Iron-oxidizing Bacteria Research Articles

Remediation of arsenic- and nitrate-contaminated groundwater through iron-dependent autotrophic denitrifying culture

Groundwater contamination with arsenic and nitrate poses a pressing concern for the safety of local communities. Bioremediation, utilizing Fe(II)-oxidizing nitrate reducing bacteria, shows promise as a solution to this problem. However, the relatively weak environmental adaptability of a single bacterium hampers practical application. Therefore, this study explored the feasibility and characteristics of a mixed iron-dependent autotrophic denitrifying (IDAD) culture for effectively removing arsenic and nitrate from synthetic groundwater. The IDAD biosystem exhibited stable performace and arsenic resistance, even at a high As(III) concentration of 800 μg/L. Although the nitrogen removal efficiency of the IDAD biosystem decreased from 71.4% to 64.7% in this case, the arsenic concentration in the effluent remained below the standard (10 μg/L) set by WHO. The crystallinity of the lepidocrocite produced by the IDAD culture decreased with increasing arsenic concentration, but the relative abundance of the key iron-oxidizing bacteria norank_f_Gallionellaceae in the culture showed an opposite trend. Metagenomic analysis revealed that the IDAD culture possess arsenic detoxification pathways, including redox, methylation, and efflux of arsenic, which enable it to mitigate the adverse impact of arsenic stress. This study provides theoretical understanding and technical support for the remediation of arsenic and nitrate-contaminated groundwater using the IDAD culture.

Estuarine mangrove niches select cultivable heterotrophic diazotrophs with diverse metabolic potentials-a prospective cross-dialog for functional diazotrophy.

Biological nitrogen fixation (BNF), an unparalleled metabolic novelty among living microorganisms on earth, globally contributes ~88-101 Tg N year-1 to natural ecosystems, ~56% sourced from symbiotic BNF while ~22-45% derived from free-living nitrogen fixers (FLNF). The success of symbiotic BNF is largely dependent on its interaction with host-plant, however ubiquitous environmental heterotrophic FLNFs face many limitations in their immediate ecological niches to sustain unhindered BNF. The autotrophic FLNFs like cyanobacteria and oceanic heterotrophic diazotrophs have been well studied about their contrivances acclimated/adapted by these organisms to outwit the environmental constraints for functional diazotrophy. However, FLNF heterotrophs face more adversity in executing BNF under stressful estuarine/marine/aquatic habitats. In this study a large-scale cultivation-dependent investigation was accomplished with 190 NCBI accessioned and 45 non-accessioned heterotrophic FLNF cultivable bacterial isolates (total 235) from halophilic estuarine intertidal mangrove niches of Indian Sundarbans, a Ramsar site and UNESCO proclaimed World Heritage Site. Assuming ~1% culturability of the microbial community, the respective niches were also studied for representing actual bacterial diversity via cultivation-independent next-generation sequencing of V3-V4 rRNA regions. Both the studies revealed a higher abundance of culturable Gammaproteobacteria followed by Firmicutes, the majority of 235 FLNFs studied belonging to these two classes. The FLNFs displayed comparable selection potential in media for free nitrogen fixers and iron-oxidizing bacteria, linking diazotrophy with iron oxidation, siderophore production, phosphorus solubilization, phosphorus uptake and accumulation as well as denitrification. This observation validated the hypothesis that under extreme estuarine mangrove niches, diazotrophs are naturally selected as a specialized multidimensional entity, to expedite BNF and survive. Earlier metagenome data from mangrove niches demonstrated a microbial metabolic coupling among C, N, P, S, and Fe cycling in mangrove sediments, as an adaptive trait, evident with the co-abundant respective functional genes, which corroborates our findings in cultivation mode for multiple interrelated metabolic potential facilitating BNF in a challenging intertidal mangrove environment.

