Members of the fungal genus Trichoderma have been extensively studied, particularly due to their ability to secrete hydrolytic enzymes or to act as biocontrol agents. In nature, these fungi are normal microflora of soils, where they contribute in the degradation of cellulosic material. Through the production of specific enzymes, these fungi are able to degrade cellulose, a complex carbohydrate found in plants and plant material, and to produce simple sugars, such as glucose. These simple sugars can be used as "food" or carbon source, thereby re-introducing Carbon into the carbon cycle. This ability to degrade cellulose could be used in industrial processes to convert waste cellulose into fermentable sugars in a clean, non- polluting fashion.

The main enzymes involved in cellulose degradation are endoglucanase, exoglucanase and cellobiase. They are normally referred to as an enzyme complex, that is, several different enzymes that act step-wise in the hydrolysis of cellulose. There is a synergistic action in this complex, meaning that the activity of one member of the complex is enhanced by the activity of another member. In other words, for a successful hydrolysis of cellulose to take place, all of the enzymes have to be present. In addition, when one of the final sugar products (cellobiose) of this chain reaction accumulates, the system is shut down (repression). One of the objectives of our work was to find a fungus that produced all of the enzymes of the complex, and to derive from it a mutant in which is not repressed by cellobiose.

In addition to cellulose-degrading enzymes, Trichoderma are able to produce and secrete other enzymes. These enzymes are capable of degrading components that are normally present in other species of fungi. One of the most interesting aspects of these enzymes is their ability to degrade components of fungi that produce diseases in plants and crops. Because the skeleton of filamentous pathogenic fungi cell walls contains chitin, glucan and proteins, the enzymes that hydrolyze these components can successfully antagonize growth of the pathogen. Therefore, a fungus that is able to produce and secrete such enzymes can be envisioned as a natural pesticide. This type of agents is known as biocontrol agents. The successful use of such agents could reduce pollution produced by chemical pesticides.

We isolated Trichoderma from soils of southern Chile. We measured the ability of these isolates to produce and secrete enzymes that degrade cellulose, and chose one, Trichoderma aureoviride, for its high levels of enzyme production. This strain seemed particularly promising because it produced high levels of cellobiase, the enzyme that hydrolyzes cellobiose, thus relieving repression of the system.

The aim of this work was to further increase the natural ability of T. aureoviride to produce cellulases, through a program of mutation. After five successive mutagenic treatments we isolated a mutant, 7-121 in which the level of extracellular enzyme production was increased several-fold. Notably, the amount of cellobiase produced by the mutant increased 4-fold. Therefore, we think that T. aureoviride mutant 7-121 is a promising candidate for enzymatic hydrolysis of waste cellulose.

We further analyzed T. aureoviride, both the wild type and mutant strain, for its ability to produce enzymes responsible for biocontrol, namely ß-1,3 glucanases, chitinases and proteases. We found that mutant 7-121 produced all of the enzymes. In additon we demonstrated that T. aureoviride is able to grow on a susbstrate made of pathogenic fungi cell walls.

We conclude that the new isolate, Trichoderma aureoviride, and its mutant strain 7-121, are able to produce and secrete enzymes related to both cellulose degradation and biocontrol.