Environmental Bacteria Involved in Manganese(II) Oxidation and Removal From Groundwater

Hydroxyl-aluminum pillared bentonite enhanced Mn(II) removal by chlorine oxidation

Al-PILC was used to catalyze the chlorine oxidation of Mn(II) in aqueous solution. The effects of various catalysts, catalyst dosage, chlorine dosage, pH value, temperature and organic content on the oxidation process were investigated. Results show that 1.5 mg/L chlorine can quickly oxidize Mn(II) from 0.5 mg/L to less than 0.04 mg/L with 10 mg/L Al-PILC. Using catalysts with higher porosity and higher SA, increase in chlorine concentration, increase in catalyst dosage, higher pH, and higher temperature can significantly enhance the rate of Mn(II) catalytic oxidation. The Mn(II) oxidation process includes the homogeneous oxidation, catalytic oxidation on the surface of the catalysts and self-catalytic oxidation produced by the newly produced MnOx. Al-PILC surface provides active sites for chlorine oxidation Mn(II) in the water, and also provides binding sites for the newly produced MnOx, which has higher catalytic activity and thus has an self-catalytic oxidation effect. The higher the porosity and SA of Al-PILC, the more catalytic oxidation active sites and loading sites, and the better the catalytic oxidation effect. The study promotes the understanding of chlorine catalyzed oxidation Mn(II) in aqueous solution, but also provide important guide to study newly efficient catalysts to oxidize Mn(II) with chlorine in aqueous solution.

Formation of Biogenic Manganese Oxide Nodules on Hyphae of a New Fungal Isolate of Periconia That Immobilizes Aqueous Copper

Mn(II)-oxidizing microorganisms are considered to play significant roles in the natural geochemical cycles of Mn and other heavy metals because the insoluble biogenic Mn oxides (BMOs) that are produced by these microorganisms adsorb other dissolved heavy metals and immobilize them as precipitates. In the present study, a new Mn(II)-oxidizing fungal strain belonging to the ascomycete genus Periconia, a well-studied plant-associating fungal genus with Mn(II)-oxidizing activity that has not yet been exami-ned in detail, was isolated from natural groundwater outflow sediment. This isolate, named strain TS-2, was confirmed to oxidize dissolved Mn(II) and produce insoluble BMOs that formed characteristic, separately-located nodules on their hyphae while leaving major areas of the hyphae free from encrustation. These BMO nodules also adsorbed and immobilized dissolved Cu(II), a model analyte of heavy metals, as evidenced by elemental mapping ana-lyses of fungal hyphae-BMO assemblages using a scanning electron microscope with energy-dispersive X-ray spectroscopy (SEM-EDX). Analyses of functional genes within the whole genome of strain TS-2 further revealed the presence of multiple genes predicted to encode laccases/multicopper oxidases that were potentially responsible for Mn(II) oxidation by this strain. The formation of BMO nodules may have functioned to prevent the complete encrustation of fungal hyphae, thereby enabling the control of heavy metal concentrations in their local microenvironments while maintaining hyphal functionality. The present results will expand our knowledge of the physiological and morphological traits of Mn(II)-oxidizing Periconia, which may affect the natural cycle of heavy metals through their immobilization.

Startup performance and microbial composition of a pilot-scale rapid sand filter for the treatment of manganese-containing mine water

The inexpensive removal of soluble manganese [Mn(II)] from mine water that contains large quantities of Mn(II) should be prioritized given that large quantities of alkaline reagents are typically used in the chemical treatment of Mn-rich water from abandoned mines. Rapid sand filter (RSF) systems are widely used as a cost-effective technology in drinking water treatment processes to remove iron and Mn from groundwater. Here, we applied a pilot-scale RSF to treat mine water with a neutral pH and containing approximately 22 mg/L of Mn(II). Following a lag phase from its startup (day 1-day 26), Mn removal rates increased to approximately 40% for around 1 month (day 27-day 55) without the use of alkaline reagents but did not increase during further operation. Quantitative elemental analysis revealed Mn oxides on the sand filters during the Mn removal period. The bacterial communities on the RSFs, recorded on day 42 and day 85, were characterized and compared using 16S rRNA gene amplicon sequencing. Although the well-known Mn-oxidizing bacteria (MOB) were not listed among the ten most dominant operational taxonomic units (OTUs) on the sand filters (relative abundances: >0.68%), a significant increase in the OTUs related to well-known alphaproteobacterial MOB, such as Pedomicrobium spp., were observed during the period.

