Enhanced survival of Pseudomonas fluorescens in soil following establishment of inoculum in a sterile soil carrier

The method by which bacterial inocula are added to soil can greatly affect survival. This study assessed the establishment of bacteria in a carrier soil, prior to inoculation, as a method of enhancing survival in an agricultural soil. Preincubation of Pseudomons fluorescens in a sterile soil carrier led to greater survival in soil microcosms than preincubation in a non-sterile soil carrier or inoculation of a liquid cell suspension. Increased preincubation time in the sterile soil carrier resulted in greater survival after inoculation. P. fluorescens colonised in a sterile soil carrier for 2 weeks declined in concentration after inoculation by only 2 and 4 log units after 1 and 2 months, respectively, whereas bacteria inoculated using a cell suspension were undetectable by 1 month. Activity of P. fluorescens in soil microcosms, as determined by luminescence, decreased rapidly in all inoculation treatments to undetectable levels by day 4. Results show that establishment and growth using nutrients in sterile soil may adapt cells to soil environmental conditions, thereby increasing survival of bacterial inocula.