Adaptive responses of Ralstonia eutropha to feast and famine conditions analysed by flow cytometry

Results obtained by flow cytometry allow conclusions to be drawn about how the physiological states of Ralstonia eutropha JMP134 are connected with su rvival strategies under distinct growth conditions. During both feast and f amine conditions the cells were found to proceed through sharply separated phases of life. Two sources of carbon and energy, one poor (0.02% phenol) a nd one rich (0.2% pyruvate and 0.1% yeast extract) were chosen to study the cellular responses. Despite the major differences in carbon source, when g rowth stages of the bacteria on the two substrates were characterised in ba tch growth, only minor differences were found in the time course of the mem brane potential related fluorescence intensity (MPRFI). This also applied t o the rRNA content and the size-correlated forward scatter (FSC) signal of the cells, both of which increased to high levels during the (early) expone ntial growth phase. On the rich medium, DNA synthesis initially occurred in an uncoupled manner, then a high rate of PHB formation followed when nutri ents began to be limiting. Under famine conditions, the cellular responses were much more complex. PHB was synthesised, then DNA synthesis occurred in a 'eukaryotic' mode, to be succeeded by renewed PHB synthesis. To obtain d efined cell physiological states, the chemostat technique was used in addit ion to batch experiments. The results obtained clearly indicated that key e vents in cell physiology, including initiation of DNA replication and overf low metabolism, occurred in a hierarchically ordered manner and were tightl y correlated with changes in the environmental conditions of the bacterial cells. (C) 1999 Elsevier Science B.V. All rights reserved.