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Ecotoxicology and Environmental Safety
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Microorganism technologies can provide a potential alternative to traditional methods of removing heavy metals
to conserve agricultural soils. This study aimed to identify and characterize heavy metals-resistant bacteria (HMRB) isolated from industry-affected soil and their desired impact as bioremediators of heavy metals-stressed
spinach plants. Three of 135 isolates were selected based on a high level of resistance to heavy metals. Based on
morphological and biochemical characteristics, the selected isolates were identified as Bacillus subtilis subsp.
spizizenii DSM 15029 T DSM (MA3), Paenibacillus jamilae DSM 13815 T DSM (LA22), or Pseudomonas aeruginosa
DSM 1117 DSM (SN36). Experiments were implemented to investigate the three isolated HM-RB ability on
improving attributes of growth, physio-biochemistry, and components of the antioxidant defense system of
spinach plant exposed to the stress of cadmium (Cd2+; 2 mM), lead (Pb2+; 2 mM) or 2 mM Cd2++2 mM Pb2+.
Compared to control, Cd2+ or Pb2+ stress markedly lowered plant fresh and dry weights, leaf contents of
chlorophylls and carotenoids, rates of transpiration (Tr), net photosynthesis (Pn) and stomatal conductance (gs),
relative water content (RWC), and membrane stability index (MSI). In contrast, contents of α.tochopherol
(α.TOC), ascorbic acid (AsA), glutathione (GSH), proline, soluble sugars, Cd2+, and Pb2+, as well as activities of
enzymatic and non-enzymatic antioxidants were markedly elevated. The application of HM-RB promoted the
tolerance to heavy metal stress in spinach plants by improving Tr, Pn, gs, RWC, and MSI, while activities of
enzymatic and non-enzymatic antioxidants were suppressed. These results reflected positively in promoting
plant growth under heavy metal stress. Therefore, the application of HM-RB as potential bioremediators may be
a promising strategy for promoting plant growth and productivity under heavy metal stress.
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