Cadmium-tolerant bacteria induce metal stress tolerance in cereals

Abstract

Cadmium usually hampers plant growth, but bacterial inoculation may improve stress tolerance in plants to Cd by involving various mechanisms. The objective was to characterize and identify bacteria that improve plant growth under Cd stress and reduce Cd uptake. Cadmium-tolerant bacteria were isolated from rhizosphere soil, which was irrigated with tannery effluent, and six strains were selected as highly tolerant to Cd, showing minimum inhibitory concentration as 500 mg L(-1) or 4.45 mmol L(-1). These strains were identified by 16S rRNA gene analysis and functional analysis in regard to plant growth promotion characteristics. To determine their effect on cereal growth under Cd stress, seeds were inoculated with these strains individually and grown in soil contaminated with three Cd levels (0, 40 and 80 mg kg(-1)). Biomass production, relative water content (RWC), electrolyte leakage (ELL) and tissue Cd concentration were measured. Biomass of both cereals was inhibited strongly when exposed to Cd; however, bacterial inoculation significantly reduced the suppressive effect of Cd on cereal growth and physiology. The bacterial isolates belonged to the genera Klebsiella, Stenotrophomonas, Bacillus and Serratia. Maize was more sensitive than wheat to Cd. Klebsiella sp. strain CIK-502 had the most pronounced effects in promoting maize and wheat growth and lowering Cd uptake under Cd stress.

Improvement of cadmium phytoremediation after soil inoculation with a cadmium-resistant Micrococcus sp.

“…Our findings corresponded well with the study of Ahmad et al (2014), who claimed that cadmium decreased the shoot and root dry biomass of Z. mays L. planted in cadmium-contaminated soil at 80 mg kg −1 compared to the uncontaminated control. The dry biomasses of Brassica campestris and Vigna radiata were lower when planted in cadmium-contaminated soil at 50 mg kg −1 (Anjum et al 2014).…”

“…CMU-H009 plays a role in promoting seed germination and root elongation in Z. mays L. In general, cadmium is toxic to plants at high concentrations in a range of 11.2 to 1123.6 mg L −1 cadmium ion by inhibiting root growth and cell division (Liu et al 2003). Maize is more sensitive to cadmium than other crops, e.g., wheat (Ahmad et al 2014). More inhibition of root growth was observed when the cadmium concentration was increased (Chen et al 2003;Liu et al 2003).…”

“…TISTR2221 play an important role in promoting plant growth (Prapagdee et al 2013). The most important mechanism to promote the growth of Z. mays L. and Triticum aestivum L. is the production of plant growth hormones by PGPB (Ahmad et al 2014). The growth promotion by heavy metal-resistant PGPB in many plant species, e.g., Brassica napus, Lolium multiflorum, Sedum alfredii, and Medicago sativa, has been reported (Chen et al 2013;Guo et al 2014;Liu et al 2015).…”

Cadmium and cadmium‐tolerant soil bacteria in cacao crops from northeastern Colombia

“…In terms of microbial bioaccumulation, an important actor to immobilize cadmium in cacao soils, which has not been taken into account so far, is a functional group of soil bacteria called 'cadmium-tolerant bacteria' (CdtB). This group of bacteria has been evaluated within other crops as rice, maize and wheat (Siripornadulsil and Siripornadulsil 2013;Ahmad et al 2014). Nonetheless, the term refers to the feature of having tolerance to cadmium as a global mechanism, and not to sequestrate it as a specific mechanism; this term excludes biomineralization, which refers to processes where biomineral formation is a highly directed process (Gadd 2010).…”

Screening of Zinc Solubilizing Bacteria and their Potential to Increase Grain Concentration in Wheat (Triticum aestivum)

“…The use of plant growth promoting microorganisms is a novel approach in this respect (Alavi et al, 2008). PGPR consist of beneficial microorganisms, which live in the rhizosphere of plant and promote plant growth by different mechanisms including biological nitrogen fixation, solubilization of phosphorus, synthesizing siderophores which can solubilize insoluble iron from the soil, production of phytohormones such as auxins, cytokinins and gibberellins (Glick, 2005;Jou et al, 2012;Ahmad et al, 2014;Mendoza, 2015). Bacterial auxin improve the uptake of mineral nutrient by enhancing the root exudation and also increase the lateral and adventitious rooting systems which ultimately increases bacterial population on and around the roots.…”