Engineering a high-performance,metagenomic-derived novel xylanase with improved soluble protein yield and thermostability

The novel termite gut metagenomic-derived GH11 xylanase gene xyl7 was expressed in Escherichia coli BL21, and the purified XYL7 enzyme exhibited high specific activity (6340 U/mg) and broad pH active range of 5.5–10.0. Directed evolution was employed to enhance the thermostability of XYL7; two mutants (XYL7-TC and XYL7-TS) showed a 250-fold increase in half-life at 55 °C, with a 10 °C increase in optimal temperature compared to that of wild-type XYL7. A truncated enzyme (XYL7-Tr3) acquired by protein engineering showed similar catalytic properties as the wild-type, with a tenfold increase in soluble protein yield by the mutant. The reducing sugar produced by XYL7-TC was about fourfold greater than that produced by their parents when incubated with xylan at 60 °C for 4 h. The engineered novel xylanase exhibited superior enzymatic performance and showed promise as an excellent candidate for industrial application due to its high specific activity, stability and soluble protein yield.     

Comparison of a xylanase and a complex of non starch polysaccharide-degrading enzymes with regard to performance and bacterial metabolism in weaned piglets

Abstract

Weaned piglets were fed a wheat based diet either non-supplemented or supplemented with a multi-enzyme preparation or a xylanase mono-enzyme preparation, respectively. Both enzyme preparations increased live weight gain nonsignificantly, but only animals of the xylanase group showed a trend (p = 0.076) for an improved feed conversion. Only precaecal digestibility of total amino acids was improved significantly when the mono-enzyme preparation was added. Improvements of digestibility of crude fat, crude protein and starch did not reach the significance level. Both enzyme preparations reduced jejunal viscosity, however viscosity in the colon was only reduced by the mono-enzyme preparation. Both enzymes significantly reduced Lactobacillus spp. cell numbers as well as bacterial metabolites in the stomach and showed similar nonsignificant modifications in jejunum contents except for acetate in the mono-enzyme group. Total jejunal bile acids were unchanged. Compared to the control, the ratio of the main conjugated to the main deconjugated bile acid was significantly higher in the mono-enzyme group. This study has shown that the mono- and multi-enzyme preparation can lead to improved performance in wheat based diets for piglets. Like in poultry, the main mode of action seems to be the reduction of small intestinal viscosity. However, the generation of fermentable carbohydrates by the multi-enzyme preparation may mask beneficial effects on performance due to the development of an active bile acid deconjugating microbiota in the small intestine.     

Production of a cellulase-free xylanase from agricultural waste materials by a thermotolerant Streptomyces sp.

1444 microorganisms were isolated from soil samples from the northern Thai and screened at 55 °C by using basal medium supplemented with 1% carboxymethyl cellulose as a sole carbon source. One isolate, Streptomyces Ab106, had a high activity of a cellulase-free xylanase also without mannanase activity. The maximum cellulase-free xylanase activities of 3.5, 3.3, 3.1 and 2.7 IU were after growth of the organism with 1% (w/v) corn hull, corncob, bagasse and oat spelt xylan, respectively, at 55 °C for 6 days, respectively. The activity was more than 5 times higher than that at 35 °C.     

Ethylene Production and Activation of Hydrolytic Enzymes during Acclimation of Maize Seedlings to Partial Flooding

The effects of partial flooding on the partial pressure of oxygen and carbon dioxide in water around the roots, ethylene production by intact maize (Zea mays L.) seedlings, the activities of hydrolytic enzymes (pectinase, xylanase, and cellulase) in adventitious roots, and the growth of adventitious and main roots were studied. Aggravated hypoxia resulted in the accelerated ethylene production and the activation of enzymes destroying cell walls in the adventitious roots; as a result, the latter changed their growth pattern. The conclusion is that the interrelated responses are adaptive ones, and the adventitious roots play a key role in plant adaptation.     

Simultaneous secretion of seven lignocellulolytic enzymes by an industrial second-generation yeast strain enables efficient ethanol production from multiple polymeric substrates

A major hurdle in the production of bioethanol with second-generation feedstocks is the high cost of the enzymes for saccharification of the lignocellulosic biomass into fermentable sugars. Simultaneous saccharification and fermentation with Saccharomyces cerevisiae yeast that secretes a range of lignocellulolytic enzymes might address this problem, ideally leading to consolidated bioprocessing. However, it has been unclear how many enzymes can be secreted simultaneously and what the consequences would be on the C6 and C5 sugar fermentation performance and robustness of the second-generation yeast strain. We have successfully expressed seven secreted lignocellulolytic enzymes, namely endoglucanase, β-glucosidase, cellobiohydrolase I and II, xylanase, β-xylosidase and acetylxylan esterase, in a single second-generation industrial S. cerevisiae strain, reaching 94.5 FPU/g CDW and enabling direct conversion of lignocellulosic substrates into ethanol without preceding enzyme treatment. Neither glucose nor the engineered xylose fermentation were significantly affected by the heterologous enzyme secretion. This strain can therefore serve as a promising industrial platform strain for development of yeast cell factories that can significantly reduce the enzyme cost for saccharification of lignocellulosic feedstocks.