A conserved vdcBCD cluster encoding a vanillate/p-hydroxybenzoate decarboxylase catalyzes the formation of phenol from p-hydroxybenzoate in the cork-associated Streptomyces graminifolii B37 strain

Abstract

Cork affected by yellow stain contains aromatic acids and volatile phenols, although the microbial reactions contributing to their formation are still poorly characterized. Streptomyces sp. B37, isolated from yellow-stained cork, was previously shown to convert p-hydroxybenzoate into phenol, but both its precise taxonomic placement and the genetic basis of this bioconversion were unknown. We combined whole-genome comparison, pangenome analysis, and heterologous expression to identify and validate the aromatic acid decarboxylation system underlying this phenotype. Phylogenomic analysis assigned strain B37 to Streptomyces graminifolii species. Comparative genomics showed that B37 belongs to a subclade of closely related Vanillate Decarboxylase (VDC)-positive genomes with an accessory repertoire enriched in functions related to aromatic compound uptake, regulation, redox metabolism and ring-cleavage pathways. In contrast, functions associated with primary cork-polymer degradation were not overrepresented. A conserved vdcBCD cluster was present in the genomes of Streptomyces species comprising this group and embedded in a partially conserved chromosomal neighborhood containing regulatory, oxidative and transport-related genes. Heterologous expression of the B37 vdcBCD cluster in Streptomyces lividans JI66 conferred the ability to decarboxylate p-hydroxybenzoate into phenol and vanillic acid into guaiacol, whereas the empty-vector control S. lividans JI66(pIJ699) showed no detectable decarboxylase activity. These results identify the B37 vdcBCD cluster as a bifunctional aromatic acid decarboxylation module and link this reaction to the formation of phenolic intermediates relevant to yellow-stained cork and cork taint-associated chemistry, including the de novo formation of chlorophenols and chloroanisoles.