Betaproteobacteria are a key component of surface water biofilters that maintain sustained manganese removal in response to fluctuations in influent water temperature

The health risks associated with manganese (Mn) in drinking water, and an improved understanding of Mn accumulation within, and subsequent release from, distribution systems, have increased the need for robust, sustainable treatment options to minimize Mn concentrations in finished water. Biofiltration is an established and effective method to remove Mn in groundwater however, Mn removal in surface water biofilters is an emerging treatment process that has not been extensively studied. Seasonal variations in water temperature can present an operational challenge for surface water biofilters which may see reduced Mn removal under colder conditions. This study examined the microbiomes of surface water biofilters at three utilities (ACWD WTP, WTP B, and WTP D) which all experienced similar seasonal fluctuations in influent water temperature. High Mn removal was observed at the ACWD WTP for much of the year, but Mn removal decreased with a concurrent decrease in the influent water temperature (58% ± 22%). In contrast, both WTP B and WTP D achieved year-round Mn removal (84% ± 5% and 93% ± 8% respectively). Marker gene (16S rRNA) sequencing analysis of the biofilter microbiomes identified a high abundance of Betaproteobacteria in WTP B and WTP D (37% ± 12% and 21% ± 3% respectively), but a low abundance of Betaproteobacteria in the ACWD WTP (2% ± 2%). The microbiomes of new bench-scale biofilters, in operation at the ACWD WTP, were also investigated. The abundance of Betaproteobacteria was significantly greater (p < 0.05) after the biofilters had acclimated than before acclimation, and differential abundance analysis identified 6 genera within the Betaproteobacteria class were enriched in the acclimated microbiome. Additionally, the acclimated biofilters were able to maintain high Mn removal performance (87% ± 10%) when the influent water temperature decreased to 10 °C or less. Further analysis of previously published studies found the abundance of Betaproteobacteria was also significantly greater (p < 0.001) in biofilters with sustained Mn removal than in biofilters which did not treat for Mn as a contaminant, despite differences in design scale, source water, and media type. Microbiome network analysis identified multiple co-occurrence relationships between Betaproteobacteria and Mn oxidizing bacteria in the WTP B and WTP D biofilters, suggesting indirect contributions by Betaproteobacteria to biological Mn oxidation. These co-occurrence relationships were not present in the full-scale ACWD WTP microbiome. Whether the role of Betaproteobacteria in biological Mn oxidation is direct, indirect, or a combination of both, they are consistently present at a high abundance in both groundwater and surface water biofilters with sustained Mn removal, and their absence may contribute to the seasonal fluctuations in Mn removal observed at the ACWD WTP. This new insight to Betaproteobacteria and their role in Mn biofiltration could contribute to water innovation and design that would improve the reliability of Mn removal.

Impact of nutrients and trace elements on freshwater microbial communities in Croatia: identifying bacterial bioindicator taxa

Since aquatic microbial communities promptly respond to environmental changes, it is now evident that they can complement traditional taxa such as fish, macroinvertebrates and algae as bioindicators of water quality. The aim of this study was to correlate the physico-chemical parameters of water with the microbial community structure and the occurrence of putative bioindicator taxa. Thirty-five water samples were collected throughout Croatia and their physico-chemical parameters, including the concentration of trace elements using the high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS), and the composition of the microbial communities by high-throughput sequencing of the 16S rRNA marker gene, were analysed in parallel. Partial least squares regression (PLS-R) modelling revealed that a number of microbial taxa were positively correlated with some of the water parameters. For example, some taxa from the phylum Proteobacteria were positively correlated with the ion content of the water (e.g. Erythrobacter, Rhodobacteraceae, Alteromonadaceae), while some Firmicutes taxa, such as the well-known faecal indicators Enterococcus and Clostridium, were correlated with nutrient content (ammonium and total phosphorus). Among the trace elements, uranium was positively correlated with a highest number of microbial taxa. The results obtained will aid in development of protocols for eDNA-based biological assessment of water quality.

Involvement of Bacterial and Fungal Extracellular Products in Transformation of Manganese-Bearing Minerals and Its Environmental Impact

Manganese oxides are considered an essential component of natural geochemical barriers due to their redox and sorptive reactivity towards essential and potentially toxic trace elements. Despite the perception that they are in a relatively stable phase, microorganisms can actively alter the prevailing conditions in their microenvironment and initiate the dissolution of minerals, a process that is governed by various direct (enzymatic) or indirect mechanisms. Microorganisms are also capable of precipitating the bioavailable manganese ions via redox transformations into biogenic minerals, including manganese oxides (e.g., low-crystalline birnessite) or oxalates. Microbially mediated transformation influences the (bio)geochemistry of manganese and also the environmental chemistry of elements intimately associated with its oxides. Therefore, the biodeterioration of manganese-bearing phases and the subsequent biologically induced precipitation of new biogenic minerals may inevitably and severely impact the environment. This review highlights and discusses the role of microbially induced or catalyzed processes that affect the transformation of manganese oxides in the environment as relevant to the function of geochemical barriers.

Banana peel extract alleviate inflammation and oxidative stress via modulation of the Nrf2/Hmox-1 and NF-κB pathways in thyroid of heavy metal mixture exposed female rats

Introduction

This is an evaluation of the effects of banana peel BP extract on the heavy metals’ mixture HMM mediated oxido-inflammatory effects in the thyroid of female albino rats.

