Vertical distribution and characterization of aerobic phototrophic bacteria at the Juan de Fuca Ridge in the Pacific Ocean

The vertical distribution of culturable anoxygenic phototrophic bacteria was investigated at five sites at or near the Juan de Fuca Ridge in the Pacific Ocean. Twelve similar strains of obligately aerobic phototrophic bacteria were isolated in pure culture, from depths ranging from 500 to 2,379 m below the surface. These strains appear morphologically, physiologically, biochemically, and phylogenetically similar to Citromicrobium bathyomarinum strain JF-1, a bacterium previously isolated from hydrothermal vent plume waters. Only one aerobic phototrophic strain was isolated from surface waters. This strain is morphologically and physiologically distinct from the strains isolated at deeper sampling locations, and phylogenetic analysis indicates that it is most closely related to the genus Erythrobacter. Phototrophs were cultivated from three water casts taken above vents but not from two casts taken away from active vent sites. No culturable anaerobic anoxygenic phototrophs were detected. The photosynthetic apparatus was investigated in strain JF-1 and contains light-harvesting I and reaction center complexes, which are functional under aerobic conditions.