Characteristics Of Bacterial Community Structure And Metabolome In The Process Of Flax Biological Degumming

Water retting system is a complex ecosystem.The essence of degumming is that the degumming enzymes produced by microorganisms on the flax stem degrade pectin or non cellulose substance contained in cementing bast fiber or fiber bundles,while the enzymes mainly are pectinase,mannase and polygalacturonic acid enzymes.And then the flax fibre will be separated from the nonfiber material.In this study,water retting ecosystem was applied as the model to explore the succession of microbial flora,the general pattern of the key degumming enzyme and its environment changes,which were performed by the comparison and analysis of microbial community structure and the abundance of material in the water retting and bacterial retting system by high-throughput sequencing technologies and metabolomics techniques.Meanwhile,a new opportunity was provided for seeking biomarkers of the metabolism of the key enzymes produced by biological degumming strains and studing the environmental effect factors of the metabolic flux of the key enzymes.The research is helpful to understand ecological processes and functions in the water retting system.First of all,the Bacillus cereus HDYM-02 strain islotaed from the water retting system was used to study the degumming enzyme-production process in BP,PEC,KGM and CMC medium respectively.The results showed that high pectinase activity?1168.8±22.2 U/m L?,mannase activity?2587.8±18.0 U/mL?,polygalacturonase?164.0+12.1 U/m L?were obtained without producing cellulase(?10^-6 U/m L),which indicated better potential application of the strain in the process of flax biological degumming.Then,the abundance and diversity of the microbial community in the bacteria-adding water retting system?BA?constructed by adding B.cereus HDYM-02strain were analyed by high-throughput sequencing technologies,while the water retting system?CK?was usd as the control..The results demonstrated that the microbial community structure could be significantly improved by the addition of B.cereus HDYM-02 strain,especially the differences of species abundance of Bacillaceae and Pseudomonadaceae in the two systems in the early fermentation process.In the mid and late process of the fermentation,Clostridiaceae?1 and Pseudomonadaceae were the dominant community in BA system;while the dominant community in the CK system were Clostridiaceae?1,Pseudomonadaceae and Enterobacteriaceae.The research further indicated that B.cereus HDYM-02 could promote the growth of the dominant community,reduce the abundance of other community and decrease the species diversity in the retting ecosystem.Furthermore,the GC/MS technology was used for the real-time monitoring of microbial metabolites in the retting system during the fermentation process.And multivariate statistical analysis was used to analysis the differences of metabolites between bacterial retting system and water retting system at each fermentation stage.The datas illuminated that significant difference of the type and abundance of the metabolites was observed as the difference varied according to fermentation stages and system,which indicated that the B.cereus HDYM-02 caused the differences of the metabolites by changing microbial community structure in two retting systems.These metabolites were mainly derived from waxes and lignin components on the surface of the flax fiber,which is the reflection of the degumming process.In addition,the relationship between microbial community structure,degumming key enzymes and metabolites in biological degumming process was comparatively analyed.The results found that the abundances of Bacillaceae,Pseudomonadaceae,Clostridiaceae?1 were enhanced by B.cereus HDYM-02,which were 8.9,2.2 and 1.1times respectively more than that in the water retting sytem,while the abundance of Enterobacteriaceae was decreased by B.cereus HDYM-02,which was 0.2 times less than the water retting system.In terms of degumming enzyme activities,pectinase and mannose activities increased by B.cereus HDYM-02 were 1.2 and 1.4 times more than the control with hardly any cellulase activity(?10^-3U/mL).While the metabolites characterized by waxes and lignin?i.e.,alkanes and its derivatives,ester,organic acid and aromatic compounds?had some abundance differences.The abundance of mainly metabolites,which were 4,6-dimethyl-Dodecane,Tetradecanoic acid,Phthalic acid,n-Hexadecanoic acid,4-?2-propenyl?-Phenol,Octadecanoic acid,reached to the highest values at 72-96 hour of the fermentation process,indicating the termination of water retting.As a result,these metabolites can be used as basical biologic indicator to reflect the differences between species abundance and diversity in the flax retting system and the level of the fermentation process.In conclusion,B.cereus HDYM-02 can be the excellent strain of degumming in the retting system for its production of pectinase,mannase and polygalacturonic acid enzymes without cellulose.In the water retting system,B.cereus HDYM-02 could promote the growth of the dominant community,reduce the abundance of other community,improve the species diversity and consequently lead to the difference of metabolites;the difference of metabolites can be the basical biologic indicator of reflecting the variations between species abundance and diversity in the flax retting system and the level of the fermentation process.