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 starvation in soil or in liquid culture. In soil, potential luminescence was measured by determining luminescence periodically during incubation 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 luminescence decreased and the time taken to reach the maximum increased. Activity measured by dehydrogenase assays did not vary during the incubation and was not significantly affected by starvation of the cells. Viable cell concentration correlated well with final potential luminescence values and with luminescence in the absence of nutrient amendment, but not with potential dehydrogenase activity. Growth of P. fluorescens, previously starved in liquid medium, was preceded by a lag which increased in length as the duration of the starvation period increased. Although luminescence of the starved cultures decreased with increased starvation period, there was no detectable lag in luminescence following addition of nutrients. Potential luminescence therefore enables rapid, non-extractive and selective determination of changes in activity of luminescence-marked microorganisms in soil, the size of the active population and the time taken to recover from periods of starvation.