of benchmark populations that differ significantly in physiological or morphological properties will also be established. The Monterey Canyon Beggiatoa sp. is, by virtue of both its relative accessibility and purity of material that can be collected, the best source of material for continued genetic, enzymatic, and physiological studies of this very interesting group of bacteria, which has no representative available in pure culture.  A partial list of the experiments planned includes: (1) a finer resolution of porewater profiles of ammonia, sulfide, sulfate and nitrate to confirm in situ metabolism, (2) cloning and sequencing of the genes that encode the unusual, membrane-associated, nitrite-reductase enzyme responsible for producing the waste product ammonia, (3) determining the kinetic complexity and genome copy number per cell of the DNA of this microbe. 

We have also established that vacuolate, Thiothrix-like populations can be found or enriched at certain Monterey canyon sites. These equally large, "hollow" bacteria do not accumulate nitrate; hence, we are exploring alternative physiological roles for their vacuole. To accomplish these studies requires access to fresh cores from the Canyon sites an average of once per month.