The mhqPOD gene cluster in lignin-degrading Paenibacillus sp. B2 encodes a pathway for the degradation of lignin-derived 5,5'-di(dehydrovanillic acid) (DDVA).

Lignin-degrading bacteria Paenibacillus sp. B2, Agrobacterium sp. B1, and Ochrobactrum sp. each contain mhqO genes encoding ring cleavage dioxygenase enzymes whose biochemical function is unknown. Each of these strains was found to degrade the biphenyl-containing lignin fragment 5,5'-di(dehydrovanillic acid) (DDVA) on solid media. An operon of five mhq genes in Paenibacillus sp. B2 was analysed via gene expression using quantitative PCR, and all five genes were highly induced (400-1000-fold overexpression) by the presence of DDVA. Recombinant azoreductase MhqP was found to demethylate DDVA to its monodemethylated derivative. Hence, these genes are proposed to be responsible for DDVA degradation, via a pathway involving the same biochemical steps as that studied in Sphingobium lignivorans SYK-6, but using several unrelated genes. Decarboxylation of later pathway intermediate 5-carboxyvanillic acid in Paenibacillus sp. B2 is proposed to be catalysed by decarboxylase UbiD, whose gene is also upregulated in the presence of DDVA. Degradation of the other fragment 4-carboxy-2-hydroxypentadienoic acid is proposed to occur via hydratase UxuA, whose gene is also upregulated by DDVA, and 4-hydroxy-4-methyl-2-oxoglutarate aldolase.