The emergence of oxygen-producing bacteria more than two billion years ago gave rise to life as we know it today, and now a new study reveals that this happening might have occurred multiple times. That is, select Cyanobacteria developed the ability to produce oxygen via photosynthesis only after diverging from the ancestor of all Cyanobacteria subgroups, the study suggests. The origin of oxygenic photosynthesis in Cyanobacteria transformed Earth, profoundly altering the course of evolution. Yet how and when Cyanobacteria came to evolve the ability to produce oxygen through photosynthesis remains poorly understood. There are at least three classes of Cyanobacteria: Oxyphotobacteria, Melainabacteria, and the ML635J-21 clade, only the first of which is known to produce oxygen. To explore the evolution of these groups in more detail, Rochelle M. Soo and colleagues analyzed 28 known Melainabacteria genomes, and 10 other Melainabacteria genomes that the authors say were previously misclassified. As well, they identified three genomes of ML635J-21, which they say were also previously misclassified. The authors found that none of these 41 genomes contain genes for energy reactions that create oxygen, suggesting that the last common ancestor of Cyanobacteria likely was not capable of photosynthesis. Rather, Oxyphotobacteria probably gained the ability for photosynthesis through lateral gene transfer after their divergence from the Melainabacteria, the authors say. Given when these bacterial groups diverged, which recent estimates peg to be about 2.5 to 2.6 billion years ago, these results strengthen the possibility that the rise of oxygen about 2.3 billion years ago was directly caused by the evolution of oxygenic photosynthesis. These results are highlighted in a Perspective by Robert E. Blankenship.
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Journal
Science