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The majority of large iron formations (IFs) were deposited leading up to Earth's great oxidation episode (GOE). Following the GOE, IF deposition decreased for almost 500 Myr. Subsequently, around 1.88 Ga, there was widespread deposition of shallow‐water granular iron formations (GIF) within a geologically short time interval, which has been linked to enhanced iron (Fe) supply to seawater from submarine hydrothermal venting associated with the emplacement of large igneous provinces. Previous studies of Fe‐rich, microfossil‐bearing stromatolites from the ca. 1.88 Ga Gunflint Formation on the Superior craton suggested direct microbial oxidation of seawater Fe2+(aq) by microaerophilic, Fe‐oxidizing bacteria (FeOB), as a driver of GIF deposition. Although Fe‐rich, microfossil‐bearing stromatolites are common in 1.88 Ga GIF deposits on several cratons, combined paleontological and geochemical studies have been applied only to the Gunflint Formation. Here, we present new paleontological and geochemical observations for the ca. 1.89 Ga Gibraltar Formation GIFs from the East Arm of the Great Slave Lake, Northwest Territories, Canada. Fossil morphology, Rare Earth element (REE) concentrations, and Fe isotopic compositions support Fe oxidation by FeOB at a redoxcline poised above the fair‐weather wave base. Small positive Eu anomalies and positive εNd (1.89 Ga) values suggest upwelling of deep, Fe‐rich, hydrothermally influenced seawater. While high [Fe2+(aq)] combined with low atmospheric pO2 in the late Paleoproterozoic would have provided optimal conditions in shallow oceans for FeOB to precipitate Fe oxyhydroxide, these redox conditions were likely toxic to cyanobacteria. As long as local O2 production by cyanobacteria was strongly diminished, FeOB would have had to rely on an atmospheric O2 supply by diffusion to shallow seawater to oxidize Fe2+(aq). Using a 1‐D reaction dispersion model, we calculate [O2(aq)] sufficient to deplete an upwelling Fe2+(aq) source. Our results for GIF deposition are consistent with late Paleoproterozoic pO2 estimates of ~1%–10% PAL and constraints for metabolic [O2(aq)] requirements for modern FeOB. Widespread GIF deposition at ca. 1.88 Ga appears to mark a temporally restricted episode of optimal biogeochemical conditions in Earth's history when increased hydrothermal Fe2+(aq) sourced from the deep oceans, in combination with low mid‐Paleoproterozoic atmospheric pO2, globally satisfied FeOB metabolic Fe2+(aq) and O2(aq) requirements in shallow‐marine subtidal environments above the fair‐weather wave base. [ABSTRACT FROM AUTHOR]

Abandoned shipwrecks are sitting at the bottom of oceans, lakes, and rivers around the world. Over time, microbial-comprised biofilms can help protect wrecks against chemical corrosion or contribute to their deterioration through microbiologically influenced corrosion (MIC) by organisms including iron-oxidizing bacteria (FeOB) and sulfate-reducing bacteria (SRB). Assessing the community assembly of these biofilms will give us a better understanding of the role these microbes play in MIC and the factors that influence it. Here, we determine if microbial community composition differs across a shallow freshwater ferrous-hulled shipwreck environment. Results suggest that there was a statistically significant difference among the sample types indicating the wreck environments around Accomac influenced the community composition. This is consistent with previous observations within an estuarine, shallow-water wreck environment. Bacteroidota, Chloroflexota, and Cyanobacteriota were the primary taxa responsible for differences among these wreck environments. Interestingly, port-side biofilm communities were significantly different than those on the starboard side suggesting physical factors of the environment drove niche partitioning on each side of the wreck. Similarly, FeOB enrichments and known FeOB taxa were found across the entire wreck but were primarily found in samples associated with the port side of the wreck. Amplicon sequencing identified both known FeOB and SRB taxa with a higher proportion of FeOB than SRB. Overall, these results indicate that there is niche partitioning of the microbial communities as well as with corrosion-causing taxa within a shallow freshwater wreck site which may lead to variation in how microbes may contribute to the protection or deterioration of these ferrous-hulled wrecks. IMPORTANCE The overall structure, abundance, and diversity of microbial communities on shipwrecks have recently been studied in marine aquatic environments. While previous studies have looked at the microbial communities associated with shallow-water ferrous-hulled wrecks in marine environments, studies focusing on freshwater wreck systems are limited. The purpose of this study was to determine microbial community diversity and composition trends across the Accomac shipwreck environment. Furthermore, shipwrecks are colonized by corrosion-causing taxa, such as iron-oxidizing bacteria and sulfate-reducing bacteria which have been shown to influence the biocorrosion of ferrous-hulled structures. Identification of various microbes in biofilms, as well as corrosion-causing microbes, can help researchers identify the role they play in aquatic ecosystem development and persistence as well as artificial reef integrity. Understanding how microbes assemble on wrecks will provide insight into preservation strategies to prevent deterioration of these wrecks over time, as well as limiting biocorrosion of similar structures. [ABSTRACT FROM AUTHOR]

Bioleaching, a process catalyzed by acidophilic microorganisms, offers a sustainable approach to metal extraction from sulfide minerals. Chalcopyrite, the world's most abundant copper sulfide, presents challenges due to surface passivation limiting its bioleaching efficiency. Also, indigenous species and microbial communities may present high copper extraction rates and offer new possibilities for application in bioleaching processes. This study examines the bioleaching potential of microbial isolates and communities obtained from Amolanas Mine in Chile. Samples were collected, cultivated, and identified by Sanger sequencing. The bioleaching potential and biofilm formation of isolates and enrichments were evaluated on pyrite and chalcopyrite. The results show the isolation of nine Leptospirillum and two Acidithiobacillus strains. The bioleaching experiments demonstrated good copper bioleaching potentials of the Leptospirillum I2CS27 strain and EICA consortium (composed mainly of Leptospirillum ferriphilum, Acidiphilium sp., and Sulfobacillus thermosulfidooxidans), with 11% and 25% copper recovery rates, respectively. Microbial attachment to the surface mineral was not mandatory for increasing the bioleaching rates. Our findings underscore the importance of indigenous microbial communities in enhancing copper bioleaching efficiency. [ABSTRACT FROM AUTHOR]

