Hydrostatic pressure is an ecological and evolutionary factor in the seas. The principal investigator, a leading authority on deep-sea bacteria and on the biological effects of hydrostatic pressure, is continuing and extending his investigations into this topic by focusing on the ability of deep-sea bacteria to synthesize polyunsaturated fatty acids (PUFAs). PUFAs are required dietary lipids for most animals in near the surface and are likely to be for those in the deep sea also. If bacteria are the major source of PUFAs in the deep sea, then they are likely to constitute an essential feature of the deep-sea food web. Thus this study will provide important insights into the synthesis and role of PUFAs in the deep-sea food web.