ARS | Publication request: Characterization of Thermostable Cellulases Produced by Bacillus and Geobacillus Strains

Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 1, 2010
Publication Date: July 29, 2010
Citation: Rastogi, G., Bhalla, A., Adhikari, A., Bischoff, K.M., Hughes, S.R., Christopher, L.P., Sani, R.K. 2010. Characterization of thermostable cellulases produced by Bacillus and Geobacillus strains. Bioresource Technology. 101(22):8798-8806.

Interpretive Summary: New enzymes that can degrade cellulose are needed to help overcome some of the technical barriers to using agricultural residues as feedstocks for fuel ethanol production. Compost systems and the deep subsurface mine of the former Homestake gold mine in Lead, SD contain microorganisms that grow at high temperature and that may be a source of new enzymes. In the present study, samples from these environments were examined for microorganisms that grew on cellulose. Eight strains of cellulose-degrading bacteria were isolated, two of which produced cellulose-degrading enzymes that were very stable at high temperatures. Results will be valuable to researchers developing new enzymes to serve as biocatalysts in the conversion of agricultural residues to fermentable sugars.

Technical Abstract: Bacterial community composition of thermophilic (60 deg C) mixed cellulose-enrichment cultures was examined by constructing a 16S rDNA clone library which demonstrated major lineages affiliated to Actinobacteria, Bacteroidetes, Chloroflexi, Deinococcus-Thermus, Firmicutes, and Proteobacteria. A total of eight isolates capable of degrading cellulose, CMC, or ponderosa pine sawdust were purified from different mixed enrichments and identified using 16S rDNA phylogenetic analysis which assigned them to genera Geobacillus, Thermobacillus, Cohnella, and Thermus. A selected compost strain WSUCFI (Geobacillus sp.) and a previously isolated deep gold mine strain DUSELR13 (Bacillus sp.) were examined for their enzyme properties and kinetics. The optimal pH for carboxymethyl cellulase (CMCase) activity was 5.0 for both isolates. The optimum temperatures for CMCase of WSUCFI and DUSELR13 were 70 and 75 deg C, respectively. Most remarkably, WSUCFI and DUSELR13 retained 89 to 78% of the initial CMCase activities, respectively, after incubation at 70 deg C for 1 day. For CMC, the DUSELR13 and WSUCF1 CMCases had Km values of 3.111 and 1.082 mg/ml, respectively.