AIMSTo identify the genes regulated by RR11, the regulator of the Streptococcus mutans HK/RR11 two-component system.METHODS AND RESULTSThe S. mutans RR11-encoding gene was inactivated, and the effects of gene disruption on the cell's ability to form biofilms under stresses and acquire extracellular DNA were tested. Biofilm was reduced in cells lacking RR11 following exposure to oxidative stress. RR11-defective cells showed approx. 20-fold reduction in transformation efficiency. Microarray used to decipher the RR11-regulated genes in biofilm showed that approx. 5% of the UA159 genome underwent a significant change in expression. RR11 was found to regulate 174 genes, including genes involved in competence, stress-response and cell division.CONCLUSIONSTarget genes controlled by RR11during biofilm growth have been identified by a comparison of transcriptional profiles between an RR11 defective mutant and the parental strain. The results demonstrated that RR11 is involved in the control of diverse cellular processes, including the formation of biofilm under oxidative stress and development of genetic competence.SIGNIFICANCE AND IMPACT OF THE STUDYThe regulator of HK/RR11 system controls a large regulon and is an important regulator involved in stress response during S. mutans biofilm growth enabling the survival and persistence of its progeny in the microbial community.