Bio-immobilization of soluble Mn(II) in aqueous solution with co-occurred Mn(II)-oxidizing bacteria: Facilitation or inhibition?

Abstract

Mn(II)-oxidizing bacteria (MOB) can immobilize soluble Mn(II) to form biogenic Mn oxides (BioMnOx) which could be recovered as useful resources. In the present study, dual-species co-cultured systems of three MOB strains, Enterobacter sp. DS02Eh01 (D1), Bacillus sp. WSE02 (W2) and Staphylococcus sp. WLS01 (W1), were developed to explore the effects of co-occurrence on Mn(II) immobilization/oxidation. The results indicated that co-occurred bacteria were able to immobilize Mn(II), although there were interactions between them. Both initial volumetric inoculum ratios (IVIRs) and initial Mn(II) levels (IMLs) affected the Mn(II) immobilization/oxidation process. Under the same IVIR, the unique Mn tolerance of strain D1 was not inhibited, leading to its superior abundance in the co-cultured system. While strain W1 and W2, which had powerful Mn(II) immobilization ability in mono-culture, showed different responses to the presence of D1: strain W2 was still able to complete Mn(II) immobilization, while the Mn(II) immobilization ability of W1 was found to be down-regulated. The Mn(II) immobilization/oxidation capabilities of strain W1 and W2 were maintained or even surpassed the mono-cultures while they were co-occurred. The physicochemical properties of Mn(II) immobilization products (MIPs) were also varied in the co-cultured systems but the enzyme-based formation mechanisms of Mn(II) oxidation were not apparently affected by the co-occurrence. The results of this study help better understand the nature of the Mn biogeochemical cycle induced by co-occurred MOB species and guide the engineering application in the treatment/recovery of Mn(II)-laden wastewater.