Complete gold extraction and recovery from double refractory gold ores by thiourea after bio-oxidation

Cyanidation, a conventional process to extract gold from gold ores, has been used for over 130 years in industrial mining because of the high efficiency and rate of formation of Au(CN)2− and the high recovery efficiency by adsorption of Au(CN)2− on activated carbon. However, carbonaceous refractory gold ores are not targeted because Au(CN)2− is easily adsorbed on carbonaceous matter in the ores, resulting in high recovery loss. In this study, the flotation concentrates of a carbonaceous refractory gold ores was subjected to biooxidation at 45 °C using a mixed culture containing iron-oxidizing and sulfur-oxidizing bacteria, followed by gold extraction using thiourea under strongly acidic conditions. The gold extraction efficiency reached ∼100% in 12 h without re-adsorption. Finally, the quantitative recovery of the Au(CS(NH2)2)2+ complex was confirmed by adsorption on strongly cationic exchange resin. Biooxidation reduced the amount of Fe-containing metal sulfides, which minimized the decomposition of thiourea, and the Au(CS(NH2)2)2+ complex had a low affinity toward carbonaceous matter, different to Au(CN)2−. Since the process described in this study does not require roasting to remove carbonaceous materials in pretreatment and does not use cyanide for gold extraction, it is environmentally friendly and should be considered for practical applications in carbonaceous gold ore-producing mines.

Microbial community response to hydrocarbon exposure in iron oxide mats: an environmental study.

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.

Research on the Corrosion Inhibition Behavior and Mechanism of 1-Hydroxy-1,1-ethyledine Disodium Phosphonate under an Iron Bacteria System

Regenerated water serves as a supplementary source for circulating cooling water systems, but it often fosters microbial growth within pipelines. Given its widespread use as a corrosion inhibitor, understanding HEDP’s efficacy in microbial environments and its impact on microorganisms is imperative. This study established an iron bacterial system by isolating and enriching iron bacteria. Through a comprehensive approach incorporating corrosion weight loss analysis, XPS analysis, SEM electron microscopy, as well as microbial and electrochemical testing, the corrosion inhibition behavior and mechanism of HEDP within the iron bacterial system were investigated. The findings reveal that within the iron bacterial system, HEDP achieves a corrosion inhibition rate of 76% following four distinct stages—weakening, strengthening, stabilizing, and further strengthening—underscoring its robust corrosion inhibition capability. Moreover, HEDP enhances the density of biofilms and elevates the activation energy of carbon steel interfaces. It alternates with oxygen to continuously suppress the activity of IRB while gradually inhibiting the activity of IOB. This process culminates in a corrosion inhibition mechanism where cathodic inhibition predominates, supported by anodic inhibition as a complementary mechanism.

Sulfur cycling likely obscures dynamic biologically-driven iron redox cycling in contemporary methane seep environments.

Deep-sea methane seeps are amongst the most biologically productive environments on Earth and are often characterised by stable, low oxygen concentrations and microbial communities that couple the anaerobic oxidation of methane to sulfate reduction or iron reduction in the underlying sediment. At these sites, ferrous iron (Fe2+) can be produced by organoclastic iron reduction, methanotrophic-coupled iron reduction, or through the abiotic reduction by sulfide produced by the abundant sulfate-reducing bacteria at these sites. The prevalence of Fe2+in the anoxic sediments, as well as the availability of oxygen in the overlying water, suggests that seeps could also harbour communities of iron-oxidising microbes. However, it is unclear to what extent Fe2+ remains bioavailable and in solution given that the abiotic reaction between sulfide and ferrous iron is often assumed to scavenge all ferrous iron as insoluble iron sulfides and pyrite. Accordingly, we searched the sea floor at methane seeps along the Cascadia Margin for microaerobic, neutrophilic iron-oxidising bacteria, operating under the reasoning that if iron-oxidising bacteria could be isolated from these environments, it could indicate that porewater Fe2+ can persist is long enough for biology to outcompete pyritisation. We found that the presence of sulfate in our enrichment media muted any obvious microbially-driven iron oxidation with most iron being precipitated as iron sulfides. Transfer of enrichment cultures to sulfate-depleted media led to dynamic iron redox cycling relative to abiotic controls and sulfate-containing cultures, and demonstrated the capacity for biogenic iron (oxyhydr)oxides from a methane seep-derived community. 16S rRNA analyses revealed that removing sulfate drastically reduced the diversity of enrichment cultures and caused a general shift from a Gammaproteobacteria-domainated ecosystem to one dominated by Rhodobacteraceae (Alphaproteobacteria). Our data suggest that, in most cases, sulfur cycling may restrict the biological "ferrous wheel" in contemporary environments through a combination of the sulfur-adapted sediment-dwelling ecosystems and the abiotic reactions they influence.

