PHENOTYPIC, GENOTYPIC, AND CHEMICAL CHANGES IN STARVING POPULATIONS OFAEROBACTER AEROGENES

Abstract

Cells harvested from postlogarithmic (maximal stationary phase) Aerobacter aerogenes cultures and starved in dilute sodium-phosphate at 40 C remained viable for many hours. On the other hand most cells from logarithmic-phase cultures succumbed, although a relatively small number remained viable. This viable segment of the original population thus responded like cells from postlog-phase cultures and (in fact) had properties in common with them. The residual segment was comprised of cells of two kinds. The first were mutants; when cultivated, harvested during log-phase growth and again starved they were resistant. The second were wild-type; they responded exactly as before. During starvation, the mutant is at an advantage because it has the ability to convert from susceptible log-phase physiology to resistant postlog-phase physiology more rapidly than can wild-type. The mutant is smaller in size, slower in growth rate, lower in ribo-nucleic-acid (RNA)-deoxyribonucleic-acid (DNA) ratio, greater in light-scattering ability and (during the first 4 hr. of starvation) it loses a higher proportion of its RNA. Selection of mutants of low growth rate between periods of active clonal growth indicates that evolutionary advantage may not necessarily be with the fast-growing members of the clone.