Methods

Five groups (5 female rats/group) were treated as follows for 60 days: Group 1: Deionized water only; Group 2: (Pb, Hg, Mn and Al); Group 3: 200 mg/kg BP extract + HMM; Group 4: 400 mg/kg BP extract + HMM; Group 5: 800 mg/kg BP extract + HMM. On day 60 animals were euthanized, thyroid was harvested and used for, malondialdehyde MDA, nitric oxide NO, antioxidants, tumor necrosis factor alpha (TNF – α), interleukin 6 (IL – 6), Caspase-3, Nuclear factor erythroid 2- related factor 2 (Nrf2), Nuclear factor kappa B (NfkB) and Heme Oxygynase – 1 (Hmox-1) and histopathology.

Results

There was significant bioaccumulation of Pb, Al, Hg and MN; elevated IL-6 and Tnf-α, MDA and NO, caspase-3 and Nrf2, NF-κB and Hmox-1 in the HMM only group in comparison to the control. There was significant ( p < 0.05) decrease in SOD, CAT GSH activities in HMM only exposed group in comparison to the control deionized water group, whereas BP co-treatment with HMM significantly ( p < 0.05) increased SOD, CAT GSH activities. Co-treatment with BP extract also reversed most of these effects.

Discussion and Conclusions

BP extract may ameliorate HMM -induced thyrotoxicity in female albino rats by blunting oxido-inflammatory activities.

Cyclic di-GMP Signaling Links Biofilm Formation and Mn(II) Oxidation in Pseudomonas resinovorans

Bioaugmentation of biological sand filters with Mn(II)-oxidizing bacteria (MOB) is used to increase the efficiency of Mn removal from groundwater. While the biofilm-forming ability of MOB is important to achieve optimal Mn filtration, the regulatory link between biofilm formation and Mn(II) oxidation remains unclear. Here, an environmental isolate of Pseudomonas resinovorans strain MOB-513 was used as a model to investigate the role of c-di-GMP, a second messenger crucially involved in the regulation of biofilm formation by Pseudomonas, in the oxidation of Mn(II). A novel role for c-di-GMP in the upregulation of Mn(II) oxidation through induction of the expression of manganese-oxidizing peroxidase enzymes was revealed. MOB-513 macrocolony biofilms showed a strikingly stratified pattern of biogenic Mn oxide (BMnOx) accumulation in a localized top layer. Remarkably, elevated cellular levels of c-di-GMP correlated not only with increased accumulation of BMnOx in the same top layer but also with the appearance of a second BMnOx stratum in the bottom region of macrocolony biofilms, and the expression of mop genes correlated with this pattern. Proteomic analysis under Mn(II) conditions revealed changes in the abundance of a PilZ domain protein. Subsequent analyses supported a model in which this protein sensed c-di-GMP and affected a regulatory cascade that ultimately inhibited mop gene expression, providing a molecular link between c-di-GMP signaling and Mn(II) oxidation. Finally, we observed that high c-di-GMP levels were correlated with higher lyophilization efficiencies and higher groundwater Mn(II) oxidation capacities of freeze-dried bacterial cells, named lyophiles, showing the biotechnological relevance of understanding the role of c-di-GMP in MOB-513. IMPORTANCE The presence of Mn(II) in groundwater, a common source of drinking water, is a cause of water quality impairment, interfering with its disinfection, causing operation problems, and affecting human health. Purification of groundwater containing Mn(II) plays an important role in environmental and social safety. The typical method for Mn(II) removal is based on bacterial oxidation of metals to form insoluble oxides that can be filtered out of the water. Evidence of reducing the start-up periods and enhancing Mn removal efficiencies through bioaugmentation with appropriate biofilm-forming and MOB has emerged. As preliminary data suggest a link between these two phenotypes in Pseudomonas strains, the need to investigate the underlying regulatory mechanisms is apparent. The significance of our research lies in determining the role of c-di-GMP for increased biofilm formation and Mn(II)-oxidizing capabilities in MOB, which will allow the generation of super-biofilm-elaborating and Mn-oxidizing strains, enabling their implementation in biotechnological applications.

Exploring structure, microbiota, and metagenome functions of epigean and hypogean black deposits by microscopic, molecular and bioinformatic approaches

This study revealed how Bacteria and Archaea communities and their metabolic functions differed between two groups of black deposits identified in gorge and cave environments. Scanning electron microscopy coupled with energy dispersive spectroscopy was used to analyse the presence of microbial biosignatures and the elemental composition of samples. Metabarcoding of the V3-V4 regions of 16S rRNA was used to investigate Bacteria and Archaea communities. Based on 16S rRNA sequencing results, PICRUSt software was used to predict metagenome functions. Micrographs showed that samples presented microbial biosignatures and microanalyses highlighted Mn concretions and layers on Al-Si surfaces. The 16S rRNA metabarcoding alpha-diversity metrics showed similar Simpson's and Shannon indices and different values of the Chao-1 index. The amplicon sequence variants (ASVs) analysis at the different taxonomic levels showed a diverse genera composition. However, the communities of all samples shared the presence of uncultured ASVs belonging to the Gemmatales family (Phylogenesis: Gemmataceae; Planctomycetes; Planctomycetota; Bacteria). The predicted metagenome functions analysis revealed diverse metabolic profiles of the Cave and Gorge groups. Genes coding for essential Mn metabolism were present in all samples. Overall, the findings on structure, microbiota, and predicted metagenome functions showed a similar microbial contribution to epigean and hypogean black deposits Mn metabolism.

