MATRIC POTENTIAL IN RELATION TO SURVIVAL AND ACTIVITY OF A GENETICALLY MODIFIED MICROBIAL INOCULUM IN SOIL

The effects of matric potential on the survival and activity of an inoculum of Escherichia coli in soil were investigated by inoculating cells into sterile soil, with or without glucose, at three different matric potentials (-5 kPa, -64 kPa and -1.5 MPa). The E. coli strain used plasmid-borne lux genes to enable expression of luminescence in active cells. Survival of cells was determined over 10 days by dilution plate counting of viable cells, and activity was estimated by luminometry (actual activity) and radio-respirometry (potential activity). Matric potential had a significant effect on both viable cell concentrations and microbial activity. Light output and carbon dioxide production per cell both decreased with greater matric stress in both glucose-amended and unamended soil. Light output decreased with time, however, while substrate-amended respiration remained fairly constant, highlighting important differences between actual and potential microbial activities.