The gut bacteria of the family
Christensenellaceae
are consistently associated with metabolic health, but their role in promoting host health is not fully understood. Here, we explored the effect of
Christensenella minuta
amendment on voluntary physical activity and the gut microbiome. We inoculated male and female germ-free mice with an obese human donor microbiota together with live or heat-killed
C. minuta
for 28 days and measured physical activity in respirometry cages. Compared to heat-killed, the live-
C. minuta
treatment resulted in reduced feed efficiency and higher levels of physical activity, with significantly greater distance traveled for males and higher levels of small movements and resting metabolic rate in females. Sex-specific effects of
C. minuta
treatment may be in part attributable to different housing conditions for males and females. Amendment with live
C. minuta
boosted gut microbial biomass in both sexes, immobilizing dietary carbon in the microbiome, and mice with high levels of
C. minuta
lose more energy in stool. Live
C. minuta
also reduced within and between-host gut microbial diversity. Overall, our results showed that
C. minuta
acts as a keystone species: despite low relative abundance, it has a large impact on its ecosystem, from the microbiome to host energy homeostasis.
IMPORTANCE
The composition of the human gut microbiome is associated with human health. Within the human gut microbiome, the relative abundance of the bacterial family
Christensenellaceae
has been shown to correlate with metabolic health and a lean body type. The mechanisms underpinning this effect remain unclear. Here, we show that live
C. minuta
influences host physical activity and metabolic energy expenditure, accompanied by changes in murine metabolism and the gut microbial community in a sex-dependent manner in comparison to heat-killed
C. minuta
. Importantly, live
C. minuta
boosts the biomass of the microbiome in the gut, and a higher level of
C. minuta
is associated with greater loss of energy in stool. These observations indicate that modulation of activity levels and changes to the microbiome are ways in which the
Christensenellaceae
can influence host energy homeostasis and health.