Characterization of tannin acylhydrolase activity in the ruminal bacterium Selenomonas ruminantium

A strain of the anaerobe Selenomonas ruminantium subsp. ruminantium that is capable of growing on tannic acid or condensed tannin as a sole energy source has been isolated from ruminal contents of feral goats browsing tannin-rich Acacia sp. Growth on tannic acid was accompanied by release of gallic acid into the culture medium but the bacterium was incapable of using gallic acid as a sole energy source. Tannin acylhydrolase (EC 3.1.1.20) activity was measured in crude cell-free extracts of the bacterium. The enzyme has a pH optimum of 7, a temperature optimum of 30-40 degrees C and a molecular size of 59 kDa. In crude extracts, the maximal rate of gallic acid methyl ester hydrolysis was 6.3 micromol min(-1) mg(-1) of protein and the K(m) for gallic acid methyl ester was 1.6 mM. Enzyme activity was displayed in situ in polyacrylamide and isoelectric focusing gels and was demonstrated to increase 17-fold and 36-fold respectively when cells were grown in the presence of gallic acid methyl ester or tannic acid.