Characterization of the Streptococcus sobrinus acid-stress response by interspecies microarrays and proteomics

Abstract

Streptococcus mutans and Streptococcus sobrinus are considered the primary organisms responsible for human dental caries. The ability to generate acids and to adapt to low pH conditions is directly associated with the cariogenic potential of these bacteria. To survive acidic conditions, both species have been shown to mount an acid-tolerance response (ATR). However, previous characterization of the S. sobrinus ATR identified critical differences in the mechanisms of acid adaptation between S. mutans and S. sobrinus. Here, interspecies microarray and proteomic approaches were used to identify novel, previously unrecognized genes and pathways that participate in the S. sobrinus acid-stress response. The results revealed that, among other things, metabolic alterations that enhance energy generation and upregulation of the malolactic fermentation enzyme activity constitute important acid-resistance properties in S. sobrinus. Some of these acid adaptive traits are shared by S. mutans and might be considered optimal targets for therapeutic treatments designed to control dental caries.

Fig. 1

2D protein patterns of S. sobrinus 6715 grown to pH 7 and pH 5 steady-state levels. The silver-stained proteins with enhanced expression at pH 5 (fold-change ≥ 1.5) that were identified by Q-TOF MS/MS are indicated in the pH 5 gel image, and proteins that were enhanced at pH 7 (fold change ≥ 1.5) are indicated in the pH 7 gel image. Underlined spot ID labels indicate proteins that were subjected to Q-TOF MS/MS analysis but the results failed to meet the criteria for confident identification. Refer to Table 2 for name and description of identified proteins. The filled triangle indicates tropomyosin (33 kDa, pI 5.2) loaded as an internal control.

Fig. 2

Malolactic fermentation activity of S. sobrinus 6715 and S. mutans UA159 at pH 5.5 and pH 7. S. sobrinus and S. mutans cells were grown in TY broth (adjusted with HCl, pH 5.5 or buffered with potassium phosphate, pH 7), supplemented with 25mM glucose and 25mM L-malate until stationary phase. Cells were harvested, washed with salt solution, and resuspended with 50 mM L-malate. The results represent the means ± the standard deviation of three independent experiments. (*) P ≤ 0.05.