Cyanobacteria are one of the unsung heroes of life on Earth. They first
evolved to perform photosynthesis about 2.4 billion years ago, pumping tons
of oxygen into the atmosphere – a period known as the Great Oxygenation
Event – which enabled the evolution of multicellular life forms.
Led by BTI faculty member Fay-Wei Li, researchers have discovered a new
species of cyanobacteria, Anthocerotibacter panamensis, which could help
illuminate how photosynthesis evolved to create the world as we know it. The
work was published in Current Biology on May 13.
“We never intended to discover a new species,” said Li. “It was a total
accident.”
His lab was working on a project to isolate cyanobacteria from hornwort
plants, and noticed something weird in a sample from a rainforest in Panama.
The researchers sequenced the cyanobacterium’s DNA, and found that it
belonged to a group called Gloeobacteria, which is extremely rare.
“Prior to this discovery, only two species of Gloeobacteria had been
isolated,” Li said. “There is also a third group of uncultured species from
the Arctic and Antarctic regions, but no one knows how many species are in
that group.”
Gloeobacteria diverged from the more commonly studied Phycobacteria about 2
billion years ago. The two groups have many differences, and A. panamensis
shares some traits with each.
Similar to other Gloeobacteria, the new species lacks thylakoids – the
membrane-bound compartments that are the site of the light-dependent
reactions of photosynthesis in Phycobacteria and plants.
“Now we can be pretty sure that the thylakoid evolved in Phycobacteria,” Li
said.
On the other hand, A. panamensis makes carotenoids – a group of compounds
that help protect an organism from sun damage – in a fashion similar to
Phycobacteria and plants, but different from the other Gloeobacteria.
“These results suggest that this particular carotenoid biosynthesis pathway
evolved in the ancestor of all cyanobacteria, and then was lost in some
Gloeobacteria,” said Li.
Li said one of the more interesting findings is that A. panamensis has very
few genes that encode the proteins that perform light-dependent reactions.
The researchers found that the new species could still perform
photosynthesis, but very slowly, which could be of interest to synthetic
biologists.
“If you want to build a complete set of photosynthetic machinery with the
fewest necessary components, then this species could inform how to do that,”
said Li. “Anthocerotibacter has a minimal set of photosystem subunits, but
it still functions.”
Reference
Rahmatpour N et al. "A novel thylakoid-less isolate fills a billion-year gap
in the evolution of Cyanobacteria". Curr. Biol. May 13, 2021. DOI:
https://doi.org/10.1016/j.cub.2021.04.042
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