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

Simultaneous Cd immobilization and oxidative stress alleviation in Brassica chinensis by a novel phosphate-solubilizing strain Sutcliffiella horikoshii P1

Microbial remediation of cadmium (Cd) pollution offers economically green and operationally simple advantages, particularly in environments with mild contamination. The acquisition of efficient strains and coupling between bacterial response and plant fitness are current research emphases in the remediation process. In this study, a novel phosphate-solubilizing strain with outstanding Cd-resistance, Sutcliffiella (S.) horikoshii P1 was isolated. Cd removal efficiency reached 98.85 % by the strain within 24 h at an initial concentration of 5 mg/L. Distribution analysis revealed that the dominant mechanism of Cd removal by the strain varies with Cd concentrations. Notably, the seed soaking of Brassica chinensis with S. horikoshii P1 could improve seed germination rate and growth potential regardless of the presence of Cd stress. Morphological and biochemical trait analysis revealed that the inoculated strain also increased fresh weight and reduced the Cd phytoavailability of Brassica chinensis by producing active substances and alleviating plant oxidative stress. Pot experiment demonstrated that the transport factor (TF) and bioconcentration factor (BCF) decreased by 22.76 % and 33.59 %, respectively, and Cd content in edible parts met food safety standards. Whole-genome sequencing analysis demonstrated that functional genes related to heavy metal resistance and transport (cadC, czcD, znuA, etc.), and gene clusters involved in siderophore secretion may regulate Cd immobilization and the plant growth-promoting effect of S. horikoshii P1. The results underscored the feasibility and effectiveness of Sutcliffiella horikoshii in addressing Cd contamination and promoting plant growth, providing a basis for the future application in agricultural safe production.

Photolysis of disposable face masks facilitates abiotic manganese oxide formation

During the COVID-19 pandemic, billions of face masks were discarded into aquatic environments, releasing micro/nanoplastics. This release threatens aquatic ecosystems, influences pollutant transport, and generates reactive oxygen species (ROS). These ROS can affect redox-active metal ions, such as manganese (Mn), in water. Mn oxide solids are commonly found in nature and serve as both electron donors and acceptors in various biogeochemical reactions of trace elements, metal ions, and organics in the environment. However, it remains unclear how disposable face masks, primarily made of polypropylene (PP), impact Mn oxidation and Mn oxides formation in natural surface waters under sunlight. This study, for the first time, reports the photolysis of PP mask layers and their impacts on the kinetics of Mn2+ (aq) oxidation to Mn oxide nanoparticles. We found that mask layers enhanced Mn2+(aq) photo-oxidation kinetics as their surface material packing density increased. Furthermore, the local concentrations of oxidized Mn2+ near the mask surfaces were two orders of magnitude greater than the bulk solution, facilitating heterogeneous Mn oxide formation near mask surfaces. Photoaging of masks further expedited Mn2+ oxidation. Superoxide radicals (O2•-) generated by mask photolysis were the main responsible ROS for boosting Mn oxidation. These findings highlight the influences of mask photolysis on Mn redox chemistry. Mn oxides formed on mask materials can alter the fate and transport of pollutants such as heavy metals and organic compounds, impacting surface water quality.

Biochemical transformation and bioremediation of thallium in the environment

Thallium (Tl) is a toxic element associated with minerals, and its redistribution is facilitated by both geological and anthropogenic activities. In the natural environment, the transformation and migration of Tl mediated by (micro)organisms have attracted increasing attention. This review presents an overview of the biochemical transformation of Tl and the bioremediation strategies for Tl contamination. In the environment, Tl exists in various forms and originates from diverse sources. The global distribution characteristics of Tl in various media are summarized here, while its speciation and toxicity mechanism to organisms are elucidated. Interactions between (micro)organisms and Tl are commonly observed in the environment. Microbial response mechanisms to typical Tl exposure are analyzed at both species and gene levels, and the possibility of microorganisms as bio-indicators for monitoring Tl contamination is also highlighted. The processes and mechanisms involved in the microbial and benthic mediated transformation of Tl, as well as its enrichment by plants, are discussed. Additionally, in situ bioremediation strategies for Tl contamination and bio-treatment techniques for Tl-containing wastewater are summarized. Finally, the existing knowledge gaps and future research challenges are emphasized, including Tl distribution characteristics in the atmosphere and ocean, the key molecular mechanisms underlying Tl transformation by organisms, the screening of potential Tl oxidizing microorganisms and hyperaccumulators, as well as the revelation of global biogeochemical cycling pathways of Tl.

