Physiological states of individual Salmonella typhimurium cells monitored by in situ reverse transcription-PCR

The possibility of using levels of specific mRNAs in individual bacteria as indicators of single-cell physiology was investigated. Estimates of the nu mbers of groEL and tsf mRNAs per cell in Salmonella typhimurium cells in di fferent physiological states were obtained by Northern analysis, The averag e number of groEL mRNAs per cell was estimated to be 22 in fast-growing cul tures and 197 in heat-shocked cultures. The average number of tsf mRNAs per cell was estimated to be 37 in fast-growing cultures, 4 in slow-growing cu ltures, and 0 in nongrowing cultures, The potential of mRNA-targeted in sit u reverse transcription (RT)-PCR to monitor quantitatively different levels of groEL and tsf mRNA in individual cells and thus monitor both specific g ene induction and general growth activity was assessed. Neither groEL nor t sf mRNA was present in stationary-phase cells, but it was shown that statio nary-phase cells contain other RNA species at high levels, which may provid e a possibility for monitoring directly stationary-phase individual cells b y the use of in situ RT-PCR, The outcome of the in situ RT-PCR analyses ind icated that a population of fast-growing cells is heterogeneous with respec t to groEL mRNA single-cell contents, suggesting a cell-cycle-controlled ex pression of groEL in S. typhimurium, whereas a fast-growing culture is homo geneous with respect to tsf mRNA single cell contents, suggesting that the level of tsf mRNA is relatively constant during the cell cycle.