Isolation and Characterization of Tannin-Degrading Bacteria from the Rumen of Goats Fed Oak (Quercus semicarpifolia) Leaves

Abstract

Tannin-degrading bacteria (TDGB) were isolated from the rumen of goats fed oak leaves containing diet. The isolates were screened for their ability to increase in vitro digestibility of oak leaves (Quercus semicarpifolia), and fifteen best isolates were selected for further characterisation. The isolates TDGB 19, 20, 406, 415, 417, 420, 425, 437, 446, and 450 were Gram-positive cocci with medium- and long-chains, and isolates TDGB 409, 428, 430, and 433 were Gram-positive cocco-bacilli of short chain length. All the isolates exhibited tannase activity with the maximum in TDGB 417 (72.0 units; nmol methyl gallate degraded/min/ml) and minimum in TDGB 433 (28.92 units). All the fifteen isolates utilized fructose, galactose, lactose, starch, maltose, glycerol, and mannose as carbon source. The isolates were tested for their tolerance to phenolic monomers like ferulic acid, vanillic acid, coumaric acid, pyrogallol acid, and gallic acid. All the isolates could tolerate the presence of pyrogallol and gallic acid up to 20 mM, but ferulic was toxic at 20 mM level for all the isolates. The isolates were able to degrade tannic acid to pyrogallol except isolates TDGB 409, 428, 430, and 433, which could degrade tannic acid only up to gallic acid after 24 h of incubation as assessed by thin-layer chromatography. None of the isolates degraded tannic acid to resorcinol even after 96 h of incubation. The phylogenetic analysis of the isolates using sequences of PCR amplicons generated by the three sets of primers, two primers sets targeting 16S rRNA gene and one targeting sodA gene for superoxide dismutase enzyme, revealed that the isolates TDGB 7, 19, 20, 406, 417, 446, and 450 formed a close cluster with Streptococcus gallolyticus with 99 to 100 % similarity in all the three phylogenetic trees. There was a maximum of 11 % improvement in vitro true degradability of tannin-rich feed in the presence of live culture of TDGB 406 and can be exploited as a probiotic to improve nutrient utilization of tannin-containing feed given to the livestock.