Journal of Basic Microbiology 2007, 47, 513 – 517 513 © 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jbm-journal.com Research Paper Chromate reducing and plant growth promoting activies of psychrotrophic Rhodococcus erythropolis MtCC 7905 Pankaj Trivedi 1, 2 , Anita Pandey 1 and Tongmin Sa 2 1 Environmental Physiology and Biochemistry, G B Pant Institute of Himalayan Environment and Development, Kosi-Katarmal, Almora, India 2 Department of Agricultural Chemistry, Chungbuk National University, Cheongju, Chungbuk, Republic of Korea A psychrotrophic bacterial strain resistant to 300 mg l –1 of Cr 6+ was isolated from metal contaminated soil samples from a site situated in the Indian Himalayan Region. Based on 16 S rRNA analysis the isolate showed maximum similarity to Rhodococcus erythropolis. Rhodococcus erythropolis MTCC 7905 reduced substantial amounts of Cr 6+ to Cr 3+ at 10 °C and showed plant growth promotion. The isolate offer promise as inoculant to promote plant growth of pea (Pisum sativum) in the presence of toxic Cr 6+ concentration. To the best of our knowledge this is the first report on a psychrotrophic strain belonging to species R. erythropolis and its functional characterization to reduce Cr 6+ and promote plant growth at low temperature. Keywords: Rhodococcus erythropolis / Psychrotroph / Bioremediation / Cr 6+ reduction / Plant growth promotion Received: July 09, 2007; accepted: August 13, 2007 DOI 10.1002/jobm.200700224 Introduction * Among heavy metals, which are widespread pollutants of soils, chromium (Cr) is one of most toxic [1]. Chro- mium occurs in oxidation states of Cr 2+ to Cr 6+ , but only Cr 3+ and Cr 6+ are of biological significance. Cr 3+ is an essential micronutrient for human diet and is relatively less toxic and soluble [2]. On the other hand, Cr 6+ is toxic, mutagenic and carcinogenic [3]. Furthermore it is not possible to grow plants at or near Cr 6+ contaminated soils as it has been shown to cause plant growth reduc- tion due to root damage [4]. Therefore, suitable meth- ods need to be developed for remediation of Cr 6+ con- taminated soils. Biotransformation of Cr 6+ to the non-toxic Cr 3+ form by chromate reducing bacteria (CRB) offers an eco- nomical as well as ecofriendly option for its detoxifica- tion and bioremediation [5]. A number of CRBs have been reported to detoxify Cr 6+ through different mechanisms [6]. Certain CRBs have shown to possess different traits related to plant growth promotion such Correspondence: Dr. Pankaj Trivedi, Department of Agricultural Chemistry, Chungbuk National University, Cheongju, Chungbuk 361- 763, Republic of Korea Email: p_trivedi29@yahoo.com Tel: + 82-43-261-2561 as fixation of atmospheric nitrogen, solubilization of mineral phosphates, production of siderophores, or plant growth regulators [7]. Several mesophilic genera capable of Cr 6+ reduction have been reported but to date only two studies have reported Cr 6+ reduction by cold tolerant psychrotrophic species [8, 9]. The objective of the present study was to characterize a novel Cr 6+ reducing psychrotrophic strain of Rhodococcus erythropolis isolated from a metal con- taminated site situated in a Himalayan location. The isolate was tested for its ability to produce auxiliary plant growth promoting substances. The efficiency of growth promotion under stress of toxic Cr 6+ concentra- tion and low temperature was evaluated through a bioassay using pea as test plant. To the best of our knowledge, this is the first report on a psychrotrophic R. erythropolis strain with the ability to reduce Cr 6+ and promote plant growth at low temperature. Materials and methods Isolation and characterization Soil samples were collected from the vicinity of Jhiroli Magnesite Mine, Almora Magnesite Ltd., District Bageshwar, Uttarakhand, India (altitude: 1550 m above