Preliminary observations on the effect of heavy metals from mining and smelting on nitrogen-fixing bacteria in some British soils

Nitrogen fixation by free-living non-symbiotic bacteria has been qualitatively estimated in several surface soils and mine wastes from mineralised areas in Derbyshire and Cornwall, using a technique based on acetylene reduction. Fresh samples contaminated with varying amounts of one or more of the metals lead, zinc, cadmium and copper, together with appropriate controls, showed no ability to reduce acetylene, indicating an absence of nitrogen fixation. Addition of activeAzotobacter chroococcum resulted in acetylene reduction in the majority but not all of the samples. The effects of varying concentrations of lead, zinc, cadmium and copper on the growth ofAzotobacter chroococcum andBeijerinckia lactogenes were tested in laboratory culture.