Laboratory Animals - June Issue - 253

Viney

Gut microbiota of wild mice, Mus spp.
The laboratory mouse (Mus musculus domesticus) is
perhaps the pre-eminent laboratory model, but there
has only been limited study of wild Mus spp.3,4
Analysis of the microbiota of M. m. domesticus from
eight diﬀerent European sites showed that the patterns
of microbiota diversity was most strongly aﬀected by
the geographical origins of the mice, more so than their
genetic relationship.5 Comparison of the caecal
mucosa-associated and caecal luminal bacterial communities, found that these were more similar within
individual mice, than mucosa-associated or lumenassociated microbiota were among diﬀerent mice, overall pointing to the substantial inter-individual diﬀerences in wild-mouse microbiota composition.5
A second study of wild M. m. domesticus also found
substantial inter-individual diﬀerences in the gut microbiota, with individuals' microbiota largely clustering
according to the three diﬀerent locations from which
they were obtained.6 This work also found that the
caecal and rectal microbiota of individuals were on
average more similar within an individual, than were
caecal or rectal samples among individuals,6 broadly
consistent with previous work.5 Despite a relatively
small sample size, there were signiﬁcant correlations
between microbiota diversity and animals' age, body
mass, body mass index, as well as virus and macroparasite infection status.5 Analysis of wild M musculus
from New York City found consistent bacterial taxa
across the city and over a six-month period, which
was broadly similar to those described from wild mice
elsewhere.6,7 There was evidence of bacteria potentially
pathogenic in people among these New York City
mouse populations.7
Analysis of the spatial organisation of bacteria at 10
sites along the gut of wild M. musculus showed that
measures of microbial diversity changed along the
gut, with the highest diversity in the caecum, colon,
rectum and faeces, where anaerobic species were more
abundant too.8 Consequently, predicted microbiota
gene function also diﬀered between the upper- and
lower-intestinal sites. Consistent with other studies in
Mus,5,6 there were signiﬁcant diﬀerences among individual mice in their gut microbiota, with this eﬀect
more pronounced for the more anterior gut sites.8
Analogous observations in wild woodrats, Neotoma
spp., also described variation in the number of live bacterial cells along the host gut, with the taxonomic variety of these also diﬀering longitudinally and being
discordant between neighbouring gut sections.9
In summary, studies of Mus spp. have concluded
that there are signiﬁcant inter-individual diﬀerences
in the gut microbiota, which raises important questions of the causes and consequences of this for
wild animals.

253

Gut microbiota of wild and laboratory animals compared
Comparison of the gut microbiota of wild M. musculus,
laboratory M. m. domesticus and laboratory M. m.
musculus showed strong diﬀerentiation of the microbiota of the wild and laboratory animals, while the
microbiota of the two laboratory sub-species did not
diﬀer.10 In a separate study, analysis of the microbiota
of wild M. m. domesticus and M. m. musculus across
their hybrid zone in central Europe and a comparison
with laboratory-generated hybrids, showed that measures of the microbiota diversity diﬀered between wild
and laboratory animals, between sub-species in the
laboratory (but not in the wild), between sub-species
and hybrids, but not between male and female animals,
nor due to macroparasite infection.11 Genetic mapping
of the diﬀerence between the mouse sub-species' microbial abundance and microbiota diversity showed that
fewer than 20 loci could explain much of this.11
The diﬀerences observed in the microbiota of wild
and laboratory Mus raise the question of the extent to
which the microbiota of wild animals persist when they
are brought into captivity? This has been explicitly studied in the desert woodrat Neotoma lepida, which found
that during 6 months' captivity there was a persistence
of the wild microbiota, though the relative abundance
of the community members changed.12 The reverse
experiment (where laboratory M. m. domesticus were
released into a near-wild environment) showed that
the microbiota of rewilded mice rapidly changed away
from those of laboratory maintained controls.13
In wild M. m. domesticus there is evidence of two
diﬀerent microbiota 'enterotypes' - community of signature taxa.12 Tracking of wild animals from when they
moved into the laboratory showed that the microbiota
moved to just one of the two enterotypes, with this
change in enterotype hypothesised to be driven by
changes in the animals' diet.14
Direct comparison of the ileocaecal microbiota of
wild and laboratory M. m. domesticus found that
in mice from diﬀerent locations the microbiota had a
similar community structure, but one that diﬀered to
that of laboratory mice.15 A series of elegant gut microbiota transplant experiments showed that the microbiota of laboratory mice could be altered by the
transplant of wild-mouse microbiota, though this
didn't completely recreate the microbiota of wild
mice.15 The gut microbiota of mice had a profound
eﬀect on their immune responses following a virus
infection, such that standard laboratory mice were
killed by the infection, whereas laboratory mice that
had received wild mouse microbiota were resistant to
it.15 These diﬀerent infection outcomes were due to
reduced inﬂammatory responses in laboratory mice in
receipt of the wild mouse microbiota, thus showing the
Laboratory Animals - June Issue

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