Coupled Mn(II) and Cr(III) Oxidation Mediated by Ascomycete Fungi

Synergistic binding mechanisms of co-contaminants in soil profiles: Influence of iron-bearing minerals and microbial communities

In contaminated soil sites, the coexistence of inorganic and organic contaminants poses a significant threat to both the surrounding ecosystem and public health. However, the migration characteristics of these co-contaminants within the soil and their interactions with key components, including Fe-bearing minerals, organic matter, and microorganisms, remain unclear. This study involved the collection of a 4.3-m-depth co-contaminated soil profile to investigate the vertical distribution patterns of co-contaminants (namely, arsenic, cadmium, and polychlorinated biphenyls (PCBs)) and their binding mechanisms with environmental factors. The results indicated a notable downward accumulation of inorganic contaminants with increasing soil depth, whereas PCBs were predominantly concentrated in the uppermost layer. Chemical extraction and synchrotron radiation analysis highlighted a positive correlation between the abundance of reactive iron (FeCBD) and both co-contaminants and microbial communities in the contaminated site. Furthermore, Mantel tests and structural equation modeling (SEM) demonstrated the direct impacts of FeCBD and microbial communities on co-contaminants within the soil profile. Overall, these results provided valuable insights into the migration and transformation characteristics of co-contaminants and their binding mechanisms mediated by minerals, organic matter, and microorganisms.

Biological Oxidation of Manganese Mediated by the Fungus Neoroussoella solani MnF107

Manganese oxides are highly reactive minerals and influence the geochemical cycling of carbon, nutrients, and numerous metals in natural environments. Natural Mn oxides are believed to be dominantly formed by biotic processes. A marine Mn-oxidizing fungus Neoroussoella solani MnF107 was isolated and characterized in this study. SEM observations show that the Mn oxides are formed on the fungal hyphal surfaces and parts of the hypha are enveloped by Mn oxides. TEM observations show that the Mn oxides have a filamentous morphology and are formed in a matrix of EPS enveloping the fungal cell wall. Mineral phase analysis of the fungal Mn oxides by XRD indicates that it is poorly crystalline. Chemical oxidation state analysis of the fungal Mn oxides confirms that it is predominantly composed of Mn(IV), indicating that Mn(II) has been oxidized to Mn (IV) by the fungus.

Sequestration and oxidation of heavy metals mediated by Mn(II) oxidizing microorganisms in the aquatic environment

Microorganisms can oxidize Mn(II) to biogenic Mn oxides (BioMnOx), through enzyme-mediated processes and non-enzyme-mediated processes, which are generally considered as the source and sink of heavy metals due to highly reactive to sequestrate and oxidize heavy metals. Hence, the summary of interactions between Mn(II) oxidizing microorganisms (MnOM) and heavy metals is benefit for further work on microbial-mediated self-purification of water bodies. This review comprehensively summarizes the interactions between MnOM and heavy metals. The processes of BioMnOx production by MnOM has been firstly discussed. Moreover, the interactions between BioMnOx and various heavy metals are critically discussed. On the one hand, modes for heavy metals adsorbed on BioMnOx are summarized, such as electrostatic attraction, oxidative precipitation, ion exchange, surface complexation, and autocatalytic oxidation. On the other hand, adsorption and oxidation of representative heavy metals based on BioMnOx/Mn(II) are also discussed. Thirdly, the interactions between MnOM and heavy metals are also focused on. Finally, several perspectives which will contribute to future research are proposed. This review provides insight into the sequestration and oxidation of heavy metals mediated by Mn(II) oxidizing microorganisms. It might be helpful to understand the geochemical fate of heavy metals in the aquatic environment and the process of microbial-mediated water self-purification.

Dual diffusive gradients in the thin films (DGT) probes provide insights into speciation and mobility of sediment chromium (Cr) from the Xizhi River basin, South China

Investigation of the speciation and remobilization mechanisms of chromium (Cr) in sediment is essential for accurate estimation of its ecological risks in aquatic systems. In this work, a three-step chemical extraction procedure and diffusive gradient in thin films (DGT) technique were combined to investigate the geochemical speciation, mobility potentials, and release characteristics of sediment Cr. The geochemical speciation of sediment Cr decreased in the following order: oxidizable > reducible > residual > acid-soluble fraction. Dissociation of OM-bound Cr(III) and oxidation by Mn oxides contributed to higher labile Cr(III) and Cr(VI) levels in winter, with the labile Cr(III) being the dominant species and accounting for 48.1%65.5% of the total concentration of labile Cr; whereas, reductive dissolution of Mn oxides was responsible for the remobilization of labile Cr(VI) in summer, leading to a shift in dominant Cr species to Cr(VI) (48.9%65.7%) due to rapid precipitation of Cr(III). Sediment acted as a major sink for labile Cr(VI) in two sampling campaigns. For labile Cr(III), sediment converted from source in winter to sink in summer. The diffusive release of labile Cr(III) deserves preferential concern due to its potential to be re-oxidized to more toxic Cr(VI) under the oxic conditions of river water in winter.