Study Of Characteristic And Synthesis Mechanism Of High-yielding Bacterial Cellulose Producing Strain Z2-3

Bacterial cellulose(BC)as an exopolysaccharide produced by bacterium is a natural aggregate of ?-(1,4)-linked glucose unit chains synthesized by bacterial cellulose synthase(BCS).The chemical composition of BC is similar to plant cellulose,while the good characteristics,such as particular nano network structure,high water absorption,cellulose purity,hydrophilicity,crystallinity,chemical intensity,and biocompatibility make BC as an excellent material.As a kind of new nanoscale biological material,BC is widely applied in food,paper,electronics and bio-medical industries,which has been industrialized in the United States,Canada and Japan.In China,the application of bacterial cellulose is mainly focus on food industry and the traditional static culture was widely used in BC production.However,BC production under agitated culture conditions such as using stirred fermentation tank showed more advantages than the traditional static culture,however,it is still under development without a mature large-scale producing system due to the lack of highyield strains and the behindhand culture technique.Furthermore,the molecular mechanism of BC biosynthesis is still not well understood.In this study,A high-yielding BC producing strain Z2-3 was isolated.The biological and genomic characteristics of strain Z2-3 were identified.The biological functions of BCSs of strain Z2-3 were studied.The optimization of culture conditions and application of cellulose in the food industry were performed.Our results will gratify the demand for industrial production of BC and improve the genetic tools of BC synthesis modification,the main research contents and results are shown as follows:1.The biological and genomic characteristics of high-yielding BC producing strain Z2-3In this study,total 54 BC producing strains belong to 12 species in 2 genera were isolated from 264 different fruits through MHS agar culture.Strain LTF-20171129Z2-3 was selected because of its high BC production under agitated culture conditions and stably heredity.The BC production of strain LTF-20171129Z2-3 was 2.69 ± 0.05 g/L after 4 days fermentation which showed highest BC yield(69.3% higher)among published BC producing strains.Based on the physiological and biochemical characteristics of strain Z2-3,it could be classified into genus Komagataeibacter,but hardly classified into the existing species.Finally based on the whole-genome analysis of the strain Z2-3,it could be classified into a new species as Komagataeibacter sp.nov..Furthermore,the results of scanning electron microscope,chemical functional group composition,crystallinity and other physical and chemical characteristics analysis indicated the excellent material properties of BC produced by strain Z2-3.2.The biological function of BCSBased on the whole-genome analysis,this study improved the metabolic pathways of various carbon sources for the synthesis of bacterial cellulose,providing the theoretical bases for the further understanding of molecular mechanism of bacterial cellulose biosynthesis.Four bcs operons were identified in the genome of strain Z2-3,which showed low sequence similarity between each operon.This study firstly reported that different bcs operons showed different contributions to BC synthesis and proved that bcs AB ? and bcs C ? played the key role in the BC synthesis and transporting BC out of cells,respectively.Moreover,the lack of bcs D ? would lead to the instability of BC structure.3.The optimization of BC production and application of BC in drink production.The maximum BC production of strain Z2-3 was 5.98 ± 0.23 g/L under agitated conditions,137 % higher than the origin using the optimal fermentation medium.The crystallinity of BC obtained from agitated culture reached the high level of 66.42%,indicating the suitableness of the strain using agitated culture.Notably,strain Z2-3could use industrial waste glycerol WG2 as the single carbon source,resulting in higher biomass and BC production,showed great economic and environmentally sustainable value.Finally,application of BC in fresh orange juice and coco milk as a kind of suspension stabilizer significantly increased the stability of drink production.Taken together,based on the whole-genome analysis of strain Z2-3,this study provided basic information on the synthesis mechanism of BC,made a good foundation for genetic modification of BC producing strains.The results of optimization of BC production and application of BC into drink production made a good foundation for industrialization of BC production.