Iron-reducing Bacteria Research Articles

Comparative assessment of a restored and natural wetland using 13C-DNA SIP reveals a higher potential for methane production in the restored wetland.

Wetlands are the largest natural source of methane (CH4), a potent greenhouse gas produced by methanogens. Methanogenesis rates are controlled by environmental factors such as redox potential, temperature, and carbon and electron acceptor availability and are presumably dependent on the composition of the active methanogen community. We collected intact soil cores from a restored and natural freshwater depressional wetland on Maryland's Delmarva Peninsula (USA) to assess the effects of wetland restoration and redox shifts on microbial processes. Intact soil cores were incubated under either saturated (anoxic) or unsaturated (oxic) conditions and amended with 13C-acetate for quantitative stable isotope probing (qSIP) of the 16S rRNA gene. Restored wetland cores supported a distinct community of methanogens compared to natural cores, and acetoclastic methanogens putatively identified in the genus Methanosarcina were among the most abundant taxa in restored anoxic and oxic cores. The active microbial communities in the restored wetland cores were also distinguished by the unique presence of facultatively anaerobic bacteria belonging to the orders Firmicutes and Bacteroidetes. In natural wetland incubations, methanogen populations were not among the most abundant taxa, and these communities were instead distinguished by the unique presence of aerobic bacteria in the phyla Acidobacteria, Actinobacteria, and class Alphaproteobacteria. Iron-reducing bacteria, in the genus Geobacter, were active across all redox conditions in both the restored and the natural cores, except the natural oxic-anoxic condition. These findings suggest an overall higher potential for methanogenesis in the restored wetland site compared to the natural wetland site, even when there is evidence of Fe reduction.IMPORTANCEMethane (CH4) is a potent greenhouse gas with an atmospheric half-life of ~10 years. Wetlands are the largest natural emitters of CH4, but CH4 dynamics are difficult to constrain due to high spatial and temporal variability. In the past, wetlands were drained for agriculture. Now, restoration is an important strategy to increase these ecosystems' potential for sequestering carbon. However, the consequences of wetland restoration on carbon biogeochemistry are under-evaluated, and a thorough assessment of the active microbial community as a driver of biogeochemical changes is needed. Particularly, the effects of seasonal flooding/drying cycles in geographically isolated wetlands might have implications for CH4 emissions in both natural and restored wetlands. Here, we found that active microbial communities in natural and restored wetlands responded differently to flooding and drying regimes, resulting in differences in CH4 production potentials. Restored wetlands had a higher potential for CH4 production compared to natural wetlands. Our results show that controls on CH4 production in a restored wetland are complex, and dynamics of active microbial communities are linked to seasonal dry-wet cycles.

Activated carbon and anthraquinone-2,6-disulfonate as electron shuttles for enhancing carbon and nitrogen removal from simultaneous methanogenesis, Feammox and denitrification system.

Anthraquinone-2,6-disulfonate (AQDS) and activated carbon (AC) were employed as exogenous electron shuttles (ESs) for enhancing the performance of an integrated simultaneous methanogenesis, Feammox, and denitrification (SMFD) system treating fish sludge. The addition of AQDS and AC led to an increased total nitrogen removal efficiency by 30.2% and 66.5%, an increased total chemical oxygen demand removal efficiency by 9.5% and 24.5%, and an improved methane yield by 5.2% and 12.6%, respectively. Regarding nitrogen removal, AQDS mainly facilitated NH4+-N oxidation into NO3--N via Feammox, while AC facilitated both Feammox and denitrification. Regarding carbon removal, both ESs promoted the hydrolysis-acidification process via stimulating dissimilatory iron reduction and established direct interspecies electron transfer (DIET) between methanogens and syntrophic bacteria. Microbial analysis confirmed the enrichment of iron-reducing bacteria, denitrifiers, DIET-related methanogens and syntrophic partners in the presence of ESs. The study provides an ESs-assisted strategy for enhancing simultaneous nitrogen and carbon removal from high-strength wastewater.

Synthesis mechanisms, property characterization, and environmental applications of biogenic FeS: A review.