Leptothrix ochracea creates distinctive iron-mineralized mats that carpet streams and wetlands. Easily recognized by its iron-mineralized sheaths, L. ochracea was one of the first microorganisms described in the 1800s. Yet it has never been isolated and does not have a complete genome sequence available, so key questions about its physiology remain unresolved. It is debated whether iron oxidation can be used for energy or growth and if L. ochracea is an autotroph, heterotroph, or mixotroph. To address these issues, we sampled L. ochracea-rich mats from three of its typical environments (a stream, wetlands, and a drainage channel) and reconstructed nine high-quality genomes of L. ochracea from metagenomes. These genomes contain iron oxidase genes cyc2 and mtoA, showing that L. ochracea has the potential to conserve energy from iron oxidation. Sox genes confer potential to oxidize sulfur for energy. There are genes for both carbon fixation (RuBisCO) and utilization of sugars and organic acids (acetate, lactate, and formate). In silico stoichiometric metabolic models further demonstrated the potential for growth using sugars and organic acids. Metatranscriptomes showed a high expression of genes for iron oxidation; aerobic respiration; and utilization of lactate, acetate, and sugars, as well as RuBisCO, supporting mixotrophic growth in the environment. In summary, our results suggest that L. ochracea has substantial metabolic flexibility. It is adapted to iron-rich, organic carbon-containing wetland niches, where it can thrive as a mixotrophic iron oxidizer by utilizing both iron oxidation and organics for energy generation and both inorganic and organic carbon for cell and sheath production. [ABSTRACT FROM AUTHOR]

Surface water can exhibit a range of colours beyond the expected blue or green. These anomalous colourations can be triggered by different factors, both natural and anthropogenic, and not always are signs of pollution. This note explores the phenomenon of water discolouration, focusing on natural causes and analysing how factors such as algal and bacterial blooms influence water colour. The study provides examples of specific events that occurred in the Emilia-Romagna region and documented by ARPAE and highlights the importance of monitoring these colouration events in order to provide valuable insights into the health of water bodies and the surrounding environment.

Kaliningrad region has a rich historical heritage, including several water sources with high iron content, known since the end of 19th century. They are rich in divalent iron, which is oxidized by bacterial communities. They include many different taxonomic groups of bacteria. In this paper, for the first time, the microbial communities of iron-bearing springs in the Kaliningrad region were profiled, and 6 samples were taken from four geographical locations during the study. The results of profiling revealed taxonomic groups belonging to phylum: Acidobacteriota, Desulfobacteriota, Cyanobacteriia, Proteobacteria, Nitrospirota, and among the predominant groups stands out a gamma-proteobacterium of the genus Gallionella. [ABSTRACT FROM AUTHOR]

Hydrocarbon pollution is a widespread issue in both groundwater and surfacewater systems; however, research on remediation at the interface of these two systems is limited. This interface is the oxic-anoxic boundary, where hydrocarbon pollutant from contaminated groundwaters flows into surface waters and iron mats are formed by microaerophilic iron-oxidizing bacteria. Iron mats are highly chemically adsorptive and host a diverse community of microbes. To elucidate the effect of hydrocarbon exposure on iron mat geochemistry and microbial community structure and function, we sampled iron mats both upstream and downstream from a leaking underground storage tank. Hydrocarbon-exposed iron mats had significantly higher concentrations of oxidized iron and significantly lower dissolved organic carbon and total dissolved phosphate than unexposed iron mats. A strong negative correlation between dissolved phosphate and benzene was observed in the hydrocarbonexposed iron mats and water samples. There were positive correlations between iron and other hydrocarbons with benzene in the hydrocarbon-exposed iron mats, which was unique from water samples. The hydrocarbon-exposed iron mats represented two types, flocculent and seep, which had significantly different concentrations of iron, hydrocarbons, and phosphate, indicating that iron mat is also an important context in studies of freshwater mats. Using constrained ordination, we found the best predictors for community structure to be dissolved oxygen, pH, and benzene. Alpha diversity and evenness were significantly lower in hydrocarbon-exposed iron mats than unexposed mats. Using 16S rDNA amplicon sequences, we found evidence of three putative nitrate-reducing iron-oxidizing taxa in microaerophile-dominated iron mats (Azospira, Paracoccus, and Thermomonas). 16S rDNA amplicons also indicated the presence of taxa that are associated with hydrocarbon degradation. Benzene remediation-associated genes were found using metagenomic analysis both in exposed and unexposed iron mats. Furthermore, the results indicated that season (summer vs. spring) exacerbates the negative effect of hydrocarbon exposure on community diversity and evenness and led to the increased abundance of numerous OTUs. This study represents the first of its kind to attempt to understand how contaminant exposure, specifically hydrocarbons, influences the geochemistry and microbial community of freshwater iron mats and further develops our understanding of hydrocarbon remediation at the land-water interface. [ABSTRACT FROM AUTHOR]

Bioleaching of Cu from the copper concentrate of Armanis gold-bearing polymetallic ore (Armenia) was investigated. The main objective was revealing high active bacteria and their association, as well as optimizing the bioleaching process with their application to ensure the most efficient recovery of copper from the tested concentrate. To obtain optimal bacterial associations, bottom-up and top-down approaches were used. Bioleaching of copper concentrate was carried out using pure cultures of iron- and sulfur-oxidizing bacteria and their mixed culture, as well as indigenous bacterial consortium. Comparative studies of copper bioleaching by mixed cultures of Acidithiobacillus caldus, Leptospirillum ferriphilum CC, Sulfobacillus thermosulfidooxidans 6, and indigenous consortium Arm of iron-oxidizing bacteria were performed. At the beginning of bioleaching, the amounts of extracted copper by mixed culture and Arm consortium were equal; afterward, between 20–27 days, the Arm indigenous consortium showed significantly higher activity in terms of copper extraction. In parallel, mineralogical and liberation analyses of feed material and bioleaching residues were performed. [ABSTRACT FROM AUTHOR]

Hydrocarbon pollution is a widespread issue in both groundwater and surface-water systems; however, research on remediation at the interface of these two systems is limited. This interface is the oxic–anoxic boundary, where hydrocarbon pollutant from contaminated groundwaters flows into surface waters and iron mats are formed by microaerophilic iron-oxidizing bacteria. Iron mats are highly chemically adsorptive and host a diverse community of microbes. To elucidate the effect of hydrocarbon exposure on iron mat geochemistry and microbial community structure and function, we sampled iron mats both upstream and downstream from a leaking underground storage tank. Hydrocarbon-exposed iron mats had significantly higher concentrations of oxidized iron and significantly lower dissolved organic carbon and total dissolved phosphate than unexposed iron mats. A strong negative correlation between dissolved phosphate and benzene was observed in the hydrocarbon-exposed iron mats and water samples. There were positive correlations between iron and other hydrocarbons with benzene in the hydrocarbon-exposed iron mats, which was unique from water samples. The hydrocarbon-exposed iron mats represented two types, flocculent and seep, which had significantly different concentrations of iron, hydrocarbons, and phosphate, indicating that iron mat is also an important context in studies of freshwater mats. Using constrained ordination, we found the best predictors for community structure to be dissolved oxygen, pH, and benzene. Alpha diversity and evenness were significantly lower in hydrocarbon-exposed iron mats than unexposed mats. Using 16S rDNA amplicon sequences, we found evidence of three putative nitrate-reducing iron-oxidizing taxa in microaerophile-dominated iron mats (Azospira, Paracoccus, and Thermomonas). 16S rDNA amplicons also indicated the presence of taxa that are associated with hydrocarbon degradation. Benzene remediation-associated genes were found using metagenomic analysis both in exposed and unexposed iron mats. Furthermore, the results indicated that season (summer vs. spring) exacerbates the negative effect of hydrocarbon exposure on community diversity and evenness and led to the increased abundance of numerous OTUs. This study represents the first of its kind to attempt to understand how contaminant exposure, specifically hydrocarbons, influences the geochemistry and microbial community of freshwater iron mats and further develops our understanding of hydrocarbon remediation at the land–water interface.

