Effect of flow rate on Streptococcus mutans gene expression

Oral bacteria are exposed to variable salivary flow. S. mutans adhesins play an important role in the initial attachment of the bacteria to the tooth surface. However, little is known about how adhesins are regulated in different environmental conditions including flow rate. Our previous work indicated that SpaP gene and protein expression increased in response to shear force induced by mechanical shaking, mimicking salivary flow.

Objective: To determine the effect of increased shear force on S. mutans adhesin expression.

Methods: To investigate whether the influence of salivary flow in the oral cavity affects S. mutans UA159 gene expression, a platform shaker was used to generate a fluid shear stress (0.8 dyne/cm2) for 24h that is similar to the average stress caused by salivary flow. RNA was isolated from static and shaken cells and used in DNA microarray studies. Microarray slides were obtained from The Institute for Genomic Research and the analysis was conducted in quadruplicate.

Results: At least 100 genes were induced by shear force accounting for about 5% of the entire genome. Increased shear induced up to a 3-fold increase in the expression of genes responsible for several important adhesin proteins. Specifically, genes encoding for S. mutans SpaP (2.5 fold), 40 kDa cell wall protein (1.9 fold), GTF-S (1.3 fold), GTF-SI (1.4 fold), GBP-C (2.4 fold), sortase (2.0 fold), LuxS (1.7 fold), several heat shock proteins (GroEL, GroES and DnaK-1.8, 1.8 and 1.3 fold, respectively), enolase (1.9 fold), competence-stimulating peptide (1.4 fold) and several Com proteins (ComYC and ComYD; 1.4 and 1.5 fold increase, respectively) were induced.

Conclusion: These data indicated that shear force has a significant effect on the expression of many S. mutans adhesins suggesting that the upregulation is an effort by the bacterium to maintain its attachment in the dental biofilm under increased fluid flow.