The Consequences of Mutation during the Growth of Biochemical Mutants of Escherichia coli

Abstract

A bacterial culture may contain a very large number of organisms. Consequently, even mutations occurring at very low rates per organism may not be uncommon. For this reason bacterial cultures are likely to be heterogeneous and their composition will depend upon mutation rates and selection pressure (Ryan, 1948). When mutations influence the growth characteristics of bacteria, the behavior of the whole culture may be drastically influenced. In the case of the so-called biochemical mutations, which affect the organisms' capacity to synthesize amino acids and growth factors, this influence is very evident. For example, by overgrowth during serial transfers in the presence of limiting concentrations of tryptophan, Wright and Skeggs (1945) have been able to select a strain of Lactobacillu8 arabino&u that does not require this substance. In the absence of tryptophan this new strain grows as fast and as far as does its tryptophan-dependent parent in the presence of tryptophan. Increasing concentrations of tryptophan, however, first depress and then allow this rapid growth of the tryptophan-independent mutant. Although the factors underlying this behavior are not yet understood in L. arabinosus, we have found a parallel situation in a histidineless mutant of Escherichia coli. This paper will present data that show that the depression of growth on intermediate concentrations of amino acid is the result of mutation and the consequent interaction between mutants and parents. The next two papers in this series will analyze the mechanism of this interaction (Ryan and Schneider, 1949a,b).

An Experimental Analysis of a Life History Theory

“…These markers were selected from a nonconjugative strain of Escherichia coli (strain 15999, American type culture collection) and have been shown to be competitively neutral with respect to one another under culture in a medium having excess histidine. The growth medium, genetic markers, and adaptation of strains have been described at length elsewhere (Ryan and Schneider 1948a, 1948b, Atwood et al 1951, Ryan and Wainwright 1954. Bacteria were stored in nutrientagar stabs, with single colony isolates used to initiate liquid cultures for experiments.…”

Growth and Metabolism of Ophiostoma multiannulatum on Different Sources of Carbon

“…Lyophilized cells f/iysiol. I'iant, 9,1956 are however relatively easily broken in a Potter-Elvehjem homogenizer or when ground with glass powder.…”

“…The heat produced during growth may thus make temperature control critical when experiments arc Phyaiol. Plant., 9,1056 performed near the upper temperature limit of growth of au organism. Wheu the temperature was lowered to less than 25° on the other hand, hyphal growlh was favoured, aud it hecame impossible to conlinue experiments for any length of time.…”

Competitive Suppression and the Detection of Mutations in Microbial Populations

“…An increase in the sugar content of the plating medium diminishes the suppresssion effect as does a decrease in the number of inhibiting auxotrophic cells present. Ryan and Schneider (1949) using K~ch. coli have shown that under anaerobic conditions the suppression of prototrophs by histidine-requiring bacteria was brought about by a somewhat similar mechanism.…”

“…Inhibition of protrophs by auxotrophs has been shown to occur in Esch. coli by Ryan and Schneider (1949) in studies of reversion of a histidine-dependent strain to histidine independence and in N. crussa by Grigg (1952) and Stephens and Mylroie (1953). Such inhibition may be demonstrated by plating a prototrophic and an auxotrophic strain, mixed in given proportions, on minimal medium.…”