July 1, 2012
Ancestral Fungus May Have Influenced Coal Formation
Brett Smith for redOrbit.com - Your Universe Online
A new study suggests that the evolution of a fungus known as white rot may have ended a 60-million-year-long period responsible for coal deposition.
Coal deposits that occurred because of the Carboniferous Period, which ended about 300 million years ago, have fueled about 50 percent of U.S. electric power generation as recently as 2010.
The research, presented online in the June 29 edition of Science, points to the evolution of fungi capable of breaking down the organic polymer lignin, which helps keep plant cell walls rigid. Scientists said this may have played a key role in ending the development of coal deposits.
"When you read about coal formation it's usually explained in terms of physical processes, and that the rate of coal deposition just crashed at the end of the Permo-Carboniferous,” said the study´s senior author David Hibbett, a Clark University biologist.
“The evolution of white rot fungi could've been a factor — perhaps a major factor. Once you have white rot you can break down lignin, the major precursor of coal. So the evolution of white rot is a very important event in the evolution of carbon cycle."
Hibbett and his team focused their research on a group of fungi known as Agaricomycetes, which includes white rot fungi and a wide variety of other species. Within that group, the researchers compared 31 fungal genomes–26 of which were sequenced at the Department of Energy's Joint Genome Institute.
The study also involved tracing the evolution of lignin-decomposing enzymes. This was done through a techniques described as "molecular clock analyses." These analyses are based on the assumption that genes add mutations through evolution at predictable rates–in the same way that the hands of a clock move at constant rates. The ability to estimate these rates enables researchers to track mutations back through time and calculate about how recently fungal lineages diverged from a common ancestor.
Results of molecular clock analyses suggest that the oldest ancestor of the Agaricomcyetes was a white rot species that possessed multiple lignin-degrading enzymes and lived around 290 million years ago.
However, because these analyses have built-in errors and assumptions, fungal "fossils" are needed to calibrate the clock. For this study, the molecular clock analyses were calibrated against three fungal fossils. Hibbett said that more fossils would help improve their age estimates.
"Unfortunately," he added, "fungal fossils are rare and easily overlooked."
The value of continued fungal research is almost incalculable as fungi currently impact many fields, including agriculture and medicine. Scientists speculate that enzymes like those found and genetically sequenced in white rot fungi could be used in the future development of new biocatalysts.
"There's an estimated 1.5 million species of fungi," study co-author Joseph Spatafora of Oregon State University said. "We have names for about 100,000 species, and we're looking at 1,000 fungi in this project. This is still the tip of the iceberg in looking at fungal diversity and we're trying to learn even more to gain a better idea of fungal metabolism and the potential to harness fungi for a number of applications, including bioenergy. It's a really exciting time in fungal biology, and part of that is due to the technology today that allows us to address the really longstanding questions."