PubMed · 1033775
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E T Reese. 1976. Cellulase production.. https://pubmed.ncbi.nlm.nih.gov/1033775/
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Cellulose is a renewable resource with broad biotechnological potential, and its hydrolysis by cellulases underpins applications such as biofuel production and biowaste valorization. This study combined isolation, screening, molecular identification, enzyme assays, genome sequencing, and bioreactor evaluation to characterize novel cellulase-producing bacteria. Preliminary screening identified and selected bacterial isolates by hydrolysis halo formation, with strains showing halos ≥ 20 mm selected for further quantitative assays. Streptomyces olivaceus C1_7A, Bacillus thuringiensis FBB7BB, and Bacillus licheniformis strains AT081C and AT082C showed the highest endoglucanase activities (from 0.11 to 0.26 U mL-1). Further testing on Arundo donax and Avicel led to the selection of B. thuringiensis FBB7BB and S. olivaceus C1_7A as the most promising strains for biotechnological application. Whole genome sequencing confirmed the presence of genes involved in polysaccharide degradation. Finally, lab-scale fermentation trials using 1-2% CMC showed that B. thuringiensis FBB7BB reached a maximum endo-1,4-β-glucanase activity of 0.30 ± 0.04 U mL-1 after 8 h at 37 °C, whereas S. olivaceus C1_7A achieved 0.36 ± 0.03 U mL-1 after 216 h at 30 °C.
An extremely highly active cellobiohydrolase (CBH IIb or Cel6B) was isolated from Chrysosporium lucknowense UV18-25 culture filtrate. The CBH IIb demonstrated the highest ability for a deep degradation of crystalline cellulose amongst a few cellobiohydrolases tested, including C. lucknowense CBH Ia, Ib, IIa, and Trichoderma reesei CBH I and II. Using purified C. lucknowense enzymes (CBH Ia, Ib, and IIb; endoglucanases II and V; beta-glucosidase, xylanase II), artificial multienzyme mixtures were reconstituted, displaying an extremely high performance in a conversion of different cellulosic substrates (Avicel, cotton, pretreated Douglas fir wood) to glucose. These mixtures were much or notably more effective in hydrolysis of the cellulosic substrates than the crude multienzyme C. lucknowense preparation and other crude cellulase samples produced by T. reesei and Penicillium verruculosum. Highly active cellulases are a key factor in bioconversion of plant lignocellulosic biomass to ethanol as an alternative to fossil fuels.
Particle size associated with accessible surface area has a significant impact on the saccharification of plant cell walls by cellulolytic enzymes. Small particle sizes of untreated cellulosic substrate are more readily hydrolyzed than large ones because of higher specific surface area. Pretreatment enlarges accessible and susceptible surface area leading to enhanced cellulose hydrolysis. These hypotheses were tested using ground corn stover in the size ranges of 425-710 and 53-75 microm. Ultrastructural changes in these particles were imaged after treatment with cellulolytic enzymes before and after liquid hot water pretreatment. The smaller 53-75 microm corn stover particles are 1.5x more susceptible to hydrolysis than 425-710 microm corn stover particles. This difference between the two particle size ranges is eliminated when the stover is pretreated with liquid hot water pretreatment at 190 degrees C for 15 min, at pH between 4.3 and 6.2. This pretreatment causes ultrastructural changes and formation of micron-sized pores that make the cellulose more accessible to hydrolytic enzymes.