High Abundances of Aerobic Anoxygenic Photosynthetic Bacteria in the South Pacific Ocean

• Published in: Applied and Environmental Microbiology 2007-07, Vol.73 (13), p.4198-4205
• Main Authors: Lami, Raphaël, Cottrell, Matthew T, Ras, Joséphine, Ulloa, Osvaldo, Obernosterer, Ingrid, Claustre, Hervé, Kirchman, David L, Lebaron, Philippe
• Format: Article
• Language: English
• Subjects: Aquatic life; Bacteria; Bacteria, Aerobic - isolation & purification; Bacteria, Aerobic - metabolism; Bacteriochlorophyll A - metabolism; Bacteriology; bacterioplankton; Biodiversity and Ecology; Biological and medical sciences; Biomass; carbon sinks; Chlorophyll - metabolism; Colony Count, Microbial; Earth Sciences; Ecology; Ecosystem; Environmental Sciences; euphotic zone; Fundamental and applied biological sciences. Psychology; heterotrophs; Life Sciences; Microbial Ecology; Microbiology; Microbiology and Parasitology; Oceanography; Oceans; Organisms; Pacific Ocean; Photosynthesis; photosynthetic bacteria; Phytoplankton - isolation & purification; Phytoplankton - metabolism; population density; Prochlorococcus; Prochlorococcus - isolation & purification; Prochlorococcus - metabolism; prokaryotic cells; Sciences of the Universe; Seawater - microbiology; Vinyl Compounds - metabolism
• ISSN: 0099-2240; 1098-5336
• DOI: 10.1128/AEM.02652-06

Little is known about the abundance, distribution, and ecology of aerobic anoxygenic phototrophic (AAP) bacteria, particularly in oligotrophic environments, which represent 60% of the ocean. We investigated the abundance of AAP bacteria across the South Pacific Ocean, including the center of the gyre, the most oligotrophic water body of the world ocean. AAP bacteria, Prochlorococcus, and total prokaryotic abundances, as well as bacteriochlorophyll a (BChl a) and divinyl-chlorophyll a concentrations, were measured at several depths in the photic zone along a gradient of oligotrophic conditions. The abundances of AAP bacteria and Prochlorococcus were high, together accounting for up to 58% of the total prokaryotic community. The abundance of AAP bacteria alone was up to 1.94 x 10⁵ cells ml⁻¹ and as high as 24% of the overall community. These measurements were consistent with the high BChl a concentrations (up to 3.32 x 10⁻³ μg liter⁻¹) found at all stations. However, the BChl a content per AAP bacterial cell was low, suggesting that AAP bacteria are mostly heterotrophic organisms. Interestingly, the biovolume and therefore biomass of AAP bacteria was on average twofold higher than that of other prokaryotic cells. This study demonstrates that AAP bacteria can be abundant in various oligotrophic conditions, including the most oligotrophic regime of the world ocean, and can account for a large part of the bacterioplanktonic carbon stock.