Denitrification performance of the nitrate-dependent manganese redox strain Dechloromonas sp. YZ8 under copper ion (Cu(Ⅱ)) stress: Promotion mechanism and immobilization efficacy

A novel nitrate-dependent manganese (Mn) redox strain was isolated and identified as Dechloromonas sp.YZ8 in this study. The growth conditions of strain YZ8 were optimized by kinetic experiments. The nitrate (NO3--N) removal efficiency was 100.0 % at 16 h at C/N of 2.0, pH of 7.0, and Mn(II) or Mn(IV) addition of 10.0 or 500.0 mg L-1, along with an excellent Mn redox capacity. Transmission electron microscopy supported the Mn redox process inside and outside the cells of strain YZ8. When strain YZ8 was exposed to different concentrations of copper ion (Cu(II)), it turned out that moderate amounts of Cu(II) increased microbial activity and metabolic activities. Moreover, it was discovered that the appropriate amount of Cu(II) promoted the conversion of Mn(IV) and Mn(II) to Mn(III) and improved electron transfer capacity in the Mn redox system, especially the Mn redox process dominated by Mn(IV) reduction. Then, δ-MnO2 and bio-manganese oxides (BMO) produced during the reaction process have strong adsorption of Cu(II). The surface valence changes of δ-MnO2 before and after the reaction and the production of BMO, Mn(III)-rich intermediate black manganese ore (Mn3O4), and Mn secondary minerals together confirmed the Mn redox pathway. The study provided new insights into the promotion mechanism and immobilization effects of redox-coupled denitrification of Mn in groundwater under Cu(II) stress.

Improved permeability in ceramsite@powdered activated carbon (PAC)-MnOx coupled gravity-driven ceramic membrane (GDCM) for manganese and ammonia nitrogen removal with intermittent short-term vertical aeration

In our work, a gravity-driven ceramic membrane bioreactor (GDCMBR) was developed to remove Mn2+ and NH3-N simultaneously through the birnessite water purification layer in-situ construction on the ceramic membrane due to chemical pre-oxidation (powdered activated carbon (PAC)-MnOx). Considering the trade-off of biofouling and water production, the daily intermittent short-term vertical aeration mode was involving to balance this contradiction with the excellent water purification and improved membrane permeability. And the GDCMBR permeability of operation flux was improved for 5-7 LHM with intermittent short-term vertical aeration. Furthermore, only ∼7 % irreversible membrane resistance (Rir) also confirmed the improved membrane permeability with intermittent short-term vertical aeration. And some manganese oxidizing bacteria (MnOB) and ammonia oxidizing bacteria (AOB) species at genus level were identified during long-term operation with the contact circulating flowing raw water, resulting in the better Mn2+ and NH3-N removal efficiency. Additionally, the nano-flower-like birnessite water purification layer was verified in ceramsite@PAC-MnOx coupled GDCMBR, which evolute into a porous flake-like structure with the increasing intermittent short-term aeration duration. Therefore, the sustainable and effective intermittent short-term aeration mode in ceramsite@PAC-MnOx coupled GDCMBR could improve the membrane permeability with the satisfactory groundwater purification efficiency, as well as providing an energy-efficient strategy for membrane technologies applications in water supply safety.

Assembly of core-shell Fe3O4 @CD-MOFs derived hollow magnetic microcubes for efficient extraction of hazardous substances: Plausible mechanisms for selective adsorption

