P88: Activity of cellodextrin and cellobiose hydrolytic enzyme preparations from Bacillus strains isolated from sugarcane bagasse hot compost

The technical feasibility of cellulose conversion into bioethanol depends on the use of cellulases. The use of most commercial fungal cellulases, cause the accumulation of non fermentable oligosaccharides such as cellobiose and cellodextrins. Additional enzyme catalysis is needed for the full conversion of cellulose into fermentable glucose. In the present study, we report the selection of thermotolerant Bacillus strains isolated from hot compost, and their use for the production of crude preparations of highly thermostable β-glucosidase and cellobiohydrolase. Thirteen previously selected thermotolerant strains were screened for the production of enzymes, using  β-D-glucopyranoside and p-nitrophenyl β-D cellobiopyranoside. All strains proved to be producers of β-glucosidase, whereas only 8 were producers of cellobiohydrolase. Three strains were selected for their ability to produce β-glucosidase at temperatures above 55 ºC. Their fermentation supernatants showed 70% of initial enzyme activity after incubation for 4 hours at 70 ºC.  In one selected strain, a very high proportion (70%) of the β-glucosidase activity, remains after the addition of glucose (120 mM)  to the reaction mix. The selected strain EDCO-9 produced up to 50mU/mL when cultured in a defined liquid medium. EDCO-9 also produced cellobiohydrolase activity, although in lower concentrations than other 4 strains. Another Bacillus isolate, EDCO-7 produces up to 5 times more cellobiohydrolase activity (52 mU/mL) than EDCO-9, also at high temperatures. Ethanol tolerance and specific monosaccharide utilization are currently under study for both EDCO-9 and EDCO-7. Both enzyme production as well as host development for heterologous expression of catabolic pathways are interesting routes for development of the selected bacterial strains.