Iron sulfide (FeS) exhibits superior reactivity toward a wide range of contaminants, making it a promising candidate for environmental remediation in various media, including surface water, wastewater, soil, and groundwater. Driven by green and sustainable development principles, efficient, low-cost, and environmentally friendly biosynthesis has attracted considerable attention and has great environmental remediation potential. This review provides a comprehensive overview of the recent advances in biogenic FeS (bio-FeS), focusing on its synthesis mechanisms, performance characterization, and environmental applications. To the best of our knowledge, this is the first review exclusively dedicated to this emerging field. This review begins with an in-depth description of the four bio-FeS biosynthetic pathways, the primary actors of which are sulfate-reducing bacteria (SRB), iron-reducing bacteria (IRB), coupled SRB and IRB, and bio-extracts. Notably, SRB account for approximately half of the bio-FeS synthesis. Various characterization techniques, including scanning electron microscopy, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and Brunauer-Emmett-Teller analysis, have been discussed in depth to better understand the structure and properties of bio-FeS. In terms of morphological structure, the bio-FeS synthesized by SRB exhibited primarily flakes (similar to mackinawite), whereas the bio-FeS synthesized by IRB was chiefly spherical. Bio-FeS transportation, migration, and permeation properties were also explored. Furthermore, bio-FeS application in the removal of various contaminants, including arsenic, chromium, uranium, complex pollutants, rare earth elements, chlorinated hydrocarbons, and antibiotics, and their underlying mechanisms were discussed. Finally, the challenges and future research directions related to bio-FeS environmental applications were discussed. This review aims to provide valuable insights into bio-FeS synthesis and environmental applications, thereby supporting the development of innovative and sustainable technologies for environmental remediation.

Characterization of the Rhizobiome of the Yellow Pitcher Plant (Sarracenia flava) in Wild and Restored Habitats of Virginia

The yellow pitcher plant, Sarracenia flava, is an insectivorous perennial distributed extensively in southeastern North America. In Virginia, it is restricted to a few wetland ecosystems, with only one natural site known to remain. To uncover whether there were microbial differences in the rhizospheres across natural and reintroduced sites of pitcher plant restoration, shotgun metagenome sequencing was undertaken to characterize the microbiomes of the healthy rhizosphere in the last remaining natural stand in Virginia compared to rhizospheres sampled in two restored habitats where pitcher plants were reintroduced and a nearby control habitat without pitcher plants. Statistical analysis showed no significant differences in rhizobiome communities among the natural, reintroduced, and control sites. Comparison of test rhizobiomes with those of other soil types revealed no significant difference in S. flava habitats versus wildland soil types but significant difference from agricultural soils. Indicator species analysis found Pseudomonas was a significantly more abundant genus in the S. flava habitats. The control site was enriched with iron-reducing bacteria compared to the rest of the sites. Further studies based on gene expression could better facilitate an understanding of the role of Pseudomonas in S. flava rhizosphere specific to habitats, which will provide better knowledge for local conservation of this plant.

Nanocomposite complex ZnO in combination with a triazoloazepinium derivative for inhibition of microbial steel corrosion

We have established the possibility of using ZnO nanoparticles to inhibit microbial corrosion with simultaneous inhibition of growth and sulfate-reducing activity of bacteria of the corrosive active group. The search for ways to increase the antibacterial and anticorrosive effect of ZnO nanoparticles makes it possible to combine them with substances, in particular, inhibitors-biocides of microbial steel corrosion. The nanocomposite complex of ZnO nanoparticles and cationic heterocyclic compound (triazoloazepinium derivative) was studied as a biocide and inhibitor of microbial corrosion on steel. The component concentrations are 3 mg/mL and 1 mg/mL accordingly. The experiments were carried out by using a microbiological and corrosion control methods. It has been established that the proposed nanocomposite complex affects the number of bacteria in the plankton and biofilm. In its presence, there is a complete inhibition of the growth of sulfate-reducing bacteria (the most aggressive component of the microbial community) in plankton. Also, the number of denitrifying bacteria and iron-reducing bacteria in plankton decreases by 3 and 4 orders, respectively. The biofilm formed in the presence of the nanocomposite in the culture medium is less dense in terms of the number of bacterial cells of the sulfidogenic community.

