recA-dependent inhibition of cell respiration is not induced by mitomycin C in Escherichia coli

Influence of S9 mix in the induction of SOS system by quercetin

The induction of recA, umuC and sfiA genes by quercetin was studied in the presence and in the absence of S9 mix. The inducing activity of quercetin is higher for sfiA than for recA and umuC genes in the absence of S9 mix. The putative genotoxic metabolites of quercetin produced by S9 mix display different inducing activities of the three SOS genes as compared to quercetin. The induction of sfiA gene is decreased by the presence of S9 mix, whereas an opposite effect was observed concerning umuC and recA. These data suggest that the error-prone repair pathway participates in mutagenesis by quercetin and its metabolites. Moreover, the type of DNA damage exerted by quercetin seems to be determined by its metabolic fate. The importance of testing for the induction of other SOS genes, together with sfiA, in the study of SOS functions as a genotoxic index is emphasized.

Expression of the SOS response following simultaneous treatment with methyl-nitrosoguanidine and mitomycin C in Escherichia coli

Simultaneous treatment of Escherichia coli cultures with methyl-nitrosoguanidine and mitomycin C induces recA-dependent inhibition of respiration but not inhibition of cell division. This pattern of SOS functions expression is the same as that is found following treatment with methyl-nitrosoguanidine alone and contrary to the pattern induced after mitomycin C addition. The same result is obtained when a culture of E. coli RecA441 (formerly tif) is shifted to 42 degrees C and treated simultaneously with methyl-nitrosoguanidine. The suppressor effect of this compound over the pattern of SOS functions expression induced by mitomycin C or high temperature in recA441 mutants is directly related to the increase in its dose. Moreover, the division temperature-sensitive mutant ftsA treated with methyl-nitrosoguanidine and high temperature does not show any decrease in its normal filamentous growth when cultured at 42 degrees C. This indicates that the effect of methyl-nitrosoguanidine on the recA-independent inhibition of cell division is not due to any indiscriminate effect of this compound over the division process. These results suggest that the specific kind of lesion caused in DNA is very important in determining which SOS function is induced.

Respiration shutoff in Escherichia coli K12 strains is induced by far ultraviolet radiations and by mitomycin C

Ultraviolet radiations (254 nm) (UV) cause respiration to shutoff in Escherichia coli B/r. It has been reported [P.A. Swenson, Photochem. Photobiol., 33 (1981) 855-859 and J. Barbé, A. Vericat and R. Guerrero, Mutation Res., 120 (1983) 1-5] that E. coli K12 strains do not shut off respiration after UV. The latter authors also reported that mitomycin C did not cause this 'SOS' response. In this paper we report that higher UV fluences than were previously used will cause respiration shutoff in K12 strain W3110 and that cyclic AMP increases the sensitivity of respiration shutoff of irradiated cell suspensions. We also report that mitomycin C shuts off respiration in this strain. Neither UV nor mitomycin C causes respiration shutoff in the recA56 derivative of W3110. Thus respiration shutoff is a recA dependent response to UV and mitomycin C in E. coli K12 strains.

Indirect induction of SOS functions in Salmonella typhimurium

Infection of non-UV-irradiated cells of Salmonella typhimurium with UV-damaged P22 or KB1 phage induces recA-dependent inhibition of cell division, cell mutagenesis and prophage induction but not inhibition of respiration. On the contrary, respiration and ATP concentration are increased after treatment with UV-damaged phage in both RecA+ and RecA- strains, showing that this increase is not recA-dependent. Furthermore, infection with UV-damaged phage prevents both inhibition of respiration and decrease in ATP level in the UV-irradiated RecA+ strain. This indirect induction of SOS functions is related to degradation of phage DNA as well as to the multiplicity of infection used, suggesting that DNA degradation may play an important role in the mechanism of expression of the SOS system. Our results give also support to the hypothesis that there exists a differentiation in the expression of the various SOS functions.

Further characterization of the expression of SOS functions in recA430 mutants of Escherichia coli

recA-dependent inhibition of cell division and cessation of cell respiration are not expressed in recA430 (formerly lexB) mutants of Escherichia coli after ultraviolet irradiation. Our results suggest that, to be induced in UV-treated cells, inhibition of division as well as cessation of respiration require the protease activity of the RecA protein.