POTENTIAL LUMINESCENCE AS AN INDICATOR OF ACTIVATION OF GENETICALLY-MODIFIED PSEUDOMONAS-FLUORESCENS IN LIQUID CULTURE AND IN SOIL

Potential luminescence was used to assess the ability of luminescence- marked cells of Pseudomonas fluorescens to regain activity following s tarvation in soil or in liquid culture. In soil, potential luminescenc e was measured by determining luminescence periodically during incubat ion of samples of inoculated soil with double-strength complex medium supplemented with sodium citrate. Luminescence increased to a maximum during incubation. Following starvation of cells in soil, maximum lumi nescence decreased and the time taken to reach the maximum increased. Activity measured by dehydrogenase assays did not vary during the incu bation and was not significantly affected by starvation of the cells. Viable cell concentration correlated well with final potential lumines cence values and with luminescence in the absence of nutrient amendmen t, but not with potential dehydrogenase activity. Growth of P. fluores cens, previously starved in liquid medium, was preceded by a lag which increased in length as the duration of the starvation period increase d. Although luminescence of the starved cultures decreased with increa sed starvation period, there was no detectable lag in luminescence fol lowing addition of nutrients. Potential luminescence therefore enables rapid, non-extractive and selective determination of changes in activ ity of luminescence-marked microorganisms in soil, the size of the act ive population and the time taken to recover from periods of starvatio n.