Modern Fe‐Si oxyhydroxide deposits occur in global marine hydrothermal vent sites. Despite their role as biogenic substrates and potential ore resources, much remains unknown about their formation processes. Here, we apply analyses of major and trace elements as well as Sr‐Nd‐Pb‐Fe isotopes combined with 238U‐230Th dating to Fe‐Si oxyhydroxides obtained from several hydrothermal fields along the Southwest Indian Ridge. These mineralized oxyhydroxides primarily consist of poorly crystalline two‐line ferrihydrite and amorphous opal‐A, with lesser amounts of nontronite and birnessite. The ubiquitous and characteristic Fe‐rich ultrastructures in the oxyhydroxides directly indicate microbial activity. The 238U‐230Th dating constrains their crystallization ages from ca. 11,873 to 384 years old. The seawater‐like 87Sr/86Sr and varying 143Nd/144Nd ratios underline a high proportion of seawater mixed with hydrothermal fluids. The radiogenic Pb isotopic patterns suggest a primary derivation of Pb leached from substrate basalts and to a lesser extent Pb from seawater. Stable iron isotopic compositions for different oxyhydroxides display a remarkable range between −1.47 and 0.82‰, which were interpreted as reflecting the fractionation processes during the formation of the deposits under evolving depositional redox conditions. The partial oxidation of Fe(II) and the subsurface removal of isotopically heavy Fe oxyhydroxides are suggested to play a vital role in shifting the Fe isotopic signature toward more negative values. Given that these Fe‐Si oxyhydroxide deposits exhibit features similar to certain ancient iron formations (IFs), Fe isotope systematics of these deposits may hold significant potential for fingerprinting the biological Fe oxidation processes that drove IF deposition on early Earth. Plain Language Summary: This study introduces a comprehensive examination of Fe‐Si oxyhydroxide deposits in marine hydrothermal vent sites along the Southwest Indian Ridge. Applying innovative techniques of major and trace element and Sr‐Nd‐Pb‐Fe isotope analysis combined with 238U‐230Th dating, the investigation uncovers new insights into the composition, age, and origin of microbial Fe‐Si oxyhydroxide ultrastructures. Notably, these deposits are found to be primarily composed of ferrihydrite and amorphous opal‐A, with ages ranging from ca. 11,873 to 384 years old. Our study provides evidence for their low‐temperature hydrothermal origin, with geochemical characteristics highlighting rare earth element patterns and radiogenic Sr‐Nd‐Pb isotopic compositions. Of particular significance is the discovery of a wide range of stable iron isotopic compositions, shedding new light on the depositional redox conditions. Our data, in concert with previous studies, reveal similarities between biogenic Fe‐Si oxyhydroxide deposits and ancient iron formations (IFs). This link indicates the potential use of Fe isotope systematics in tracing Fe oxidation processes and the biosignatures that may have shaped IF deposition on early Earth. These novel findings contribute fresh perspectives to the understanding of low‐temperature hydrothermal deposit geochemistry and the search for geological biosignatures. Key Points: We present a comprehensive Sr‐Nd‐Pb‐Fe isotope investigation of modern Fe‐Si oxyhydroxide deposits in marine hydrothermal vent sitesSr‐Nd‐Pb isotope variations in Fe‐Si oxyhydroxides were produced by varying degrees of seawater mixing with diffuse hydrothermal fluidsFe isotope systematics of Fe‐Si oxyhydroxides can provide key information for Fe oxidation processes during the formation of the deposits [ABSTRACT FROM AUTHOR]

On the roots of wetland plants such as rice, Fe(II) oxidation forms Fe(III) oxyhydroxide-rich plaques that modulate plant nutrient and metal uptake. The microbial roles in catalyzing this oxidation have been debated and it is unclear if these iron-oxidizers mediate other important biogeochemical and plant interactions. To investigate this, we studied the microbial communities, metagenomes, and geochemistry of iron plaque on field-grown rice, plus the surrounding rhizosphere and bulk soil. Plaque iron content (per mass root) increased over the growing season, showing continuous deposition. Analysis of 16S rRNA genes showed abundant Fe(II)-oxidizing and Fe(III)-reducing bacteria (FeOB and FeRB) in plaque, rhizosphere, and bulk soil. FeOB were enriched in relative abundance in plaque, suggesting FeOB affinity for the root surface. Gallionellaceae FeOB Sideroxydans were enriched during vegetative and early reproductive rice growth stages, while a Gallionella was enriched during reproduction through grain maturity, suggesting distinct FeOB niches over the rice life cycle. FeRB Anaeromyxobacter and Geobacter increased in plaque later, during reproduction and grain ripening, corresponding to increased plaque iron. Metagenome-assembled genomes revealed that Gallionellaceae may grow mixotrophically using both Fe(II) and organics. The Sideroxydans are facultative, able to use non-Fe substrates, which may allow colonization of rice roots early in the season. FeOB genomes suggest adaptations for interacting with plants, including colonization, plant immunity defense, utilization of plant organics, and nitrogen fixation. Taken together, our results strongly suggest that rhizoplane and rhizosphere FeOB can specifically associate with rice roots, catalyzing iron plaque formation, with the potential to contribute to plant growth. [ABSTRACT FROM AUTHOR]

The possibility of processing sulfide copper-nickel raw materials by heap bioleaching due to the environmental attractiveness of this approach is becoming an increasingly relevant topic for mining and processing. On the example of the Allarechensk technogenic deposit ore, the effectiveness of the bioleaching method for the copper and nickel recovery has been considered. The content of metals in the original ore sample: nickel – 2.42 % and copper – 0.75 %. The ore grinded to the size of –5+3 mm has been irrigated with a solution containing a strain of Acidithiobacillus ferrivorans. The S : L ratio is 4 : 1, the flow rate is equal to 0.1 mL/min. In pregnant solutions, the pH and redox potential values have been controlled, and the concentrations of ferrous and ferric iron, copper, and nickel ions have also been measured. The experiment duration is 11 months, 8.9 % nickel and 6.1 % copper have been recovered. Copper has been extracted from pregnant solutions by cementation on iron, the maximum recovery is 97.3 %. Thus, it has been shown that the proposed scheme for the recovery of metals is promising for the processing of sulfide raw materials, in particular, low-grade ores and enrichment waste.

