The era of COVID-19 and the need to constantly wash one’s hands and sanitize
things have brought microbes to new levels of scrutiny, particularly for
their impact on an individual’s health.
While associations between microbes and their hosts, from the beneficial —
think probiotics in yogurt — to the harmful — such as with viruses spread by
touch — have long been known, little is known about how microbes evolve and
how their evolution affects the health of their hosts.
Now, researchers at the University of Toronto and the University of Illinois
at Urbana-Champaign have found that as microbes evolve and adapt to their
unique hosts, they become less beneficial to hosts of other genotypes.
The findings suggest that there is probably not one universally healthy
microbiome. Rather, transplanted microbes might need time to adapt to a new
host before they bring benefits.
“There is this prevailing idea that the ‘survival of the fittest’ means that
individuals should reap the benefits others have to offer without
reciprocating,” says Megan Frederickson, associate professor in the
Department of Ecology & Evolutionary Biology at the University of
Toronto, and senior author of a study published in Science. “We found that
over time, microbes became better adapted to their hosts through the
evolution of more, rather than less, cooperation.”
The researchers, led by Frederickson and lead author Rebecca Batstone, a
graduate of Frederickson’s lab and now a postdoctoral fellow at the
University of Illinois at Urbana-Champaign, set out to learn what happens to
microbes when paired with the same host across multiple generations of that
host.
Their first step was to grow several hundred specimens of the clover-like
Medicago truncatula plant in a greenhouse, giving each an initial mixture of
two strains of the nitrogen-fixing bacteria Ensifer meliloti. Subsequently,
they re-planted new seeds into the same pots, and repeated the process for a
total of five plant generations.
After a year in the greenhouse, the researchers grew a new batch of plants,
and tested the evolved microbes on them, mixing and matching different
evolved microbes and different hosts. They compared how well the plants grew
and how many associations they formed when they were given the original or
evolved microbes, and when they were given microbes that evolved on
different hosts.
Finally, the researchers sequenced the entire genomes of original and
evolved microbes to see how they differed genetically.
“When we put microbes from the beginning and the end of the experiment back
onto hosts, we found they did best with the same hosts they evolved on,
suggesting they adapted to their local host,” said Batstone. “The derived
microbes were more beneficial when they shared an evolutionary history with
their host.”
The researchers say the finding suggests that evolution might favour
cooperation and that scientists might be able to use experimental evolution
in a laboratory setting to make microbes that provide more benefits to their
hosts.
“When plants or even animals arrive in new environments, perhaps as invasive
species or because they are responding to a changing climate, the microbes
they encounter may be initially poor partners. But these microbes might
rapidly adapt and develop a more beneficial relationship,” said
Frederickson.
Reference:
“Experimental evolution makes microbes more cooperative with their local
host genotype” by Rebecca T. Batstone, Anna M. O’Brien, Tia L. Harrison and
Megan E. Frederickson, 23 October 2020, Science.