Microbial degradation of lignin: how a bulky recalcitrant polymer is efficiently recycled in nature and how we can take advantage of this.
Bottom Line: Lignin is the second most abundant constituent of the cell wall of vascular plants, where it protects cellulose towards hydrolytic attack by saprophytic and pathogenic microbes.Ligninolytic microbes have developed a unique strategy to handle lignin degradation based on unspecific one-electron oxidation of the benzenic rings in the different lignin substructures by extracellular haemperoxidases acting synergistically with peroxide-generating oxidases.These peroxidases poses two outstanding characteristics: (i) they have unusually high redox potential due to haem pocket architecture that enables oxidation of non-phenolic aromatic rings, and (ii) they are able to generate a protein oxidizer by electron transfer to the haem cofactor forming a catalytic tryptophanyl-free radical at the protein surface, where it can interact with the bulky lignin polymer.
Affiliation: Centro de Investigaciones Biológicas, CSIC, Ramiro de Maeztu 9, E-28040 Madrid, Spain. FJRuiz@cib.csic.esShow MeSH
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Mentions: Lignin is a complex aromatic polymer, highly recalcitrant towards both chemical and biological degradation, characteristic of the cell wall of vascular plants (Fig. 1). Around 20% of the total carbon fixed by photosynthesis in land ecosystems is incorporated into lignin, being the second main constituent of plant biomass after cellulose. In addition of providing plant stems the rigidity required for growth on land, and waterproofing vascular tissues for sap circulation, a main role of lignin is to protect the cellulose polymer towards hydrolytic attack by most pathogen and saprophytic organisms. In spite of this, lignin‐degrading microbes evolved simultaneously with the colonization of land by vascular plants in the Palaeozoic era, around 400 million year ago (Taylor and Osborne, 1996). Microbial degradation of lignin (Martínez et al., 2005; Kersten and Cullen, 2007) represents a key step for closing the carbon cycle, since removal of the lignin barrier enabled the subsequent use of plant carbohydrates by other microorganisms.
Affiliation: Centro de Investigaciones Biológicas, CSIC, Ramiro de Maeztu 9, E-28040 Madrid, Spain. FJRuiz@cib.csic.es