Effect of cell density and attachment on resuscitation in soil of starved Pseudomonas fluorescens MON787

The effect of cell density and attachment on starvation survival and recovery was determined using luminometry to measure activity of a lux-marked strain of Pseudomonas fluorescens MON787. Bioluminescence was found to be a sensitive indicator of in situ activity of P. fluorescens MON787 in soil. The activity of a bacterial inoculum could be monitored during growth in soil, and was found to correlate with an increase in cell numbers. Luminescence could detect decreasing activity of P. fluorescens during starvation in soil, and recovery of activity and cell numbers following exposure to starvation and matric potential stress. The effect of localised cell density and attachment in soil on recovery from lag phase after nutrient addition was investigated and compared to recovery of starved liquid cultures. Nutrient addition to starved P. fluorescens in soil or liquid medium resulted in an immediate recovery of activity, followed by a second increase in luminescence after 5 h. Cells exposed to both starvation and matric potential stress in soil did not show a detectable immediate increase of activity, but required a 5-h lag phase before recovery of both activity and cell growth. The lag phase values were not significantly different over a range of localised cell densities. This suggests that cell density of P. fluorescens in the range tested is not a factor which affects recovery of soil bacteria from starvation.