Origin of the arthropod microbiota
Arthropod endogenous microbiota is typically adapted to the host and
genetically determined (Smee et al. 2021; Suppa et al.2020). However, environmentally acquired bacteria are also found in both
endogenous and exogenous microbiota of arthropods. These bacteria may
have specific regulatory responses and, therefore, may be selectively
acquired from the environment in each generation (Engel & Moran 2013;
Hannula et al. 2019). Typically, the exogenous microbiota is more
diverse than the endogenous one (Oliveira Ramalho et al. 2019).
Consistent with previous studies, we found that the captured arthropods
had significantly distinct microbiota and that the diversity of these
microbial communities varied among morphospecies showing, on average, a
lower diversity in endogenous than exogenous microbiota. Arthropods vary
in the extent to which microorganisms are essential to their survival
and fitness, with extremes represented by insects with little to no gut
microbiota but dependent on intracellular symbionts (e.g., sap feeding
insects), to insects with large and complex communities (e.g.,
termites). Most insects fall within this range with most having
moderately complex gut microbiota with ca. 20 abundant taxa (Hammeret al. 2017; McFall-Ngai 2007). Less is known about the diversity
of the exogenous microbiota associated with arthropods.
We found that human pathogenic bacteria were abundant in both the
endogenous and exogenous microbiota of the studied arthropods. However,
these pathogens were only present in indoor arthropods ecologically
associated with humans (synanthropic arthropods), and absent in the
microbiota of outdoor arthropods. This suggests that the microbiota may
be influenced by the environment, but that the establishment of
environmental microbes is genetically determined.
The culture-based approach showed severe limitations as compared to the
unbiased metabarcoding approach. Through metabarcoding, we were able to
identify a higher number of bacteria families and to obtain an unbiased
characterization of the arthropod’s associated microbiota. The
metabarcoding approach was also able to identify a higher number of
potentially opportunistic pathogens associated with the arthropods,
improving our understanding of the role of non-pest arthropods as
carriers of human pathogens. A parallel analysis of opportunistic
infections in humans and the opportunistic pathogens in indoor the
arthropods is necessary to establish the risk associated with non-pest
arthropods as carriers of human diseases. However, our study provides
important insights into the role that non-pest arthropods may have as
carriers of opportunistic pathogens in households.