Abstract Modern Fe‐Si oxyhydroxide deposits occur in global marine hydrothermal vent sites. Despite their role as biogenic substrates and potential ore resources, much remains unknown about their formation processes. Here, we apply analyses of major and trace elements as well as Sr‐Nd‐Pb‐Fe isotopes combined with 238U‐230Th dating to Fe‐Si oxyhydroxides obtained from several hydrothermal fields along the Southwest Indian Ridge. These mineralized oxyhydroxides primarily consist of poorly crystalline two‐line ferrihydrite and amorphous opal‐A, with lesser amounts of nontronite and birnessite. The ubiquitous and characteristic Fe‐rich ultrastructures in the oxyhydroxides directly indicate microbial activity. The 238U‐230Th dating constrains their crystallization ages from ca. 11,873 to 384 years old. The seawater‐like 87Sr/86Sr and varying 143Nd/144Nd ratios underline a high proportion of seawater mixed with hydrothermal fluids. The radiogenic Pb isotopic patterns suggest a primary derivation of Pb leached from substrate basalts and to a lesser extent Pb from seawater. Stable iron isotopic compositions for different oxyhydroxides display a remarkable range between −1.47 and 0.82‰, which were interpreted as reflecting the fractionation processes during the formation of the deposits under evolving depositional redox conditions. The partial oxidation of Fe(II) and the subsurface removal of isotopically heavy Fe oxyhydroxides are suggested to play a vital role in shifting the Fe isotopic signature toward more negative values. Given that these Fe‐Si oxyhydroxide deposits exhibit features similar to certain ancient iron formations (IFs), Fe isotope systematics of these deposits may hold significant potential for fingerprinting the biological Fe oxidation processes that drove IF deposition on early Earth.

ABSTRACT The iron-oxidizing Gallionellaceae drive a wide variety of biogeochemical cycles through their metabolisms and biominerals. To better understand the environmental impacts of Gallionellaceae, we need to improve our knowledge of their diversity and metabolisms, especially any novel iron oxidation mechanisms. Here, we used a pangenomic analysis of 103 genomes to resolve Gallionellaceae phylogeny and explore their genomic potential. Using a concatenated ribosomal protein tree and key gene patterns, we determined Gallionellaceae has four genera, divided into two groups: iron-oxidizing bacteria (FeOB) Gallionella, Sideroxydans, and Ferriphaselus with iron oxidation genes (cyc2, mtoA) and nitrite-oxidizing bacteria (NOB) Candidatus Nitrotoga with the nitrite oxidase gene nxr. The FeOB and NOB have similar electron transport chains, including genes for reverse electron transport and carbon fixation. Auxiliary energy metabolisms, including S oxidation, denitrification, and organotrophy, were scattered throughout the FeOB. Within FeOB, we found genes that may represent adaptations for iron oxidation, including a variety of extracellular electron uptake mechanisms. FeOB genomes encoded more predicted c-type cytochromes than NOB genomes, notably more multiheme c-type cytochromes (MHCs) with >10 CXXCH motifs. These include homologs of several predicted outer membrane porin-MHC complexes, including MtoAB and Uet. MHCs efficiently conduct electrons across longer distances and function across a wide range of redox potentials that overlap with mineral redox potentials, which can expand the range of usable iron substrates. Overall, the results of pangenome analyses suggest that the Gallionellaceae genera Gallionella, Sideroxydans, and Ferriphaselus have acquired a range of adaptations to succeed in various environments but are primarily iron oxidizers.IMPORTANCENeutrophilic iron-oxidizing bacteria (FeOB) produce copious iron (oxyhydr)oxides that can profoundly influence biogeochemical cycles, notably the fate of carbon and many metals. To fully understand environmental microbial iron oxidation, we need a thorough accounting of iron oxidation mechanisms. In this study, we show the Gallionellaceae FeOB genomes encode both characterized iron oxidases as well as uncharacterized multiheme cytochromes (MHCs). MHCs are predicted to transfer electrons from extracellular substrates and likely confer metabolic capabilities that help Gallionellaceae occupy a range of different iron- and mineral-rich niches. Gallionellaceae appear to specialize in iron oxidation, so it would be advantageous for them to have multiple mechanisms to oxidize various forms of iron, given the many iron minerals on Earth, as well as the physiological and kinetic challenges faced by FeOB. The multiple iron/mineral oxidation mechanisms may help drive the widespread ecological success of Gallionellaceae.

Iron (Fe) toxicity in rice is one of the serious problems in some paddy fields in West African areas. Microbial community structures involved in the redox cycle of Fe have not been revealed in the Fe-toxic paddy fields. The present study investigated the bacterial community structure and the abundance of Gallionellaceae, Geobacteraceae, and Anaeromyxobacteraceae, as the representative indicator bacteria of Fe oxidizers and reducers, in the bulk and rhizosphere soils and rice roots of a Fe-toxic paddy field in Burkina Faso (BF)in 2017-2019. Thosein a paddy field in Anjo, Japan (AN) were also analyzed for comparison. The amplicon sequencing analysis revealed that the BF rhizosphere soil was characterized by typical anaerobic bacterial groups like Firmicutes and Deltaproteobacteria, including several potential Fe reducers. The relative abundance of Gallionellaceae, lithotrophic Fe oxidizers, in the BF rice roots was significantly lower than that in the AN rice roots. Quantitative PCR analysis showed that the ratios of Gallionellaceae to Geobacteraceae and to Anaeromyxobacteraceae were higher in the rice roots than in the soils irrespective of the fields. However, the ratios of Gallionellaceae to Geobacteraceae were lower in the BF soils and roots than in the AN soils and roots. The ratios of Gallionellaceae to Anaeromyxobacteraceae in the BF soils were also lower than those in the AN soils. These findings indicated the relative predominance of Geobacter- and Anaeromyxobacter-related Fe reducers over Gallionellaceae-related Fe oxidizers in the rice rhizosphere of the BF field, corresponding well to the circumstances of Fe-toxic soil: higher Fe(II) amounts in the soil. Since Fe(II)-oxidizing activity at rice roots is an important factor as a primary defense system against Fe(II) in the soil solution, the ratios of Gallionellaceae to Geobacteraceae and to Anaeromyxobacteraceae may serve as an indicator of potential Fe(II)-oxidizing activity of rice rhizosphere. Further studies focusing on the activity of Fe oxidizers and Fe reducers at rice roots under effective cultivation practices and in various types of Fe-toxic paddy fields will help to promote a better understanding of the Fe-toxic soil circumstances and to establish sustainable rice cultivation in the Fetoxic soils. [ABSTRACT FROM AUTHOR]

