Cellulase production by Trichoderma : a crosstalk between the fungus and bacteria

Abstract

In recent years research concerning interactions of fungi and bacteria increased, due to the awareness that these might greatly influence properties of both organisms, such as antibiotics resistance or enzyme production. Fungal-bacterial interactions are not limited to specific species but can be found in different taxonomic groups. We recently found that Trichoderma spp. might form associations with Achromobacter sp. (esp. Trichoderma harzianum) and Burkholderia spp. (esp. Trichoderma reesei). Up to this point there is not much known about the impact of these relations; however, they are of great interest because of the industrial and agricultural importance of Trichoderma spp.. The ability of Trichoderma reesei to secrete large amounts of cellulases has long been known, but as a result of a continuously growing demand for cellulases in industrial applications, further improved strains are required in order to maximize efficiency, yield and minimize costs of cellulase production. In this thesis we investigated the effect of naturally associated bacteria on secretion of cellulases by Trichoderma. For this purpose T. reesei strains were cured of bacteria by a mixture of imipenem and ceftazidime and the success of the procedure was proven by molecular techniques. The effect on cellulase production was studied by fermenting two high cellulase producers of Trichoderma with and without their naturally associated bacteria, namely B. tropica and A. xylosoxidans, for 4 days in liquid medium with microcrystalline cellulose or lactose as carbon source. Samples were analyzed with regard to biomass production, secreted protein concentration and endo- and exocellulase activity. The results of this thesis show that T. reesei can be cured from B. tropica without visibly affecting or harming the fungus. Furthermore naturally associated bacteria do have an effect on cellulase production; however this effect is not uniform, but depends on the involved species and the available carbon-source. Results also suggest that the ratio of bacterial to fungal biomass is essential for optimal and probably beneficial interaction.