In recent years, we're finding out more and more that our guts are actually an impressive ecosystem, influencing not only how we digest our food, but also how we think and behave. But now, researchers have taken it even one step further: we may need to define a whole new life form to describe these tiny residents.
The whole digestive tract is about nine metres (30 feet) long, and it's quite a unique environment, especially in terms of biochemistry; this uniqueness generated some rather strange relationships. Not only do microorganisms live in our stomach and they can help us digest food better, but they can even affect how we think. Previous studies have suggested gut bacteria may communicate directly with the brain. Notably, some people with liver disease experience positive mental ability change after given antibiotics. But as if that wasn't enough, a team from the Pierre and Marie Curie University in Paris, France reported that they found DNA sequences in these microorganisms that are beyond the three forms of life that we currently know of.
Basically, the three domain system divides cellular life forms into archaea, bacteria, and eukaryote domains. Archaea are somewhat similar to bacteria, but they have a different biochemical system and can survive in more extreme environments, bacteria are well... bacteria, and eukaryote is everything else: fungi, plants and animals. Now, it's important not to get ahead of ourselves, but if their study is correct, then we may have to re-think the complexity of our gut system, which makes its interaction with the rest of our body even harder to understand.
Researchers analyzed 230,000 DNA sequences that are related to known sequences in those 86 gene families, using these sequences as a starting point for their next analysis, through which they found an additional 80,000 stretches of microbial DNA that belonged in the 86 gene families. But in one third of this DNA, the structure was very strange, not belonging to any known domain of life. All in all, 40% of the DNA was previously unknown, a high enough figure to justify thinking about a new domain of life.
"Given that archaeal and bacterial homologs shared at least 60 % sequence identity, any environmental homologs of these gene families presenting > 40 % divergence (i.e., <60 % identity) would be more divergent from its homologs than sequences from two distinct domains of life. Such a high divergence, for these families, deserves to be considered significant, possibly hinting at very divergent organismal lineages, and/or reflecting a major genetic plasticity for these functionally important, apparently ancient gene families."
But before this is actually confirmed, researchers have to isolate and study these organisms in a lab environment, which of course, is no easy feat.
"These results underline how limited our understanding of the most diverse elements of the microbial world remains, and encourage a deeper exploration of natural communities and their genetic resources, hinting at the possibility that still unknown yet major divisions of life have yet to be discovered," concludes the report.
Journal Reference: Philippe Lopez, Sébastien Halary and Eric Bapteste - Highly divergent ancient gene families in metagenomic samples are compatible with additional divisions of life. Biology Direct 2015, 10:64 doi:10.1186/s13062-015-0092-3