Deciphering the Impact of Acinetobacter sp. SG-5 Strain on Two Contrasting Zea mays L. Cultivars for Root Exudations and Distinct Physio-Biochemical Attributes Under Cadmium Stress

Promising strategies involving beneficial bacteria to promote plant growth which diminishes Cd phytotoxicity and reduces Cd bioaccumulation in edible parts are of great importance to conserve agricultural soils and food safety. The current study investigated the interaction between Acinetobacter sp. SG-5 and two maize cultivars {3062 (Cd tolerant), 31P41 (Cd susceptible)} in terms of physio-biochemical traits, elemental contents, and root exudation patterns under Cd stress. Two maize cultivars were grown in hydroponics having 0, 6, 12, 18, 24, and 30 µM CdCl2 levels in Petri plates with or without Acinetobacter sp.SG-5. From Petri plates, maize seedlings were shifted to rhizoboxes, and after 48 h, treated plants were analyzed for their growth, physio-biochemical traits, and organic acid exudates. Without SG-5 application, Cd stress caused significant reduction in biomass, chlorophyll, anthocyanin, antioxidants, mineral acquisition, and increased MDA, nutrient leaking from root exudates as well as in planta Cd deposition of both cultivars. However, this diminution was cultivar specific and found maximum in 31P41 than 3062. Meanwhile, inoculation with Acinetobacter sp. SG-5 significantly augmented plant biomass, chlorophyll contents, anthocyanins, total soluble sugars, antioxidative machinery while reduced MDA production under Cd stress. In addition, SG-5 inoculation significantly promoted the level of essential nutrients (Fe, Zn, K, Ca, Mg) in root and shoots while decreased their efflux through root exudates via diminishing Cd accumulation. Further, the secretion of citric, acetic, malic, formic, oxalic, succinic, and glutamic acid was significantly down regulated which likely improved nutrient accumulation while reducing oxidative damage via Cd immobilization. Consequently, both maize cultivars benefited from SG-5 symbiosis by increased detoxification ability, ionic status, and decreased organic acid exudation in response to Cd stress, but substantial Cd tolerance was attained by Cd susceptible cultivar. It was concluded that Acinetobacter sp. SG-5 is a potential candidate to be used in bioremediation and food safety programs.