Amplicon-based assessment of bacterial diversity and community structure in three tropical forest soils in Kenya

Forest soils provide a multitude of habitats for diverse communities of bacteria. In this study, we selected three tropical forests in Kenya to determine the diversity and community structure of soil bacteria inhabiting these regions. Kakamega and Irangi are rainforests, whereas Gazi Bay harbors mangrove forests. The three natural forests occupy different altitudinal zones and differ in their environmental characteristics. Soil samples were collected from a total of 12 sites and soil physicochemical parameters for each sampling site were analyzed. We used an amplicon-based Illumina high-throughput sequencing approach. Total community DNA was extracted from individual samples using the phenol-chloroform method. The 16S ribosomal RNA gene segment spanning the V4 region was amplified using the Illumina MiSeq platform. Diversity indices, rarefaction curves, hierarchical clustering, principal component analysis (PCA), and non-metric multidimensional scaling (NMDS) analyses were performed in R software. A total of 13,410 OTUs were observed at 97% sequence similarity. Bacterial communities were dominated by Proteobacteria, Bacteroidetes, Firmicutes, Actinobacteria, and Acidobacteria in both rainforest and mangrove sampling sites. Alpha diversity indices and species richness were higher in Kakamega and Irangi rainforests compared to mangroves in Gazi Bay. The composition of bacterial communities within and between the three forests was also significantly differentiated (R = 0.559, p = 0.007). Clustering in both PCA and NMDS plots showed that each sampling site had a distinct bacterial community profile. The NMDS analysis also indicated that soil EC, sodium, sulfur, magnesium, boron, and manganese contributed significantly to the observed variation in the bacterial community structure. Overall, this study demonstrated the presence of diverse taxa and heterogeneous community structures of soil bacteria inhabiting three tropical forests of Kenya. Our results also indicated that variation in soil chemical parameters was the major driver of the observed bacterial diversity and community structure in these forests.

Manganese oxidation counteracts the deleterious effect of low temperatures on biofilm formation in Pseudomonas sp. MOB-449

Mn removal from groundwater by biological sand filter technology is negatively impacted by low temperatures in winter periods. Therefore, the need to study Mn(II)-oxidizing bacteria (MOB) having the potential to oxidize Mn(II) and form biofilms at low temperatures is imperative. These MOB can have potential as inocula for sand filter bioaugmentation strategies to optimize Mn removal during winter periods. We previously showed that a Pseudomonas sp. MOB-449 (MOB-449), isolated from a Mn biofilter, oxidizes Mn(II) in a biofilm-dependent way at low temperatures. In this work, MOB-449 Mn(II) oxidation and growth capacities were evaluated under planktonic and biofilm conditions at different temperatures. At 18°C, MOB-449 showed enhanced biofilm formation due to the addition of Mn(II) to the medium correlating with Mn(II) oxidation, compared to biofilms grown in control medium. Moreover, this enhancement on biofilm formation due to the addition of Mn(II) was only observed at 18°C. At this temperature, Mn(II) oxidation in membrane fractions collected from biofilms was induced by uncoupling oxidative phosphorylation from the electron transport chain with 2,4-Dinitrophenol. In Pseudomonas, a role for c-type cytochrome in Mn(II) oxidation has been demonstrated. Accordingly, transcriptional profiles of all terminal oxidases genes found in MOB-449 showed an induction of cytochrome c terminal oxidases expression mediated by Mn(II) oxidation at 18°C. Finally, heme peroxidase activity assays and MS analysis revealed that PetC, a cytochrome c5, and also CcmE, involved in the cytochrome c biogenesis machinery, are induced at 18°C only in the presence of Mn(II). These results present evidence supporting that cytochromes c and also the cytochrome c terminal oxidases are activated at low temperatures in the presence of Mn(II). Overall, this work demonstrate that in MOB-449 Mn(II) oxidation is activated at low temperatures to gain energy, suggesting that this process is important for survival under adverse environmental conditions and contributing to the understanding of the physiological role of bacterial Mn(II) oxidation.