The release of endogenous phosphorus (P) from sediments is the main cause of lake eutrophication, even after the successful control of exogenous P. Among others, the release of iron-bound P is a major source of endogenous P, and it is necessary to reduce the P concentration by enhancing iron–phosphorus binding. Iron (Fe)-modified biochar adsorption is an effective and widely used method for fixing P in sediments. In this paper, the modification method, mechanism, and application effect of Fe-modified biochar are reviewed. It is found that most of the modification methods are realized through a physicochemical pathway. Therefore, the prospect of biochar modification through a biological pathway is presented. In particular, the possible application of iron-oxidizing bacteria (IOB) for promoting iron–phosphorus binding and biochar modifications is discussed. The potential effects of biochar additions on microbial communities in water and sediments are also discussed. In the future research, emphasis should be placed on the adsorption mechanism and effect analysis in simulated polluted environments before large-scale use, to ensure the economic practicability and sustainability of Fe-modified biochar applications. [ABSTRACT FROM AUTHOR]

Microorganisms are acknowledged to be responsible for corrosion failures worldwide; however, some recent studies have indicated that in some environments, bacteria activities can decelerate the corrosion rate of metals. This research investigated the microbial corrosion behavior of welded stainless steel 316L by sulfate-reducing, sulfur-oxidizing, and iron-oxidizing bacteria. The corrosion evaluations were performed using potentiodynamic and cyclic polarization tests. Furthermore, the scanning electron microscope and energy-dispersive spectroscopy analysis were executed after 90 days of bacteria exposure to determine the biofilm morphology changes over time. The results suggested that while the base metal (unwelded area) was unaffected by SRB, a vast increase in corrosion rate was observed in HAZ and welded area. On the other hand, analyzing the SEM morphology, EDS results, electrochemical tests and the corrosion rate obtained from Tafel extrapolation showed that SOB and IOB reduced the corrosion rate of the alloy and acted as inhibitors [ABSTRACT FROM AUTHOR]

Extracellular polymeric substances (EPS) are an important medium for communication and material exchange between iron-oxidizing bacteria and the external environment and could induce the iron (oxyhydr) oxides production which reduced arsenic (As) availability. The main component of EPS secreted by iron-oxidizing bacteria (Ochrobactrum EEELCW01) was composed of polysaccharides (150.76-165.33 mg/g DW) followed by considerably smaller amounts of proteins (12.98–16.12 mg/g DW). Low concentrations of As (100 or 500 µmol/L) promoted the amount of EPS secretion. FTIR results showed that EPS was composed of polysaccharides, proteins, and a miniscule amount of nucleic acids. The functional groups including -COOH, -OH, -NH, -C=O, and -C-O played an important role in the adsorption of As. XPS results showed that As was bound to EPS in the form of As3+. With increasing As concentration, the proportion of As3+ adsorbed on EPS increased. Ferrihydrite with a weak crystalline state was only produced in the system at 6 hr during the mineralization process of Ochrobactrum sp. At day 8, the minerals were composed of goethite, galena, and siderite. With the increasing mineralization time, the main mineral phases were transformed from weakly crystalline hydrous iron ore into higher crystallinity siderite (FeCO 3) or goethite (α-FeOOH), and the specific surface area and active sites of minerals were reduced. It can be seen from the distribution of As elements that As is preferentially adsorbed on the edges of iron minerals. This study is potential to understand the biomineralization mechanism of iron-oxidizing bacteria and As remediation in the environment. [ABSTRACT FROM AUTHOR]

Groundwater is one of the alternatives to surface water that can be used for drinking water; however, it normally exists with high iron and manganese content. In this study, a column study was conducted to observe the elimination of iron (Fe) and manganese (Mn) in the groundwater under different retention times by using zeolite immobilized with iron‐oxidizing bacteria (IOB). Rossellomorea sp., representing an IOB, was found from the isolation process and was further cultured in the laboratory for immobilization into the natural zeolite as replacement materials for the sand filter. When the zeolite assisted with the Rossellomorea sp. was used, the elimination of Fe and Mn were 99.34% and 88.92%, respectively, compared to the removal of Fe and Mn, which were 93.62% and 93.73%, respectively, for media without immobilization. The presence of Rossellomorea sp. enhances the Fe oxidation, resulting in high removal of Fe. The Thomas and Yoon–Nelson models were performed in both raw zeolite and zeolite with IOB. The total coliform (most probable number [MPN]) increased from 70.8 to 307.6 MPN/100 mL because of the Rossellomorea sp. present that promotes the growth of coliform bacteria. In conclusion, the immobilization of zeolite with IOB is a potential technique to extract the Fe and Mn in the groundwater. Practitioner Points: Zeolite incorporated with Rossellomorea sp. has higher removal performance of Fe, whereas the removal of Mn reduced compared to the raw zeolite.The presence of Rossellomorea sp. enhances the oxidation of ferrous iron and improves the removal of Fe in the groundwater because the ferric iron is the priority ion to be exchanged.The removal of UV254 increase when Rossellomorea sp. present in the zeolite because the Rossellomorea sp. consume the natural organic matter as carbon source. [ABSTRACT FROM AUTHOR]

Abstract A public trout hatchery in Colorado recorded repeat episodes of morbidity and mortality in early life stages of Rainbow Trout (Oncorhynchus mykiss) stocks. The water source for the affected tanks is a groundwater well with a pH of 6.3 and a ferrous iron concentration of 120 µg/L. Iron oxidizing bacteria (FeOB) were suspected as the underlying cause due to insoluble red particulate matter (iron oxide precipitate) in the water, and the presence of thick red slime (biofilm) that coated tanks and pipes of the facility and adhered to gills, opercula, and fins of fry. On necropsy, gill and fin clippings from moribund fish had mats of adherent red‐orange material. Histopathology revealed severe diffuse proliferative branchitis. There was abundant debris including granular to sheath‐like and stalk‐like pigmented material within the oral and branchial chambers, intimately associated with gill filaments. A Gram preparation demonstrated florid Gram‐negative bacteria within this debris. A Perls’ Prussian blue preparation revealed colocalization of abundant iron. Bacteria were identified morphologically to be of the iron oxidizing bacterial genera Gallionella and Leptothrix. This is the first known report of disease in fish associated with iron‐oxidizing bacteria.

