||High-pressure treatment (>100 MPa) is known to induce several heat shock proteins as well as an SOS response in Escherichia coli. In the current work, we have investigated properties with respect to high-pressure treatment of mutants-deficient in Lon, a pressure-induced ATP-dependent protease that belongs to the heat shock regulon but that also has a link to the SOS regulon. We report that lon mutants show increased pressure sensitivity and exhibit hyperfilamentation during growth after high-pressure treatment. Both phenotypes could be entirely attributed to the action of the SOS protein SulA, a potent inhibitor of the cell division ring protein FtsZ and a specific target of the Lon protease, since they were suppressed by knock-out of SulA. Introduction of the lexA1 allele, which effectively blocks the entire SOS response, also suppressed the high pressure hypersensitivity of lon mutants, but not their UV hypersensitivity. These results indicate the existence of a SulA-dependent pathway of high-pressure-induced cell filamentation, and suggest involvement of the SOS response, and particularly of SulA, in high-pressure-mediated cell death in E. coli strains which are compromised in Lon function.