Hazardous heavy metals and organic substances removal is of great significance for ensuring the safety of aquatic-ecosystem, yet the highly effective and selective extraction always remains challenging. To address this problem, magnetic hollow microcubes were fabricated through thermal carbonization of Fe3O4-COOH@ γ-CD-MOFs, and core-shell structured precursors were in-situ greenly constructed on a large scale via microwave-assisted self-assembly strategy. As noted, the development of secondary crystallization was utilized to achieve uniform dispersion of cores within MOFs frameworks and thus improved magnetic and adsorption ability of composites. Acquired magnetic Fe3O4 @HC not only can harvest excellent extraction of heavy metals (Cd, Pb, and Cu of 129.87, 151.05, and 106.98 mg·g-1) but also exhibit highly selective adsorption ability for cationic organics (separation efficiency higher than 95.0 %). Impressively, Fe3O4 @HC achieved outstanding adsorption (60-80 %) of Cd in realistic mussel cooking broth with no obvious loss in amino acid. Characterizations better offer mechanistic insight into the enhanced selectivity of positively charged pollutants can be attributed to synergistic effect of ions exchange and electrostatic interaction of abundant oxygen-containing functional groups. Our study provides a feasible route by rationally developing core-shell structured composites to promote the practical applications of sustainable water treatment and value-added utilization of processing by-products.

Role of phosphate in microalgal-bacterial symbiosis system treating wastewater containing heavy metals

Phosphorus is one of the important factors to successfully establish the microalgal-bacterial symbiosis (MABS) system. The migration and transformation of phosphorus can occur in various ways, and the effects of phosphate on the MABS system facing environmental impacts like heavy metal stress are often ignored. This study investigated the roles of phosphate on the response of the MABS system to zinc ion (Zn2+). The results showed that the pollutant removal effect in the MABS system was significantly reduced, and microbial growth and activity were inhibited with the presence of Zn2+. When phosphate and Zn2+ coexisted, the inhibition effects of pollutants removal and microbial growth rate were mitigated compared to that of only with the presence of Zn2+, with the increasing rates of 28.3% for total nitrogen removal, 48.9% for chemical oxygen demand removal, 78.3% for chlorophyll-a concentration, and 13.3% for volatile suspended solids concentration. When phosphate was subsequently supplemented in the MABS system after adding Zn2+, both pollutants removal efficiency and microbial growth and activity were not recovered. Thus, the inhibition effect of Zn2+ on the MABS system was irreversible. Further analysis showed that Zn2+ preferentially combined with phosphate could form chemical precipitate, which reduced the fixation of MABS system for Zn2+ through extracellular adsorption and intracellular uptake. Under Zn2+ stress, the succession of microbial communities occurred, and Parachlorella was more tolerant to Zn2+. This study revealed the comprehensive response mechanism of the co-effects of phosphate and Zn2+ on the MABS system, and provided some insights for the MABS system treating wastewater containing heavy metals, as well as migration and transformation of heavy metals in aquatic ecosystems.

Promoting nitrogen conversion in aerobic biotransformation of swine slurry with the co-application of manganese sulfate and biochar

This study aimed to explore the co-application of MnSO4 (Mn) and biochar (BC) in nitrogen conversion during the composting process. A 70-day aerobic composting was conducted using swine slurry, supplemented with different levels of Mn (0, 0.25%, and 0.5%) and 5% BC. The results demonstrated that the treatment with 0.5MnBC had the highest levels of NH4+-N (3.07 g kg-1), TKN (29.90 g kg-1), and NO3--N (1.94 g kg-1) among all treatments. Additionally, the 0.5MnBC treatment demonstrated higher urease, protease, nitrate reductase, and nitrite reductase activities than the other treatments, with the peak values of 18.12, 6.96, 3.57, and 15.14 mg g-1 d-1, respectively. The addition of Mn2+ increased the total organic nitrogen content by 29.59%-47.82%, the acid hydrolyzed ammonia nitrogen (AN) content by 13.84%-57.86% and the amino acid nitrogen (AAN) content by 55.38%-77.83%. The richness of Chloroflexi and Ascomycota was also enhanced by the simultaneous application of BC and Mn. Structural equation modeling analysis showed that Mn2+ can promote the conversion of Hydrolyzed Unknown Nitrogen (HUN) into AAN, and there is a positive association between urease and NH4+-N according to redundancy analysis. Firmicutes, Basidiomycota, and Mortierellomycota showed significant positive correlations with ASN, AN, and NH4+-N, indicating their crucial roles in nitrogen conversion. This study sheds light on promoting nitrogen conversion in swine slurry composting through the co-application of biochar and manganese sulfate.

