Co-expression of lignocellulase from termite and their endosymbionts / 生物工程学报

Natural lignocellulosic materials contain cellulose, hemicellulose, and lignin. Cellulose hydrolysis to glucose requires a series of lignocellulases. Recently, the research on the synergistic effect of lignocellulases has become a new research focus. Here, four lignocellulase genes encoding β-glucosidase, endo-1,4-β-glucanase, xylanase and laccase from termite and their endosymbionts were cloned into pETDuet-1 and pRSFDuet-1 and expressed in Escherichia coli. After SDS-PAGE analysis, the corresponding protein bands consistent with the theoretical values were observed and all the proteins showed enzyme activities. We used phosphoric acid swollen cellulose (PASC) as substrate to measure the synergistic effect of crude extracts of co-expressing enzymes and the mixture of single enzyme. The co-expressed enzymes increased the degradation efficiency of PASC by 44% compared with the single enzyme mixture; while the degradation rate increased by 34% and 20%, respectively when using filter paper and corn cob pretreated with phosphoric acid as substrates. The degradation efficiency of the co-expressed enzymes was higher than the total efficiency of the single enzyme mixture.

Isolation of fungi from dung of wild herbivores for application in bioethanol production

ABSTRACT Producing biofuels such as ethanol from non-food plant material has the potential to meet transportation fuel requirements in many African countries without impacting directly on food security. The current shortcomings in biomass processing are inefficient fermentation of plant sugars, such as xylose, especially at high temperatures, lack of fermenting microbes that are able to resist inhibitors associated with pre-treated plant material and lack of effective lignocellulolytic enzymes for complete hydrolysis of plant polysaccharides. Due to the presence of residual partially degraded lignocellulose in the gut, the dung of herbivores can be considered as a natural source of pre-treated lignocellulose. A total of 101 fungi were isolated (36 yeast and 65 mould isolates). Six yeast isolates produced ethanol during growth on xylose while three were able to grow at 42 °C. This is a desirable growth temperature as it is closer to that which is used during the cellulose hydrolysis process. From the yeast isolates, six isolates were able to tolerate 2 g/L acetic acid and one tolerated 2 g/L furfural in the growth media. These inhibitors are normally generated during the pre-treatment step. When grown on pre-treated thatch grass, Aspergillus species were dominant in secretion of endo-glucanase, xylanase and mannanase.

Isolation and Physico-Chemical Characterization of Extracellular Ligno-Cellulolytic Enzymes of Pleurotus Pulmonarius in Submerged Fermentation.

Pleurotus pulmonarius, a member of oyster mushroom can produced lignocellulosic enzymes laccase, peroxidise and cellulase in liquid potato-dextrose medium in submerged stationary condition. The lignocellulolytic activities were assayed using the extracellular culture filtrate which was partially purified using 0- 80% ammonium sulphate saturation. Different physico-chemical studies were performed using the partially purified culture filtrate. The fungus produced more laccase and peroxidase than the cellulase. The optimum laccase production was found on 17th day whereas cellulase & peroxidase productions were found on 9th& 10th day, respectively. Km of laccase is 4.1mM against guaiacol and 1.25 mM against o-dianisidine whereas Km of peroxidase was 0.72mM and cellulase was 0.06 mM. Optimum pH of laccase was 6.0 but for peroxidase and cellulase it was 7.0. The temperature optima of cellulase (50⁰C) was more than laccase (40⁰C) and peroxidase (30⁰C). All the lignocellulosic enzymes showed a wide range of temperature and pH stabilities. Laccase and peroxidase were fully inhibited by NaCl but it was not so effective against cellulase. P. pulmonarius showed higher ligninolytic (Laccase and peroxidase) activity than cellulolytic (cellulase) activity. The lignocellulosic enzymes isolated from submerged fermentation of P. pulmonarius might be industrially significant as they showed a wide range of temperature and pH stabilities.