Effect of acid shock on protein expression by biofilm cells of Streptococcus mutans

• Streptococcus mutans is a component of the dental plaque biofilm and a major causal agent of dental caries. Log-phase cells of the organism are known to induce an acid tolerance response (ATR) at sub-lethal pH values ( approximately 5.5) that enhances survival at lower pH values such as those encountered in caries lesions. In this study, we have employed a rod biofilm chemostat system to demonstrate that, while planktonic cells induced a strong ATR at pH 5.5, biofilm cells were inherently more acid resistant than such cells in spite of a negli-gible induction of an ATR. Since these results suggested that surface growth itself triggered an ATR in biofilm cells, we were interested in comparing the effects of a pH change from 7.5 to 5.5 on protein syn-thesis by the two cell types. For this, cells were pulse labeled with [(14)C]-amino acids following the pH change to pH 5.5, the proteins extracted and separated by two-dimensional (2D) electrophoresis fol-lowed by autoradiography and computer-assisted image analysis. A comparison between the cells incubated at pH 5.5 and the control biofilm cells revealed 23 novel proteins that were absent in the control cells, and 126 proteins with an altered relative rate of synthesis. While the number of changes in protein expression in the biofilm cells was within the same range as for planktonic cells, the magnitude of their change was significantly less in biofilm cells, supporting the observa-tion that acidification of biofilm cells induced a negligible ATR. Mass spectrometry and computer-assisted protein sequence analysis revealed that ATR induction of the planktonic cells resulted in the downregula-tion of glycolytic enzymes presumably to limit cellular damage by the acidification of the external environment. On the other hand, the gly-colytic enzymes in control biofilm cells were significantly less down-regulated and key enzymes, such as lactate dehydrogenase were upregulated during pH 5.5 incubation, suggesting that the enhanced acid resistance of biofilm cells is associated with the maintenance of pH homeostasis by H+ extrusion via membrane ATPase and increased lactate efflux.

Subject headings

MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Odontologi (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Dentistry (hsv//eng)

Keyword

Cardiovascular disease

Bacteria

Micrococcales

Streptococcaceae

Shock

Protein synthesis

Biofilm

Protein

Streptococcus mutans

Publication and Content Type

ref (subject category)

art (subject category)