Competition between an Escherichia coli tyrosine auxotroph and a prototrophic revertant in glucose- and tyrosine-limited chemostats

Abstract

A tyrosine-requiring strain of Escherichia coli was grown in tyrosine-limited chemostats at a range of dilution rates between 0.08 h-1 and 0.42 h-1, conditions which always resulted in the selection of a prototrophic revertant population able to synthesise tyrosine. Analysis of the two-membered mixed cultures which arose showed that the prototrophic population outgrew the auxotroph since its growth rate was not restricted by the growth-limiting concentrations of exogenous tyrosine. During the take-over of the culture, the prototroph population grew exponentially but the specific growth rate increased with decreasing dilution rate of the competition experiments. In glucose-limited chemostats (in the presence of non-growth-limiting concentrations of tyrosine) of the tyrosine-requiring strain, prototrophs were never detected. Constructed two-membered mixed cultures with both populations competing for limiting amounts of glucose, showed that the prototroph was less competitive than the auxotroph.