Characterization and assessment of iron-reducing capacity of cultivable bacteria from iron-toxic rice soils in Burkina Faso

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Résumé

Iron toxicity is a major constraint for rice production, particularly in lowland ecosystems where reduced iron (Fe[II]) accumulates due to activities by iron-reducing bacteria (IRB). This study investigated the dominant cultivable IRB strains in three iron-rich rice-growing areas of Burkina Faso: Moussodougou, Tiefora, and Kou Valley. Soil Fe(II) concentrations and IRB abundance were quantified using colorimetric and most probable number (MPN) methods to highlight the process ofFe(II) generation. Bacteria were isolated and characterized based on morphological traits (cell shape, Gram staining, sporulation), motility, and carbon source utilization. The isolates were also tested for their capacity to reduce Fe(III) in two iron oxides—ferrihydrite and magnetite—into Fe(II). The results revealed the presence of active IRB populations and elevated Fe(II) levels across all sites. Five bacterial isolates (VDK5AN, VDK12AE, M14AN, M16AN, and Ti13AN) were characterized. All were Gram-positive, rod-shaped, motile, and capable of forming endospores. 16 S rDNA analysis showed that VDK5AN and M16AN were closely related to Lysinibacillus spp., VDK12AE and Ti13AN to Bacillus spp., and M14AN to the genus Terrilactibacillus. Significant (p < 0.001) differences in Fe(III)-reducing abilities were observed among isolates, with VDK5AN showing the highest Fe(II) production from both ferrihydrite and magnetite. This study highlighted that bacteria belonging to Lysinibacillus, Bacillus, and Terrilactibacillus may play a role in Fe(III) reduction in submerged rice soils. The spore-forming and fermentative abilities of these bacteria can enhance their persistence in flooded paddy soils, thereby complicating the mitigation of iron toxicity through conventional agricultural practices.

Mots-clés

Iron toxicity, rice production, iron-reducing bacteria