1. Monterey Bay Aquarium Research Institute, Moss Landing, California 95039-0628, USA
2. The Institute for Genomic Research, Rockville, Maryland 20850, USA
3. Marine Biotechnology Institute, Kamaishi Laboratories, Kamaishi City, Iwate 026-0001, Japan
4. Present addresses: Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel (O.B.); Nara Institute of Science and Technology, Takayama, Ikoma 630-0101, Japan (T.H.).

Correspondence to: Edward F. DeLong¹ Correspondence and requests for materials should be addressed to E.F.D. (e-mail: Email: delong@mbari.org). The sequences reported in this study are deposited with GenBank under accession numbers AB018690, AB027515, AF393983–AF393991, AF393993-AF394002, AY044244–AY044250 and AE008919–AE008921.

Abstract

Aerobic, anoxygenic, phototrophic bacteria containing bacteriochlorophyll a (Bchla) require oxygen for both growth and Bchla synthesis^{1, 2, 3, 4, 5, 6}. Recent reports suggest that these bacteria are widely distributed in marine plankton, and that they may account for up to 5% of surface ocean photosynthetic electron transport⁷ and 11% of the total microbial community⁸. Known planktonic anoxygenic phototrophs belong to only a few restricted groups within the Proteobacteria -subclass. Here we report genomic analyses of the photosynthetic gene content and operon organization in naturally occurring marine bacteria. These photosynthetic gene clusters included some that most closely resembled those of Proteobacteria from the -subclass, which have never before been observed in marine environments. Furthermore, these photosynthetic genes were broadly distributed in marine plankton, and actively expressed in neritic bacterioplankton assemblages, indicating that the newly identified phototrophs were photosynthetically competent. Our data demonstrate that planktonic bacterial assemblages are not simply composed of one uniform, widespread class of anoxygenic phototrophs, as previously proposed⁸; rather, these assemblages contain multiple, distantly related, photosynthetically active bacterial groups, including some unrelated to known and cultivated types.

1. Monterey Bay Aquarium Research Institute, Moss Landing, California 95039-0628, USA
2. The Institute for Genomic Research, Rockville, Maryland 20850, USA
3. Marine Biotechnology Institute, Kamaishi Laboratories, Kamaishi City, Iwate 026-0001, Japan
4. Present addresses: Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel (O.B.); Nara Institute of Science and Technology, Takayama, Ikoma 630-0101, Japan (T.H.).

Correspondence to: Edward F. DeLong¹ Correspondence and requests for materials should be addressed to E.F.D. (e-mail: Email: delong@mbari.org). The sequences reported in this study are deposited with GenBank under accession numbers AB018690, AB027515, AF393983–AF393991, AF393993-AF394002, AY044244–AY044250 and AE008919–AE008921.