Microbially Induced Redistribution of Chromium Geochemical Fractions in Distinct Soil and Sediment Types

Chromium contamination remains a significant concern globally due to its mobility and toxicity. While microbial reduction of Cr(VI) has been widely reported, the information regarding microbial effects on the Cr geochemical fractions and their mobility across the soil-sediment system is limited. This study investigates the capacity of an indigenous Cr(VI)-reducing bacterium, Bacillus cereus jv10, to drive Cr geochemical fraction redistribution and mobility attenuation in three distinct environmental matrices: municipal solid waste dumpsite soil, agrarian wetland soil, and estuarine lagoon sediments. The isolate demonstrated 95% reduction of 100 mg/L Cr(VI) within 72 h. FTIR and XPS analysis revealed the involvement of cell-surface functional groups (hydroxyl, carboxyl, amine, phosphate) consistent with extracellular Cr(VI) biotransformation to Cr(III). Cellular fractionation showed 90% of Cr products localized within the supernatant and cell-associated components. Microcosm experiments coupled with Tessier sequential extraction demonstrated a pronounced shift of exchangeable Cr (F1) toward organic matter-bound (F4) and residual (F5) fractions following bacterial treatment. The reduction in F1-bound Cr reached 85% in dumpsite soil, 47% in lagoon sediments, and 11% in wetland soil, indicating matrix-dependent redistribution dynamics. The findings advance understanding of microbially mediated speciation transformation and support the development of eco-compatible strategies for in situ Cr risk mitigation.