NONGENETIC POPULATION HETEROGENEITY STUDIED BY IN-SITU POLYMERASE-CHAIN-REACTION

Expression of a lac operon in Salmonella typhimurium single cells was monitored using lac mRNA targeting in situ reverse transcription-polym erase chain reaction (RT-PCR). It is demonstrated that suboptimal indu ction of the lac operon in a culture of S. typhimurium/F' lac(+) cells generates a subpopulation in which transcription of the lac operon oc curs and another subpopulation in which transcription of the lac opero n is repressed, whereas suboptimal induction of the lac operon in a cu lture of S. typhimurium/F' lac Y cells generates a population with uni form levels of lac mRNA. The outcome of the single-cell lac mRNA detec tion assay was compared with the outcome of a single-cell beta-galacto sidase assay. In cultures grown under different suboptimal lac inducti on conditions, the fraction of cells in which transcription of the lac operon occurred was concurrent with the fraction of cells showing bet a-galactosidase activity. Besides supporting the hypothesis that the l actose permease has a role in generating non-genetic heterogeneity in suboptimally induced cultures of Lac(+) cells, these results demonstra te the usefulness of in situ RT-PCR for the study of non-genetic popul ation heterogeneities.