The copper-resistant (1318 mu M CuSO4 center dot 5H(2)O) strain KNP3 of Proteus vulgaris was isolated from soil near the Panki power plant, Kanpur, India, and was used to inoculate pigeon pea (Cajanus cajan var. UPS-120) seeds grown in soil for 60 days in the presence of 600 mu M CuSO4 center dot 5H(2)O. A study of siderophore production (126.34 +/-0.52 mu g ml(-1)) and its subsequent effects on plant growth promotion under in situ conditions was conducted. The parameters that were monitored included the plants' wet weight, dry weight, shoot length, chlorophyll content, and concentration of copper in plant roots and shoots. The results showed that the strain caused a significant (p < 0.05) increase in wet weight, dry weight, root length, shoot growth, and chlorophyll content (57.8%, 60%, 19.7%, 47.8%, and 36.3%, respectively) in the presence of copper. Furthermore, the strain reduced accumulation of Cu in the roots and shoots to 36.8% and 60.5%, respectively. Apart from this, copper concentration in the soil was measured on 0, 7, 15, 30, and 45 days consecutively and the results indicated that the bioinoculant KNP3 causes a significant decrease in Cu concentration in soil (55.6%), which was unlikely in the control (10.5%) treatment. The data suggested that the bacterial strain has the ability to protect plants against the inhibitory effects of copper besides reducing the copper load of the soil.