Trichoderma, Sex, and Fuel

Aug 17, 2009

Trichoderma, Sex, and Fuel

A website featuring posts and blogs on green technology has posted an article about the genetic manipulation of a common fungus Trichoderma reesei, in order to develop biofuels. Scientists Force Fungus to Have Sex to Create Biofuel by Brian Nelson appears at CleanTechnica.com. The methods described seem to be good old fashioned selective breeding—not genetic engineering. This particular interest in Trichoderma is possibly related to ethanol production, as described in the paper Isolation and characterization of a Trichoderma strain capable of fermenting cellulose to ethanol. Interestingly, Trichoderma finds commercial use in the bleaching of denim for blue jeans and in manufacturing of paper, detergent, and chicken feed.

Typical appearance of Trichoderma sp. growing on wood (Robert L. Anderson)

From the article: “Originally discovered in the Solomon Islands during World War II eating away at the canvas and garments of the U.S. Army, scientists have long known that the soil fungus Trichoderma reesei was particularly good at converting cellulose– a major component of plant biomass– into glucose. But until now it has been difficult for researchers to improve the fungus because it was believed to be asexual.”

Interesting but the sexual phase of Trichoderma was actually discovered in the 1990’s. Read all about it in Sexual Trichoderma discovered.

But, there must be something new going on because another article Powerful Ideas: Fungus Sex Forced for Fuel, by Charles Q. Choi (funny comment on the bottom of that one too), mentions that the research was published online August 10, 2009 in PNAS. Sure enough. According to the abstract, the mating type loci have been discovered. Here’s the abstract (it’s an open access article) and a link to the full paper:

Sexual development in the industrial workhorse Trichoderma reesei

Abstract

Filamentous fungi are indispensable biotechnological tools for the production of organic chemicals, enzymes, and antibiotics. Most of the strains used for industrial applications have been—and still are—screened and improved by classical mutagenesis. Sexual crossing approaches would yield considerable advantages for research and industrial strain improvement, but interestingly, industrially applied filamentous fungal species have so far been considered to be largely asexual. This is also true for the ascomycete Trichoderma reesei (anamorph of Hypocrea jecorina), which is used for production of cellulolytic and hemicellulolytic enzymes. In this study, we report that T. reesei QM6a has a MAT1-2 mating type locus, and the identification of its respective mating type counterpart, MAT1-1, in natural isolates of H. jecorina, thus proving that this is a heterothallic species. After being considered asexual since its discovery more than 50 years ago, we were now able to induce sexual reproduction of T. reesei QM6a and obtained fertilized stromata and mature ascospores. This sexual crossing approach therefore opens up perspectives for biotechnologically important fungi. Our findings provide a tool for fast and efficient industrial strain improvement in T. reesei, thus boosting research toward economically feasible biofuel production. In addition, knowledge of MAT-loci and sexual crossing techniques will facilitate research with other Trichoderma spp. relevant for agriculture and human health.