The microbial 7-OH epimerisation of cholic and chenodeoxycholic acids with
Xanthomonas maltophilia CBS 827.97 to ursocholic and ursodeoxycholic acids
with scarsity of oxygen is described. With normal pressure of oxygen the 7-
ketocholic and the 7-ketochenodeoxycholic acids are obtained. No biotransfo
rmation is achieved in anaerobic conditions.