Iron-oxidizing bacteria played an important role in the treatment of Sb-containing wastewater. In this study, effect of different iron sources on Sb(III) removal ability by isolated iron-oxidizing bacteria (named as IOB-L) was conducted systemically in batch experiment. Moreover, ferrous lactate and zero-valent iron were chosen as iron sources for IOB-L. The results showed that after inoculation of 2% volume of IOB-L, Sb(III) concentration in water decreased from initial 18 mg/L to 4.1 mg/L at optimal pH of 7.0. There was no reaction between Sb(III) and ferrous lactate, whereas corrosion product of iron can adsorb a certain amount of Sb. When active IOB-L cultivated in ferrous lactate, a better removal rate of Sb(III) can be reached with a longer stagnate phase for bacteria. However, Sb(III) removal ability of IOB-L using zero-valent iron as iron source was lower. SEM-EDS, FTIR, and XPS analysis further indicated that ferrous lactate was oxidized by IOB-L and precipitated as biogenic iron oxides which had strong adsorption ability towards Sb(III), whereas zero-valent iron was not a good iron source. HIGHLIGHTS IOB-L biomass had a little adsorption ability towards Sb(III).; Biogenic iron oxides was generated and played an important role in Sb removal from water.; Although ferrous lactate could be used as iron source for IOB-L, a longer adaptation period was necessary.; Ferrous ions from zero-valent iron corrosion was hard to be oxidized directly by IOB-L.; Oxidation of Sb(III) by biogenic iron oxides was not observed.;

At deep-sea hydrothermal vents, sulfur oxidation and iron oxidation are of the highest importance to microbial metabolisms, which are thought to contribute mainly in chemolithoautotrophic groups. In this study, 17 mixotrophic neutrophilic thiosulfate- and iron-oxidizing bacteria were isolated from hydrothermal fields on the Carlsberg Ridge in the Indian Ocean, nine to the γ-proteobacteria (Halomonas (4), Pseudomonas (2), Marinobacter (2), and Rheinheimera (1)), seven to the α-proteobacteria (Thalassospira, Qipengyuania, Salipiger, Seohaeicola, Martelella, Citromicrobium, and Aurantimonas), and one to the Actinobacteria (Agromyces), as determined by their 16S rRNA and genome sequences. The physiological characterization of these isolates revealed wide versatility in electron donors (Fe(II) and Mn(II), or thiosulfate) and a variety of lifestyles as lithotrophic or heterotrophic, microaerobic, or anaerobic. As a representative strain, Pseudomonas sp. IOP_13 showed its autotrophic gowth from 105 cells/ml to 107 cells/ml;carbon dioxide fixation capacity with the δ13CVPDB in the biomass increased from −27.42‰ to 3460.06‰; the thiosulfate-oxidizing ability with produced SO42− increased from 60 mg/L to 287 mg/L; and the iron-oxidizing ability with Fe(II) decreased from 10 mM to 5.2 mM. In addition, iron-oxide crust formed outside the cells. Gene coding for energy metabolism involved in possible iron, manganese, and sulfur oxidation, and denitrification was identified by their genome analysis. This study sheds light on the function of the mixotrophic microbial community in the iron/manganese/sulfur cycles and the carbon fixation of the hydrothermal fields. [ABSTRACT FROM AUTHOR]

As the current depletion of fossil resources and global warming emerging, it is expected to establish sustainable production processes that circulate and utilize the resources available on the earth’s surface. In particular, there are expectations for the production of a value-added chemical from atmospheric carbon dioxide (CO2), however it is necessary to require a large amount of reducing power and energy. In recent studies, electrochemically active bacteria (EAB), microbes can be able to interact with a conductive material via extracellular electron transfer pathway, receive attention from application to bioelectrochemical systems such as microbial electrosynthesis system (MES). Since it is estimated that a value-added chemical production process combing EAB and solar cells can achieve an energy conversion efficiency higher than that of photosynthesis. In this report, we first describe EAB and subsequently summarize one of the attractive microbes, autotrophic acidophile iron-oxidizing bacteria and laboratory studies that have been conducted to towards development for a sustainable bioprocess using MES. We also discuss possibilities of MES biotechnology to utilize that facilitate the development of eco-friendly future industry. [ABSTRACT FROM AUTHOR]

The bioleaching process is carried out by aerobic acidophilic iron-oxidizing bacteria that are mainly mesophilic or moderately thermophilic. However, many mining sites are located in areas where the mean temperature is lower than the optimal growth temperature of these microorganisms. In this work, we report the obtaining and characterization of two psychrotolerant bioleaching bacterial strains from low-temperature sites that included an abandoned mine site in Chilean Patagonia (PG05) and an acid rock drainage in Marian Cove, King George Island in Antarctic (MC2.2). The PG05 and MC2.2 strains showed significant iron-oxidation activity and grew optimally at 20 °C. Genome sequence analyses showed chromosomes of 2.76 and 2.84 Mbp for PG05 and MC2.2, respectively, and an average nucleotide identity estimation indicated that both strains clustered with the acidophilic iron-oxidizing bacterium Acidithiobacillus ferrooxidans. The Patagonian PG05 strain had a high content of genes coding for tolerance to metals such as lead, zinc, and copper. Concordantly, electron microscopy revealed the intracellular presence of polyphosphate-like granules, likely involved in tolerance to metals and other stress conditions. The Antarctic MC2.2 strain showed a high dosage of genes for mercury resistance and low temperature adaptation. This report of cold-adapted cultures of the At. ferrooxidans species opens novel perspectives to satisfy the current challenges of the metal bioleaching industry. [ABSTRACT FROM AUTHOR]

Tailings ponds Slovinky and Markušovce (Slovakia) belong to the group of high-risk areas threatening human health and the environment due to the high concentrations of potentially toxic elements. The aim of this study was to identify iron bacteria living in these extreme environments and to assess the impact of selected physicochemical parameters of drainage water, flowing from tailings ponds, on the dynamics of their population. The material deposited on the Slovinky and Markušovce tailings pond showed a circumneutral pH. The values of electrical conductivity and total dissolved solids were significantly higher in drainage water in Slovinky compared to Markušovce. The concentration of total iron was notably higher in drainage water in Markušovce than in Slovinky. Direct microscopic observations showed the presence of iron-oxidizing bacteria as Gallionella spp. and Leptothix spp. exhibiting significant seasonal changes in their prevalence. The differences in the environmental characteristics of drainage waters did not affect the dynamics of iron-oxidizing bacteria populations, but cultivable heterotrophic bacterial community showed significantly lower abundance in Markušovce drainage water. The findings contribute to the understanding of bacterial diversity in neutral mine drainage waters and demonstrate an important role of environmental factors in shaping the microbial population in mine environments. [ABSTRACT FROM AUTHOR]

Corrosion in drinking water distribution systems (DWDSs) may lead to pipe failures and water quality deterioration; biocorrosion is the most common type. Chlorine disinfectants are widely used in DWDSs to inhibit microorganism growth, but these also promote electrochemical corrosion to a certain extent. This study explored the independent and synergistic effects of chlorine and microorganisms on pipeline corrosion. Sodium hypochlorite (NaOCl) at different concentrations (0, 0.25, 0.50, and 0.75 mg/L) and iron-oxidizing bacteria (IOB) were added to the reaction system, and a biofilm annular reactor (BAR) was employed to simulate operational water supply pipes and explain the composite effects. The degree of corrosion became severe with increasing NaOCl dosage. IOB accelerated the corrosion rate at an early stage, after which the reaction system gradually stabilized. When NaOCl and IOB existed together in the BAR, both synergistic and antagonistic effects occurred during the corrosion process. The AOC content increased due to the addition of NaOCl, which is conducive to bacterial regrowth. However, biofilm on cast iron coupons was greatly influenced by the disinfectant, leading to a decrease in microbial biomass over time. More research is needed to provide guidelines for pipeline corrosion control. [ABSTRACT FROM AUTHOR]

