Sphingobium sp. SYK-6 can utilize lignin biphenyl compounds, such as 2,2'-dihydroxy-3,3'-dimethoxy-5,5'-dicarboxybiphenyl (DDVA). In the metabolism of DDVA, this microorganism exploits two O -demethylation systems with different substrate specificities, namely, a DDVA-specific oxygenative O -demethylation system and a vanillate-specific (VA-specific) tetrahydrofolate-dependent (THF-dependent) methyltransferase system. We examined the way in which these two systems interact in the metabolism of lignin in Sphingobium sp. SYK-6. Our results indicate that THF accepts methyl groups derived not only from the THF-dependent O -demethylation of VA but also from the oxygenative O -demethylation of DDVA. Thus, the methoxyl groups of lignin model compounds are an essential source of carbon in Sphingobium sp. SYK-6. ((c) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim).