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

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.

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Phenolic Acid-Mediated Regulation of the padC Gene, Encoding the Phenolic Acid Decarboxylase of Bacillus subtilis

Journal of Bacteriology ◽

10.1128/jb.01936-07 ◽

2008 ◽

Vol 190 (9) ◽

pp. 3213-3224 ◽

Cited By ~ 41

Author(s):

Ngoc Phuong Tran ◽

Jerôme Gury ◽

Véronique Dartois ◽

Thi Kim Chi Nguyen ◽

Hélène Seraut ◽

...

Keyword(s):

Bacillus Subtilis ◽

Phenolic Acids ◽

Phenolic Acid ◽

Acid Stress ◽

Acid Decarboxylase ◽

Decarboxylase Activity ◽

Gene Encoding ◽

Coding Sequence ◽

Phenolic Acid Decarboxylase

ABSTRACT In Bacillus subtilis, several phenolic acids specifically induce expression of padC, encoding a phenolic acid decarboxylase that converts these antimicrobial compounds into vinyl derivatives. padC forms an operon with a putative coding sequence of unknown function, yveFG, and this coding sequence does not appear to be involved in the phenolic acid stress response (PASR). To identify putative regulators involved in the PASR, random transposon mutagenesis, combined with two different screens, was performed. PadR, a negative transcriptional regulator of padC expression, was identified. padR is not located in the vicinity of padC, and the expression of padR is low and appears constitutive. This is in contrast with what occurs in other gram-positive bacteria, in which padR is autoregulated and induced by phenolic acids. Further screening of the transposon library failed to identify genes other than padR involved in the PASR. Modest inactivation of padR by phenolic acids was obtained in recombinant Escherichia coli expressing padC and padR, and this translates into induction of decarboxylase activity. Gel shift promoter binding assays performed with and without MgCl2, and with and without phenolic acids, demonstrated that phenolic acids were able to abolish the binding of PadR to the yveFG-padC promoter in the absence of MgCl2. Altogether, our results indicate that (i) PadR is inactivated directly by phenolic acids in vitro, (ii) inhibition of PadR in response to phenolic acids may occur without the need for a sensor-like effector in B. subtilis, and (iii) phenolic acids are able to modulate PadR activity in E. coli in the absence of any additional effector.

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