Complete genome sequence of iron-oxidizing Stutzerimonas stutzeri strain FeN3W isolated from Catalina Harbor sediment.

Stutzerimonas stutzeri strain FeN3W is an iron-oxidizing bacterium isolated from marine sediment. FeN3W's 5.9 Mb genome encodes complete pathways for glycolysis, gluconeogenesis, TCA cycle, pentose phosphate pathway, and aerobic and anaerobic (nitrate) respiration. The genome contains 32 putative heme-binding proteins predicted to localize to the cell envelope.

Vertical distribution of arsenic and bacterial communities in calcareous farmland amending by organic fertilizer and iron-oxidizing bacteria: Field experiment on concomitant remediation

The migration and transformation mechanisms of arsenic (As) in soil environments necessitate an understanding of its influencing processes. Here, we investigate the subsurface biogeochemical transformation of As and iron (Fe) through amended in the top 20 cm with iron oxidizing bacteria (FeOB) and organic fertilizer (OF). Our comprehensive 400-day field study, conducted in a calcareous soil profile sectioned into 20 cm increments, involved analysis by sequential extraction and assessment of microbial properties. The results reveal that the introduction of additional OF increased the release ratio of As/Fe from the non-specific adsorption fraction (136.47 %) at the subsoil depth (40–60 cm), underscoring the importance of sampling at various depths and time points to accurately elucidate the form, instability, and migration of As within the profile. Examination of bacterial interaction networks indicated a disrupted initial niche in the bottom layer, resulting in a novel cooperative symbiosis. While the addition of FeOB did not lead to the dominance of specific bacterial species, it did enhance the relative abundance of As-tolerant Acidobacteria and Gemmatimonadetes in both surface (39.2 % and 38.76 %) and deeper soils (44.29 % and 23.73 %) compared to the control. Consequently, the amendment of FeOB in conjunction with OF facilitated the formation of poorly amorphous Fe (hydr)oxides in the soil, achieved through abiotic and biotic sequestration processes. Throughout the long-term remediation process, the migration coefficient of bioavailable As within the soil profile decreased, indicating that these practices did not exacerbate As mobilization. This study carries significant implications for enhancing biogeochemical cycling in As-contaminated Sierozem soils and exploring potential bioremediation strategies. Environmental implicationThe long-term exposure of sewage irrigation has potential adverse effects on the local ecosystem, causing serious environmental problems. Microorganisms play a vital role in the migration and transformation of arsenic in calcareous soil in arid areas, which highlights the necessity of understanding its dynamics. The vertical distribution, microbial community and fate of arsenic in calcareous farmland soil profile in northwest China were studied through field experiments. The results of this work have certain significance for the remediation of arsenic-contaminated soil in arid areas, and provide new insights for the migration, transformation and remediation of arsenic in this kind of soil.