Dual anaerobic reactor model to study biofilm and microbiologically influenced corrosion interactions on carbon steel

Continual challenges due to microbial corrosion are faced by the maritime, offshore renewable and energy sectors. Understanding the biofilm and microbiologically influenced corrosion interaction is hindered by the lack of robust and reproducible physical models that reflect operating environments. A novel dual anaerobic biofilm reactor, using a complex microbial consortium sampled from marine littoral sediment, allowed the electrochemical performance of UNS G10180 carbon steel to be studied simultaneously in anaerobic abiotic and biotic artificial seawater. Critically, DNA extraction and 16S rRNA amplicon sequencing demonstrated the principal biofilm activity was due to electroactive bacteria, specifically sulfate-reducing and iron-reducing bacteria.

Iron-reducing bacteria bioremediation for organic contaminated urban river sediment enhanced by chemical regulation: Strategy, effect and mechanism

Iron-reducing bacteria bioremediation for organic contaminated urban river sediment enhanced by chemical regulation: Strategy, effect and mechanism

Effect of sulfate-reducing bacteria (SRB) and dissimilatory iron-reducing bacteria (DIRB) coexistence on the transport and transformation of arsenic in sediments

Sulfate-reducing bacteria (SRBs) and dissimilatory iron-reducing bacteria (DIRBs) are recognized as significant contributors to the occurrence of elevated arsenic (As) levels in groundwater. However, the precise effects and underlying mechanisms of their interactions on As behavior within sediments remain poorly understood. In this investigation, we compared the impacts and mechanisms of DIRBs, SRBs, and mixed bacterial consortia on the migration behavior of As and Fe/S species. Our findings revealed that during the initial phase of the reaction (0–8 days, Stage 1), the mixed bacterial consortium facilitated As release by intensifying the reduction of Fe (III) and sulfate, resulting in a maximum As concentration 1.5 times higher than that observed with either DIRBs or SRBs in isolation. Subsequently, in the intermediate phase (8–20 days, Stage 2), the mixed consortium suppressed the synthesis of sulfate reductase and the secretion of toxic substances (e.g., o-Methyltoluene) associated with steroid degradation pathways. This inhibition consequently reduced the formation of secondary Fe minerals and the fixation of As. Finally, in the latter stage (20–30 days, Stage 3), the system responded to the threat of toxic substances by secreting significant amounts of organic acids to facilitate their decomposition. However, this process also led to the re-decomposition of iron oxides, resulting in the release of As. These observations shed light on the intricate interplay between DIRBs and SRBs within bacterial consortia, elucidating their coordinated actions in inducing the migration and transformation of arsenic.

Nano-Fe3O4/FeCO3 modified red soil-based biofilter for simultaneous removal of nitrate, phosphate and heavy metals: Optimization, microbial community and possible mechanism

The pollution of nitrogen, phosphorus and heavy metals in surface water is becoming more and more serious, affecting the safety of water quality. In this study, three biofilters were constructed using iron-modified red soil-based filler carriers (RSC, nano-Fe3O4@RSC, and FeCO3@RSC) combined with strain Zoogloea sp. ZP7 to simultaneously remove nitrate (NO3--N), phosphate (PO43--P), copper (Cu2+), and zinc (Zn2+). The long-term operation results showed that the three groups of biofilters could remove 85.0 %, 90.0 %, and 89.8 % of NO3--N, respectively. Furthermore, the addition of iron compounds enhanced the removal of PO43--P and the resistance to the stress of Cu2+ and Zn2+ in the biofilter. The analysis illustrated that iron modification improved the redox activity and zeta potential of RSC surface. The secondary structure analysis of the protein showed that the microbial secreted proteins were more compact on the surface of the iron-modified RSC, which facilitated the formation of biofilm on the carrier surface. In addition, the iron-modified RSC-based biofilter also showed excellent NO3--N and PO43--P removal efficiency in the treatment of actual surface water. The microbial community analysis results showed that Zoogloea became the dominant species in the biofilter. On the other hand, the presence of iron-reducing bacteria and the expression iron cycle-related genes may contribute to denitrification under low nutrient conditions.

