Humic acid facilitates microbial manganese oxidation-driven arsenic remediation in soil across a wide temperature...

Biogenic manganese oxides (MnO_x), produced by manganese-oxidizing bacteria (MnOB), exhibit strong potential for remediating arsenic (As)-contaminated soils due to their oxidative and adsorptive properties. However, the synergistic interactions between MnOB and soil humic acid (HA), and their combined effect on As remediation efficiency across environmentally relevant temperature gradients, remain poorly understood. This study therefore aimed to elucidate the role of HA in enhancing MnOB-driven As remediation under a wide temperature range (10-30 °C), a key knowledge gap for field applications. In this study, a MnOB strain was isolated from high Mn-laden soil, Pseudomonas sp. XY4, to investigate HA enhancement of microbial Mn(II) oxidation and subsequent soil As remediation across 10-30 °C. Strain XY4 showed broad adaptability to pH, carbon sources, and salinity. HA stimulated enzymatic Mn(II) oxidation and promoted the formation of biogenic MnO_x with higher crystallinity and Mn(III) content. Consequently, HA-enhanced strain XY4 quickly oxidized toxic As(III) to less mobile As(V), achieving high immobilization in soil and solution. The removal rate of As(III) in soil solution reached 89.9%-96.6%, and 41.0%-49.0% of bioavailable As was transformed into stable Fe/Mn oxide-bound form in soil. Finally, ryegrass grown in the soil remediated by both strain XY4 and HA, accumulated minimal As, with consistent efficacy across temperatures. These findings highlight the potential of the MnOB and HA combined strategy for sustainable As remediation in soil under actual field conditions.