American researchers have found that a class of anaerobic fungi in the stomachs of herbivores can degrade lignin, the hardest component of plants. The discovery will help develop new ways to produce biofuels or fine chemicals from lignin. The related paper was recently published in the British journal Nature Microbiology.
Previous research on biodegradation of lignin has focused on aerobic reactions, such as certain enzymes from termite symbiotic fungi that degrade lignin in an aerobic environment, say researchers at the University of California, Santa Barbara. They demonstrated experimentally for the first time that two strains of the anaerobic fungus Neoribacteria flagellata were able to degrade lignin with higher efficiency than termite symbiotic fungi.
Fungi of the phylum Neoribacteria are important members of the microbiota of the digestive tract of herbivores. The researchers used two of these strains, placed in untreated chemically treated lignocellulosic media of willow jelly, sorghum and poplar, which represent the three main sources of lignin in nature: grass leaves, straw and wood.
By measuring the activity of the fungi in different media and changes in the composition of the lignocellulosic mixture before and after cultivation, the researchers confirmed that both fungi can degrade lignin, including that in wood, in an anaerobic environment.
Spectroscopic analysis also confirmed that some chemical bonds of the lignin molecule were broken.
Plants are mainly composed of cellulose, hemicellulose and lignin, collectively known as lignocellulose. Of these, lignin has the strongest structure and it is what makes wood hard and resistant to decay, but this property also makes lignin difficult to use in the modern biochemical industry.
The rumen of herbivores such as cattle and sheep has a large number of microorganisms that can degrade cellulose and hemicellulose in plants in an anaerobic environment, but it was previously uncertain whether these microorganisms could degrade lignin. The results open up new research directions for the utilization of lignin. Lignin is very abundant in nature, accounting for up to 30% of the dry weight of herbaceous plants, and effective degradation means can not only convert lignin into biofuels, but also be used to produce a variety of aromatic compounds.
