The sfiA11 mutation prevents filamentation in a response to cell wall damage only in a recA + genetic background

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Abstract
N-α-palmitoyl-l-lysyl-l-lysine dihydrochloride ethyl ester (PLL) at sublethal doses causes filamentous growth of E. coli strains except sfiA mutants, which divide normally in its presence. PLL does not elicit the SOS responses as judged by λ prophage induction, an increase of RecA protein synthesis or induction of the sfiA operon in a sfiA::lacZ fusion strain. Thus, it appears that filamentation caused by PLL is not an SOS function and might be the result of membrane damage by PLL, which is an amphipathic compound and at higher doses causes cell lysis. This indicates that basal levels of the sfiA gene product are sufficient to inhibit cell division in the presence of PLL. We have found further that the phenotype of the sfiA mutation in the presence of PLL requires a recA + genetic background and does not occur in E. coli recA1 sfiA11, recA13 sfiA11, recA56 sfiA11 and recA441 sfiA11. All these strains, but rec441 sfiA11, however, regain the ability of sfiA11 mutants to divide in the presence of PLL after transformation with the RecA overproducing-plasmid pXO2. This supports the conclusion that the RecA protein positively affects sfiA11-mediated cell division in the presence of the cell membrane damaging compound, PLL. The basal level of the RecA protein in the recA +sfiA11 strain is sufficient for this process. An increased level due to overproduction from the multicopy plasmid pXO2 exerts the same effect.