Suppression by the ColV, I-K94 Plasmid of a Growth Lesion in ompA Mutants of Escherichia coli

Abstract

Organisms of three independently isolated ompA mutants of Escherichia coli failed to form colonies on glucose minimal agar (glucosa MA) at 44.degree. C after growth in glucose minimal salts medium at 37.degree. C, although all three strains formed colonies on nutrient agar at 44.degree. C. Supplementation of the glucose MA with individual amino acids including L-methionine and/or L-cysteine did not allow colony formation at 44.degree. C, although addition of 0.1% Casamino acids was effective; replacement of glucose with other energy sources or ammonium ions with glutamate also did not allow growth at 44.degree. C. The failure to form colonies at 44.degree. C was not due to killing of the organisms, because colonies were formed if plates of the ompA mutant initially incubated at 44.degree. C were shifted to 30.degree. C after 16 h. Introduction of the CoIV, I-K94 plasmid into P678-54 ompA, 1131 ompA or an ompC ompA mutant suppressed the 44.degree. C growth lesion, but other plasmids (F lac, R483ColIa, RI, ColB-K98, R124) tested in P678-54 ompA did not. Growth of the CoIV, I-K94+ derivative at 44.degree. C was due to a suppressing effect of the plasmid rather than to introduction of the plasmid into a variant with normal or altered OmpA protein. An attempt was made to ascertain which component(s) encoded by CoIV, I-K94 was (were) responsible for allowing growth at 44.degree. C. Transfer components appeared unlikely to be involved and plasmids which conferred individual colicins (plus the corresponding immunity component) did not suppress. The findings that the CoIV, I-K94-encoded VmpA protein resembles the OmpA protein (a) immunologically and (b) in being a transmembrane component of the outer membrane suggested that it might be the presence of the VmpA protein which allowed growth at 44.degree. C. Several experiments were in accord with this possibility.