Study On Screening,Identification And Synthetic Characteristics Of Bacterial Cellulose Synthetic Bacterium

Bacterial Cellulose?BC?is an extracellular polysaccharide synthesized by some bacteria.It is a high molecular biopolymer polymerized by glucose monomer molecules with?-1,4-glycosidic bonds.Compared with plant fibers,BC does not contain impurities such as lignin,pectin and hemicellulose;besides having excellent biocomp atibility and biodegradability;it also has a nano-network structure,high purity and high tensile strength and unique properties such as high water holding capacity.Based on these unique properties,BC has been widely used in the fields of biomedicine,papermaking,cosmetics,environmental pollution control,and food manufacturing.At present,domestic research on BC is still in its infancy.The main technical obstacles are the low number and variety of strains,the low fermentation yield and high cost,and the single functional group of cellulose materials,which leads to difficult modification.In this study,a bacterial consortium HJ2-2 with the ability to synthesize BC was successfully obtained from spoiled grapes.The 16S rRNA genome high-throughput sequencing results showed that the HJ2-2 mainly includes Komagataeibacter,Lacto bacillus,and Acetobacter,which accounted for 60.93%,25.65%,and 12.16%,respectively.From this bacterial consortium,three monoclonal strains were further isolated and identified,namely Komagataeibacter xylinus XJL-06-4,Lactobacillus plantarum XJL-2 and Acetobacter sp.D3.Co-cultivation experiments of three strains showed that Komagataeibacter xylinus XJL-06-4 was able to synthesize cellulose with the help of Lactobacillus plantarum XJL-2 or Acetobacter sp.D3,with maximum wet weight of 5.5 g/L.In addition,Komagataeibacter xylinus XJL-06-4's bacterial genome sequencing results showed that it contains four subunit fragmentsof cellulose synthase,namely BcsQ,BcsA,BcsZ,and BcsC.Based on the above data,the HJ2-2 leads to BC synthesis through the synergistic interaction between strains and the regulation of organic acid metabolism.In order to further investigate the possibility of the HJ2-2 as a BC-producing bacteria,this study optimized the culture conditions of the HJ2-2 and identified the structure of its products.The results of optimization of culture conditions showed that the HJ2-2 could produce 0.77 g/L membrane with glucose at the concentration of3%as the best carbon source at pH=7.0 and temperature 30?.FT-IR,SEM,and ¹³C-NMR were used for characterization analysis.The results showed that the film was a nano-network BC with typical cellulose chemical functional groups and carbon peaks.In order to improve the problem of single functional groups on BC surface and poor compatibility.Therefore,two water-soluble polysaccharides,sodium carboxymethyl cellulose?CMC?and sodium alginate?SA?were added to MS fermentation medium by means of biological in situ modification to investigate the effects of the two additives on the yield and properties of BC.The experimental results show that when the added concentration is 2%?CMC?and 0.5%?SA?,the yield of BC is increased to 1.59 g/L and 1.30 g/L,respectively,compared to the yield?0.77 g/L?without added polysaccharide.FT-IR and SEM analysis showed that the carboxyl groups in CMC and SA successfully replaced the hydroxy groups in BC to synthesize BC/C MC and BC/SA with smaller fiber diameters.XRD and TGA analysis results show that the crystallinityof the modified materials?BC/CMC and BC/SA?are 72%and 78%,respectively,and the thermal decomposition temperatures are 344?and 350?,respectively;compared with the crystallinity of BC?80%?and thermal decomposition temperature?355??,the crystallinity and thermal decomposition temperature of the modified materials have decreased,which may be caused by the substitution of some hydroxyl groups in BC by polysaccharides.The results of mechanical property tests show that the moisture content of the modified materials?BC/CMC and BC/SA?are 98.47%and 98.33%,the tensile strengths are 3.54 MPa and 2.36 MPa,and the Young's modulus are 47.95 MPa and 33.21 MPa;Compare BC's water content?98.33%?,tensile strength?1.27 MPa?and Young's modulus?25.08 MPa?.Except that the hold content of the modified material has not changed significantly,itstensile strength and Young's modulus are both significantly enhanced.All in all,this study not only enriched the species and quantity of BC synthetic bacteria,but also provided a reliable method and approach forthe large-scale production of BC and the research on the synthesis characteristics of its materials,and also provided important reference value for expanding the commercial application of BC.