Because ACC is an intermediate precursor in ethylene synthesis, the ability of cadmium-resistant PGPR to use ACC as a sole nitrogen source was tested. Briefly, DF salts minimal medium (Dworkin and Foster, 1958) containing 3.0mM ACC (Sigma, USA) instead of ammonium sulfate ((NH4)2SO4), as a nitrogen source (Penrose and Glick, 2003) was inoculated with the bacteria. DF salts minimal medium containing (NH4)2SO4 was used as a control (Rajkumar and Freitas, 2008). The cultures were incubated at 28 °C with shak- ing at 150 rpm for 24 h. The bacterial growth was monitored by measuring the optical density at a wavelength of 600 nm (OD600).