ACE2 and COVID-19: Interestingly, the expression of ACE2 is, at least in part, modulated by the GM as some species within the Bacteroides genus, such as B. dorei, B. thetaiotaomicron, B. massiliensis, and B. ovatus, have been shown to downregulate ACE2 expression in murine colonocytes, potentially limiting viral entry and correlating with less severe COVID-19 outcomes (Zuo et al., 2020).