Integrated Assessment of Antioxidant Defense, Phytohormonal Responses, and Rhizomicrobial Dynamics in Maize Cultivated on Heavy Metal Impacted Mining Soils, Kilembe, Uganda.

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Background Heavy metal contamination of agricultural soils, particularly from mining activities, poses serious risks to food safety and public health. At the Kilembe mining site in Uganda, elevated levels of heavy metals have been reported in soils where maize ( Zea mays L.) is widely cultivated. This study investigated the biochemical stress response and culturable rhizobacteria in maize grown in heavy metal-contaminated soils to understand their mechanisms of adaptation. Methods Maize seeds were planted on farms obtained at varying distances from the Kilembe mining site (0, 1, 3, and 5 km) and a control site in Bushenyi (95 km), serving as groups 1-5, respectively. Oxidative stress and hormone profiles of germinated leaves and rhizospheric bacterial composition were determined using standard analytical and microbiological methods. Results Maize plants near the site had higher malondialdehyde levels and lower antioxidant enzyme activities (superoxide dismutase, catalase, and glutathione peroxidase). Brassinosteroid levels increased at 0 km, whereas auxin and abscisic acid levels decreased significantly across all distances compared to the control. Bacillus sp. was dominant at 39.71%, and Acinetobacter sp. was the least abundant (1.47%). The 3 km site had the highest bacterial load, while the 0 km site had high counts at lower dilutions. Plant growth-promoting rhizobacteria ( Bacillus sp. , Staphylococcus sp. , and Klebsiella sp. ) were highly distributed across sites. Conclusion The study showed that the presence of plant growth-promoting rhizobacteria, such as Bacillus spp., which were dominant, provided insight into the role of these rhizospheric organisms in conferring tolerance and is a probable adaptive mechanism that ensures the survival of maize plants grown around mining-associated farmlands, as seen in Kilembe, Uganda.

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