Study Of Ironmetabolism And Oxidative Stress Functions For LuxS Gene Of The Streptococcus Mutans

Objective In orde to study the role of luxS in iron metabolism of Streptococcus mutans by comparing the growth of the Streptococcus mutans standard strain and luxS mutant strain. To investigate the effect of luxS inactivation on the oxidative stress of Streptococcus mutans and perform preliminary analysis of potential mechanism by comparing the survival rate of two kinds of strains,growing different times in medium containing hydrogen peroxide or hydrogen peroxide and iron chelator.Methods The growth with absorbance value (A value) of both Streptococcus mutans standards strains and luxS gene mutant strains were measured in the iron-limited defined medium at24hours, luxS gene mutant strains was successfully built in our previous experiments; and the growth with absorbance value of the mutant strains was also measured in the iron-limited defined medium with exogenous iron or the supernatant fluid of standard strains were added at24hours, then the growth difference of two kinds of strains was compared;The two strains were grown to mid-logarithmic phase and devided into three groups, one was used as control and inoculated into normal TPY (tryptone-polypetone-yeast) medium,and the other two groups were experimental groups, and there were separately inoculated into TPY containing58.8mmol/Lhydrogen peroxide or TPY containing58.8mmol/Lhydrogen peroxide and0.1mmol/L2,2’-dipyridyl.The survival rate of strains was calculated at0.5,1,and2h.All the data were statistically analyzed.Results After incubation for24hours, the growths of both standard and luxS gene mutant strains in medium containing0.1mmol/L of2,2’-bipyridyl were not significantly inhibited. However, the growths of luxS gene mutant strains in medium containing0.3mmol/L and0.5mmol/L of2,2’-bipyridyl were significantly inhibited. The growth inhibition of luxS gene mutant strains in medium containing0.3mmol/L of2,2’-bipyridyl was relieved by adding exogenous iron and culture supernatant of standard strain to the medium. Comparedwith the control group,the survival rate of luxS mutationwasalways higher than standard strain at all pre-determined time inexperimental groups;and compared with experimental group without iron chelator, the survival rate of strains was not raised with the added of iron chelator.Conclusions luxS gene plays a role in iron metabolism; luxS gene is involved in oxidative stress tolerance of Streptococcus mutans;and The oxidative stress tolerance is not achieved by avoiding the toxic effects of the Fenton reaction.