To further investigate the role of ctsR and hrcA in ethanol adaptation, mutants of L. plantarum WCFS1 that lack one or both of these genes were constructed. The role of the transcriptional repressor CtsR in adaptation of L. plantarum to ethanol and heat stress was observed previously (11). The slightly higher growth rate of L. plantarum ΔctsR::cat than of wild-type cells in the presence of 8% ethanol confirms the contribution of the ctsR regulon members to counteracting ethanol-induced stress. The growth rate of this mutant under normal growth conditions in MRS was slightly reduced relative to that of wild-type cells. While inactivation of hrcA did not affect the growth rate of L. plantarum in MRS culture medium with or without ethanol present, notably, in the presence of 8% ethanol the L. plantarum hrcA-ctsR mutant grew with a rate equal to that of the wild type, suggesting an interaction between the ctsR and hrcA stress response regulons in L. plantarum.