A new enrichment strategy of dissimilatory iron-reducing bacteria for remediation of organic-contaminated river sediments: Process, performance, and mechanism

Dissimilatory iron-reducing bacteria (DIRB) have been widely applied to organic matter metabolism in sediments due to their specific biological properties, which are significantly affected by environmental factors. Until now, there has been no systematic study on applying these effects of environmental factors to DIRB enrichment. In this study, we identified the critical environmental factors through RDA, PLS-PM, and correlation analysis and then adjusted the proportion of these factors (C/Fe, C/N, and Fe/S) through single-factor and response surface experiments to enrich DIRB. The performance of the enriched DIRB in carbon metabolism of organic-rich sediments was analyzed by remediation experiment, and the metabolic mechanism was revealed through iron-reducing performance, community structure, and functional genes. The results showed that the carbon, nitrogen, phosphorus, and sulfur were crucial factors influencing the activity of DIRB in river sediments, and the enriched mud-bacteria mixture containing a large amount of DIRB (referred to as “DMB”) obtained by domestication under C/Fe = 0.492 and C/N = 13.659 showed the highest iron reduction rate of 55.51% ± 2.53%. The DMB exhibited better-sustained removal of total organic matter (TOM), which was higher than the control (MB) by 8.81%. Moreover, we discovered that the enriched DIRB: (1) had a better reduction effect on different Fe(III) forms, especially in carbon-limited and iron-limited conditions. (2) increased in abundance and established a beneficial symbiotic relationship with hydrolytic acidifying bacteria. (3) showed an increased abundance of functional pathways associated with organismal systems and signal processing (such as ABC transporters and Translation). These findings revealed the reasons for the improved efficiency of organic matter metabolism.

Adsorption characteristics of As(III) by schwertmannite: new findings in mineral-phase transformation and microbial effects

The amount of As(III) adsorbed and the interfacial process are closely associated with the phase transformation of Schwertmannite (SCH). At present, studies on the adsorption characteristics of As(III) on SCH and the accompanying phase transformation process, especially the related mechanisms under the mediation of iron-reducing bacteria (FeRB) and sulfate-reducing bacteria (SRB), are limited in existing literature. With the help of continuous characterization, the adsorption behavior of As(III) on SCH was explored, as well as the transformation processes of SCH during these processes. The findings revealed that the SCH, synthesized by the KMnO4 oxidation and ethanol modification methods, exhibited excellent physical adsorption capacity for As(III) due to their increasing specific surface area and porosity. At room temperature (20°C), the saturation adsorption capacities of As(III) by M-SCH and Y-SCH reached 62.69 and 58.62 mg/g, respectively. Moreover, the generation and phase transformation of As(III)-bearing ferrihydrite were observed within a 60-min timeframe. It is the first time this phenomenon has been observed in such a short time, which is presumed to be an intermediate stage in the transformation of SCH into goethite. Furthermore, both FeRB and SRB could enhance the adsorption capacity of SCH for As(III). Comparatively, SRB has a more substantial impact on SCH’s phase transformation. These insights are valuable for the practical application of SCH in treating As(III) pollution.

Biochar changes iron-reducing bacteria community in paddy soils and promotes the bacterial iron reduction

Biochar changes iron-reducing bacteria community in paddy soils and promotes the bacterial iron reduction

The effect of Fenton sludge on anaerobic digestion of papermaking wastewater in an upflow anaerobic sludge blanket reactor

An upflow anaerobic sludge blanket (UASB) reactor was used to investigate the effect of adding Fenton sludge (FS) on the anaerobic digestion of actual papermaking wastewater. The results showed that a one-time addition of 10 g/L FS could sustainably promote the performance of UASB for more than 40 days. The organic matter removal efficiency increased by 15.56%, and the biogas production increased by 24.52%. The proportion of methane in biogas increased by 12.87%. Adding FS increased the capacitance values of sludge extracellular polymeric substances and the electron transfer system activity in reactor increased by 1.76 times. The dehydrogenase activity and coenzyme F420 of the sludge increased by 1.54 and 2.11 times, respectively. Adding FS enriched the iron-reducing bacteria (Thermodesulfobacteriota) and hydrolytic acid-producing bacteria (Chloroflexota and Synergistota), thereby promoting the hydrolysis and acidification process. Adding FS was beneficial to the enrichment of methanogen, especially Methanosaeta, significantly increasing the methane production.

