ACE2 and COVID-19: Four Bacteroides species, i.e., Bacteroides dorei, Bacteroides thetaiotaomicron, Bacteroides massiliensis and Bacteroides ovatus were reported to downregulate ACE2 expression in the murine colon, and were found to be inversely correlated with the fecal SARS-CoV-2 loads in severe COVID-19 patients (Geva-Zatorsky et al., 2017; Zuo et al., 2020c).