This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Scientists have discovered a previously unknown microorganism that has the smallest genome ever found and may be able to replicate and express its own genetic information. The microorganism belongs to the archaea, a group of single-celled organisms that are fundamentally different from bacteria.
The microbe is named Candidatus Sukunaarchaeum mirabile, or Sukunaarchaeum for short, in honor of a small Japanese god. It has an unusually small genome, but despite this, Sukunaarchaeum still contains the genes needed to copy its DNA and use its genetic information to make proteins. What makes the discovery particularly interesting is what Sukunaarchaeum does not have—it has lost almost all the genes needed to produce its own nutrients and energy.
This suggests that it depends heavily on other organisms for the resources it needs to survive. The research was carried out by an international team including researchers from the University of Nottingham and the University of Tsukuba in Japan. The findings are published in Current Biology.
Thorsten Allers, a professor in the School of Life Sciences at the University of Nottingham and a co-author of the study, said, "The key to defining life is whether something can replicate itself, and whether it can do this autonomously. This exciting discovery provides new clues about how simple a living cell can become while remaining capable of reproducing and maintaining its own genetic information." The research team discovered Sukunaarchaeum while analyzing the genetic material of individual marine microorganisms (plankton). The genome of Sukunaarchaeum is less than half the size of the smallest archaeal genome previously known and contains just 189 protein-coding genes.
The organism is also genetically very different from all previously known groups of archaea. Related genetic sequences found in marine samples suggest that Sukunaarchaeum is part of a much larger group of organisms that has so far gone largely unnoticed. Most organisms with very small genomes have given up some of their ability to function independently.
For example, mitochondria and chloroplasts inside cells, which were originally free-living bacteria, rely on their host cells for some of the machinery needed to copy and use their genetic information. Sukunaarchaeum, however, appears to have taken a different evolutionary path. "Although it has lost almost all of the genes needed to make nutrients and energy, it has kept much of the machinery required to copy its genome and produce proteins from its genetic information," says Allers.
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