Monday, August 11, 2008
P94

Isolation and Selection of Thermotolerant Bacterial Strains Which Utilize Cellobiose and Cellodextrins as Sole Carbon Sources

C. De La Cerna - Hernandez, M. Plascencia - Espinosa, and S. R. Trejo - Estrada. Biotechnology, Centro de Investigación en Biotecnología Aplicada del Instituto Politécnico Nacional, CIBA-IPN Tlaxcala, Carretera Estatal Santa Ines Tecuexcomac - Tepetitla Km. 1.5, Exhacienda San Juan Molinos., Tepetitla, Mexico

Cellulose is the most abundant raw material for the production of biofuels. The technical feasibility of its use depends largely on the use of cellulases for hydrolysis. Most commercial cellulases, from fungal origin cause the accumulation of cellobiose and other oligosaccharides (cellodextrins) after the enzymatic treatment. These sugars are difficult to assimilate by the microorganisms commonly used for the conversion of sugars into ethanol. The present study is oriented towards the isolation and primary selection of bacterial strains capable of assimilation of cellobiose, cellotriose and cellotetraose as sole carbon sources. Thermotolerant grampositive bacilli were extracted from hot compost samples taken at the thermophilic stage of sugarcane bio-pile traditional processing. Enriched liquid cultures were prepared using minimal media with cellobiose or specific oligosaccharides as carbon sources. After incubation at 80 °C for 48 h, aliquots were plated in agar plates containing selective media. Fifty different strains were isolated in media containing cellobiose as a whole carbon source. A secondary screening comprised direct selection in cellotriose and/or cellotetraose, prepared by generated by enzymatic hydrolysis of Avicel and the subsequent fractionation by ultrafiltration of the hydrolysate. Thermotolerant bacilli strains capable of the utilization of oligosaccharides derived from cellulose are now under study in both pure culture and mixed culture fermentations for the production of ethanol.

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