Life and Depth

Although oceans cover nearly three-quarters of Earth’s surface, little is known about how organisms living deep in the ocean cope with the pressures of their environment. At the American Chemical Society meeting in San Diego last week, Douglas H. Bartlett of Scripps Institution of Oceanography described the first genomic blueprint of an organism from the cold, deep ocean, which should shed light on how life can persist at great depths.

The deep-sea bacterium Photobacterium profundum is widely used as a model to study how organisms adapt to the high pressures of deep-ocean living. It was isolated from the Suluwesi Sea at a depth where pressures can reach 25 megapascals. Because P. profundum also can tolerate lower pressures, it is easy to grow and study in the lab, according to Bartlett. In San Diego, he reported the genomic sequence and protein expression profiles of this bacterium, work done in collaboration with Giorgio Valle at the University of Padova, in Italy (Science 2005, 307, 1459).

These studies "hint at how this organism copes with the pressures of living at depth," Bartlett told C&EN. For example, P. profundum contains two subtly different copies of certain housekeeping genes—;including those that encode proteins involved in cytochrome biosynthesis, ATP synthesis, and the cell's propulsion system. He hypothesizes that one copy might be optimized for use at low pressure and the other for use at high pressure. His genetic work has suggested that the bacterium may control which copy is expressed via specialized membrane-bound transcription factors that can sense pressure-induced changes in the lipid bilayer.

The deep-sea bacterium also appears to use alternative carbon sources at higher pressure, as evidenced by activation of enzymes that degrade chitin, pullulan, and cellulose"all relatively recalcitrant carbon sources—at high pressure. "This is consistent with what we expect deep-sea organisms might get in the way of food," Bartlett told C&EN.