Journal of Hazardous Materials 195 (2011) 230–237 Contents lists available at ScienceDirect Journal of Hazardous Materials j our na l ho me p age: www.elsevier.com/locate/jhazmat Inoculation of endophytic bacteria on host and non-host plants—Effects on plant growth and Ni uptake Ying Ma a,c,∗ , Mani Rajkumar b , YongMing Luo a , Helena Freitas c a Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China b National Environmental Engineering Research Institute (NEERI), CSIR Complex, Taramani, Chennai 600113, India c Centre for Functional Ecology, Department of Life Sciences, University of Coimbra, Coimbra 3001-401, Portugal a r t i c l e i n f o Article history: Received 10 May 2011 Received in revised form 9 August 2011 Accepted 10 August 2011 Available online 17 August 2011 Keywords: Phytoremediation Endophyte Plant growth promoting traits Hydrolyzing enzymes Ni contaminated soil a b s t r a c t Among a collection of Ni resistant endophytes isolated from the tissues of Alyssum serpyllifolium, four plant growth promoting endophytic bacteria (PGPE) were selected based on their ability to promote seedling growth in roll towel assay. Further, the PGPE screened showed the potential to produce plant growth promoting (PGP) substances and plant polymer hydrolyzing enzymes. These isolates were further screened for their PGP activity on A. serpyllifolium and Brassica juncea under Ni stress using a phytagar assay. None of the four isolates produced any disease symptoms in either plant. Further, strain A3R3 induced a maximum increase in biomass and Ni content of plants. Based on the PGP potential in phytagar assay, strain A3R3 was chosen for studying its PGP effect on A. serpyllifolium and B. juncea in Ni con- taminated soil. Inoculation with A3R3 significantly increased the biomass (B. juncea) and Ni content (A. serpyllifolium) of plants grown in Ni contaminated soil. The strain also showed high level of colonization in tissue interior of both plants. By 16S rRNA gene sequencing analysis, A3R3 was identified as Pseudomonas sp. Successful colonization and subsequent PGP potentiality of Pseudomonas sp. A3R3 indicate that the inoculation with PGPE might have significant potential to improve heavy metal phytoremediation. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Industrial operations such as mining, smelting, metal forging, manufacturing of alkaline storage batteries, combustion of fossil fuel, and sewage sludge, cause accumulation of metals or metal- loids in natural resources such as soil, water and air. Since the heavy metals seriously affect terrestrial and aquatic ecosystems and induce potential health risks [1], various physicochemical and biological methods have been developed to remove the metals from the environment. Phytoremediation refers to the use of plants that can uptake high levels of heavy metals from soil and accu- mulate them in a harvestable part [2]. Although the efficiency of heavy metal phytoremediation is dependent on an adequate yield of plants and their capacity for metal ion accumulation, the plant associated beneficial microbes also play significant roles as they can provide nutrients and reduce the deleterious effects of metals to the plants [3,4]. Considering such beneficial features, it may be envisaged that inoculation of metal resistant plant growth promot- ∗ Corresponding author at: Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China. Tel.: +86 025 86881844; fax: +86 025 86881126. E-mail address: cathymaying@yahoo.com.cn (Y. Ma). ing bacteria would increase plant growth and phytoremediation potential in metal contaminated soils [5–7]. In recent years, the use of metal resistant endophytic bacteria in phytoremediation of heavy metal contaminated soils has attracted more attention [8–11]. Although the heavy metals such as Ni, Pb are toxic to plants and their associated microbes at high concentrations, the metal resistant plant growth promoting endophytic bacteria (PGPE) have been reported to occur widely in tissue interiors of various hyperaccumulator plants [12–14]. This indicates that endo- phytic bacteria have evolved to be resistant to high levels of heavy metals and that they might confer to the plant higher tolerance to heavy metal stress. Moreover, the endophytic bacteria are proved to be able to enhance the plant growth by various mechanisms including production of siderophores, 1-aminocyclopropane-1- carboxylic acid (ACC) deaminase, indole-3-acetic acid (IAA) or solubilization of phosphate (P) [15]. In addition, certain endophytes have also been shown to alter heavy metal toxicity/availability to the plant by producing siderophores, biosurfactants and organic acids [10,16]. Despite these beneficial actions on plant, however, the endophytic bacteria must be compatible with various hyper- accumulators and able to colonize the tissues of the host plants without producing any disease symptoms. Because of the ability to produce the plant growth beneficial substance in metal stressed environment, the colonization potential of PGPE in the rhizosphere and/or tissue interior of plants has been considered as a major 0304-3894/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2011.08.034