A partial chloroform-fumigation technique to characterise the spatial location of bacteria introduced into soil

Bioluminescence-marked cells of Pseudomonas fluorescens were inoculated into soil by introduction into pores of two different size classes (< 6 and 30–60 m neck diameter). Partial chloroform fumigation resulted in a differential killing of cells depending on the placement of the inoculum within the soil pore network and on the period of fumigation. Reduced survival was associated with increasing periods (30–120 min) of fumigation, and with inoculum placement into larger rather than smaller pores. Comparison of the effects of partial fumigation on cells introduced into four soils of contrasting pore-size distribution highlighted the need to calibrate the method on the basis of air/water-filled pore space and chloroform diffusion dynamics for different soil types. It is proposed that partial fumigation facilitates spatial characterisation of the distribution of bacterial cells introduced into soils.