Construction Of Xylose And Cellobiose Metabolic Pathwayand Its Effect On Bacterial Cellulose Synthesis

Bacterial cellulose(BC),which is composed of β-1,4 glycosidic bonds,is a nano-polymer synthesized by microbial fermentation.Compared with plant cellulose containing hemicellulose and lignin,BC is composed of cellulose and has higher purity and biodegradability.Therefore,functional BC has a good application prospect in many fields such as chemical sensing,biological imaging and biomedical materials.Lignocellulose is the most abundant green renewable resource on land and is composed of natural polymers such as cellulose,hemicellulose and lignin.The intermediate products of cellulose and hemicellulose and the final products of glucose and xylose could be used as carbon source for BC producing strain Komagataeibacter xylinus(K.xylinus)to grow and produce BC.However,compared with glucose,wild-type K.xylinus CGMCC 2955 can only use part of xylose and fibrinose,and the yield of BC is lower.Therefore,xyl E、xyl1、mxyl2 and XKS were heterologous expressed in K.xylinus to construct the XR-XDH two-step redox pathway.Lac Y,cep94 A and Bgl3 C were heterologous expressed in K.xylinus to construct the biobiose phosphorylation pathway and biobiose hydrolysis pathway.Accordingly,xylose and cellulobiose were used as carbon sources respectively to study the effects of different carbon sources on the growth and production of BC by engineering strains.The main research results are as follows:(1)Using 5 g/L xylose as medium,compared with CGMCC 2955,GX083 increased xylose consumption by 36 % and BC yield by 189 %,respectively.The introduction of this pathway effectively improved xylose utilization capacity and BC yield.During fermentation,glucose dehydrogenase(gcd)acted on xylose to produce xyloic acid,so XR-XDH was constructed in GX08 with gcd knockout.It was found that the p H in the medium did not decrease after gcd was knocked out,and compared with the control strain GX08,the construction of XR-XDH increased xylose utilization and BC production by41 % and 69 %,respectively.After 9 days of fermentation in GX medium,THE BC yield of GX083 and GX084 was increased by 124 % and 40 % compared with of CGMCC 2955 and GX08 respectively.(2)In CM medium,GX073 had a better performance in the consumption of cellobiose and BC production.Compared with the original strain,its carbon source utilization and BC yield increased by 31 % and 38 %,respectively.(3)Scanning electron microscopy showed that the microstructure of BC fiber bundle did not change with the construction of metabolic pathway.Fourier transform infrared spectroscopy(FTIR)showed that XR-XDH,the phosphorylation and hydrolysis pathways of fibrinose did not affect the functional groups of BC.