Of fungi, coal and oil
The earth’s oil and coal reserves are remnants of ancient forests. The formation of coal beds stopped about 300 million years ago. A recent article published in Science magazine confirms that this was not only because of the climate, but also because of the evolution of fungi.
Wood is the most important source of organic coal in the earth’s terrestrial ecosystems. Tree trunks mainly consist of cellulose, hemicellulose and lignin. Wood is hard and highly resistant to decay, owing largely to the lignin it contains.
– White rot fungi are the only organisms capable of lignin decay. These include some of the bracket, cap and corticioid fungi. The development of the enzymatic ability of white rot fungi to decay lignin prevented the further formation of vast coal beds in the earth’s crust, says University Lecturer Taina Lundell from the Department of Food and Environmental Sciences. She was the only Finnish member in the international research group that studied the Paleozoic origin of enzymatic lignin decomposition.
The evolutionary lineage of fungi spans nearly a billion years. The first peroxidase enzyme capable of decaying lignin was introduced in basidiomycetous fungi about 295 million years ago. This means that the genetic development of the ability of white rot bracket and cap fungi to decay lignin took place in the late Carboniferous period and the early Permian period, about 300 to 250 million years ago.
– Genomics research strongly supports an earlier, unconventional hypothesis of the connection of fungal evolution on the earth’s geological periods, says Lundell.
The reasons behind the development of white rot fungi into powerful decomposers of wood were examined by means of bioinformatics and comparative genomics. The research project further specified recent genomics information on 31 fungal species, focusing on the decomposition of the constituents of wood and the diverse protein families of the enzymes required for the conversion.
The researchers also studied fungal evolution and development of wood decay. White rot fungi belong to a class that also includes species incapable of lignin decay. Some fungal lineages lost the genes encoding the powerful peroxidases needed in the decay process.
– This resulted in the development of brown rot fungi as well as mycorrhizal fungi, Lundell explains.
More than 70 mycologists and enzyme researchers from North America, Europe and Japan participated in the research project, which was coordinated by Prof. David S. Hibbett at Clark University, MA, USA. The sequencing of fungal genomes was carried out at the DOE Joint Genome Institute in California. Lundell’s research group focuses on studies in the enzymology, ecophysiology and genomics of wood decay fungi.
Text: Sanna Schildt
Photo: Taina Lundell
Translation: AAC Global
University of Helsinki, digital communications
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