Isolation and characterization of tanninolytic bacteria from sheep rumen contents: Assessment of tannin degrading, fibrolytic and feed digestibility potential

To counteract the negative effects of phytotannins, ruminants host a diverse community of bacteria that break down tannins. These bacteria not only possess tanninolytic activity but also have other functional relevance that hasn't been properly examined. Therefore, the present study was conducted to isolate and characterize tannin degrading bacteria (TDB) from rumen of sheep fed tannin-rich diet with possible fibrolytic activity. Based on the development of a clear zone on tannin-enriched agar plates, a total of 24 isolates were screened as tannin hydrolyzing bacteria. Majority of the isolates were gram positive cocci. The isolates could tolerate phenolic monomers such as ferulic acid, gallic acid, vanillic acid up to 30mM and pyrogallol up to 10mM, while failed to grow in presence of syringic acid, p-coumaric acid and p-hydroxybenzoic acid. Highest and lowest tannase activity was observed in TDB23 and TDB2 and TDB5 isolates, respectively. In terms of fibrolytic activity, maximum endoglucanase, exoglucanase, and FPase activity was observed for TDB9. In vitro digestibility of Prosopis cineraria leaves was considerably enhanced by inoculation of isolate TDB23 followed by TDB9. Therefore, the screened isolates demonstrated promising tannin and fibre degrading potential as measured by their tannase and fibrolytic enzyme activities, which can be further explored as direct-fed microbial in ruminants for effective utilization of tannin-rich fibrous feeds.