Indexed on: 25 Jan '17Published on: 25 Jan '17Published in: Applied and environmental microbiology
Lactobacillus plantarum is a lactic acid bacterium able to degrade food tannins by the subsequent action of tannase and gallate decarboxylase enzymes. In the L. plantarum genome the gene encoding the catalytic subunit of gallate decarboxylase (lpdC or lp_2945) is only 6.5 kb distant relative to the gene encoding inducible tannase (tanBLp or lp_2956). This genomic context suggests a concomitant activity and regulation of both enzymatic activities. Reverse transcription analysis revealed that B (lpdB or lp_0271) and D (lpdD or lp_0272) subunits of gallate decarboxylase are cotranscribed, whereas C subunit (lpdC or lp_2945) is cotranscribed with a transport protein (gacP or lp_2943). Contrarily, tannase is transcribed as a monocistronic mRNA. Knockout mutants of genes located in this chromosomal region indicated that only mutants of gallate decarboxylase (B and C subunits), tannase, GacP transport protein and TanR transcriptional regulator (lp_2942) genes, exhibited an altered tannin metabolism. The expression profile of genes involved in tannin metabolism was also analysed in these mutants under the presence of methyl gallate and gallic acid. Noteworthy, the inactivation of tanR suppress the induction of all genes overexpressed in the presence of methyl gallate and gallic acid. This transcriptional regulator was also induced in presence of other phenolic compounds such as kaempferol and myricetin. This study complement the catalog of L. plantarum expression profiles responsive to phenolic compounds that enable this bacterium to better fit in a plant food environment.Lactobacillus plantarum is a bacterial species frequently found in the fermentation of vegetables when tannins are present. L. plantarum strains degrade tannins to the less toxic pyrogallol by the successive action of tannase and gallate decarboxylase enzymes. The genes encoding these enzymes are close located in the chromosome suggesting a concomitant regulation. Proteins involved in tannin metabolism and regulation, such GacP (gallic acid permease) and TanR (tannin transcriptional regulator) were identified by differential gene expression on knockout mutants on genes from this region. This study provides insights on the highly coordinated ways that enable L. plantarum to better adapt to plant food fermentations.