Mineralogical and Genomic Constraints on the Origin of Microbial Mn Oxide Formation in Complexed Microbial Community at the Terrestrial Hot Spring

Manganese (Mn) oxides are widespread on the surface environments of the modern Earth. The role of microbial activities in the formation of Mn oxides has been discussed for several decades. However, the mechanisms of microbial Mn oxidation, and its role in complex microbial communities in natural environments, remain uncertain. Here, we report the geochemical, mineralogical, and metagenomic evidence for biogenic Mn oxides, found in Japanese hot spring sinters. The low crystallinity of Mn oxides, and their spatial associations with organic matter, support the biogenic origin of Mn oxides. Specific multicopper oxidases (MCOs), which are considered Mn-oxidizing enzymes, were identified using metagenomic analyses. Nanoscale nuggets of copper sulfides were, also, discovered in the organic matter in Mn-rich sinters. A part of these copper sulfides most likely represents traces of MCOs, and this is the first report of traces of Mn-oxidizing enzyme in geological samples. Metagenomic analyses, surprisingly, indicated a close association of Mn oxides, not only in aerobic but also in anaerobic microbial communities. These new findings offer the unique and unified positions of Mn oxides, with roles that have not been ignored, to sustain anaerobic microbial communities in hot spring environments.

Mn(II) Sorption on Stream Sediments Sampled in Manganese Mining Area: Dynamics and Mechanisms

The stream sediments that have been impacted by manganese (Mn) containing wastewater for decades contain not only abundant microorganisms but also organic/inorganic substances. To achieve effective treatment of manganese (Mn)-containing effluent and recovery of Mn from water/sediments, the Mn(II) sorption behaviors and mechanism on sediments of a stream in Mn mining areas were studied. In addition, the study analyzed the effects of various factors (initial concentration, solution pH, sediment dose, contact time, and coexisting cations) on the Mn sorption efficiency of Daxin sediments, and explored the contribution of microbial activity in the sediment sorption of Mn(II). The results showed that the sorption process of Mn(II) on the sediments was consistent with the Elovich and Freundlich models, and the removal of heavy metals was maximum at 40 °C (62.47–98.93%), pH = 8 (77.51%), initial concentration of 1 mmol·L−1 (95.37%) and sediment dosing of 12 g·L−1 (98.93%). The addition of 50 mM NaN3 inhibited the microbial activity in the Daxin sediment, reducing the sorption and removal rates of Mn(II) by 0.605 mg·g−1 and 8.92%, respectively. After sorption, the proportion of the Fe–Mn oxidation(iron–manganese) state in Daxin sediments decreased from 54% to 43%, while the proportion of the exchangeable state increased by 10.80%. Microorganisms in the sediment had a positive effect on inhibiting heavy metal migration and reducing the bioavailability of contaminants in the soil. Through this study, we hope to further understand the sorption and desorption mechanism of manganese by stream sediments in manganese ore areas, so as to provide a guide on the management and recovery of Mn from stream sediments in manganese mining areas.

Kinetic Modeling and Mechanisms of Manganese Removal from Alkaline Mine Water Using a Pilot Scale Column Reactor

Manganese (Mn) is a major element in various aqueous and soil environments that is sometimes highly concentrated in mine water and other mineral processing wastewater. In this study, we investigated Mn removal from alkaline mine water (pH > 9) with an Mn-coated silica sand packed into a pilot-scale column reactor and examined the specific reaction mechanism using X-ray absorption near-edge structure (XANES) analysis and geochemical kinetic modeling. The kinetic effect of dissolved Mn(II) removal by birnessite (δ-Mn(IV)O2) at pH 6 and 8 was evaluated at different Mn(II)/Mn(IV) molar ratios of 0.1–10. Our results confirmed the positive effect of the presence of δ-MnO2 on the short-term removal (60 min) of dissolved Mn. XANES analysis results revealed that δ-MnO2 was more abundant than Mn(III)OOH in the reactor, which may have accumulated during a long-term reaction (4 months) after the reactor was turned on. A gradual decrease in dissolved Mn(II) concentration with depth was observed in the reactor, and comparison with the kinetic modeling result confirmed that δ-MnO2 interaction was the dominant Mn removal mechanism. Our results show that δ-MnO2 contents could play a significant role in controlling Mn removability from mine water in the reactor.

Key factors controlling microbial distribution on a DNAPL source area

Chlorinated solvents are among the common groundwater contaminants that show high complexity in their distribution in the subsoil. Microorganisms play a vital role in the natural attenuation of chlorinated solvents. Thus far, how the in situ soil microbial community responds to chlorinated solvent contamination has remained unclear. In this study, the microbial community distribution within two boreholes located in the source area of perchloroethene (PCE) was investigated via terminal restriction fragment length polymorphism (T-RFLP) and clone library analysis. Microbial data were related to the lithological and geochemical data and the concentration and isotopic composition of chloroethenes to determine the key factors controlling the distribution of the microbial communities. The results indicated that Proteobacteria, Actinobacteria, and Firmicutes were the most abundant phylums in the sediment. The statistical correlation with the environmental data proved that fine granulometry, oxygen tolerance, terminal electron-acceptor processes, and toxicity control microbial structure. This study improves our understanding of how the microbial community in the subsoil responds to high concentrations of chlorinated solvents.

