Functional genomic analysis of bacterial lignin degraders: diversity in mechanisms of lignin oxidation and metabolism.

Although several bacterial lignin-oxidising enzymes have been discovered in recent years, it is not yet clear whether different lignin-degrading bacteria use similar mechanisms for lignin oxidation and degradation of lignin fragments. Genome sequences of 13 bacterial lignin-oxidising bacteria, including new genome sequences for Microbacterium phyllosphaerae and Agrobacterium sp., were analysed for the presence of lignin-oxidising enzymes and aromatic degradation gene clusters that could be used to metabolise the products of lignin degradation. Ten bacterial genomes contain DyP-type peroxidases, and ten bacterial strains contain putative multi-copper oxidases (MCOs), both known to have activity for lignin oxidation. Only one strain lacks both MCOs and DyP-type peroxidase genes. Eleven bacterial genomes contain aromatic degradation gene clusters, of which ten contain the central β-ketoadipate pathway, with variable numbers and types of degradation clusters for other aromatic substrates. Hence, there appear to be diverse metabolic strategies used for lignin oxidation in bacteria, while the β-ketoadipate pathway appears to be the most common route for aromatic metabolism in lignin-degrading bacteria.