Manganese redox cycling in immobilized bioreactors for simultaneous removal of nitrate and 17β-estradiol: Performance, mechanisms and community assembly potential

The application of bio-manganese (Mn) redox cycling for continuous removal of contaminants provides promise for addressing coexisting contaminants in groundwater, however, the feasibility of constructing Mn redox cycling system (MCS) through community assembly remains to be elucidated. In this study, Mn-reducing strain MFG10 and Mn-oxidizing strain MFQ7 synergistically removed 94.67 % of 17β-estradiol (E2) within 12 h. Analysis of potential variations in Mn oxides suggested that MCS accelerated the production of reactive oxygen species (ROS) and Mn(III), which interacted to promote E2 removal. After continuous operation of the Mn ore-based immobilized bioreactor for 270 days, the experimental group (EG) achieved average removal efficiencies of 89.63 % and 97.57 % for NO₃^--N and E2, respectively. High-throughput sequencing results revealed complex symbiotic relationships in EG. Community assembly significantly enhanced the metabolic and physiological activity of the bioreactor, which promoting the expression of core functions including nitrogen metabolism, Mn cycling and organic matter resistance.

Deciphering microbial syntrophic mechanisms for simultaneous removal of nitrate and Cr(VI) by Mn@Corn cob immobilized bioreactor: Performance, enhancement mechanisms and community assembly

When bioremediation is applied to Cr(VI) and NO3--N contaminated groundwater, the lack of carbon sources and weak physiological activity dramatically affect the treatment efficacy. Hence, a bioreactor consisting of cellulose degradation-manganese (Mn) cycling bilayer carrier and two core strains was established. After 270 operating days, the experimental group (EG) achieved 96.34 and 95.37% of NO3--N and Cr(VI) removal efficiency, respectively. When the C/N ratio was reduced to 1.0, cellulose-degrading strain CDZ9 produced significantly hydrolyzed cellulose from the corn cob substrate. Meanwhile, the balance between microbial metabolic activity and carbon supply was manipulated by the dissimilatory Mn-reducing strain MFG10. Dissolved organic matter response in EG provided evidence for enhanced carbon utilization and electron transfer processes. The syntrophic relationship between EG core strains significantly enhanced bioreactor metabolism and bioactivity. It drove the coupling of different elemental cycles with contaminant removal including carbon metabolism, nitrogen metabolism, Mn cycle and Cr(VI) reduction.

Anaerobic microbial manganese oxidation and reduction: A critical review

Manganese is a vital heavy metal abundant in terrestrial and aquatic environments. Anaerobic manganese redox reactions mediated by microorganisms have been recognized for a long time, which promote elements mobility and bioavailability in the environment. Biological anaerobic redox of manganese serves two reactions, including Mn(II) oxidation and Mn(IV) reduction. This review provides a comprehensive analysis of manganese redox cycles in the environment, closely related to greenhouse gas mitigation, the fate of nutrients, microbial bioremediation, and global biogeochemical cycle, including nitrogen, sulfur, and carbon. The oxidation and reduction of manganese occur cyclically and simultaneously in the environment. Anaerobic reduction of Mn(IV) receives electrons from methane, ammonium and sulfide, while Mn(II) can function as an electron source for manganese-oxidizing microorganisms for autotrophic denitrification and photosynthesis. The anaerobic redox transition between Mn(II) and Mn(IV) promotes a dynamic biogeochemical cycle coupled to microorganisms in water, soil and sediment environments. The discussion of reaction mechanisms, microorganism diversity, environmental influence bioremediation and application identify the research gaps for future investigation, which provides promising opportunities for further development of biotechnological applications to remediate contaminated environments.

Intensifying anoxic ammonium removal by manganese ores and granular active carbon fillings in constructed wetland-microbial fuel cells: Metagenomics reveals functional genes and microbial mechanisms

The conventional biological ammonium removal process is challenged for lack of electron acceptors. A lab-scale integrated constructed wetland coupled with microbial fuel cells (CW-MFC) filling manganese ores (MO) and granular active charcoal (GAC) has been developed, named CW-CM. It enhanced the nitrogen removal two times over the control. A metagenomic-based study illustrated the functional genes and taxonomic groups related to N transformations, explored metabolic mechanisms of nitrogen and carbon sources, and then revealed some characteristics of the extracellular electron transfer (EET). Many nitrifying bacteria and autotrophic and heterotrophic denitrifiers were enriched in CW-CM. Furthermore, most nitrification and denitrification reactions except for the conversion of ammonium to hydroxylamine were significantly enhanced in CW-CM. Glycolysis and the TCA cycle were also improved. Overall, a novel anoxic ammonia removal process was achieved in the experimental group with no need of anammox functional bacteria and anammox key genes.

Biologically mediated abiotic degradation (BMAD) of bisphenol A by manganese-oxidizing bacteria

Bisphenol A (BPA), a chemical of environmental concern, is recalcitrant under anoxic conditions, but is susceptible to oxidative degradation by manganese(IV)-oxide (MnO₂). Microbial Mn(II)-oxidation generates MnO_2-bio; however, BPA degradation in cultures of Mn(II)-oxidizing bacteria has not been explored. We assessed MnO_2-bio-mediated BPA degradation using three Mn(II)-oxidizing bacteria, Roseobacter sp. AzwK-3b, Erythrobacter sp. SD-21, and Pseudomonas putida GB-1. In cultures of all three strains, enhanced BPA degradation was evident in the presence of Mn(II) compared to replicate incubations without Mn(II), suggesting MnO_2-bio mediated BPA degradation. Increased Mn(II) concentrations up to 100 µM resulted in more MnO_2-bio formation but the highest BPA degradation rates were observed with 10 µM Mn(II). Compared to abiotic BPA degradation with 10 μM synthetic MnO₂, live cultures of strain GB-1 amended with 10 μM Mn(II) consumed 9-fold more BPA at about 5-fold higher rates. Growth of strain AzwK-3b was sensitive to BPA and the organism showed increased tolerance against BPA in the presence of Mn(II), suggesting MnO_2-bio alleviated the inhibition by mediating BPA degradation. The findings demonstrate that Mn(II)-oxidizing bacteria contribute to BPA degradation but organism-specific differences exist, and for biologically-mediated-abiotic-degradation (BMAD), Mn-flux, rather than the absolute amount of MnO_2-bio, is the key determinant for oxidation activity.

Seasonal dynamics of manganese accumulation in European larch (Larix decidua Mill.), silver birch (Betula pendula Roth), and bilberry (Vaccinium myrtillus L.) over 10 years of monitoring

Leaves of European larch, silver birch, and bilberry were sampled 5-7 times per growing season in 2010-2019 in a locality near the city of Litvínov in the Krušné Hory Mts. (Ore Mts.) near the Czech/German border. The locality is characterised by a large amount of plant-available Mn because of acidic soils in the study area. All three investigated plants at the studied site acquired manganese concentrations close to the definition of hyperaccumulation (ca. 10,000 mg kg^-1). This paper presents the most detailed collection of plant material for the characterisation of seasonal dynamics of Mn concentrations in the foliage of the three studied plants under field conditions and compares this information with that in published studies. Time (day in the year or day in the growing season) and cumulative precipitation anomalies were major and minor variables, respectively, explaining Mn dynamics in leaves, while temperature and insolation anomalies were not significant. The three investigated species showed plant-specific Mn acquisition rates in the growing season and specific effects of precipitation. Seasonal dynamics must be considered if plant leaves are used for environmental monitoring.