Vol.:(0123456789) 1 3 Environmental Sustainability https://doi.org/10.1007/s42398-019-00055-3 ORIGINAL ARTICLE Cadmium resistant plant growth promoting rhizobacteria Serratia marcescens S2I7 associated with the growth promotion of rice plant Rhitu Kotoky 1  · Sudipta Nath 1  · Dinesh Kumar Maheshwari 2  · Piyush Pandey 1 Received: 17 December 2018 / Revised: 16 April 2019 / Accepted: 4 May 2019 © Society for Environmental Sustainability 2019 Abstract Cadmium (Cd) is one of the most toxic contaminants in the environment. The contamination of crop felds with metals like Cd may lead to a signifcant decrease in productivity due to related toxicity. The present study was conducted with aim to enhance the growth of rice (Oryza sativa), in Cd contaminated soil, by the application of heavy metal resistant—plant growth promoting rhizobacteria, Serratia marcescens S2I7. S2I7 was found to be highly resistant to Cd and positive for phosphate solubilization, production of siderophore, indole acetic acid (IAA), and hydrogen cyanide (HCN). The organism was found to have Glutathione S-transferase (GST) mechanism for detoxifcation of Cd. GST was induced and its activity was increased signifcantly in the presence of Cd. When the bacterial strain was applied to rice seedlings, the germination index and growth of seedling were improved in spite of Cd contamination in soil. Pot trial experiments in laboratory conditions showed that the growth of the plants was not afected up to the moderate concentration of Cd (0.75 M), and removal of Cd from the soil was also high (66 mg/kg after 20 days). Interestingly, at low concentration of Cd (0.25 M), there was no signifcant removal of residual Cd from the soil. However, under the high concentration, rate of removal of Cd was very less after 20 days which may be due to toxic efects (of higher concentration). Here the plant–microbe association may need more time to overcome the efects of Cd and to lead to removal of the metal. Moreover, with the application of isolate S2I7, the growth of the rice plant was comparatively better, as the mean shoot length was increased by 7.9%, and mean root length was increased by 53.7%. Therefore, the application of multifunctional plant-growth promoting bacteria exhibiting resistance for Cd may result in better growth of rice under the stress of the heavy metal. This may also improve the remediation of contaminated sites by alleviating Cd-induced phytotoxicity and promoting the growth of plants. Keywords Cadmium · PGPR · Oryza sativa · Bioremediation Serratia marcescens  Introduction Increasing industrialization has led to heavy metal contami- nation of the environment, which has posed various threats to humans, other living organisms and the stability of the ecosystems. Unlike organic contaminants, heavy metals are not biologically degradable, and therefore remain in the environment for a long time. Most of the heavy metals are categorized as toxic (Wood 1974), but the toxicity of difers greatly with the metal (Fergusson 1990). Cadmium (Cd) and lead (Pb) cause toxicity to microorganisms by binding to essential respiratory proteins (Vallee and Ulmer 1972), and through oxidative damage by the production of reactive oxy- gen species (ROS) (Stohs and Bagchi 1995). As Cd and Pb are currently not known to have any biological function in bacteria therefore, less concentration of these may also dis- turb the normal functioning of the microorganisms (Kotoky and Pandey 2018). Microorganisms play an important role in the biogeo- chemical cycling of heavy metals and therefore in cleaning up metal-contaminated soil. Microorganisms, exposed to the higher concentrations of toxic heavy metals develop resist- ance against the elevated levels of these metals. Such metal resistant microorganisms are useful for successful bioreme- diation, as they use diferent detoxifcation mechanisms that are helpful to remove the contaminants. Apart from this, microorganisms play a crucial part in the growth of plants * Piyush Pandey piyushddn@gmail.com 1 Department of Microbiology, Assam University, Silchar, Assam 788011, India 2 Department of Botany & Microbiology, Gurukul Kangri University, Haridwar 249404, Uttarakhand, India