Abstract
Streptococcus mutans, a primary causative agent of dental caries, is known to synthesize adhesive glucans from sucrose by the actions of glucosyltransferases (GTFs ; GTFB, GTFC, and GTFD), which are considered to mediate firm adherence of bacterial cells to tooth surfaces, leading to biofilm formation. The recombinase A (RecA) protein has been shown to be essential for transformation of plasmid and chromosomal DNA in Streptococcus pneumoniae. In this study, a RecA-deficient mutant strain RAD was constructed by insertional inactivation of the recA gene encoding the RecA protein in S. mutans MT8148, after which the biological functions of acid tolerance and biofilm formation were investigated. The RAD strain had a lower rate of growth in pH 5.0 medium as compared to the parental strain MT8148. In an attempt to evaluate the viability of biofilm formed by the strains, the biofilm formed by RAD had a greater number of dead cells scattered throughout. The decreased viability of RAD biofilm was caused by sensitivity to acid, which may also contribute to defects in its formation. In addition, when the sucrose concentration in the medium was increased, MT8148 formed higher quality biofilm with greater cell density as compared to that formed by RAD, which was altered and had a lower density. These results suggest that RecA is an important factor for acid tolerance and gtf expression in biofilm formation by S. mutans.
