EFFECTS OF STARVATION AND OSMOTIC-STRESS ON VIABILITY AND HEAT-RESISTANCE OF PSEUDOMONAS-FLUORESCENS AH9

This study addresses the responses to starvation and osmotic stress of Pseudomonas-fluorescens isolated from spoiled fish. Culturability and viability of stressed cells were determined. Cells maintaining an act ive electron transport system were considered to be viable and this ac tivity was assessed by the ability of the cells to reduce the 5-cyano- 2,4-ditolyl tetrazolium chloride (CTC) to fluorescent CTC-formazan. Ce lls starved of carbon maintained high culturability and a high proport ion of the cells were capable of reducing CTC during short-time (up to 5 d) experiments. ATP concentrations were lower in carbon-starved tha n in log-phase cells but the measured levels suggested that metabolic activity was retained. Carbon-starved cells developed an increased hea t resistance and prolonged starvation resulted in further protection. Viable, but non-culturable cells were found during heat challenge impl ying that culture methods underestimate the recovery potential of thes e cells. Osmotically-stressed Ps. fluorescens maintained a high viabil ity, whereas culturability was rapidly lost. In contrast to starved ce lls, no protection against a subsequent heat challenge was found in os motically-stressed (4 or 18 h) cells, but an increased salinity of the heating menstruum alone resulted in elevated heat resistance.