Failure analysis of leaking firefighting pipeline used in nuclear power plant: Corrosion development process and key influence factors

A penetrating hole has been found in the inner wall of the firefighting pipeline (A106 steel) used for 20 years in a nuclear power plant of China, and the pipeline is filled with almost stagnant tap water before failure. The failed pipeline is taken from a vertically placed water outlet pipeline. The corrosion process and key influence factors of the failed firefighting pipeline were studied using optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that there exist two typical corrosion characteristics on the inner wall of the failed pipeline besides leakage hole, that is, corrosion nodulation and corrosion bulge. The corrosion nodulation, mainly consisting of a mixture of calcium and iron oxides, is the initiation position of perforation corrosion, and the iron-oxidizing bacteria (IOB) play a key role in the formation of corrosion nodulation. Then the sulfate-reducing bacteria (SRB) is involved in the propagation of corrosion nodulation when the dissolved oxygen concentration is low. The corrosion nodulation gradually become loose and form large bulge with extended service time. The corrosion pits under the corrosion bulge also develop gradually. Eventually, the inner wall of the pipeline is thinned and perforated.

Fe(II)Cl2 amendment suppresses pond methane emissions by stimulating iron-dependent anaerobic oxidation of methane.

Aquatic ecosystems are large contributors to global methane (CH4) emissions. Eutrophication significantly enhances CH4-production as it stimulates methanogenesis. Mitigation measures aimed at reducing eutrophication, such as the addition of metal salts to immobilize phosphate (PO43-), are now common practice. However, the effects of such remedies on methanogenic and methanotrophic communities-and therefore on CH4-cycling-remain largely unexplored. Here, we demonstrate that Fe(II)Cl2 addition, used as PO43- binder, differentially affected microbial CH4 cycling-processes in field experiments and batch incubations. In the field experiments, carried out in enclosures in a eutrophic pond, Fe(II)Cl2 application lowered in-situ CH4 emissions by lowering net CH4-production, while sediment aerobic CH4-oxidation rates-as found in batch incubations of sediment from the enclosures-did not differ from control. In Fe(II)Cl2-treated sediments, a decrease in net CH4-production rates could be attributed to the stimulation of iron-dependent anaerobic CH4-oxidation (Fe-AOM). In batch incubations, anaerobic CH4-oxidation and Fe(II)-production started immediately after CH4 addition, indicating Fe-AOM, likely enabled by favorable indigenous iron cycling conditions and the present methanotroph community in the pond sediment. 16S rRNA sequencing data confirmed the presence of anaerobic CH4-oxidizing archaea and both iron-reducing and iron-oxidizing bacteria in the tested sediments. Thus, besides combatting eutrophication, Fe(II)Cl2 application can mitigate CH4 emissions by reducing microbial net CH4-production and stimulating Fe-AOM.

Driving mechanism of different nutrient conditions on microbial mediated nitrate reduction in magnetite-present river infiltration zone

Significant research is focused on the ability of riparian zones to reduce groundwater nitrate contamination. Owing to the extremely high redox activity of nitrate, naturally existing electron donors, such as organic matter and iron minerals, are crucial in facilitating nitrate reduction in the riparian zone. Here, we examined the coexistence of magnetite, an iron mineral, and nitrate, a frequently observed coexisting system in sediments, to investigate nitrate reduction features at various C/N ratios and evaluate the response of microbial communities to these settings. Additionally, we aimed to use this information as a foundation for examining the effect of nutritional conditions on the nitrate reduction process in magnetite-present environments. These results emphasise the significance of organic matter in enabling dissimilatory nitrate reduction to ammonium (DNRA) and enhancing the connection between nitrate reduction and iron in sedimentary environments. In the later phases of nitrate reduction, nitrogen fixation was the prevailing process in low-carbon environments, whereas high-carbon environments tended to facilitate the breakdown of organic nitrogen. High-throughput sequencing analysis revealed a robust association between C/N ratios and alterations in microbial community composition, providing insights into notable modifications in essential functioning microorganisms. The nitrogen-fixing bacterium Ralstonia is more abundant in ecosystems with scarce organic matter. In contrast, in settings rich in organic matter, microorganisms, such as Acinetobacter and Clostridia, which may produce ammonia, play crucial roles. Moreover, the population of iron bacteria grows in such an environment. Hence, this study proposes that C/N ratios can influence Fe(II)/Fe(III) conversions and simultaneously affect the process of nitrate reduction by shaping the composition of specific microbial communities.