Manganese Stress Adaptation Mechanisms of Bacillus safensis Strain ST7 From Mine Soil

The mechanism of bacterial adaption to manganese-polluted environments was explored using 50 manganese-tolerant strains of bacteria isolated from soil of the largest manganese mine in China. Efficiency of manganese removal by the isolated strains was investigated using atomic absorption spectrophotometry. Bacillus safensis strain ST7 was the most effective manganese-oxidizing bacteria among the tested isolates, achieving up to 82% removal at a Mn(II) concentration of 2,200 mg/L. Bacteria-mediated manganese oxide precipitates and high motility were observed, and the growth of strain ST7 was inhibited while its biofilm formation was promoted by the presence of Mn(II). In addition, strain ST7 could grow in the presence of high concentrations of Al(III), Cr(VI), and Fe(III). Genome-wide analysis of the gene expression profile of strain ST7 using the RNA-seq method revealed that 2,580 genes were differently expressed under Mn(II) exposure, and there were more downregulated genes (n = 2,021) than upregulated genes (n = 559) induced by Mn stress. KAAS analysis indicated that these differently expressed genes were mainly enriched in material metabolisms, cellular processes, organism systems, and genetic and environmental information processing pathways. A total of twenty-six genes from the transcriptome of strain ST7 were involved in lignocellulosic degradation. Furthermore, after 15 genes were knocked out by homologous recombination technology, it was observed that the transporters, multicopper oxidase, and proteins involved in sporulation and flagellogenesis contributed to the removal of Mn(II) in strain ST7. In summary, B. safensis ST7 adapted to Mn exposure by changing its metabolism, upregulating cation transporters, inhibiting sporulation and flagellogenesis, and activating an alternative stress-related sigB pathway. This bacterial strain could potentially be used to restore soil polluted by multiple heavy metals and is a candidate to support the consolidated bioprocessing community.

Biological and physico-chemical mechanisms accelerating the acclimation of Mn-removing biofilters

This study investigated treatment strategies which accelerated the acclimation of new Mn-removing biofilters to help utilities respond to changing Mn regulations, such as the recent introduction of a health-based maximum acceptable concentration and a reduction in the aesthetic objective for Mn in drinking water by Health Canada. Bench-scale filters of either GAC or anthracite media were fed with applied water containing Mn (17-61 μg/L) from a full-scale plant over 294 days. Treatment strategies included the addition of H₂O₂ (1 mg/L) and/or an increase in pH from 6.8 to 7.5 through the addition of NaOH. The potential physico-chemical and biological mechanisms responsible for accelerated biofilter acclimation under the various redox conditions were investigated through thermodynamic modelling, to predict homogeneous Mn oxide formation, and 16S rRNA gene amplicon sequencing, to characterize the microbial community within the filters. GAC filters treated with NaOH, and both H₂O₂ and NaOH, were the first to acclimate (< 20 μg/L Mn in filter effluent) after 59 and 63 days respectively, while the ambient GAC filter took almost 3 times as long to acclimate (168 days), and the anthracite filters which received the same chemically adjusted water took almost 4 times as long (226 and 251 days, respectively). The accelerated acclimation in the treated GAC filters was likely due to physico-chemical oxidation via three potential mechanisms: (1) homogeneous oxidation of dissolved Mn(II) to Mn(III)/Mn(IV) oxides and the subsequent removal of oxides from solution through adherence to the GAC surface, (2) adsorption of dissolved Mn(II) to GAC and subsequent homogeneous or biological oxidation, or (3) formation of colloidal Mn(III)/Mn(IV) oxides and subsequent adsorption of dissolved Mn(II) to the Mn colloids. In the untreated GAC filter and all anthracite filters, which did not benefit from improved redox conditions or an active surface, physico-chemical mechanisms alone were insufficient for consistent Mn removal to less than 20 μg/L. Acclimation in these filters was delayed until a microbiome enriched with bacteria capable of biological nitrification and Mn oxidation evolved within the filters. The acclimated microbiome was consistent between GAC and anthracite filters and was significantly different from the non-acclimated microbiome (p < 0.001) initially formed during the early operation of the filters. Interestingly, treatment with NaOH, and NaOH and H₂O₂, which accelerated physico-chemical oxidation in GAC filters, was observed to delay the development of biological oxidation in anthracite filters, and thus deferred acclimation. Although some filters took longer to acclimate than others, once acclimation was reached all filters had a similar microbiome and were able to consistently remove Mn to below 20 µg/L.

