A key issue in the comprehension of the Enterococcus faecalis stress response is to understand how this bacterium is able to modulate its gene expression in accordance to environmental conditions. Through bioinformatic analysis of the E. faecalis V583 genome, nine two-component systems and a single orphan response regulator were identified. A transcriptional study gave evidence of four systems whose expression is induced by at least one environmental stress. In addition, gene disruption experiments allowed the isolation of eight response regulator mutants. Insertional inactivation of the response regulator gene err 05 resulted in growth default and cell morphology alterations; and also in expression default of the sagA gene, this latter being recently shown involved in E. faecalis stress resistance toward numerous lethal treatments (Y. Le Breton, A. Mazé, A. Hartke, S. Lemarinier, Y. Auffray and A. Rincé (2002) Current Microbiol 45: 434-439). Disruption of the err 04, err 08 or err 18 genes resulted in sensitivity towards heat. Finally, the err 10 mutant was shown to be more sensitive to acid pH and NaCl whereas its growth was less affected by bile salts or heat. We also demonstrated that the heat resistance phenotype of the err 10 mutant was correlated with an increase of the heat shock proteins DnaK and GroEL level.