Metal-oxide precipitation influences microbiome structure in hyporheic zones receiving acid rock drainage.

In streams receiving acid-rock and mine drainage, the abundant precipitation of iron minerals can alter how groundwater and surface water mix along streams (in what is known as the "hyporheic zone") and may shape the distribution of microbial communities. The findings presented here suggest that neutral pH streams with large, well-mixed hyporheic zones may harbor and transport diverse microorganisms attached to particles/colloids through hyporheic pore spaces. In acidic streams where metal oxides clog pore spaces and limit hyporheic exchange, iron-oxidizing bacteria may dominate and phylogenetic diversity becomes low. The abundance of iron-oxidizing bacteria in acid mine drainage streams has the potential to contribute to additional clogging of hyporheic pore spaces and the accumulation of toxic metals in the hyporheic zone. This research highlights the dynamic interplay between hydrology, geochemistry, and microbiology at the groundwater-surface water interface of acid mine drainage streams.

Influence of supplementation with iron and probiotic bacteria Lactobacillus plantarum and Lactobacillus curvatus on selected parameters of inflammatory state in rats on a high-fat iron-deficient diet.

A high-fat (HF) diet, diet iron deficiency and iron supplementation may affect inflammatory parameters. Probiotics influence both iron metabolism and inflammation. We compared the inflammatory state in rats on a HF iron-deficient diet receiving oral iron, Lactobacillus plantarum and Lactobacillus curvatus in different combinations. This was a two-stage experiment. In groups C (n = 8) and HF (n = 8), rats ate a control or HF diet, respectively, for 16 weeks. In the group HFDEF (n = 48), rats ate a HF iron-deficient diet for 8 weeks (first stage) and were subsequently divided into 6 groups (n = 8 each) receiving the following for a further 8 weeks (second stage): HFDEF - a HF iron-deficient diet; HFDEFFe - a HF iron-deficient diet with iron; HFDEFLp and HFDEFLc - a HF iron-deficient diet with L. plantarum or L. curvatus, respectively; and HFDEFFeLp and HFDEFFeLc - a HF iron-deficient diet with iron and L. plantarum or L. curvatus, respectively. Body composition analysis and blood sampling was performed. Markers of iron status and levels of total antioxidant status (TAS), C-reactive protein (CRP), tumour necrosis factor alpha (TNF-α) and interleukin 6 (IL-6) were measured in the blood. TAS was higher in the HFDEF group (756.57 ± 489.53 ng mL-1) versus the HFDEFLc group (187.04 ± 47.84 ng mL-1; P = 0.022). No more differences were found between groups, or in TAS, CRP, TNF-α and IL-6 concentrations. Also, no differences were found between groups for alanine and aspartate aminotransferases, glucose, total cholesterol, low- and high-density lipoproteins and triglycerides. TAS level was positively correlated with ferritin concentration, IL-6 with TAS and TNF-α with hepcidin level. Supplementation with L. plantarum, L. curvatus and iron in combinations exerts no influence on inflammatory status, lipid profile, hepatic function and serum fasting glucose in rats on a HF iron-deficient diet. © 2024 Society of Chemical Industry.

Interplay between desiccation and oxidative stress responses in iron-oxidizing acidophilic bacteria