Manganese-Oxidizing Antarctic Bacteria (Mn-Oxb) Release Reactive Oxygen Species (ROS) as Secondary Mn(II) Oxidation Mechanisms to Avoid Toxicity

Manganese (Mn) oxidation is performed through oxidative Mn-oxidizing bacteria (MnOxb) as the main bio-weathering mechanism for Mn(III/IV) deposits during soil formation. However, with an increase in temperature, the respiration rate also increases, producing Reactive Oxygen Species (ROS) as by-products, which are harmful to microbial cells. We hypothesize that bacterial ROS oxidize Mn(II) to Mn(III/IV) as a secondary non-enzymatic temperature-dependent mechanism for cell protection. Fourteen MnOxb were isolated from Antarctic soils under the global warming effect, and peroxidase (PO) activity, ROS, and Mn(III/IV) production were evaluated for 120 h of incubation at 4 °C, 15 °C, and 30 °C. ROS contributions to Mn oxidation were evaluated in Arthrobacter oxydans under antioxidant (Trolox) and ROS-stimulated (menadione) conditions. The Mn(III/IV) concentration increased with temperature and positively correlated with ROS production. ROS scavenging with Trolox depleted the Mn oxidation, and ROS-stimulant increased the Mn precipitation in A. oxydans. Increasing the Mn(II) concentration caused a reduction in the membrane potential and bacterial viability, which resulted in Mn precipitation on the bacteria surface. In conclusion, bacterial ROS production serves as a complementary non-enzymatic temperature-dependent mechanism for Mn(II) oxidation as a response in warming environments.

Oxidants-assisted sand filter to enhance the simultaneous removals of manganese, iron and ammonia from groundwater: Formation of active MnOx and involved mechanisms

Oxidants are routinely employed to remove manganese from groundwater deeply, but the conversion pathway of manganese in the process still needed to be explored. In this study, potassium permanganate and sodium hypochlorite were introduced to explore their start-up effect on sand filters in treating high concentration of manganese (1.42-1.94 mg/L). The addition of potassium permanganate would effectively enhance the manganese removal (>97%) and significantly shorten the start-up period (36 days) compared to sodium hypochlorite-added filter (90 days). A good correlation between manganese deposition concentration and manganese removal rate was obtained, which indicated that the removal of manganese in pre-adding oxidants sand filters was dominated by adsorption and auto-catalytic oxidation processes, where δ-MnO₂ played a crucial role and the contribution of bacteria was negligible. The addition of potassium permanganate facilitated the production of MnO₂ and promoted the conversion of Mn(II)-γ-MnO₂-δ-MnO₂/todorokite during the 120-day operation. Besides, the residual Mn(II) contributed to converting the freshly generated MnO₂ by pre-adding oxidants into active MnOx. XPS results demonstrated the co-existence system of Mn(II), Mn(III) and Mn(IV) in δ-MnO₂. The proportion of Mn(III) with high catalytic oxidative activity in potassium permanganate-assisted formed MnOx (57%) was much higher than in sodium hypochlorite-assisted formed MnOx (22%). These findings have practical significance to develop new strategies for rapid, safe and deep removal of manganese.

Bacterial isolates from Argentine Pampas and their ability to degrade glyphosate

Glyphosate is a synthetic phosphonate compound characterized by a carbon‑phosphorus bond. Glyphosate based herbicides (GBH) are widely distributed in most of the economically productive lands in which crop production is mainly based on glyphosate-resistant genetically modified plants. Naturally, glyphosate is remediated by soil microorganisms, which accelerate its degradation. Technology based on microorganisms is considered highly efficient, low-cost and eco-friendly to remediate contaminated environments, denoting the importance of characterizing new bacterial strains able to degrade glyphosate to perform its bioremediation. In this work, 13 different bacterial strains able to grow in GBH as only phosphorous source were isolated from different environmental samples from the Argentine vastly productive glyphosate-resistant soybean crop area. These strains were identified and they belong to the genera Acinetobacter, Achromobacter, Agrobacterium, Ochrobactrum, Pantoea and Pseudomonas. Their ability to grow and consume GBH, glyphosate or the aminomethylphosphonic acid (AMPA), another phosphonate derived from glyphosate degradation, was evaluated. The best degradation performance was observed for bacteria from the genera Achromobacter, Agrobacterium and Ochrobactrum. The genome of the highly efficient GBH degrader Agrobacterium tumefaciens CHLDO was sequenced revealing the presence of a phn cluster, responsible for phosphonate metabolization. Expression analysis of A. tumefaciens CHLDO phn genes in the presence of 1.5 mM GBH compared to inorganic phosphorous showed that most of them are highly expressed during growth in the presence of the herbicide, suggesting a strong participation of phn cluster in GBH degradation. The importance of discovering new bacterial strains and the value of deciphering molecular determinants of GBH degradation give promising tools for bioremediation techniques to be used in glyphosate-contaminated environments is discussed.

