Figure 3. An overview of the main constituents of the E. faecalis response to high NaCl concentrations.

Among the responses observed was an immediate down-regulation of mscL to prevent plasmolysis (A), accompanied by an up-regulation of genes involved in the adjustment of membrane properties (B) and an up-regulation of genes involved in uptake of osmoprotectants (C). The main mechanism for extrusion of excess Na⁺ appeared to be the V-type ATPase encoded by the ntp operon (D). An up-regulation of genes coding for the molecular chaperone DnaK and GroEL/ES is indicative of NaCl-induced aggregation and misfolding of proteins (E). Finally, the exposure to NaCl also resulted in a strict repression of the gelE-sprE operon. Follow-up experiments established that this regulation was due to salt interfering with the receptor-pheromone interaction of the Fsr quorum sensing system (F). Significantly regulated genes are given in parenthesis when only parts of an operon were significantly differentially expressed.