Like humans, most animals have microbes in and on their bodies. All of these microbes together are called a microbiome. In the case of humans, large animals, and insects, these microbes are very important to their health. The microbes help with digestion, they make all kinds of essential substances and train the immune system. They live in symbiosis with their "host," which benefits both parties.
It was long thought that microbiomes of all animals function like ours. However, scientists at the University of British Columbia in the United States found that this is by no means the case in all animals.
The scientists looked at a large group of 1037 species from 21 phyla, which contains a broad group of tiny marine animals. These microscopic invertebrates belong to one of the largest, but least studied groups. The research showed that the bacteria living in these marine animals have a hidden agenda.
The exact composition of our microbiome varies from person to person. It depends on your genes, environment and diet. Moreover, our microbiome is specifically adapted to life in our body and not every bacterium can just live in our gut. The microbiome of the marine animals studied consisted mainly of microbes from their environment. Thus, the microbes are not specialized to live on the marine animals. Therefore, there are also no mutual benefits; the marine animals get nothing in return.
Our microbiome is more like the microbiome of our relatives, than the microbiome of strangers. And the microbiome of an elephant is more like the microbiome of other elephants, than that of an ostrich. In these invertebrates, this is not the case. The microbiomes of different types of marine animals may be more similar. So these bacteria do like to live in a host, but they don't care which host it is.
Take good care of this special relationship
From these special bacteria – that like to live inside hosts – likely evolved the symbiotic bacteria which are well researched in more complex animals and insects. So our special relationship with our microbes turns out not to be so obvious at all. So, we should cherish this.
Boscaro, V., Holt, C.C., Van Steenkiste, N.W.L. et al. Microbiomes of microscopic marine invertebrates do not reveal signatures of phylosymbiosis. Nat Microbiol 7, 810–819 (2022). https://doi.org/10.1038/s41564-022-01125-9
University of British Columbia. "Professional 'guilds' of bacteria gave rise to the modern microbiome." ScienceDaily. ScienceDaily, 26 May 2022. <www.sciencedaily.com/releases/2022/05/220526112858.htm.