Variations in water availability represent a foremost stress factor affecting the growth and survival of microorganisms. Acidophilic bioleaching bacteria are industrially applied for releasing metals from mineral sulphides, and they are considered extremely tolerant to oxidative conditions prevailing in acidic bioleaching environments. Such processes usually are performed in heaps and thus these microorganisms are also exposed to intermittent desiccations or high osmolarity periods that reduce the water availability. However, the tolerance to water stress and the molecular basis of adaptation to it are still largely unknown. The aim of this work was to determine the cellular response to desiccation stress and establish its relationship to oxidative stress response in the acidophilic iron-oxidizing bacteria Acidithiobacillus ferrooxidans ATCC 23270 and Leptospirillum ferriphilum DSM 14647. Results showed that the exposure of cell cultures to desiccation (0–120 min) led to a significant reduction in cell growth, and to an increase in content in reactive oxygen species in both bacteria. However, Leptospirillum ferriphilum turned out to be more tolerant than Acidithiobacillus ferrooxidans. In addition, the pre-treatment of the cell cultures with compatible solutes (trehalose and ectoine), and antioxidants (glutathione and cobalamin) restored all stress parameters to levels exhibited by the control cultures. To evaluate the role of the osmotic and redox homeostasis mechanisms in coping with desiccation stress, the relative expression of a set of selected genes was approached by RT-qPCR experiments in cells exposed to desiccation for 30 min. Results showed a generalized upregulation of genes that code for mechanosensitive channels, and enzymes related to the biosynthesis of compatible solutes and oxidative stress response in both bacteria. These data suggest that acidophiles show variable tolerance to desiccation and allow to establish that water stress can trigger oxidative stress, and thus anti-oxidative protection capability can be a relevant mechanism when cells are challenged by desiccation or other anhydrobiosis states.

Biochar co-pyrolyzed from peanut shells and maize straw improved soil biochemical properties, rice yield, and reduced cadmium mobilization and accumulation by rice: Biogeochemical investigations

Biochar is an eco-friendly amendment for the remediation of soils contaminated with cadmium (Cd). However, little attention has been paid to the influence and underlying mechanisms of the co-pyrolyzed biochar on the bioavailability and uptake of Cd in paddy soils. The current study explored the effects of biochar co-pyrolyzed from peanut shells (P) and maize straw (M) at different mixing ratios (1:0, 1:1, 1:2, 1:3, 0:1, 2:1 and 3:1, w/w), on the bacterial community and Cd fractionation in paddy soil, and its uptake by rice plant. Biochar addition, particularly P1M3 (P/M 1:3), significantly elevated soil pH and cation exchange capacity, transferred the mobile Cd to the residual fraction, and reduced Cd availability in the rhizosphere soil. P1M3 application decreased the concentration of Cd in different rice tissues (root, stem, leaf, and grain) by 30.0%− 49.4%, compared to the control. Also, P1M3 enhanced the microbial diversity indices and relative abundance of iron-oxidizing bacteria in the rhizosphere soil. Moreover, P1M3 was more effective in promoting the formation of iron plaque, increasing the Cd sequestration by iron plaque than other treatments. Consequently, the highest yield and lowest Cd accumulation in rice were observed following P1M3 application. This study revealed the feasibility of applying P1M3 for facilitating paddy soils contaminated with Cd.

High-efficient nitrogen removal with low demand of Fe source and mechanism analysis driven by Fe(II)/Fe(III) cycle

Feammox (Fe(III) reduction coupled with anaerobic ammonium oxidation) is less studied for nitrogen removal in wastewater treatment, and the limited studies show its low removal efficiency and need for continuous resupply of Fe(III) sources. In this study, sustainable and efficient nitrogen removal was obtained by the Fe redox cycle with only 1 g/L Fe2O3 dosage. The removal efficiencies of NH4+-N and TN were 100% and 92.45%, respectively, significantly higher than previous studies (∼50%). Fe(III) was reduced to Fe(II) by Feammox and subsequently regenerated by NDFO (NOx--N-dependent Fe(II) oxidation) and chemical oxidization. NOx--N produced by Feammox was also reduced to N2 by NDFO. The iron-reducing bacteria (Ferruginibacter and Dechloromonas) and the iron-oxidizing bacteria (Rhodanobacter and Thermomonas) were enriched by the addition of Fe2O3 and played important roles in Feammox and NDFO, respectively. Results of X-ray diffraction showed that Fe(OH)2 was produced from Feammox and then transformed to lepidocrocite by Fe(II) oxidation. Metagenomic analysis showed D/ANRA (dissimilatory/ assimilatory nitrate reduction to ammonia) were the potential nitrogen conversion pathways. N2O as an intermediate product of Feammox or NDFO was undetected. The genes associated with Fe transport were upregulated, accelerating the transfer of electrons between microorganisms and Fe(Hydr)oxide. The process for nitrogen removal by the Fe redox cycle requires no aeration and no organic carbon source, and can reduce the need for Fe(III) sources. It offers a promising method for nitrogen removal from wastewater.

