The global impact of the delta subunit RpoE of the RNA polymerase on the proteome of Streptococcus mutans.

Abstract

Transcriptional specificity in low-G+C Gram-positive bacteria is maintained by RpoE, the delta subunit of the RNA polymerase. Here, we studied the effect of RpoE at the proteome level in the human dental pathogen Streptococcus mutans by comparing the ΔrpoE mutant with the wild-type under five conditions: (0) exponential growth, (1) early stationary phase, (2) acid stress, (3) oxidative stress, and (4) combined acid and oxidative stress. A total of 280 cellular protein spots were reproducibly detected, of which 97 differentially expressed protein spots were identified by MALDI-TOF MS. Lack of RpoE caused downregulation of proteins for carbohydrate metabolism and energy production, including phosphoglucomutase (PGM), the phosphopentomutase DeoB and the pyruvate formate-lyase Pfl. The ΔrpoE mutant had extensive changes in the abundance of proteins involved in acid and oxidative tolerance and protein turnover, and of chaperones, at exponential phase in the absence of stress, suggesting a potential internal stress. In addition, the mutant had reduced amounts of proteins for adaptation responses, e.g. the multiple sugar transport and metabolism enzymes required for entering early stationary phase, and the proteins for stress-defence mechanisms and glycolysis under oxidative stress. Comparison of the proteome data with the corresponding transcriptome data suggested that the effects were the result of altered transcriptional and post-transcriptional regulation. The data are consistent with the reduced transcriptional specificity of the RNA polymerase in the ΔrpoE mutant, and suggest a general impact, but not a specific regulatory role, of RpoE in stress adaptation.