EFFECT OF AN INTRODUCED INOCULUM ON SOIL MICROBIAL DIVERSITY

A laboratory study was carried out to evaluate the impact of the intro duction of genetically modified microorganisms into soil, in terms of effect on the diversity of the indigenous microflora, and at the proce ss level. The impact on microbial phenotypic diversity, and on soil de nitrification of an inoculum of a [we-modified denitrifier, Pseudomona s fluorescens, was examined using two different soil types in re-packe d soil microcosms. The effect on diversity was found to depend on the soil pore size class into which the modified inoculum was introduced. The introduction of lux-modified cells into the 15-30 mu m pore neck s ize class caused a short-term reduction in the overall microbial diver sity. There was no significant change in the diversity of the indigeno us microbial community, however, when cells were introduced into the 4 0-60 mu m pore class. Partial chloroform fumigation proved useful in d ifferentiating cell populations with respect to pore location. No chan ge in diversity was observed when dead cells (either heat killed or gl utaraldehyde fixed) were introduced into either pore size class. At th e process level, the effect on soil denitrification of introduction of lux-modified P. fluorescens was not significantly different from intr oduction of the equivalent inoculum of the parental wild-type, althoug h denitrification was found to be dependent upon both soil structure a nd pore size location of the introduced inoculum.