Diversity and distribution of iron-oxidising bacteria belonging to Gallionellaceae in different sites of a hydroelectric power plant.

Iron (Fe) is the fourth most abundant element on the planet, and iron-oxidising bacteria (FeOB) play an important role in the biogeochemical cycle of this metal in nature. FeOB stands out as Fe oxidisers in microaerophilic environments, and new members of this group have been increasingly discussed in the literature, even though their isolation can still be challenging. Among these bacteria is the Gallionellaceae family, mainly composed of neutrophilic FeOB, highlighting Gallionella ferruginea, and nitrite-oxidiser genera. In the previous metagenomic study of the biofilm and sediments of the cooling system from the Irapé hydroelectric power plant (HPP-Irapé), 5% of the total bacteria sequences were related to Gallionellaceae, being 99% unclassified at genus level. Thus, in the present study, a phylogenetic tree based on this family was constructed, in order to search for shared and unique Gallionellaceae signatures in a deep phylogenetic level affiliation and correlated them with geomorphologic characteristics. The results revealed that Gallionella and Ferrigenium were ubiquitous reflecting their ability to adapt to various locations in the power plant. The cave was considered a hotspot for neutrophilic FeOB since it harboured most of the Gallionellaceae diversity. Microscopic biosignatures were detected only in the CS1 sample, which presented abundance of the stalk-forming Ferriphaselus and of the sheath-forming Crenothrix. Further studies are required to provide more detailed insights on Gallionellaceae distribution and diversity patterns in hydroelectric power plants, particularly its biotechnological potential in this industry.

Linking Zetaproteobacterial diversity and substratum type in iron-rich microbial mats from the Lucky Strike hydrothermal field (EMSO-Azores observatory).

Zetaproteobacteria have been reported in different marine and terrestrial environments all over the globe. They play an essential role in marine iron-rich microbial mats, as one of their autotrophic primary producers, oxidizing Fe(II) and producing Fe-oxyhydroxides with different morphologies. Here, we study and compare the Zetaproteobacterial communities of iron-rich microbial mats from six different sites of the Lucky Strike Hydrothermal Field through the use of the Zetaproteobacterial operational taxonomic unit (ZetaOTU) classification. We report for the first time the Zetaproteobacterial core microbiome of these iron-rich microbial mats, which is composed of four ZetaOTUs that are cosmopolitan and essential for the development of the mats. The study of the presence and abundance of different ZetaOTUs among sites reveals two clusters, which are related to the lithology and permeability of the substratum on which they develop. The Zetaproteobacterial communities of cluster 1 are characteristic of poorly permeable substrata, with little evidence of diffuse venting, while those of cluster 2 develop on hydrothermal slabs or deposits that allow the percolation and outflow of diffuse hydrothermal fluids. In addition, two NewZetaOTUs 1 and 2 were identified, which could be characteristic of anthropic iron and unsedimented basalt, respectively. We also report significant correlations between the abundance of certain ZetaOTUs and that of iron oxide morphologies, indicating that their formation could be taxonomically and/or environmentally driven. We identified a new morphology of Fe(III)-oxyhydroxides that we named "corals." Overall, our work contributes to the knowledge of the biogeography of this bacterial class by providing additional data from the Atlantic Ocean, a lesser-studied ocean in terms of Zetaproteobacterial diversity.IMPORTANCEUp until now, Zetaproteobacterial diversity studies have revealed possible links between Zetaproteobacteria taxa, habitats, and niches. Here, we report for the first time the Zetaproteobacterial core microbiome of iron-rich mats from the Lucky Strike Hydrothermal Field (LSHF), as well as two new Zetaproteobacterial operational taxonomic units (NewZetaOTUs) that could be substratum specific. We highlight that the substratum on which iron-rich microbial mats develop, especially because of its permeability to diffuse hydrothermal venting, has an influence on their Zetaproteobacterial communities. Moreover, our work adds to the knowledge of the biogeography of this bacterial class by providing additional data from the hydrothermal vent sites along the Mid-Atlantic Ridge. In addition to the already described iron oxide morphologies, we identify in our iron-rich mats a new morphology that we named corals. Finally, we argue for significant correlations between the relative abundance of certain ZetaOTUs and that of iron oxide morphologies, contributing to the understanding of the drivers of iron oxide production in iron-oxidizing bacteria.

