Fungus genome opens pathways to next-generation biofuels
A team of French and US researchers have completed sequencing the entire genome of Trichoderma reesei, a fungus which is best known for its ability to break down and convert plant biomass into simple sugars. The work, which is partly EU-funded, is expected to open new and more efficient avenues for producing biofuels using non-food plants. Trichoderma reesei contains a number of enzymes, known as cellulases that have potent catalytic properties for breaking down plants. The fungus was first discovered in the South Pacific during the Second World War, where it wreaked havoc by eating through uniforms and canvas tents belonging to the US military corps based there. To find out more about these incredible enzymes, the researchers compared the fungus to 13 other fungal genomes. Much to their surprise, they found that T. reesei has a much smaller number of genes encoding its cellulases, a lot less than in other fungi that are capable of breaking down plant cell wall. 'We were aware of T. reesei's reputation as a producer of massive quantities of degrading enzymes, however we were surprised by how few enzyme types it produces, which suggested to us that its protein secretion system is exceptionally efficient,' said Diego Martinez, the study's lead author and researcher at the University of New Mexico. The researchers then turned their attention to the complexities of T. reesei's secretory pathway components. 'While little appears to have changed in the secretion machinery since divergence with a common ancestor with yeast,' said Dr Martinez. 'There are some intriguing differences in the way T. reesei processes some protein bonds important for cellulase production.' In their comparative analysis of T. reesei with other fungi, the team observed clustering of carbohydrate-active enzyme genes, which suggested a specific biological role: polysaccharide degradation. 'While plant tissues are not likely the main source of nutrients for T. reesei, upon detection of cellulose and hemicellulose it seems that the organization of these degrading genes may be the key to a rapid response,' explains Dr Martinez. The researchers say that the fungus could become the organism of choice for the production of second-generation biofuels. Because first-generation biofuels are made from many of the world's staple food crops, the race is on to develop second-generation fuels that don't interfere with the food chain and that use agricultural waste such as straw, tree cutting and corn cobs. 'The capacity for secreting copious amounts of extracellular enzymes, the availability of genetic tools and the straightforward, inexpensive fermentation of T. reesei make it an ideal candidate for producing enzymes useful for the conversion of biomass feedstocks such as corn stover, cereal straw and switch grass to fuel ethanol and manufacturing chemicals that are currently derived from nonrenewable resources,' write the authors of the study. Before these enzymes can be produced at economically viable levels, an increased understanding of the dynamics of cell growth and enzyme production will be needed. 'Mathematical and kinetic models are already being developed to optimize these processes, and the availability of a complete genome sequence will provide a blueprint to improve the models and to empower strain improvement strategies for creating superior enzyme mixtures from a single highly productive strain,' say the researchers. The study findings are published in the latest edition of Nature biotechnology. EU support for the research came from the EU-funded project FungWall project.