Competitive Mn(II) removal occurs in Lysinibacillus sp. MHQ-1 through microbially-induced carbonate precipitation (MICP) and indirect Mn(II) oxidation

Biological Mn(II) removal usually involves adsorption and precipitation of Mn(II) in the form of various minerals. Manganese oxides (MnOx) formation through the activity of Mn(II) oxidation bacteria (MnOB) contributes to the majority of Mn(II) removal. However, whether other bacterial-mediated pathway could couple or competitive with Mn(II) oxidation during Mn(II) removal is scarcely reported. In this study, we reported a competitive Mn(II) removal occurred in nutrient-rich condition during the indirect Mn(II) oxidation of Lysinibacillus sp. MHQ-1, i.e., microbially-induced carbonate precipitation (MICP). In the presence of 1 mM Mn(II), 39.4% of free Mn(II) converted to MnCO3(s) quickly within 100 h, and then 11.6% of initial Mn(II) slowly oxidized to MnOx within 442 h. The urease activity assay and the genome sequencing confirmed the existence of urease and the absence of Mn(II)-oxidizing enzymes in the genome of strain MHQ-1. The urease catalyzed the formation of carbonate ion that reacts with Mn(II) and the formed ammonia raises the pH to initiate indirect Mn(II) oxidation. Genome survey suggests the urease widely exists in various Mn(II)-oxidizing bacteria (MnOB), emphasizing the importance to reconsider the composition, stability and environmental effects of biological Mn(II) removal products in nutrient-rich environment.