Deletion of luxS gene mediated byλRed gene recombination technology reduces biofilm formation and stress resistance of Lactobacillus fermentum

This study investigated the effects of the luxS gene on the biofilm formation of Lactobacillus fermentum and its stress resistance.Deletion of the luxS gene was related to the physiological characteristics of biofilm development,strain resistance,bacterial morphology,biofilm morphology,functional group types,the main components of the biofilm,and the expression of related genes.Therefore,a luxS gene-deficient strain was constructed usingλRed gene recombination technology,and the biofilm production and stress resistance of the WT andΔluxS strains were compared.Deletion of the gene reduced the biofilm formation of L.fermentum and its resistance to acid,bile salt,high temperatures,and a hypertonic environment.Further,this work found that its deletion affects the types of functional groups in biofilms,and at the same time downregulate the expressions of the fabI,cysE,argR,and purD genes,thus reducing the levels of fatty acids,exopolysaccharide,protein,and eDNA in biofilms.A correlation analysis found that protein in biofilms was the most important factor affecting biofilm formation.In conclusion,the luxS gene in L.fermentum is involved in the regulation of biofilm formation and stress resistance.These findings provide a theoretical basis for the study of the mechanism of biofilm formation in beneficial bacteria.

Simple and rapid determination of dioxin in fish and sea food using a highly sensitive reporter cell line,CBG 2.8D

Food,especially animal origin food is the main source of polychlorinated dibenzo-p-dioxins and dibenzofurans(PCDD/Fs),and dioxin-like polychlorinated biphenyls(dl-PCBs)for human exposure.So,a simple,rapid and cheap bioassay method is needed for determination of dioxins in food samples.In this study,we used a new highly sensitive reporter cell line to determine the concentration of dioxins in 33 fish and seafood samples.The samples were extracted by shaking with water/isopropanol(1:1 v/v)and hexane and cleaned-up by a multi layered silica gel column and an alumina column,then analyzed using CBG 2.8 D cell line.We compared the results obtained from the CBG 2.8 D cell assay to those obtained from conventional High-Resolution Gas Chromatography-High Resolution Mass Spectrometry(HRGC-HRMS)analysis.Good correlations were observed between these two methods(r^2=0.93).While the slope of regression line was 1.76,the bioanalytical equivalent(BEQ)values were 1.76 folds higher than WHO-TEQ values and the conversion coefficient was 0.568(the reciprocal of 1.76).In conclusion,CBG 2.8 D cell assay was an applicable method to determine dioxins levels in fish and sea food samples.