Abstract
Abstract
The human gut is home to more than 100 trillion bacteria, where various environmental factors, such as nutrients and gases, exist and influence them. The levels of fermentation gases in the gut, including CO
2
, fluctuate depending on the host’s diet. However, how CO
2
, an environmental factor, affects the physiological states of gut anaerobes remains poorly understood, but CO
2
is often utilized in their cultivation.
Akkermansia muciniphila
(
A. muciniphila
) is widely studied as a beneficial human gut microbe. However, the effects of CO
2
on the physiological state of
A. muciniphila
are not fully understood. In this study, we focused on CO
2
as an environmental factor and aimed to clarify how CO
2
affects the physiological state of
A. muciniphila
. Culture experiments showed that compared with the absence of CO
2
, the presence of CO
2
significantly increased the growth of
A. muciniphila
. The results of the metabolomic analysis revealed distinct metabolic profiles in the presence or absence of CO
2
. The tracing analysis using stable
13
C-labelled CO
2
demonstrated that CO
2
was incorporated into various metabolites in the TCA cycle, the de novo purine/pyrimidine synthesis pathways, and other pathways. In addition, the activity of pyruvate carboxylase, which catalyses an anaplerotic reaction involving CO
2
fixation to supply oxaloacetate (OAA) to the TCA cycle, was significantly higher in
A. muciniphila
cells grown in the presence of CO
2
. Moreover, supplementation with OAA increased the growth of
A. muciniphila
in a dose-dependent manner, mirroring the effects of CO
2
supplementation. These findings suggest that
A. muciniphila
utilizes CO
2
for an anaplerotic reaction in the TCA cycle and other pathways involving CO
2
incorporation, facilitating metabolic flux to promote its robust growth.