Survival and nodulating ability of indigenous and inoculated Rhizobium leguminosarum biovar trifolii in sterilized and unsterilized soil treated withsewage sludge

Rhizobium leguminosarum biovar trifolii was detected in soil from 41 of 47 plots, within nine sewage sludge-treated sites with different soil characte ristics and heavy metal contents. However, although population size varied widely, there was no consistent correlation with soil heavy metal concentra tion. Indigenous populations in 20 plots within four selected sites retaine d their ability to induce effective nodule formation after incubation of so il in the dark for 165 days. In sterilized (gamma -irradiated) soil, Rhizob ium survival varied from 0.01% to 95% depending on the soil sample and stra in used. Metal-resistant strains with non-mucoid colonies survived less wel l than mucoid metal-sensitive strains.