Microbes mediated alleviation of chromium (Cr VI) stress for improved phytoextraction in fodder maize (Zea mays L.) cultivar

This study investigates the potential of chromium (VI) resistant bacterial isolates to alleviate heavy metal stress in fodder maize plants and enhance phytoremediation. Twenty-one bacterial strains were isolated from contaminated water, with five strains; Bacillus thuringiensis (BHR1), Bacillus cereus (BHR2), Enterobacter cloacae (BHR4), Bacillus pumilus (BHR5), and Bacillus altitudinis (BHR6) selected based on their significant plant-growth promoting (PGP) traits and heavy metal tolerance. Under chromium (Cr VI) stress, the BHR1 strain significantly improved seed germination, seedling length and vigor index of fodder maize variety (J 1007) especially at 150 mg/L Cr (VI), where these parameters increased by 3.75, 3.23 and 6.44 folds, respectively. After 60 days, BHR1 also enhanced shoot and root lengths by 4.91 and 4.06 folds, respectively and increase fresh and dry biomass, especially at higher Cr (VI) concentrations. Photosynthetic pigments, chlorophyll a and b, were also elevated by 3.04 and 2.26 times, respectively. Additionally, BHR1 reduced oxidative stress markers, including proline and malondialdehyde (MDA), and decreased electrolyte leakage, thus improving membrane stability. The strain further increased antioxidant enzyme activities and chromium uptake in root and shoot tissues, enhancing the translocation factor by 95 %. This suggests that BHR1 can significantly promote fodder maize growth and accelerate chromium removal from contaminated soil, offering valuable insights into plant-microbe interactions under Cr (VI) stress.