Effects Of Shear Force And Inhibitors On Synthesis Of Bacterial Cellulose By Gluconacetobacter Xylinus And Selection Of Resistant Strain

Bacterial cellulose (BC) has unique structure, which determines its physical and chemical properties. BC has been recognized as a new biological nanometer material with outstanding characteristics in the world. It has been widely applied in food, medicine, biological material, paper, textile, medicine and other fields. In the production of BC by agitated culture, intensive shear force tends to reduce cellulose synthesis. Liginocellulose is a promising raw material for fermentation industry. It has been demonstrated that inhibitors produced in the pretreatment of liginocellulose negatively affect synthesis of BC. In this study, the effects of shear force and inhibitors on bacterial growth and cellulose synthesis were investigated, and screening of resistant strains to shear stress and to inhibitor in acid hydrolysate of wheat straw were tried by mutation and selecting.Shaking flask cultivation with glass beads and fermentation with mechanical agitation of impellers were choosed to study the effect of shear force on bacterial growth and cellulose synthesis under dNAmic culture condition. The shear force reduced the bacterial cellulose production. It was found that, after9cycles of culture in shaking flask, bacterial cellulose production was only25%of that from original strain. In the fermentation with mechanical agitation,6-flat-Disc-turbine with high shear force gave the lowest bacterial cellulose production, and the frame blender with low shear force gave high bacterial cellulose production. The shear force had no effects on soluble cellulose for both fermentation system. After continuously running dNAmic culture, the size of bacterial cell became small and colony morphology changed. The number of bacterial cells decreased in unit volume of culture broth. The logarithmic phase of Gluconacetobacter xylinus delayed, and the whole growth period prolonged. Tolerant strains to shear force screened from continuous dNAmic culture still gave low production of BC.The acid hydrolysate of wheat straw was choosed to study the effects of inhibitor on bacteria and cellulose synthesis. It was found that hydrolysate had effects on cell growth, cellulose structure and cellulose synthesis. In the medium composed of hydrolysate, the yield of bacterial cellulose decreased with the increase of hydrolysate concentrations. When the medium contained100%hydrolysate, the yield of bacterial cellulose was0.07g/L, which is22%of the yield in glucose medium. The diameter of bacterial cellulose became wider (35-100nm) as compared to that in glucose medium (25nm) and the cellulose formed uneven web with clusters and nodes. Due to the inhibitor, logarithmic phase of G. xylinus delayed, and the growth period prolonged. The size of cell became large after continuous culture in the hydrolysate medium. There were two colonies on plate, one colony looked like small, moist and white, which was capable of synthesizing cellulose, and the other was like mucus tiling on the plate. The number of bacterial cells decreased significantly in unit volume of fermentation liquid.Nitrous acid mutation, UV mutation, nitrous acid combined with UV mutation were tried to select resistant strains. One resistant strain was got in the nitrous acid mutation and gave120%higher yield of BC as compared with that of the mother strain. Several resistant strains selected from UV mutation gave15%higher yield of BC as compared with the mother strain. By combining nitrous acid mutation with and UV mutation,150%higher yield of bacterial cellulose was got as compared to the mother strain. The results provided a foundation for plenary application of acid hydrolysate of lignocellulose, for further improvement of bacterial cellulose yield and for reducing the cost of production.