The bioleaching process is carried out by aerobic acidophilic iron-oxidizing bacteria that are mainly mesophilic or moderately thermophilic. However, many mining sites are located in areas where the mean temperature is lower than the optimal growth temperature of these microorganisms. In this work, we report the obtaining and characterization of two psychrotolerant bioleaching bacterial strains from low-temperature sites that included an abandoned mine site in Chilean Patagonia (PG05) and an acid rock drainage in Marian Cove, King George Island in Antarctic (MC2.2). The PG05 and MC2.2 strains showed significant iron-oxidation activity and grew optimally at 20°C. Genome sequence analyses showed chromosomes of 2.76 and 2.84 Mbp for PG05 and MC2.2, respectively, and an average nucleotide identity estimation indicated that both strains clustered with the acidophilic iron-oxidizing bacterium Acidithiobacillus ferrooxidans. The Patagonian PG05 strain had a high content of genes coding for tolerance to metals such as lead, zinc, and copper. Concordantly, electron microscopy revealed the intracellular presence of polyphosphate-like granules, likely involved in tolerance to metals and other stress conditions. The Antarctic MC2.2 strain showed a high dosage of genes for mercury resistance and low temperature adaptation. This report of cold-adapted cultures of the At. ferrooxidans species opens novel perspectives to satisfy the current challenges of the metal bioleaching industry.

The objective of this study was to remove heavy metals from metallurgical industry sludge by bioleaching alone and bioleaching combined with persulfate (PDS). The results showed that the removal of Cu, Zn, Pb, and Mn reached 70%, 83.8%, 25.2%, and 76.9% by bioleaching alone after 18 days, respectively. The experiment of bioleaching combined with PDS was carried out in which the optimal additive dosage of K2S2O8, 8 g/L, was added to bioleaching after 6 d. After 1 h, the removal of four heavy metals reached 75.1, 84.3, 36.7, and 81.6%, respectively. Compared with bioleaching alone, although the increase in removal efficiency was only slightly increased, the treatment cycle was distinctly shortened from 18 to 6 days + 1 h. The scanning electron microscopy (SEM) results showed that the surface morphology of the sludge was changed significantly by the combined treatment. The content of heavy metals was significantly reduced after bioleaching combined with PDS by energy dispersive X-ray spectroscopy (EDX). Through electron paramagnetic resonance (EPR) and free radical quenching experiments, it was indicated that sulfate radicals (SO 4 ∙ -) plays a leading role in the combined treatment. The treated sludge mainly existed in a stable form, and the bioavailability was reduced with European Community Bureau of Reference (BCR) morphology analysis. This study proved that the combination of bioleaching and PDS could not only shorten the treatment cycle but also further improve the efficiency of heavy metal leaching. It provides a novel treatment method for the removal of heavy metals from metallurgical industry sludge. [ABSTRACT FROM AUTHOR]

Iron-oxidizing bacteria (FeOB) could oxidize Fe(II) and mediate biomineralization, which provides the possibility for its potential application in arsenic (As) remediation. In the present study, a strain named Ochrobactrum EEELCW01 isolated previously, was inoculated into paddy soils to investigate the effect of FeOB inoculation on the As migration and transformation in paddy soils. The results showed that inoculation of Ochrobactrum sp. increased the proportion of As in iron-aluminum oxide binding fraction, which reduced the As bioavailability in paddy soils and effectively reduced the As accumulation in rice tissues. Moreover, the inoculation of iron oxidizing bacteria increased the abundance of KD4-96, Pedosphaeraceae and other bacteria in the soils, which could reduce the As toxicity in the soil through biotransformation. The abundance of metabolites such as carnosine, MG (0:0/14:0/0:0) and pantetheine 4’-phosphate increased in rhizosphere soils inoculated with FeOB, which indicated that the defense ability of soil-microorganism-plant system against peroxidation caused by As was enhanced. This study proved that FeOB have the potential application in remediation of As pollution in paddy soil, FeOB promotes the formation of iron oxide in paddy soil, and then adsorbed and coprecipitated with arsenic. On the other hand, the inoculation of Ochrobactrum sp. change soil microbial community structure and soil metabolism, increase the abundance of FeOB in soil, promote the biotransformation process of As in soil, and enhance the resistance of soil to peroxide pollution (As pollution).

Iron-oxidizing bacteria (FeOB) could oxidize Fe(II) and mediate biomineralization, which provides the possibility for its potential application in arsenic (As) remediation. In the present study, a strain named Ochrobactrum EEELCW01 isolated previously, was inoculated into paddy soils to investigate the effect of FeOB inoculation on the As migration and transformation in paddy soils. The results showed that inoculation of Ochrobactrum sp. increased the proportion of As in iron-aluminum oxide binding fraction, which reduced the As bioavailability in paddy soils and effectively reduced the As accumulation in rice tissues. Moreover, the inoculation of iron oxidizing bacteria increased the abundance of KD4-96, Pedosphaeraceae and other bacteria in the soils, which could reduce the As toxicity in the soil through biotransformation. The abundance of metabolites such as carnosine, MG (0:0/14:0/0:0) and pantetheine 4'-phosphate increased in rhizosphere soils inoculated with FeOB, which indicated that the defense ability of soil-microorganism-plant system against peroxidation caused by As was enhanced. This study proved that FeOB have the potential application in remediation of As pollution in paddy soil, FeOB promotes the formation of iron oxide in paddy soil, and then adsorbed and coprecipitated with arsenic. On the other hand, the inoculation of Ochrobactrum sp. change soil microbial community structure and soil metabolism, increase the abundance of FeOB in soil, promote the biotransformation process of As in soil, and enhance the resistance of soil to peroxide pollution (As pollution). [ABSTRACT FROM AUTHOR]

Microbiologically influenced corrosion (MIC) and biofouling in the marine environment are two main mechanisms of marine corrosion. The present review summarizes the results of recent studies and demonstrates that both MIC and marine biofouling are closely related to biofilms on the surface of materials formed by marine microorganisms and their metabolites. As a result, to prevent the emergence of MIC and biofouling, it is important to control microorganisms in biofilms or to prevent adhesion and formation of biofilms. The present review describes research approaches involving the use of new materials and innovative technologies in combination with traditional chemicals to achieve longer-lasting effects with the least environmental pollution due to the emerging synergistic effect. [ABSTRACT FROM AUTHOR]