Removal of thallium by MnOx coated limestone sand filter through regeneration of KMnO4: Combination of physiochemical and biochemical actions

Treatment of industrial thallium(Tl)-containing wastewater is crucial for mitigating environmental risks and health threats associated with this toxic metal. The incorporation of Mn oxides (MnOx) into the filtration system is a promising solution for efficient Tl(I) removal. However, further research is needed to elucidate the underlying mechanism behind MnOx-enhanced filtration and the rules of its stable operation. In this study, limestone, a cost-effective material, was selected as the filter media. Raw water with Mn(II), Tl(I), and other pollutants was prepared after a thorough investigation of actual industrial wastewater conditions. KMnO4 was added to induce the formation of MnO2 on limestone surfaces, while long-term operation led to enrichment of manganese oxidizing microorganisms (MnOM). Results revealed a dual mechanism. Firstly, most Mn(II) were oxidized by KMnO4 to form MnO2 attaching to limestone sands, and both Tl(I) and residual Mn(II) were adsorbed onto the newly formed MnO2. Subsequently, enzymes secreted by MnOM facilitated oxidation of remaining Mn(II), resulting in the generation of biogenic manganese oxides (BioMnOx) with numerous vacancies during long-term operation. The generated BioMnOx not only adsorbed Mn(II) and Tl(I) but also promoted their oxidation process. This approach offers an effective and sustainable method for removing both Mn(II) and Tl(I) from industrial wastewater, thereby addressing the challenges posed by thallium-contaminated effluents.

Treatment of wastewater containing thallium(I) by long-term operated manganese sand filter: Synergistic action of MnOx and MnOM

The long-term and stable removal of thallium (Tl) from industrial wastewater generated by mining and smelting operations remains challenging. While sand filters are commonly applied for the simultaneous removal of Mn(II) and other heavy metals, they have limited efficacy in treating Tl-contaminated wastewater. To address this gap, we operated a lab-scale Mn sand filter (MF) without added microorganisms to investigate the efficiency and mechanisms of Mn(II) and Tl(I) removal. Trends in effluent Mn(II) and Tl(I) concentrations indicated three operational stages: start-up, developing and maturation. Over time, the removal efficiency of Tl(I) gradually improved, plateauing at approximately 80 % eventually. Throughout operation, Tl(I) was sequestrated via surface complexation and ion exchange. Besides, enrichment of Sphingobium and other typical manganese oxidizing microorganisms (MnOM) during operation facilitated Mn(II) and Tl(I) oxidation and sequestration by generating biogenic manganese oxides (BioMnOx). Additionally, the accurate control of water quality and operating conditions during operation could also enhance removal efficiency. In summary, physicochemical actions of Mn oxides and biochemical actions of microorganisms synergistically contributed to the sequestration of Mn(II) and Tl(I). These findings provided a novel and sustainable method for the long-term and stable treatment of industrial wastewater containing thallium.

Solutions for an efficient arsenite oxidation and removal from groundwater containing ferrous iron

Manganese (Mn) oxides are extensively used to oxidize As(III) present in ground, drinking, and waste waters to the less toxic and more easily removable As(V). The common presence of multiple other cations in natural waters, and more especially of redox-sensitive ones such as Fe2+, may however significantly hamper As(III) oxidation and its subsequent removal. The present work investigates experimentally the influence of Mn(III) chelating agents on As(III) oxidation process in such environmentally relevant complex systems. Specifically, the influence of sodium pyrophosphate (PP), an efficient Mn(III) chelating agent, on As(III) oxidation by birnessite in the presence of Fe(II) was investigated using batch experiments at circum-neutral pH. In the absence of PP, competitive oxidation of Fe(II) and As(III) leads to Mn oxide surface passivation by Fe(III) and Mn(II/III) (oxyhydr)oxides, thus inhibiting As(III) oxidation. Addition of PP to the system highly enhances As(III) oxidation by birnessite even in the presence of Fe(II). PP presence prevents passivation of Mn oxide surfaces keeping As and Fe species in solution while lower valence Mn species are released to solution. In addition, reactive oxygen species (ROS), tentatively identified as hydroxyl radicals (•OH), are generated under aerobic conditions through oxygen activation by Fe(II)-PP complexes, enhancing As(III) oxidation further. The positive influence of Mn(III) chelating agents on As(III) oxidation most likely not only depend on their affinity for Mn(III) but also on their ability to promote formation of these active radical species. Finally, removal of As(V) through sorption to Fe (oxyhydr)oxides is efficient even in the presence of significant concentrations of PP, and addition of such Mn(III) chelating agents thus appears as an efficient way to enhance the oxidizing activity of birnessite in large-scale treatment for arsenic detoxification of groundwaters.

