Environment-microbe-host interactions: understanding the relationship between the external environment, gut microbiome diversity, and host immunocompetence

Abstract

Microorganisms inhabiting the gastrointestinal tract of vertebrates co-exist with their hosts and may provide them with health and physiological benefits. However, environment-microbehost interactions within gut microbiome communities (GMCs) are poorly understood. In this study deer mice (Peromyscus maniculatus) were used to determine a) how the natural (wild) environment influences GMCs compared to captivity and b) how microbes associated with the natural environment as well as overall GMC α-diversity influences host immunocompetence. Captive- and wild-born deer mice were sampled twice (initial and post-translocation phases), twoweeks apart. After the initial sampling period a sub-sample of deer mice were reciprocally translocated between environments to assess how the external environment influences host GMCs and immunocompetence. Non-translocated individuals served as captive- and wild-born controls. GMCs were analysed via fecal samples, sequenced using 16S rRNA next –generation Illumina HiSeq sequencing. Host immunocompetence was determined using blood cell counts and a functional immune challenge (i.e. bacteria killing assay). Captive individuals possessed less diverse GMCs compared to wild individuals. Individuals translocated from captivity to the wild increase in GMC α-diversity, while individuals reciprocally translocated experienced a decrease. Individual’s GMCs clustered closer together with deer mice sharing the same environment. In natural environments deer mice had higher abundances of Ruminococcaceae, Helicobacteraceae, and Lachnospiraceae spp., than in captivity. No strong correlations were found between GMC α- diversity and host immunocompetence. Findings suggest that despite containing less diverse GMCs in captivity, upon reintroduction to natural environments deer mice GMCs rapidly changed, homogenizing with deer mice in the same environment. Future experiments should further study the effects of reduced exposure to Ruminococcaceae, Helicobacteraceae, and Lachnospiraceae during early-life stages, to better understand environment-microbe-host interactions.