Removal of Mn(II) by a nitrifying bacterium Acinetobacter sp. AL-6: efficiency and mechanisms

A nitrifying bacterium Acinetobacter sp. AL-6 showed a high efficiency of 99.05% for Mn(II) removal within 144 h when the Mn(II) concentration was 200 mg L^-1; meanwhile, 64.23% of NH₄⁺-N was removed. With the Mn(II) concentration increased from 25 to 300 mg L^-1, bacterial growth and Mn(II) removal were stimulated. However, due to the electron acceptor competition between Mn(II) oxidation and nitrification reactions, the increase in NH₄⁺-N concentration would inhibit Mn(II) removal. By measuring Mn metabolic form and locating oxidative active factors, it was proved that extracellular oxidation effect played a dominant role in the removal process of Mn(II). The self-regulation of pH during strain metabolism further promoted the occurrence of biological Mn oxidation. Characterization results showed that the Mn oxidation products were tightly attached to the surface of the bacteria in the form of flakes. The product crystal composition (mainly MnO₂ and Mn₂O₃), Mn-O functional group, and element level fluctuations confirmed the biological oxidation information. The changes of -OH, N-H, and -CH₂ groups and the appearance of new functional groups (such as C-H and C-O) provided more possibilities for Mn ion adsorption and bonding.

Temperature management potentially affects carbon mineralization capacity and microbial community composition of a shallow aquifer

High-temperature aquifer thermal energy storage (HT-ATES) is a promising technique to reduce the CO2 footprint of heat supply in the frame of transitioning to renewable energies. However, HT-ATES causes temperature fluctuations in groundwater ecosystems potentially affecting important microbial-mediated ecosystem services. Hence, assessing the impact of increasing temperatures on the structure and functioning of aquifer microbiomes is crucial to evaluate potential environmental risks associated with HT-ATES. In this study, we investigated the effects of temperature variations (12-80°C) on microbial communities and their capacity to mineralize acetate in aerobically incubated sediment sampled from a pristine aquifer. Compared to natural conditions (12°C), increased acetate mineralization rates were observed at 25°C, 37°C and 45°C, whereas mineralization was decelerated at 60°C and absent at 80°C. Sequencing of 16S rRNA genes revealed that the bacterial diversity in acetate-amended and non-acetate-amended sediments decreased with rising temperatures. Distinct communities dominated by bacterial groups affiliated with meso- and thermophilic bacteria established at 45°C and 60°C, respectively, while the number of archaeal phylotypes decreased. The changes in microbial diversity observed at 45°C and 60°C indicate a potential loss of ecosystem functioning, functional redundancy and resilience, while heat storage at 80°C bears the risk of ecological collapse.

Complete genome sequence of plant growth-promoting and heavy metal-tolerant Enterobacter tabaci 4M9 (CCB-MBL 5004)

Enterobacter tabaci 4M9 (CCB-MBL 5004) was reported to have plant growth-promoting and heavy metal tolerance traits. It was able to tolerate more than 300 mg/L Cd, 600 mg/L As, and 500 mg/L Pb and still maintained the ability to produce plant growth-promoting substances under metal stress conditions. To explore the genetic basis of these beneficial traits, the complete genome sequencing of 4M9 was carried out using Pacific Bioscience (PacBio) sequencing technology. The complete genome consisted of one chromosome of 4,654,430 bp with a GC content of 54.6% and one plasmid of 51,135 bp with a GC content of 49.4%. Genome annotation revealed several genes involved in plant growth-promoting traits, including the production of siderophore, indole acetic acid, and 1-aminocyclopropane-1-carboxylate deaminase; solubilization of phosphate and potassium; and nitrogen metabolism. Similarly, genes involved in heavy metals (As, Co, Zn, Cu, Mn, Se, Cd, and Fe) tolerance were detected. These support its potential as a heavy metal-tolerant plant growth-promoting bacterium and a good genetic resource that can be employed to improve phytoremediation efficiency of heavy metal-contaminated soil via biotechnological techniques. This, to the best of our knowledge, is the first report on the complete genome sequence of heavy metal-tolerant plant growth-promoting E. tabaci.

Microbial community composition in iron deposits and manganese crusts formed in riverine environments around the Aso area in Japan

The Kurokawa river flowing through the Aso Caldera in Southwest Japan is influenced by groundwater containing high concentration of dissolved metals (Fe²⁺ and Mn²⁺) and is associated with orange deposits in the upstream and thick black crusts on the wall of artificial waterway tunnel with several km lengths in the midstream regions. X-ray fluorescence analysis revealed that the orange deposits contained up to 34.4% Fe and black crusts comprised up to 25.4% and 10.6% Mn and Fe, respectively. Although naturally occurring Mn-oxides and crusts are considered biogenic in pH-neutral freshwater environments, the whole microbial community in Mn crust and their contribution to Mn crust formation in these environments remain unclear. High-throughput molecular sequencing for bacteria and eukaryotes including fungi revealed black Mn crusts had a high abundance of Sphingomonas, Hyphomicrobium, Bacillus, Pseudomonas, and Mortierella, previously reported genera including several species with Mn-oxidizing activity in Mn crusts or nodules of other marine and freshwater environments. In addition, one bacterial isolate and one fungal isolate with Mn-oxidizing activity were obtained from black Mn crust. These results suggest that multiple Mn-oxidizing bacteria including Pseudomonas and fungi are involved in Mn crust formation on the wall of dark waterway tunnel in the oligotrophic environment of the Kurokawa river.