Growth of Escherichia coli cells in the presence of cysteine on sulphate-deficient media

Summary

The behaviour of E. coli B culture grown on SO₄ ^2--free minimal glucose-salt medium was examined in the presence of exogenous cysteine at various concentrations. This was done by means of using the following parameters: length of lag, growth rate and total population. Up to a concentration of cysteine at 0.2mm the growth sets in without a lag phase, the growth rate is optimal (identical with that of cultures grown on media containing Na₂SO₄ as source of sulphur), only the size of total population being decreased by cysteine. At concentrations of 0.2mm and upwards, after a concentration-dependent lag-period, the cultures were found to increase at various lower growth rates.

The toxic effect of cysteine was reduced by leucine itself, as well as by a mixture of leucine, isoleucine, valine and threonine. The anti-cysteine action of these amino acids showed itself in the shortening of the lag period and in the recovery of the growth rate which, however, failed to reach the original level.

Cysteamine failed to provide sulphur for cultures of E. coli B grown on the above medium. Neither was the utilization of cysteamine affected by the application of amino acids possessing an anti-cysteine action.

We have postulated that beside the inhibition of the biosynthesis of amino acids having an anti-cysteine effect, toxic concentrations of cysteine posses additional sites of action.