Cloning and expression in Escherichia coli of a Thermoanaerobacter cellulolyticus gene coding for heat-stable β-glucanase

Insights into Thermophilic Plant Biomass Hydrolysis from Caldicellulosiruptor Systems Biology

Plant polysaccharides continue to serve as a promising feedstock for bioproduct fermentation. However, the recalcitrant nature of plant biomass requires certain key enzymes, including cellobiohydrolases, for efficient solubilization of polysaccharides. Thermostable carbohydrate-active enzymes are sought for their stability and tolerance to other process parameters. Plant biomass degrading microbes found in biotopes like geothermally heated water sources, compost piles, and thermophilic digesters are a common source of thermostable enzymes. While traditional thermophilic enzyme discovery first focused on microbe isolation followed by functional characterization, metagenomic sequences are negating the initial need for species isolation. Here, we summarize the current state of knowledge about the extremely thermophilic genus Caldicellulosiruptor, including genomic and metagenomic analyses in addition to recent breakthroughs in enzymology and genetic manipulation of the genus. Ten years after completing the first Caldicellulosiruptor genome sequence, the tools required for systems biology of this non-model environmental microorganism are in place.

The enzymes from extreme thermophiles: bacterial sources, thermostabilities and industrial relevance

This review on enzymes from extreme thermophiles (optimum growth temperature greater than 65 degrees C) concentrates on their characteristics, especially thermostabilities, and their commercial applicability. The enzymes are considered in general terms first, with comments on denaturation, stabilization and industrial processes. Discussion of the enzymes subsequently proceeds in order of their E.C. classification: oxidoreductases, transferases, hydrolases, lyases, isomerases and ligases. The ramifications of cloned enzymes from extreme thermophiles are also discussed.

Isolation, characterization and manipulation of cellulase genes

The complete hydrolysis of cellulose requires a number of different enzymes including endoglucanase, exoglucanase and beta-glucosidase. These enzymes function in concert as part of a 'cellulase'complex called a cellulosome. In order (i) to develop a better understanding of the biochemical nature of the cellulase complex as well as the genetic regulation of its integral components and (ii) to utilize cellulases either as purified enzymes or as part of an engineered organism for a variety of purposes, researchers have, as a first step, used recombinant DNA technology to isolate the genes for these enzymes from a variety of organisms. This review provides some perspective on the current status of the isolation, characterization and manipulation of cellulase genes and specifically discusses (i) strategies for the isolation of endoglucanase, exoglucanase and beta-glucosidase genes; (ii) DNA sequence characterization of the cellulase genes and their accompanying regulatory elements; (iii) the expression of cellulase genes in heterologous host organisms and (iv) some of the proposed uses for isolated cellulase genes.

Releasing profiles of gene products from recombinant Escherichia coli in a high-voltage pulsed electric field

Release of recombinant proteins from gene-engineered Escherichia coli by applying a pulsed electric field (PEF) to a cell suspension was studied. When E. coli/pNC1, which produces beta-glucosidase and accumulates it in cytoplasm, was exposed to PEF, the most effective release of this enzyme was achieved in the cell suspension of 5% glycine and 15% PEG solution under 10kV/cm and 280J/ml of a PEF in a needle-plate electrode chamber. However, the amount of released beta-glucosidase by PEF treatment was only 26% of that by ultrasonic treatment. On the other hand, alpha-amylase produced by E. coli/pHI301A and accumulated in the periplasmic space could be easily released by PEF treatment. When this recombinant E. coli was suspended in 0.9% NaCl and 10% PEG solution and exposed to 10kV/cm and 200J/ml of a PEF in a plate-plate electrode chamber, 89% of intracellular alpha-amylase with nine-times higher specific activity compared with that by ultrasonic treatment was released. The release tendency of cellobiohydrolase, produced by E. coli/pNB6 and accumulated in both the cytoplasm and periplasmic space, was intermediate between those of beta-glucosidase and alpha-amylase. In this case, 70% of cellobiohydrolase with 1.9-times higher specific activity compared with that by ultrasonic treatment could be released when E. coli/pNB6 was suspended in 15% PEG and 10kV/cm and 200J/ml of a PEF was applied in a needle-plate electrode chamber. These results indicated that PEF treatment could easily disrupt the outer membrane, but it was difficult to disrupt the cytoplasmic membrane simultaneously. Therefore, PEF treatment is useful for easy release of periplasmic protein with selectivity.

Phylogenetic analysis of anaerobic thermophilic bacteria: aid for their reclassification

Small subunit rDNA sequences were determined for 20 species of the genera Acetogenium, Clostridium, Thermoanaerobacter, Thermoanaerobacterium, Thermoanaerobium, and Thermobacteroides, 3 non-validly described species, and 5 isolates of anaerobic thermophilic bacteria, providing a basis for a phylogenetic analysis of these organisms. Several species contain a version of the molecule significantly longer than that of Escherichia coli because of the presence of inserts. On the basis of normal evolutionary distances, the phylogenetic tree indicates that all bacteria investigated in this study with a maximum growth temperature above 65 degrees C form a supercluster within the subphylum of gram-positive bacteria that also contains Clostridium thermosaccharolyticum and Clostridium thermoaceticum, which have been previously sequenced. This supercluster appears to be equivalent in its phylogenetic depth to the supercluster of mesophilic clostridia and their nonspore-forming relatives. Several phylogenetically and phenotypically coherent clusters that are defined by sets of signature nucleotides emerge within the supercluster of thermophiles. Clostridium thermobutyricum and Clostridium thermopalmarium are members of Clostridium group I. A phylogenetic tree derived from transversion distances demonstrated the artificial clustering of some organisms with high rDNA G+C moles percent, i.e., Clostridium fervidus and the thermophilic, cellulolytic members of the genus Clostridium. The results of this study can be used as an aid for future taxonomic restructuring of anaerobic sporogenous and asporogenous thermophillic, gram-positive bacteria.