| Summary: | Tannins biodegradation by a microorganism is one of the most efficient ways to produce bioproducts of high value. However, the mechanism of tannins biodegradation by yeast has been little explored. In this study, <i>Aureobasidium melanogenum</i> T9 isolated from red wine starter showed the ability for tannins degradation and had its highest biomass when the initial tannic acid concentration was 20 g/L. Furthermore, the genes involved in the tannin degradation process were analyzed. Genes <i>tan A</i>, <i>tan B</i> and <i>tan C</i> encoding three different tannases respectively were identified in the <i>A. melanogenum</i> T9. Among these genes, <i>tan A</i> and <i>tan B</i> can be induced by tannin acid simultaneously at both gene transcription and protein expression levels. Our assay result showed that the deletion of <i>tanA</i> and <i>tanB</i> resulted in tannase activity decline with 51.3 ± 4.1 and 64.1 ± 1.9 U/mL, respectively, which is much lower than that of <i>A. melanogenum</i> T9 with 91.3 ± 5.8 U/mL. In addition, another gene coding gallic acid decarboxylase (<i>gad</i>) was knocked out to better clarify its function. Mutant <i>Δgad</i> completely lost gallic acid decarboxylase activity and no pyrogallic acid was seen during the entire cultivation process, confirming that there was a sole gene encoding decarboxylase in the <i>A. melanogenum</i> T9. These results demonstrated that <i>tanA</i>, <i>tanB</i> and <i>gad</i> were crucial for tannin degradation and provided new insights for the mechanism of tannins biodegradation by yeast. This finding showed that <i>A. melanogenum</i> has potential in the production of tannase and metabolites, such as gall acid and pyrogallol.
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