Interrelationships between lysine and α∈-diaminopimelic acid and their derivatives and analogues in mutants of Escherichia coli

Abstract

The logarithmic growth rate of diaminopimelic acid (DAPA)-requiring E. coli mutants in a salts-glucose medium containing lysine is independent of the concentration of added DAPA. At concentrations below 20 [mu][image] lysis occurs during logarithmic phase after exhaustion of DAPA from the medium. One of the mutants, has no requirement for lysine; in the absence of lysine it does not lyse. During lysis, phase-contrast microscopy shows the appearance of spherical bodies which later lyse. Electron micrographs after lysis show cell envelopes which have lost their protoplasmic contents. Lysis occurs during the logarithmic growth phase of all strains of E. coli examined when grown in the presence of penicillin. Lysine and DAPA have no effect on this lysis. DD-Diaminopimelic acid, cystine, lanthionine and several straight-chain diaminodicarboxylic acids do not act as growth factors for the DAPA-requiring mutants. Lanthionine prevents lysis in the presence of lysine and inhibits growth in its absence. Nisin has no such effect. Cystine inhibits growth; the inhibition is overcome competitively by DAPA. The lysine requirements of the mutants are satisfied by a-N-acetyl-lysine but not by [alpha]-acetyl-lysine. [alpha]-N-Acetyl-lysine does not produce lysis of the mutants when it replaces lysine. [epsilon]-Hydroxy-[alpha]-aminocaproic acid and S-([beta]-aminoethyl)cysteine have no effect on growth or lysis. D-Lysine produces all the effects of L-lysine when present in concentrations 5 times higher. Polylysines do not affect lysis but they inhibit growth, lysine-requiring mutants being more sensitive than the parent strain. The cell walls of the mutants are indistinguishable from the parent wild strain, all containing rather more DAPA than lysine. Hydrolysates of certain caseins stimulate growth of the DAPA-requiring mutants, for unknown reasons. It is suggested that lysis of these mutants in the presence of lysine and suboptimum concentrations of DAPA is due partly to the shortage of DAPA, which is an essential cell-wall constituent. This would result in failure to synthesize cell wall, causing either protoplast formation or complete disintegration of the cell.