Integrated Approaches to Reveal Genes Crucial for Tannin Degradation in Aureobasidium melanogenum T9.

Lin-Lin Zhang,Jie Li,Song Liu,Xin-Jun Yu,Zhi-Peng Wang,Yi-Lin Wang

doi:10.3390/biom9090439

Abstract

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, Aureobasidium melanogenum 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 tan A, tan B and tan C encoding three different tannases respectively were identified in the A. melanogenum T9. Among these genes, tan A and tan B can be induced by tannin acid simultaneously at both gene transcription and protein expression levels. Our assay result showed that the deletion of tanA and tanB 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 A. melanogenum T9 with 91.3 ± 5.8 U/mL. In addition, another gene coding gallic acid decarboxylase (gad) was knocked out to better clarify its function. Mutant Δgad 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 A. melanogenum T9. These results demonstrated that tanA, tanB and gad were crucial for tannin degradation and provided new insights for the mechanism of tannins biodegradation by yeast. This finding showed that A. melanogenum has potential in the production of tannase and metabolites, such as gall acid and pyrogallol.

Highlights

IntroductionAureobasidium genus is popularly known as black yeast due to its melanin production and is frequently encountered in soil, water, the phylloplane, wood, and many other plant materials [1,2]
Aureobasidium genus is popularly known as black yeast due to its melanin production and is frequently encountered in soil, water, the phylloplane, wood, and many other plant materials [1,2].Their ubiquitous distribution in diverse environmental conditions makes them an accessible source for biotechnological and environmental applications [3]
Most of the microorganism species used for tannin biodegradation were determined as fungi or bacteria, few researches were related with yeast

Summary

Introduction

Aureobasidium genus is popularly known as black yeast due to its melanin production and is frequently encountered in soil, water, the phylloplane, wood, and many other plant materials [1,2]. Their ubiquitous distribution in diverse environmental conditions makes them an accessible source for biotechnological and environmental applications [3]. Tannins are the second most abundant group of phenols in nature, and their molecular weight depends on the bonds possessed with proteins and polysaccharides [9]. Tannins negatively affect the nutritional quality of the feed and significantly reduce the intake by livestock because of their bitter taste [12,13]

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Findings

Discussion

Conclusion