Isolation And Salt Tolerance Mechanism Of Bacillus Cereus From Soy Bean Sauce Residue

As a basic condiment, soy sauce has more than two thousand years of history in China. The market demand of soy sauce is huge and increasing year by year,which occupies an more and more important position. Soy sauce residue is produced after brewing soy sauce. Five million tons of soy sauce were produced in China each year, leading to a large number of soy sauce residue. However, soy sauce residue is able to produce odor, which will pollute environment as a result of accumulation. Soy sauce residues emission in our country is huge, but the development and utilization of soy sauce is limited, mainly used as fertilize or discarded. The discard not only pollute the environment but also waste resources. The salt concentration is too high to apply the soy sauce residue. For example, when the animals were fed directly by soy sauce residue, the high salt content could cause animal poisoning. Therefore, the development of products with high added value is the key to improve the utilization ratio of soy sauce residues.With the wide application of industrial microorganisms, salt-tolerance microorganisms will be an important developing orientation. The salt tolerance determines the survival and reproduction of microorganisms in high-salt soy sauce residue. Bacillus cereus, a gram-positive bacterium, is widely distributed in the environment with salt-tolerance. External features are decided by genes; therefore, salt-tolerance genes can be identified to study the salt bearing ability of Bacillus cereus separated from soy sauce residue. The ability and molecular regulation mechanism of Bacillus cereus is controlled by the expression of salt-tolerance genes. In this study, the transcriptome studies of the Bacillus cereus B25, cultured in gradient salt concentration, were conducted with aims to find growth characteristics and salt-tolerant genes, the conclusion of which can be used for further application and utilization of soy sauce residue.Based on two Bacillus cereus B25 and B26, this work studied the salt-tolerance of microorganisms including salt-tolerance ability, growth characters, genomic sequencing, bioinformatics analysis, salt-tolerance genes and its expression of Bacillus cereus. The main content of this study were as follows:(1) Study on growth curve and growth characters of B25 and B26 in different salinity, through which the fundamental was provided for the application of fermentation of soy sauce residue using Bacillus cereus.(2) Solexa sequencing was applied on B25 and B26 to acquire the whole genome of Bacillus cereus. The whole genome of two Bacillus cereus was 5.41 Mb long. In order to clarify the molecular regulation mechanism of salt tolerance, sequencing results was evaluated and analyzed.(3) Based on the bioinformatics, B25 and B26 were analyzed, including GO path, COG path and KEGG path. After genome annotation combined with salt-tolerance relevant genes, 49 related-genes were acquired, which was an accumulation of salt-tolerance feature of foodborne microorganisms.(4) Gene quantification was applied to Bacillus cereus B25 using QR-PCR, based on the expression profile of salt-tolerance gene under normal and high salt condition. It turned out that Bacillus cereus may decrease the expression of gene BC0669 and BC0754, increase the expression of gene BC2114 and BC4071 to acquire the ability of salt-tolerance. The result provided an important evidence of regulatory mechanism of salt-tolerant microorganisms.