The arom. polymer lignin represents a possible renewable source of arom. chems., if biocatalytic routes for lignin breakdown can be developed. The availability of a genome sequence for Rhodococcus jostii RHA1, a bacterium that breaks down lignin, has allowed the application of a targeted pathway engineering strategy to lignin breakdown to produce vanillin, a valuable food/flavor chem. A gene deletion strain of R. jostii RHA1 in which the vanillin dehydrogenase gene had been deleted, when grown on minimal medium contg. 2.5% wheat straw lignocellulose and 0.05% glucose, was found to accumulate vanillin with yields of up to 96 mg/L after 144 h, together with smaller amts. of ferulic acid and 4-hydroxybenzaldehyde. [on SciFinder(R)]