Lignin degradation by bacteria

The complex aromatic polymer lignin comprises about 25% of the land based biomass on earth, and its recycling is a vital component of the earth's carbon cycle. Its breakdown involves multiple biochemical reactions. Though the role of fungal lignin peroxidases has been well established only in recent years, bacterial lignin degradation has gained importance. Bacteria gain access to the polymer by mechanisms, such as tunnelling, erosion, and scavenging. Bacteria of several genera such as Alcaligenes, Acinetobacter, Pseudomonas, Rhizobium, Bradyrhizobium, Bacillus, and Streptomyces readily degrade numerous lignin model compounds. Acinetobacter utilized veratrylglycerol-∼-guaiacyl ether, indulin, 2-methoxy-4-formylphenoxyacetic acid, u-conidendrin and dehydrodiisoeugenol. Plasmid-mediated dissimilation of ferulic acid and guaiacolglyceryl ether has been established in Bacillus subtilis. Cloning, sequencing, and expression of the genes involved in the dissimilation of lignin substances have been done from Bacillus subtilis to improve the degradation efficiency. The most recent advances in genetic engineering are to create potential lignin-degrading bacteria and also to elucidate the molecular mechanisms involved.