Soil chromium bioremediation: Synergic activity of actinobacteria and plants Marta A. Polti a, b, * , Mariana C. Atjián a , María J. Amoroso a, c , Carlos M. Abate a, b, c a Planta Piloto de Procesos Industriales y Microbiológicos (PROIMI), CONICET, Av. Belgrano y Pasaje Caseros, 4000 Tucumán, Argentina b Facultad de Ciencias Naturales e Instituto Miguel Lillo, Universidad Nacional de Tucumán, 4000 Tucumán, Argentina c Facultad de Bioquímica, Química y Farmacia, Universidad Nacional de Tucumán, 4000 Tucumán, Argentina article info Article history: Received 7 September 2011 Received in revised form 21 September 2011 Accepted 21 September 2011 Available online 13 October 2011 Keywords: Bioremediation Chromium Maize Actinobacteria Soil abstract The aim of this work was to evaluate a strategy to reduce the bioavailable chromium fraction in soil, using a Cr(VI) resistant microorganism, Streptomyces sp. MC1, under non sterile conditions, with maize plants as bioindicator and/or bioremediator. Soil samples were contaminated with 100, 200 and 400 mg kg 1 of Cr(VI) or Cr(III). Bioavailable chromium (35%) was only detected in samples with Cr(VI). Soil samples with Cr(VI) 200 mg kg 1 were inoculated with Streptomyces sp. MC1, and bioavailable chromium decreased up to 73%. Zea mays seedlings were planted in soil samples contaminated with chromium. Plantlets accumulated chromium mainly as Cr(III), and biomass decreased up to 88%. Streptomyces sp. MC1 was inoculated in soil samples contaminated with 200 mg kg 1 of Cr(VI) and Z. mays seedlings were planted. Streptomyces sp. MC1 caused Z. mays biomass increase (57%), chromium accumulation and bioavail- able chromium decreased up to 46% and 96%, respectively. This work constitutes the first contribution of cooperative action between actinobacteria and Z. mays in the bioremediation of Cr(VI) contaminated soil. The large removal capacity of bioavailable chromium by Streptomyces sp. MC1 and Z. mays infers that they could be successfully applied together in biore- mediation of soils contaminated with Cr(VI). Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Hexavalent chromium, Cr(VI), is widely used in many industrial processes such as electroplating, wood preservation, etc. The chromium manufacturing industry produces a large quantity of solid and liquid waste containing hexavalent chromium. Cr(VI) compounds are highly water soluble, toxic and carcinogenic in mammals (Jeyasingh and Philip, 2005). Cr(VI) as chromate and dichromate is considered one of the principal pollutants in the United States by the Environment Protection Agency (Polti et al., 2009). In contrast, trivalent chromium, Cr(III), is considered nontoxic as it precipitates at higher pH than 5.5 with the formation of insoluble oxides and hydroxides in soil and water systems (Jeyasingh and Philip, 2005). The behavior of chromium (Cr) in water and soil and its subse- quent bioavailability have been the subject of active investigation because of the existence of chromium in two environmentally important oxidation states (þ3 and þ6) and the ease with which it can complex with naturally occurring chemical species in the soil (Mishra et al., 1995). Many technologies are currently used to clean up heavy metal contaminated soils. The most commonly used ones are soil removal and land filling, stabilization/solidification, physico-chemical extraction and soil washing. These techniques generally release secondary contamination and costly when applied to large areas. Bioremediation is a promising technology. The bioremediation strategy pursue detoxify Cr(VI) in the soil reducing it to Cr(III), immobilizing in the soil matrix. Besides eliminating the toxicity of Cr(VI) by its reduction to Cr(III) the latter forms a particularly insoluble Cr(OH) 3 in the pH range of 6e9 (Ksp, 6.7  10 31 ) severely restricting its ability to migrate to groundwater (Jeyasingh and Philip, 2005). Many microbes were reported to reduce Cr(VI) under aerobic and anaerobic conditions and Cr(VI) reducing microbial pop- ulations is widespread in soil with potential to aerobic reduction of this metal (Jeyasingh and Philip, 2005). Although most studies have been carried out with Gram- negative bacteria (Puzon et al., 2002; Cheung and Gu, 2007; Chai et al., 2009; Mohanty and Patra, 2011), several Gram- positive bacteria, including certain actinobacteria, have also shown to possess Cr(VI) reducing ability (Das and Chandra, 1990; * Corresponding author. Planta Piloto de Procesos Industriales y Microbiológicos (PROIMI), CONICET, Av. Belgrano y Pasaje Caseros, 4000 Tucumán, Argentina. Tel.: þ54 381 4344888; fax: þ54 381 4344887. E-mail address: mpolti@proimi.org.ar (M.A. Polti). Contents lists available at SciVerse ScienceDirect International Biodeterioration & Biodegradation journal homepage: www.elsevier.com/locate/ibiod 0964-8305/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ibiod.2011.09.008 International Biodeterioration & Biodegradation 65 (2011) 1175e1181