Discussion
Here, we attempted to determine the role of very rapid (co)evolution of
taxa within a complex methanogenic community in shaping community
methane production. Methane production was increased by the addition of
a pre-adapted community, and this increase could not be explained by
direct changes in community composition.
Taken together, our findings data strongly suggests that only rapid
evolution, i.e within taxon variation, can explain the observed increase
in gas production, either directly, or indirectly through the resultant
changes in community composition. We emphasise that taxa here are
defined as 16S rRNA Amplicon Sequence Variants with <99%
similarity in the 254 bp V4 region of the gene. Within-ASV variation, on
which selection acted, may have been standing variation or have arisende novo by mutation or horizontal gene transfer, including
infection by mobile genetic elements. Unfortunately, current sequencing
and analytical approaches preclude identification of anything but a tiny
subset of genetic changes associated with microevolution within such
complex communities in the absence of target genes or multiple reference
genomes of each taxon , so we are unable to directly quantify the extent
of molecular evolution of individual community members.
It is unclear how far our results are generalisable to different
systems. Rapid evolution could potentially play an even more important
role in high nutrient, aerobic environments, where microbial population
growth rates are much faster because of greater energy availability .
That said, we used this experimental system because we anticipated rapid
evolution would play a particularly important role in altered community
functions. Methanogenic communities have a linear biochemistry,
funneling all the substrates to methane, and as a consequence selection
on many taxa likely acts in the same direction to ultimately increase
methane production, especially when a community is introduced to a novel
environment .
Irrespective of whether our findings are limited to methanogenic
communities, our results have relevance for understanding how methane
production may change in the face of environmental change. In addition,
from a more practical point, our novel approach could be used to enhance
industrial biogas production by, for example, pre-adapting industrial
communities to a feed shift. If our findings can be confirmed in other
non–AD systems, it opens doors for further applications, including
pre-adaption of gut microbiomes to help coping with gut-related
illnesses, rather than recruiting already adapted species by random
processes like fecal transplant , as a tool in harnessing rhizosphere
microbes to improve agricultural yields or to study the impact of rapid
evolution on adaptation to the warming planet .