An article published in the journal “Current Biology” reports the discovery of a cyanobacterium that was named Anthocerotibacter panamensis. A team of researchers led by Fay-Wei Li of the Boyce Thompson Institute examined this bacterium discovered on a tropical plant in Panama and found that it has very rare characteristics that make it related to the rarest group of cyanobacteria, Gloeobacteria, which diverged from the most common group, Phycobacteria, about 2 billion years ago. The new species has some characteristics in common with both groups, which offers new insights into these oxygen-producing photosynthetic bacteria.
Generally only scientists care for cyanobacteria but their evolution of photosynthesis radically changed the planet Earth. At that time, large quantities of oxygen were released into the Earth’s atmosphere for the first time thanks to cyanobacteria. However, this resulted in a mass extinction of anaerobic life forms for which oxygen was lethal, and for this reason, that event is known by names such as Great Oxidation Event, Great Oxygenation Event, Oxygen Catastrophe, Oxygen Crisis, Oxygen Holocaust, or Oxygen Revolution. From the point of view of organisms that could use oxygen in their metabolism, it represented the possibility of generating greater amounts of energy and consequently accelerated their evolution.
The history of cyanobacteria is crucial in the history of life on Earth but is not yet well known. The classification of these bacteria has been under discussion for years and today there’s a tendency to adopt the one that divides them into Gloeobacteria, very rare, and Phycobacteria, very common. The rarity of the Gloeobacteria group increases the difficulties in reconstructing the evolution of cyanobacteria and any new information can make a difference.
The chance discovery of a new species with characteristics closer to Gloeobacteria but also with some typical of Phycobacteria can help to reconstruct their evolution. This also means having new clues about their role in producing the oxygen present in the Earth’s atmosphere.
The species Anthocerotibacter panamensis is devoid of thylakoids, a feature in common with other Gloeobacteria. This is an interesting discovery considering that thylakoids are the site of the reactions of photosynthesis in cyanobacteria. Despite this, this cyanobacterium can perform photosynthesis, albeit very slowly. This finding indicates that thylakoids evolved into Phycobacteria.
Another feature of Anthocerotibacter panamensis is that it produces carotenoids, compounds that protect organisms from damage that can result from exposure to sunlight. This production occurs in a way that is typical of the Phycobacteria group and different from the way used by the Gloeobacteria. This suggests that it’s a type of biosynthesis that evolved into the common ancestor of all cyanobacteria and was lost in Gloeobacteria.
Any cyanobacterium not classifiable in the Phycobacteria group can offer important information about cyanobacteria. An article published in “The ISME Journal” in May 2020 reports the description of a new cyanobacterium candidate that was named Aurora vandensis closely related to the Gloeobacteria group. It’s a result of a metagenomic study so there may be follow-up analyzes.
In addition to useful information to reconstruct the history of cyanobacteria, the discovery of Anthocerotibacter panamensis could be useful in the development of biotechnologies related to photosynthesis. This cyanobacterium is slow in photosynthesis but the genetic structure that manages this function is relatively simple compared to other cyanobacteria, making it interesting to study and perhaps to introduce into other types of organisms.
