Mechanism research of srtA gene on the oxidation tolerance of Streptococcus mutans

Abstract

Objective To investigate the effects of srtA on the oxidation tolerance of the Streptococcus mutans UA159 strain and to explore the potential mechanism. Methods The oxidation tolerance in the planktonic state and biofilm state were compared among UA159, the srtA-deleted strain and the complementary strain through oxidative tolerance experiments. The RNA-sequencing data from both the exponential and stationary phases of UA159 and the srtA-deleted strain were obtained by using the Illumina HiSeq 4 000 sequencing platform to determine the impact of srtA knockout on S. mutans genomic transcription. We compared the differences in the transcriptional expression of oxidative tolerance-related genes between the UA159 strain and the srtA gene deletion strain and further explored the intrinsic relationship between the changes in oxidative tolerance and the genetic transcriptome. qPCR was used to verify the changes in the expression level of oxidation tolerance-related genes. Results The oxidation tolerance of the srtA-deleted strain decreased significantly in both the planktonic state and the biofilm state compared to that of UA159 (P < 0.05). A total of 33 oxidation tolerance-related genes were differentially expressed according to transcriptome sequencing. There was no significant change in the expression of peroxide synthesis- and metabolic-related enzyme genes, but in the stationary phase samples, the two-component signal transcription systems lrgA, lrgB, and lytT were significantly downregulated (2.2- to 2.4-fold) in the srtA-deleted strain. qPCR further confirmed that in both the exponential and stationary phases, lrgB and lytT expression in the planktonic state was reduced 11.01-53.51-fold, while the expression of the other two-component system-encoding gene vicK was reduced by 6.57-10.88-fold (P < 0.001). Conclusion SrtA gene deletion did not change the expression level of peroxide synthesis-related and metabolic enzyme-encoding genes but downregulated the expression of the associated transcription regulation factors to reduce the oxidation tolerance of S. mutans.

Keywords

• streptococcus mutans
• dental caries
• biofilm
• sortase a
• srta gene
• oxidative stress
• oxidation tolerance
• reactive oxygen species
• rna-seq
• two-component signal transduction systems