Pistachio soft hulls contain tannins that are polyphenolic compounds with some antinutritional effects. This research aims to isolate and characterize tannin-degrading bacteria from goat feces consuming soft pistachio hulls as a TRD (tannin rich diet) with high potential application in tannin biodegradation.
Enrichment culture was used in minimal media containing tannin to isolate degrading bacteria. The isolates were identified by morphological, biochemical, and molecular characterization. In addition, tannase production, the maximum tolerable concentration (MTC), pH, and the tannic acid amount of the media were determined during degradation.
Four strains with tannin-degrading ability were isolated from feces of goat before (TA1) and after (TA2-4) consuming the TRD. In addition, 16S rDNA gene sequenceing, assigned TA1 and TA3 isolates to the genus Pseudomonas (ATTA 34), and TA2 to the genus Pantoea (ATTA33), and submitted to the GenBank (accession numbers KJ783441 and KJ783440). The isolates showed the MTC of 32 and 64g/L. The degradation percentage reached a maximum of more than 95% after 72h in the presence of 15g/L tannin. The pH as well as tannin utilization decreased except in the case of TA2, in which it increased again after 48h, which could be related to the gallate decarboxylase activity.
The TRD was able to induce adaptive responses. Although the bacteria were capable to detoxify and degrade the tannins, they needed to adapt to high concentrations of them (up to 64g/L). This study is the first report of Pantoa stewartii subsp indologenes with both tannase and gallate decarboxylase activities. These isolates possess wonderful potential for utilization in bioremediation, also minimization of tannins antinutritional effects in animal diets.
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