"Candidatus Siderophilus nitratireducens": a putative nap-dependent nitrate-reducing iron oxidizer within the new order Siderophiliales.

Nitrate leaching from agricultural soils is increasingly found in groundwater, a primary source of drinking water worldwide. This nitrate influx can potentially stimulate the biological oxidation of iron in anoxic groundwater reservoirs. Nitrate-dependent iron-oxidizing (NDFO) bacteria have been extensively studied in laboratory settings, yet their ecophysiology in natural environments remains largely unknown. To this end, we established a pilot-scale filter on nitrate-rich groundwater to elucidate the structure and metabolism of nitrate-reducing iron-oxidizing microbiomes under oligotrophic conditions mimicking natural groundwaters. The enriched community stoichiometrically removed iron and nitrate consistently with the NDFO metabolism. Genome-resolved metagenomics revealed the underlying metabolic network between the dominant iron-dependent denitrifying autotrophs and the less abundant organoheterotrophs. The most abundant genome belonged to a new Candidate order, named Siderophiliales. This new species, "Candidatus Siderophilus nitratireducens," carries genes central genes to iron oxidation (cytochrome c cyc2), carbon fixation (rbc), and for the sole periplasmic nitrate reductase (nap). Using thermodynamics, we demonstrate that iron oxidation coupled to nap based dissimilatory reduction of nitrate to nitrite is energetically favorable under realistic Fe3+/Fe2+ and NO3-/NO2- concentration ratios. Ultimately, by bridging the gap between laboratory investigations and nitrate real-world conditions, this study provides insights into the intricate interplay between nitrate and iron in groundwater ecosystems, and expands our understanding of NDFOs taxonomic diversity and ecological role.

Effective removal of iron, nutrients, micropollutants, and faecal bacteria in constructed wetlands cotreating mine water and sewage treatment plant effluent.

Regulators in England and Wales have set new targets under the Environment Act 2021 for freshwater quality by 2038 that include halving the length of rivers polluted by harmful metals from abandoned mines and reducing phosphorus loadings from treated wastewater by 80%. In this context, an intriguing win-win opportunity exists in the removal of iron from abandoned mines and phosphate from small sewage treatment plants by coprecipitation in constructed wetlands (CWs). We investigated such a CW located at Lamesley, Northeast England, which cotreats abandoned coal mine and secondary-treated sewage treatment plant effluents. We assessed the removal of nutrients, heavy metals, organic micropollutants, and faecal coliforms by the CW, and characterized changes in the water bacteriology comprehensively using environmental DNA. The CW effectively removed ammonium-nitrogen, phosphorus, iron, and faecal coliforms by an average of 86, 74, 98, and 75%, respectively, to levels below or insignificantly different from those in the receiving river. The CW also effectively removed micropollutants such as acetaminophen, caffeine, and sulpiride by 70-100%. Molecular microbiology methods showed successful conversion of sewage and mine water microbiomes into a freshwater microbiome. Overall, the CW significantly reduced impacts on the rural water environment with minimal operational requirements.