The unique compositions of bacteria residing in the guts of mice are inherited from parents and remain more or less the same over many generations, according to a new study. The results suggest that vertical inheritance is the dominant mode of transmission for mammalian gut microbiota, though some human bacterial pathogens belong to genera that are well-suited for horizontal transmission in indoor environments, the authors say. The great diversity of bacteria that inhabit the mammalian gut affect their hosts' digestive, immune and neuroendocrine systems. However, how the specific bacterial populations that create these microbiomes are transmitted between hosts is not well-understood. Untangling the complex lineages of individual bacteria and differentiating the various modes of transmission over multiple generations has remained a challenge. To address these challenges, Andrew Moeller and colleagues conducted a long-term, multi-generational evaluation of microbiota transmission in the mammalian gut. Moeller et al. captured two populations of wild mice, from Arizona and Alberta, Canada, with distinct microbiota and monitored their microbiomes and those of their descendants for three years. The authors found that the individual- and population-level microbiota compositions were maintained within each of the mouse lineages and remained compositionally distinct after ten generations, indicating the dominance of vertical inheritance of microbiota. However, some gut bacteria were shown to be transmitted horizontally, likely through the laboratory environment. According to the authors, the types of bacteria that were shown to be transmitted horizontally throughout the shared environment tended to show more virulence than those transmitted vertically. This, say the authors, indicates that human bacterial pathogens belong to genera well-adapted to transmission in indoor environments, perhaps aided by increased oxygen tolerance.

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