Study of Tannin- degrading bacteria isolated from Pistachio soft hulls and feces of goat feeding on it

Introduction: Tannins (tannic acid) are toxic, high molecular weight and watersoluble polyphenols that are present in many plants such as pistachio and its byproducts. Wide ranges of microorganisms including bacteria tolerate tannin and degrade it. The aim of this study was to isolate and characterize tannintolerant bacteria from pistachio soft hulls (PSH) and feces of goat before and after feeding on this byproduct as tannin rich diet. Materials and methods: Tannin tolerant bacteria were isolated from enrichment cultures of samples in medium containing tannic acid as a sole source of carbon and energy. Tannin hydrolyzing ability of isolates was confirmed by observation of clear zones around the colonies. The increasing concentrations of tannin on minimal salt medium (MSM) agar plates were used to test the maximum tolerable concentrations (MTCs). Furthermore, in the supplemented media tannin concentrations were measured by bovine serum albumin (BSA) precipitation assay during time intervals. Results: Tannindegrading bacterial population of PSH was about only 10.3% of total population. More than 50 percent of tannin degrading strains were isolated from goat feces after grazing on tannin rich diet. Isolated bacteria were Gramnegative and positive rod species belonging to Klebsiella, Pseudomonas, Bacillus, Escherichia and Enterobacter genera. Among the isolated bacteria 71.4% could tolerate the concentration of 64 g/l of tannin in their media while only 7.2% were able to tolerate the maximum tannin concentration of 16 g/l. Bacterial isolates of goat feces could degrade tannin more than 72% after 72 h of incubation. In the case of soft PSH isolates, the biodegradation percentage was between 1775%. Discussion and conclusion: Feeding of tannin rich diet induced a shift in digestive system microbial profile with increased population of tannin tolerant bacteria. The ability of isolated strains provides novel insights for the role they can play in composting tannin containing wastes.