Bacteria Genomes - SILICIBACTER POMEROYI

Silicibacter pomeroyi is the first genome to be sequenced from any major heterotrophic clade. It is a member of the marine Roseobacter clade, the relatives of which comprise around 10-20% of coastal and oceanic mixed-layer bacterioplankton. It is a Gram-negative , rod-shaped, aerobic bacteria and consists of a chromosome (4,109,442 base pairs) and megaplasmid (491,611 base pairs). It was named after UGA emeritus professor Lawrence Pomeroy.

This genome sequence reveals an organism equipped to take advantage of transient occurrences of high-nutrient niches within a bulk low-nutrient environment. Living and dead plankton and microscale 'hot spots' of the surface ocean might provide such niches. Lithoheterotrophic growth could allow Silicibacter -like bacterioplankton to use a greater proportion of organic carbon for biomass production as it becomes available. Although most ecologically relevant marine heterotrophs were previously assumed to be oligotrophs that subsist on dilute organic substrates dissolved in sea water, an 'opportunitroph' strategy might be a successful alternative. The available metagenomic data from coastal and oceanic sites indicate that such a strategy is not atypical among marine bacterioplankton

Genetic analyses suggest that the plankton is able to maximize its nutritional intake when it swims into pockets of other organisms by, for example, supplementing its diet of organic compounds with inorganic compounds such as carbon monoxide and sulphide. The plankton also possesses genes that help it to grow rapidly and take up compounds produced by algae. Silicibacter pomeroyi also has genes advantageous for associations with plankton and suspended particles, including genes for uptake of algal-derived compounds, use of metabolites from reducing microzones, rapid growth and cell-density-dependent regulation. This bacterium has a physiology distinct from that of marine oligotrophs, adding a new strategy to the recognised repertoire for coping with a nutrient-poor ocean.

One of the compounds that S. pomeroyi releases is dimethyl sulfide gas, which photoxidizes in sunlight to form microscopic sulfate particles. The particles serve as sites for water to condense into cloud droplets. The concentration of these droplets impacts how clouds reflect and absorb radiation, which affects climate. The sequence reveals a new strategy used by organisms to survive in nutrient-poor marine waters, and illustrates scientists' growing interest in applying new genomic technologies to their studies of the ocean.

References:

Nature 432(7019):910-913(2004)http://www.separationsnow.com/basehtml/SepH/1,1353,6-1-1-0-0-news_detail-0-1869,00.html