The world’s coal deposits were roughly formed during a 60-million year period from 360 to 300 million years ago. Then, it stopped at the end of the Carboniferous period. What happened?
A team of 71 researchers from 12 countries, including the U.S. Department of Energy Joint Genome Institute (JOE JGI), published their study in the June 29 issue of Science. They postulated that the evolution of a white rot fungal ancestor was linked to the end of coal formation.
White rot fungi from the class of fungi known as Agaricomycetes are capable of degrading the polymer lignin. Lignin is found in plant tissues and is largely responsible for the rigid structure of plant cell walls.
The researchers postulated that fungal degradation of lignin caused plant matter to be broken down into its basic components and eventually released as carbon dioxide. Prior to this, dead matter accumulates as peat that later transforms as coal.
In order to test their theory, they studied 31 fungal genomes from the Agaricomycetes class of fungi. They used molecular clock analyses to trace the fungal lineage backwards to discover the evolution of the lignin-degrading peroxidases enzyme. The results of the analyses were calibrated against three fungal fossils.
The analyses showed peroxidases enzyme first appeared in a white rot fungal ancestor around 290 million years ago, roughly the end of the Carboniferous period. According to the researchers, once the white rot fungi became an ecological force, it destroyed great accumulations of plant matter that would have fossilized as coal.
Studies on fungal genome have many important applications, according to David Hibbet, senior author of the study and biologist at Clark University. Knowledge of fungal metabolism could help address the problem of breaking down cellulose, a plant carbohydrate, for conversion into biofuels via a fermentation process.
The ability of white rot fungi to decompose complex organic matter could also be exploited to break down hard to degrade contaminants. It could be a valuable tool for bioremediation processes.