U.S. JGOFS (the Joint Global Ocean Flux Study, 1983-)

Piezophilic bacteria are microorganisms which grow optimally or preferentially at pressures greater than 1 atmosphere (DeLong et al., 1997). Numerous deep-sea piezophilic bacterial strains have been isolated from the water column, sediments, intestinal tracts and decaying parts of invertebrates in the deep-sea, and characterized physiologically, genetically, and biochemically (Yayanos et al., 1981; Nakayama et al., 1994; DeLong and Yayanos, 1985, 1986; Kato et al., 1995, 1996; Takami et al., 1997; Tamegai et al., 1998; Kato et al., 1998; Li et al., 1999a, b; Fang et al., 2000). The seafloor is an active site of elemental cycling, a critical long-term sink in the global cycles of major constituents, including carbon, nitrogen, and sulfur. Thus, the distribution of piezophilic bacteria and the interplay between organisms and sediment can strongly affect the carbon and energy cycles in the deep-sea.
Despite decades of the extensive studies on the genetics, phylogeny, and biochemistry of piezophilic bacteria in the past, little is known of the sedimentary geochemistry and carbon cycle in the deep-sea. So far only limited number of deep-sea microorganisms has been isolated in the laboratory and most of the microorganisms could not be cultivated by standard laboratory techniques (Li and Kato, 1999).

Given the magnitude of the deep-sea biosphere (Whitman et al., 1998; Parkes et al., 2000; D’Hondt et al., 2002), the impact of piezophilic bacteria on global carbon cycle cannot be overestimated. To understand and predict the interactions between the biology and chemistry of piezophilic bacteria and deep-sea sediments, as well as the coupling between the deep-sea carbon cycle and global ocean carbon cycle, models must be developed to permit the basic microbiological and geochemical processes to respond to the activities of piezophilic bacteria, and vice versa. Some pertinent questions include: (1) Do piezophilic bacteria and archaea comprise a large fraction of deep-sea microbial abundance and biovolume? (2) Do piezophilic microorganisms consume dissolved organic compounds that support a large fraction of bacterial production and comprise much of the dissolved organic matter input? (3) Are piezophilic microorganisms responsible for a large fraction of the measured bacterial production? And (4) how important quantitatively the piezophilic bacterial and archaeal production to global carbon cycle?

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In the past decade, the Joint Global Ocean Flux Study and the World Ocean Circulation Experiment have provided unprecedented understanding of ocean carbon distribution, ecosystem dynamics, and major biogeochemical cycles in the marine environment (The EDOCC Group, 2001), and gained a new appreciation of the complexity of biogeochemical systems and their variability over time and space (Buesseler, 2001). However, our current understanding of the role of the deep-sea subsurface microbiota in global ocean carbon cycle remains very poorly constrained, in comparison to the upper ocean and interior ocean biota. We have little current basis by which to predict the interactions and the coupling and/or decoupling between the subsurface microbiota and the upper ocean chemistry and the global ocean carbon cycle.