An elusive marine photosynthetic bacterium is finally unveiled

In the early 2000s, the realization that a significant fraction of the so-called heterotrophic marine bacterioplankton is capable of phototrophy has challenged our views of the carbon and energy budgets in the oceans (1) and, consequently, the biosphere. Because of their widespread occurrence and high abundance, bacterioplankton represent large pools of major elements and are catalysts in many biogeochemical cycles of global significance. In 2000–2002, a new picture of marine aerobic anoxygenic phototrophs (AAnPs) in the oceans was revealed. Using biophysical techniques, Kolber et al. (2, 3) detected a significant signal originating from these organisms in different regions of the World Ocean. These findings came as a big surprise because this type of photosynthesis was believed to be limited to a few organisms living in specialized ecological niches (4, 5). Based on cultivation studies (3–8), these newly discovered AAnPs were thought to be limited to members of Alphaproteobacteria. This notion was challenged in 2002 when a study based on environmental genomics (9) suggested that some marine AAnPs genes likely originated from members of Gammaproteobacteria (10). The work of Fuchs et al. (11) in this issue of PNAS is the first to unequivocally assign these elusive AAnP genes to a cultured member of Gammaproteobacteria. Diversity of puf operons. Homologous regions are connected by dark gray areas. Puf …