Removal of oxytetracycline from wastewater by biochar modified with biosynthesized iron oxide nanoparticles and carbon nanotubes: Modification performance and adsorption mechanism

The pollution problem of oxytetracycline (OTC) from wastewater becomes more serious, so an efficient, economical, and green adsorption material is urgently explored. In this study, the multilayer porous biochar (OBC) was prepared by coupling carbon nanotubes with iron oxide nanoparticles synthesized by Aquabacterium sp. XL4 to modify corncobs under medium temperature (600 °C) conditions. The adsorption capacity of OBC could reach 72.59 mg g-1 after preparation and operation parameters were optimized. In addition, various adsorption models suggested that OTC removal resulted from the combined effect of chemisorption, multilayer interaction, and disordered diffusion. Meanwhile, the OBC was fully characterized and exhibited a large specific surface area (237.51 m2 g-1), abundant functional groups, stable crystal structure, high graphitization, and mild magnetic properties (0.8 emu g-1). The OTC removal mechanisms mainly included electrostatic interactions, ligand exchange, π-π bonding reactions, hydrogen bonds, and complexation. pH and coexistence substance experiments revealed that the OBC possesses a wide pH adaptation range and excellent anti-interference ability. Finally, the safety and reusability of OBC were confirmed by repeated experiments. In summary, OBC as a biosynthetic material shows considerable potential for application in the field of purifying new pollution from wastewater.

Effects of Algal Extracellular Polysaccharides on the Formation of Filamentous Manganese Oxide Particles in the Near-Bottom Layer of Lake Biwa

Filamentous manganese (Mn) oxide particles, which occur in the suboxic zone of stratified waterbodies, are important drivers of diverse elemental cycles. These particles are considered to be bacteriogenic; despite the importance of biogeochemical implications, however, the environmental factor responsible for their formation has not been identified. The aim of this study was to demonstrate the involvement of algal extracellular polysaccharides in Mn oxide particle formation. Based on this study of laboratory cultures of a model Mn(II)-oxidizing bacterium, the supply of algal extracellular mucilage was shown to stimulate Mn(II) oxidation and thus the production of filamentous Mn oxide particles. This observation was consistent with the results obtained for naturally occurring particles collected from a near-bottom layer (depth of approximately 90 m) in the northern basin of Lake Biwa, Japan, that is, most Mn particles resembling δ-MnO₂ were associated with an extracellular mucilage-like gelatinous matrix, which contained dead algal cells and was lectin-stainable. In the lake water column, polysaccharides produced by algal photosynthesis sank to the bottom layer. The analysis of the quality of water samples, which have been collected from the study site for 18 years, reveals that the annual average total phytoplankton biovolume in the surface layer correlates with the density of filamentous Mn particles in the near-bottom layer. Among different phytoplankton species, green algae appeared to be the key species. The results of this study suggest that algal extracellular polysaccharides serve as an important inducer for the formation of filamentous Mn oxide particles in the near-bottom layer of the northern basin of Lake Biwa.

Biotransformation of sulfamethoxazole by newly isolated surfactant-producing strain Proteus mirabilis sp. ZXY4: Removal efficiency, pathways, and mechanisms

In this study, the SMX degrading strain Proteus mirabilis sp. ZXY4 with surfactant manufacturing potential was isolated from sludge utilizing blood agar and CTAB agar plate. FTIR analysis indicated that the biosurfactant generated by strain ZXY4 was glycolipid. 3D-EEM demonstrated that SMX biodegradation was strongly connected to biosurfactants, the synergistic effect of biodegradation and biosurfactant made strain ZXY4 have excellent SMX degradation performance. Under the optimal conditions of inoculation dosage of 15%, temperature of 30 ℃, pH of 7 and initial SMX concentration of 5 mg L^-1, strain ZXY4 could completely degrade SMX within 24 h. SMX biodegrades at low concentrations (less than5 mg L^-1) followed by the zero-order kinetic model, high concentration (>5 mg L^-1) is more consistent with the first-order kinetic model. LC-MS analysis revealed 14 SMX degradation intermediates, and five potential biodegradation mechanisms were postulated. The findings provide new insights into the biodegradation of SMX.