Bacteria of the Parcubacteria group discovered in the Mariana Trench

Sea sediments examined to look for bacteria (Photo courtesy Michael Graw/ University of Delaware)
Sea sediments examined to look for bacteria (Photo courtesy Michael Graw/ University of Delaware)

An article published in the journal “Environmental Microbiology” describes a study on a group of bacteria called Parcubacteria, a group that could be so large that it could be a superphylum. A team of scientists studied these bacteria that were found during the Deepsea Challenge expedition in the Mariana Trench by director James Cameron, who is among the authors of the article, to understand their characteristics with similarities and differences from bacteria living on the mainland.

In recent years, more and more sophisticated genetic research allowed to greatly expand the tree of life. In April 2016 an article published in the journal “Nature Microbiology” described a genetic research that offers a wider vision, adding a large branch that was called only with the vague expression “candidate phyla radiation”. In the evolutionary field, the term radiation indicates the diversification of life forms, in this case bacteria.

Douglas Bartlett of the Scripps Institution of Oceanograph, one of the authors of the article, was the chief scientist of the Deepsea Challenge expedition. Later he was the doctoral advisor of Rosa Leon-Zayas, the article’s lead author. During that expedition there was a collection of samples, including those in the Pacific Ocean’s Mariana Trench, the deepest in the world with the 10,994 meter depth measured in the area called Challenger Deep where the collection was carried out.

The “candidate phyla radiation” branch includes a number of phyla and superphyla candidates. One of them was initially identified only as OD1 and subsequently as Parcubacteria. Taxonomic definitions are not accurate and in this case there are scientists who are still analyzing newer groups of bacteria more or less different from each other so that whether Parcubacteria is a phylum or superphylum is still to be established.

Regardless, Parcubacteria species were discovered in groundwater and in shallow sediments in some areas of the mainland, for example among the many discovered in the area near the town of Rifle, Colorado. The examination of the samples taken in the Mariana Trench by James Cameron’s team revealed that Parcubacteria species also live there. Their metabolism is quite simple but their genomes are larger than those of their cousins ​​living on the mainland with some extra features.

For example, the bacteria of the abyss can perform anaerobic breathing, using compounds such as nitrates to breathe instead of oxygen. They also have proteins and enzymes associated with cold environments and scientists weren’t surprised thinking that the bottom of the Mariana Trench is a cold and dark place. It’s an environment in which self-sufficiency improves the chances of survival.

Jennifer Biddle, a professor at the University of Delaware and one of the authors of the article, confirmed that at this time those phyla and superphyla candidates are a major scientific area for discoveries and explained how a number of technological developments were the key to these progress. From a submarine capable of transporting scientists to the bottom of the Mariana Trench to new sophisticated specimen analysis instruments, everything contributed to these discoveries and will keep on doing it in the future.

However, the more scientists discover the more they realize what is still to be learned. In fact, over the last few years, thousands of species belonging to the phyla and superphya candidates of the “candidate phyla radiation” have been discovered but they’re groups of organisms that are very large from the point of view of diversification. New research and further technological developments could allow the discovery of a much larger number of species.

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