Cloning of endoglucanase genes from Cellulomonas biazotea into E. coli and S. cerevisiae using shuttle vector YEp24

Cloning and heterologous expression of a novel endoglucanase gene egVIII from Trichoderma viride in Saccharomyces cerevisiae

Endoglucanase is a major cellulolytic enzyme produced by the fungus Trichoderma viride. The 1,317 bp cDNA of endoglucanase gene egVIII was cloned from T. viride AS3.3711, encoding a 438 amino acid protein with a calculated molecular mass of 46.86 kDa and isoelectric point of 4.32. Sequence analysis suggested that EGVIII belonged to the glycosyl hydrolase family 5. The N-terminal region of EGVIII contains a signal peptide sequence of 19 amino acid residues, indicating that it is an extracellular enzyme. Transcription of the egVIII gene in T. viride AS3.3711 can be induced by carboxymethyl cellulose sodium (CMC-Na), sucrose, microcrystalline cellulose, and corn stalk, and inhibited by glucose and fructose. The alpha-mating factor signal can effectively enhance the secretion of the recombinant EGVIII in Saccharomyces cerevisiae, as demonstrated by the enzymatic activity of recombinant yeast IpYEMalpha-xegVIII in the supernatant, which was 0.86 times higher than that of the IpYES2-egVIII. Recombinant endoglucanase EGVIII showed optimal activity at a temperature of 60 degrees C and pH of 6.0. It was stable when incubated from 35 degrees C to 70 degrees C for 1 h. The enzymatic activity of recombinant EGVIII was stable at a pH 3.0 to 7.5 at 50 degrees C and reached the highest level at 0.174U when activated by 75 mM of Zn(2+). The Michaelis-Menten constant (Km) and Kcat values for CMC-Na and cellotriose hydrolysis were 3.82 mg/ml, 9.56 s(-1) and 1.75 mg/ml, 7.08 s(-1), respectively. Transgenic yeast strain IpYEMalpha-xegVIII might be useful for renewable fuels industries.

Consolidated bioprocessing for bioethanol production using Saccharomyces cerevisiae

Consolidated bioprocessing (CBP) of lignocellulose to bioethanol refers to the combining of the four biological events required for this conversion process (production of saccharolytic enzymes, hydrolysis of the polysaccharides present in pretreated biomass, fermentation of hexose sugars, and fermentation of pentose sugars) in one reactor. CBP is gaining increasing recognition as a potential breakthrough for low-cost biomass processing. Although no natural microorganism exhibits all the features desired for CBP, a number of microorganisms, both bacteria and fungi, possess some of the desirable properties. This review focuses on progress made toward the development of baker's yeast (Saccharomyces cerevisiae) for CBP. The current status of saccharolytic enzyme (cellulases and hemicellulases) expression in S. cerevisiae to complement its natural fermentative ability is highlighted. Attention is also devoted to the challenges ahead to integrate all required enzymatic activities in an industrial S. cerevisiae strain(s) and the need for molecular and selection strategies pursuant to developing a yeast capable of CBP.

Microbial cellulose utilization: fundamentals and biotechnology

Fundamental features of microbial cellulose utilization are examined at successively higher levels of aggregation encompassing the structure and composition of cellulosic biomass, taxonomic diversity, cellulase enzyme systems, molecular biology of cellulase enzymes, physiology of cellulolytic microorganisms, ecological aspects of cellulase-degrading communities, and rate-limiting factors in nature. The methodological basis for studying microbial cellulose utilization is considered relative to quantification of cells and enzymes in the presence of solid substrates as well as apparatus and analysis for cellulose-grown continuous cultures. Quantitative description of cellulose hydrolysis is addressed with respect to adsorption of cellulase enzymes, rates of enzymatic hydrolysis, bioenergetics of microbial cellulose utilization, kinetics of microbial cellulose utilization, and contrasting features compared to soluble substrate kinetics. A biological perspective on processing cellulosic biomass is presented, including features of pretreated substrates and alternative process configurations. Organism development is considered for "consolidated bioprocessing" (CBP), in which the production of cellulolytic enzymes, hydrolysis of biomass, and fermentation of resulting sugars to desired products occur in one step. Two organism development strategies for CBP are examined: (i) improve product yield and tolerance in microorganisms able to utilize cellulose, or (ii) express a heterologous system for cellulose hydrolysis and utilization in microorganisms that exhibit high product yield and tolerance. A concluding discussion identifies unresolved issues pertaining to microbial cellulose utilization, suggests approaches by which such issues might be resolved, and contrasts a microbially oriented cellulose hydrolysis paradigm to the more conventional enzymatically oriented paradigm in both fundamental and applied contexts.

Cloning and expression of beta-glucosidase genes in Escherichia coli and Saccharomyces cerevisiae using shuttle vector pYES 2.0

Genes for beta-glucosidase (Bgl) isolated from a genomic library of the cellulolytic bacterium, Cellulomonas biazotea, were cloned in pUC18 in its SacI cloning site and transformed to E. coli. Ten putative recombinants showed blackening zones on esculin plates, yellow zones on pNPG plates, in liquid culture and on native polyacrylamide gel electrophoresis activity gels. They fell into three distinct groups. Three representative E. coli clones carried recombinant plasmids designated pRM54, pRM1 and pRM17. The genes were located on 5.6-, 3.7- and 1.84-kb fragments, respectively. Their location was obtained by deletion analysis which revealed that 5.5, 3.2, and 1.8 kb fragments were essential to code for BglA, BglB, and BglC, respectively, and conferred intracellular production of beta-glucosidase on E. coli. Expression of the bgl genes resulted in overproduction of beta-glucosidase in the three clones. Secretion occurred into the periplasmic fractions. Three inserts carrying bgl genes from the representative recombinant E. coli were isolated with SacI, ligated in the shuttle vector pYES 2.0 in its SacI site and transformed to E. coli and S. cerevisiae. The recombinant plasmids were redesignated pRPG1, pRPG2 and pRPG3 coding for BglA1, BglB1 and BglC1. The cloned genes conferred extracellular production of beta-glucosidase on S. cerevisiae and enabled it to grow on cellobiose and salicin. The gall promoter of shuttle vector pYES 2.0 enabled the organisms to produce twice more beta-glucosidase than that supported by the lacZ-promoter of pUC18 plasmid in E. coli. The cloned gene can be used as a selection marker for introducing recombinant plasmids in wild strains of S. cerevisiae. The enzyme produced by bgl+ yeast and E. coli recombinants resembles that of the donor with respect to temperature and pH requirement for maximum activity. Other enzyme properties of the beta-glucosidases from S. cerevisiae were substantially the same as those from C. biazotea.