ASSESSMENT OF THE ROLE OF A TERRESTRIAL ISOPOD IN THE SURVIVAL OF A GENETICALLY-MODIFIED PSEUDOMONAD AND ITS DETECTION USING THE POLYMERASECHAIN-REACTION

The effects of a terrestrial isopod, Porcellio scaber, on the survival of a genetically modified pseudomonad were studied. Pseudomonas fluor escens KTG was inoculated onto ash leaf litter and supplied to populat ions of P. scaber. Plate counts were lower in fresh faeces than the as h leaf litter for P. fluorescens KTG, and higher counts were detected in the faeces for the total bacterial population. When faeces were age d by incubation for up to 7 days at 15-17 degrees C, plate counts for P. fluorescens KTG increased during the first day to a level similar t o those in the corresponding ash leaf litter, and remained relatively constant thereafter. The total bacterial population in the faeces cont inued to increase steadily over the 7 days, whilst remaining at a cons tant level in the ash leaf litter during the same period. Counts of ba cteria in faecal material showed that P. fluorescens KTG was present f or 6 days after the isopods had fed on inoculated litter although tran sit times of food through the gut were as little as 5 h. The implicati ons for GEMMO dispersal of bacterial retention in the gut is considere d. The polymerase chain reaction was utilised in the detection of the inserted DNA. Positive amplification of the inserted DNA sequence of P . fluorescens KTG was achieved in ash leaf litter, fresh faeces, and f aeces from animals which were supplied uninoculated litter for one day after feeding on the inoculated litter. However, plate counts were mo re sensitive than the polymerase chain reaction in detecting P. fluore scens KTG in the faeces. Our findings suggest that when the GEMMO is i ngested by the woodlouse it can survive within the guts and faeces. Th is has implications for risk assessment of genetically modified bacter ia in terrestrial environments.