The host genotype actively shapes its microbiome across generations

The microbiome greatly affects health and wellbeing. Evolutionarily, it seems unlikely that a host leaves microbial colonization of its offsprings to mere chance. Existing literature is inconclusive about two alternatively hypothesized mechanisms, active microbial shaping by host genetic factors or transmission of a microbial maternal legacy. To disentangle both factors we here obtained 2-cell stage embryos of two representative wildtypes, C57BL6/J and BALB/c, and transferred a mix of both genotype embryos into hybrid recipient mice to be inoculated by an identical microbiome at birth. Following the offspring along six generations clearly favors host genetic factors over maternal legacy in constant environments, like in murine laboratory experiments. Interestingly, only in the first offspring generation, maternal legacy dominated composition of the microbiome; reconciling the above dispute, as existing data in favor of maternal legacy did never extend beyond this first generation.