Study On The Screening Of Low Temperature-Resistant Strain And Modification Of Bacterial Cellulose

Acetobacter xylinum strain M12 which preserved in our laboratory was the starting strain, the original strain was treated by ultraviolet ray mutation and liCl- ultraviolet ray composite mutation, and then using Petri dish to cultivate the bacterium which has been induced with CMC solid medium, by recording the number of the colony, we can make the lethal curve, obtaining the best mutation dosage. The primitive strain was treated under this dosage, using preliminary screening and second screening as well as consecutive passage experiments,a mutant strain UV3 which could resist low temperature and produce less acid and more cellulose, and the output of the cellulose is also stable, the yield of the bacterial cellulose increased by 27.2% in contrast with the original strain.First of all, through single- factor test, we analyzed effect of carbon source and concentration, nitrogen source and concentration, organic acids, inorganic salts and other substances added in the medium on the yield of bacterial cellulose, confirmed fermentation conditions such as the training time, inoculum size and pH value. By orthogonal design of experiment, the medium constituents and the best combination of various factors of the low-temperature-Acetobacter xylinum, which was preserved in our lab were ascertained: glucose 25g/L, yeast extract powder 5g/L, peptone 3g/L, citric acid 1.2g/L, Na2HP04 2.2g/L, K2HP04 1g/L, alcohol 6mL/L, fermentation time 6 days, fermentation temperature 25℃, pH 5.0, inoculum size 8%. The consecutive passage experiments had proved that the production of bacterial cellulose was 7.6g/L, increased by 35.7% in contrast with the original media.The effect on bacterial cellulose was reserched through appending 0.5, 1.0, 1.5, and 2.0g/L water-soluble polymer material, such as sodium alginate, methyl cellulose, carboxymethylcellulose, poly(vinyl alcohol) and poly(glutamic acid) , respectively, in the culture medium, it was characterized by scanning electron microscopy and infrared spectra, then we determined its production, water content, rehabilitation of water, and other indicators as well as physical properties, such as thickness, hardness, shear stress. Thus we can conclude that the modified bacterial cellulose is much better than the product of the original culture medium in the production, rehabilitation of water, thickness and other respects. The investigations of all kinds of modified bacterial cellulose with electron microscopy indicated their structures changed obviously and the diameter of fiber bundles became bigger. The result of IR test showed that the characteristic peaks of additional material have increased obviously. And poly- glutamate-modified bacterial cellulose changes largest in the physical and chemical properties, which showed that poly(glutamic acid) can integrate into the fiber structure in greater degree. Then it can be concluded that adding water-soluble polymer material can improve production of bacterial cellulose significantly, and improve its performance.