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 μm 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.