Regulation of feed intake rumen microbiology and fermentation nutrient absorption and splanchnic metabolism endogenous regulatory and pregnancy lactation tissue growth host resistance against parasites and pathogens.

Ruminant Physiology: Digestion, Metabolism, Growth and Reproduction

Bacterial 1,3-1,4-β-glucanases: structure, function and protein engineering

There is huge potential for genetic exchange to occur within the dense, diverse anaerobic microbial population inhabiting the gastrointestinal tract (GIT) of humans and animals. However, the incidence of conjugative transposons (CTns) and the antibiotic resistance genes they carry has not been well studied among this population. Since any incoming bacteria, including pathogens, can access this reservoir of genes, this oversight would appear to be an important one. Recent evidence has shown that anaerobic bacteria native to the rumen or hindgut harbour both novel antibiotic resistance genes and novel conjugative transposons. These CTns, and previously characterized CTns, can be transferred to a wide range of commensal bacteria under laboratory and in vivo conditions. The main evidence that gene transfer occurs widely in vivo between GIT bacteria, and between GIT bacteria and pathogenic bacteria, is that identical resistance genes are present in diverse bacterial species from different hosts.

The role of conjugative transposons in spreading antibiotic resistance between bacteria that inhabit the gastrointestinal tract.

Beta-1,3-1,4-glucanase (EC3.2.1.73) as an important industrial enzyme has been widely used in the brewing and animal feed additive industry. To improve expression efficiency of recombinant beta-1,3-1,4-glucanase from Bacillus licheniformis EGW039(CGMCC 0635) in methylotrophic yeast Pichia pastoris GS115, the DNA sequence encoding beta-1,3-1,4-glucanase was designed and synthesized based on the codon bias of P. pastoris, the codons encoding 96 amino acids were optimized, in which a total of 102 nucleotides were changed, the G+C ratio was simultaneously increased from 43.6 to 45.5%. At shaking flask level, beta-1,3-1,4-glucanase activity is 67.9 and 52.3 U ml(-1) with barley beta-glucan and lichenan as substrate, respectively. At laboratory fermentor level, the secreted protein concentration is approximately 250 mg l(-1). The beta-1,3-1,4-glucanase activity is 333.7 and 256.7 U ml(-1) with barley beta-glucan and lichenan as substrate, respectively; however, no activity of this enzyme on cellulose is observed. Compared to the nonoptimized control, expression level of the optimized beta-1,3-1,4-glucanase based on preferred codons in P. pastoris shown a 10-fold higher level. The codon-optimized enzyme was approximately 53.8% of the total secreted protein. The optimal acidity and temperature of this recombinant enzyme were pH 6.0 and 45 degrees C, respectively.

Codon optimization of Bacillus licheniformis β-1,3-1,4-glucanase gene and its expression in Pichia pastoris

1,3-1,4-beta-D-glucanase is an important endoglycosidase in the brewing and animal feed industries. To achieve high-level expression of recombinant glucanase in Pichia pastoris, we designed sequences encoding the alpha-factor signal peptide from Saccharomyces cerevisiae and the truncated 1,3-1,4-beta-D-glucanase from Fibrobacter succinogenes as a whole. The codons encoding the 52 amino acids of the signal peptide and 106 residues of the glucanase protein were optimized for expression in P. pastoris; 189 nucleotides were changed. The G + C content was adjusted to 48-49%, and AT-rich stretches were eliminated to avoid premature termination. The messenger ribonucleic acid secondary structure near the AUG start codon was also adjusted to ensure efficient translation; the resulting glucanase production was twofold higher compared with that achieved with gene structure optimization alone. We also propose a new fermentation strategy for the induction phase, in which 5/95% glycerol/methanol mixed feed was used in days 1-3 and 100% methanol was used on days 4-6. By comparison with methanol feed and glycerol/methanol-mixed feed alone, the yield of recombinant glucanase increased by 38.5 and 16.5%, respectively. The expressed optimized recombinant 1,3-1,4-beta-D-glucanase constituted approximately 90% of the total secreted protein, reaching up to 3 g l(-1) in the medium.

High-level expression of a truncated 1,3-1,4-β-d-glucanase from Fibrobacter succinogenes in Pichia pastoris by optimization of codons and fermentation

Streptococcus bovis JB1 was found to produce a 25-kDa extracellular enzyme active against beta-(1,3-1,4)-glucans. A gene was isolated encoding a specific beta-(1,3-1,4)-glucanase that corresponds to this size and belongs to glycoside hydrolase family 16. A 4- to 10-fold increase in supernatant beta-glucanase activity was obtained when the cloned beta-glucanase gene was reintroduced into S. bovis JB1 by use of constructs based on the plasmid vector pTRW10 or pIL253. The beta-(1,3-1,4)-glucanase gene was also expressed upon introduction of the pTRW10 construct pTRWL1R into Lactococcus lactis IL2661 and Enterococcus faecalis JH2-SS, although extracellular activity was 8- to 50-fold lower than that in S. bovis JB1. The beta-(1,3-1,4)-glucanase purified from the culture supernatant of S. bovis JB1 carrying pTRWL1R showed a K(m) of 2.8 mg per ml and a Vmax of 338 mumol of glucose equivalents per min per mg of protein with barley beta-glucan as the substrate. The S. bovis beta-(1,3-1,4)-glucanase may contribute to the ability of this bacterium to utilize starch by degrading structural polysaccharides present in endosperm cell walls.

Isolation and overexpression of a gene encoding an extracellular beta-(1,3-1,4)-glucanase from Streptococcus bovis JB1.

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Isolation and overexpression of a gene encoding an extracellular beta-(1,3-1,4)-glucanase from Streptococcus bovis JB1.