Study On Inhibitor Tolerance Of Pediococcus Strains For Lactic Acid Production And Xylanase Properties Using Lignocellulosic Biomass As Feedstock

Two significant problems in lignocelluloses biorefining technology were studied in this thesis. First, Pediococcus acidilactici DQ2, an isolate from corn stover hydrolysate, was compared with the other two pedicoccus strains of P. acidilactic DSM20284and P. pentosaceus ATCC25745for lactic acid production from glucose in the presence of inhibitors often found in lignocellulosic hydrolysates. Pediococcus acidilactici DQ2showed the best results among the three strains tested, suggesting that the excellent performance of DQ2is a unique feature of this specific strain.In addition, cloning, expression and characterization of the thermostable Geobacillus thermoglucosidasius xylanase and its mutants and their production in Bacillus subtilis were also studied. Firstly, the wild type xylanase gene (xylwt) was amplified by PCR using genome of Geobacillus thermoglucosidasius KCCM12265as tempelate. Then xylwt gene was subcloned to the expression vector pJK to obtain the recombinant plasmid to be expressed in BHM host strain. To improve the thermostability and production of xylanase, this gene was modified by point mutation to get a new thermostable gene xylA. On this basis, rational site-directed mutagenesis was also employed to xylA to get xylAl. It showed that the optimal pHs of the three xylanases of Xylwt, Xy1A and XylAl were all pH6.0and enzyme activities increased with the raise of temperature on the conditions tested. The crude broth activity of Xy1A was around8times higher than that of Xylwt.The residual activities of Xy1A and Xy1A1could both remain80%after heat treatment at80℃for30minutes. All of these results indicate that industrial application of Xy1A is of great potential.