At deep-sea hydrothermal vents, sulfur oxidation and iron oxidation are of the highest importance to microbial metabolisms, which are thought to contribute mainly in chemolithoautotrophic groups. In this study, 17 mixotrophic neutrophilic thiosulfate- and iron-oxidizing bacteria were isolated from hydrothermal fields on the Carlsberg Ridge in the Indian Ocean, nine to the γ-proteobacteria (Halomonas (4), Pseudomonas (2), Marinobacter (2), and Rheinheimera (1)), seven to the α-proteobacteria (Thalassospira, Qipengyuania, Salipiger, Seohaeicola, Martelella, Citromicrobium, and Aurantimonas), and one to the Actinobacteria (Agromyces), as determined by their 16S rRNA and genome sequences. The physiological characterization of these isolates revealed wide versatility in electron donors (Fe(II) and Mn(II), or thiosulfate) and a variety of lifestyles as lithotrophic or heterotrophic, microaerobic, or anaerobic. As a representative strain, Pseudomonas sp. IOP_13 showed its autotrophic gowth from 105 cells/ml to 107 cells/ml;carbon dioxide fixation capacity with the δ13CVPDB in the biomass increased from −27.42‰ to 3460.06‰; the thiosulfate-oxidizing ability with produced SO42− increased from 60 mg/L to 287 mg/L; and the iron-oxidizing ability with Fe(II) decreased from 10 mM to 5.2 mM. In addition, iron-oxide crust formed outside the cells. Gene coding for energy metabolism involved in possible iron, manganese, and sulfur oxidation, and denitrification was identified by their genome analysis. This study sheds light on the function of the mixotrophic microbial community in the iron/manganese/sulfur cycles and the carbon fixation of the hydrothermal fields.

Iron is one of the Earth's most abundant elements and is required for essentially all forms of life. Yet, iron's reactivity with oxygen and poor solubility in its oxidized form (Fe 3+ ) mean that it is often a limiting nutrient in oxic, near-neutral pH environments like Earth's ocean. In addition to being a vital nutrient, there is a diversity of aerobic organisms that oxidize ferrous iron (Fe 2+ ) to harness energy for growth and biosynthesis. Accordingly, these organisms rely on access to co-existing Fe 2+ and O 2 to survive. It is generally presumed that such aerobic iron-oxidizing bacteria (FeOB) are relegated to low-oxygen regimes where abiotic iron oxidation rates are slower, yet some FeOB live in higher oxygen environments where they cannot rely on lower oxygen concentrations to overcome abiotic competition. We hypothesized that FeOB chemically alter their environment to limit abiotic interactions between Fe 2+ and O 2 . To test this, we incubated the secreted metabolites (collectively known as the exometabolome) of the deep-sea iron- and hydrogen-oxidizing bacterium Ghiorsea bivora TAG-1 with ferrous iron and oxygen. We found that this FeOB's iron-oxidizing exometabolome markedly impedes the abiotic oxidation of ferrous iron, increasing the half-life of Fe 2+ 100-fold from ∼3 to ∼335 days in the presence of O 2 , while the exometabolome of TAG-1 grown on hydrogen had no effect. Moreover, the few precipitates that formed in the presence of TAG-1's iron-oxidizing exometabolome were poorly crystalline, compared with the abundant iron particles that mineralized in the absence of abiotic controls. We offer an initial exploration of TAG-1's iron-oxidizing exometabolome and discuss potential key contributors to this process. Overall, our findings demonstrate that the exometabolome as a whole leads to a sustained accumulation of ferrous iron in the presence of oxygen, consequently altering the redox equilibrium. This previously unknown adaptation likely enables these microorganisms to persist in an iron-oxidizing and iron-precipitating world and could have impacts on the bioavailability of iron to FeOB and other life in iron-limiting environments., (© The Author(s) 2023. Published by Oxford University Press on behalf of National Academy of Sciences.)

The laws of cathodic polarization on bacterial growth, biofilm formation and effects on the corrosion process of X65 steel were investigated when sulfate-reducing bacteria (SRB) and iron-oxidizing bacteria (IOB) are mixed using surface analysis and electrochemical measurements. Results indicate that insufficient potentials could not inhibit the localized corrosion, but increased the metabolic activities of bacteria. Effective protection could be achieved when the potential was negatively shifted to − 1050 mV vs. SCE. The effects of cathodic polarization on the precess of biofilms formation were also investigated. The − 1050 mV vs. SCE polarization potential could inhibit the biological activity of sessile bacteria, destroy the biofilm structure and inhibit the corrosion process induced by each biofilm. • Electrostatic repulsion from strong polarization inhibited bacterial adhesion and biofilm formation in SRB and IOB mixed bacterial system. • Generation of OH- and deposition of Ca2+ further inhibiting bacterial activity and adhesion. • Strong polarization can lead to structural disruption of mature biofilms. [ABSTRACT FROM AUTHOR]

• Iron precipitates clog groundwater heat pump systems in Melhus, Norway. • The groundwater quality is anoxic and saline with high iron concentrations. • Both iron oxide and iron sulfide incrustations are identified. • Microbes seem to catalyze iron oxidation. • Cost-effective well rehabilitations require thorough clogging investigations. Clogging by incrustations of nine groundwater heat pump (GWHP) systems in Melhus, Norway have been investigated by field and laboratory methods for water quality and incrustation composition. Iron oxides incrust systems extracting relatively shallow, low-saline groundwater, while iron sulfides are associated with deeper, more saline groundwater. Hydrochemical conditions in iron oxide clogged GWHP systems are favorable for the growth of iron-oxidizing bacteria. Also, sediment deposits clog the well systems. The variety of incrustation problems detected in Melhus emphasizes that clogging must be expected and dealt with, instead of solely attempted avoided through system design or re-location. [Display omitted] [ABSTRACT FROM AUTHOR]

Nano zero-valent iron (nZVI) is used for soil remediation; however, the impact of nZVI on soil solid iron phases and its interactions with soil microorganisms in relation to the fate of Cd in soil remains unclear. In the current study, we investigated the mechanisms underlying the change in mobility of Cd in exogenous Cd-contaminated soil with nZVI and γ radiation treatments. The results showed that nZVI treatment decreased Cd availability but also increased the soil pH and dissolved Mn and poorly crystalline Fe contents. However, the increased poorly crystalline Fe(II) levels contributed to a reduction in Cd availability in soils treated with nZVI by immobilizing Cd associated with Fe oxides, rather than by increasing pH or Mn oxide levels. Moreover, Cd stabilization efficiency was higher in γ-irradiated soils than in non-irradiated soils regardless of the Cd level, with noticeable differences in bacterial community composition between the non-irradiated and irradiated soils. The genera Bacillus , Pullulanibacillus , and Alicyclobacillus are important in the redox of poorly crystalline Fe(II)-containing minerals in non-irradiated soil. This research provides a new method for further improving the Cd stabilization efficiency of nZVI in combination with microbial iron oxidization inhibitors. [Display omitted] • Soil Cd was stabilized by nZVI-induced poorly crystalline Fe(II)-containing minerals. • Soil bacteria play a key role in the transformation of the nZVI oxidation products. • Presence of bacteria in the soil decreased the Cd stabilization efficiency of nZVI. • Added 0.1% nZVI was oxidized almost completely within 7 days. [ABSTRACT FROM AUTHOR]