A slow-release reduction material of Escherichia sp. F1 coupled with micron iron powder achieves the remediation of trichloroethylene-contaminated soil

Trichloroethylene (TCE) is a prevalent organic pollutant found in soil. The oxide passivation layer on the surface of micron iron powder inhibits the release of its reducing components, leading to ineffective reduction and purification of TCE in soil. To enhance TCE degradation, a slow-release reduction material "Escherichia sp. F1-micron iron powder" was developed. A novel iron-reducing bacterium, Escherichia sp. F1, was isolated from soil contaminated with chlorinated hydrocarbons. This bacterium demonstrated a sustained iron reduction capability, achieving a reduction rate of 38.7% for Fe(Ⅲ) within 15 days. Genome sequencing revealed that strain F1 harbors 53 functional iron reduction genes and 2 dehalogenation genes. Single-factor experiments identified the optimal conditions for TCE degradation in soil using the coupling material: glucose concentration at 40 mmol/kg, soil water content at 50%, and bacterial inoculum at 1% (v:w). Under these optimal conditions, the coupled material achieved 86.86% degradation of TCE in soil within 28 days. Further analysis using X-ray photoelectron spectroscopy of micron iron powder, soil Fe(Ⅱ) concentration, and soil physicochemical properties demonstrated that the addition of strain F1 to the soil could disrupt the passivation layer of iron oxide on the surface of micron iron powder, promoting the exposure of its reactive sites and internal reducing active components. This resulted in an in situ self-actuated activation of passivated micron iron powder, leading to an improved removal rate and complete dechlorination of TCE in the soil. Soil microbial high-throughput sequencing revealed that the addition of strain F1 regulated the soil bacterial community, significantly enriching of Escherichia-Shigella species associated with iron-reducing functions. This enrichment facilitated the degradation of TCE in the soil through coupling materials. The functional material plays a crucial role in achieving green treatment and risk control of sites contaminated with chlorinated organic pollutants.

Biogenic Sulfide-Mediated Iron Reduction at Low pH

Acid mine drainage (AMD) pollutes natural waters, but some impacted systems show natural attenuation. We sought to identify the biogeochemical mechanisms responsible for the natural attenuation of AMD. We hypothesized that biogenic sulfide-mediated iron reduction is one mechanism and tested this in an experimental model system. We found sulfate reduction occurred under acidic conditions and identified a suite of sulfate-reducing bacteria (SRB) belonging to the groups Desulfotomaculum, Desulfobacter, Desulfovibrio, and Desulfobulbus. Iron reduction was not detected in microcosms when iron-reducing bacteria or SRB were selectively inhibited. SRB also did not reduce iron enzymatically. Rather, the biogenic sulfide produced by SRB was found to be responsible for the reduction of iron at low pH. Addition of organic substrates and nutrients stimulated iron reduction and increased the pH. X-ray diffraction and an electron microprobe analysis revealed that the polycrystalline, black precipitate from SRB bioactive samples exhibited a greater diversity of iron chalcogenide minerals with reduced iron oxidation states, and minerals incorporating multiple metals compared to abiotic controls. The implication of this study is that iron reduction mediated by biogenic sulfide may be more significant than previously thought in acidic environments. This study not only describes an additional mechanism by which SRB attenuate AMD, which has practical implications for AMD-impacted sites, but also provides a link between the biogeochemical cycling of iron and sulfur.

Microbial magnetite oxidation via MtoAB porin-multiheme cytochrome complex in Sideroxydans lithotrophicus ES-1.

Mineral-bound iron could be a vast source of energy to iron-oxidizing bacteria, but there is limited evidence of this metabolism, and it has been unknown whether the mechanisms of solid and dissolved Fe(II) oxidation are distinct. In iron-reducing bacteria, multiheme cytochromes can facilitate iron mineral reduction, and here, we link a multiheme cytochrome-based pathway to mineral oxidation, broadening the known functionality of multiheme cytochromes. Given the growing recognition of microbial oxidation of minerals and cathodes, increasing our understanding of these mechanisms will allow us to recognize and trace the activities of mineral-oxidizing microbes. This work shows how solid iron minerals can promote microbial growth, which if widespread, could be a major agent of geologic weathering and mineral-fueled nutrient cycling in sediments, aquifers, and rock-hosted environments.

Phase transformation of schwertmannite changes microbial iron and sulfate-reducing processes in flooded paddy soil and decreases arsenic accumulation in rice (Oryza sativa L.)

Rice (Oryza sativa L.) is known to accumulate inorganic arsenic (iAs) and dimethylarsenate (DMA) in its grains, which threatens both human health and rice yield. Although schwertmannite, a metastable Fe (Ⅲ)-oxyhydroxysulfate mineral with extremely high adsorption capacity for iAs, has been proposed to remediate paddy soil to decrease As accumulation in rice, it remains unclear whether the phase transformation of schwertmannite would occur in flooded paddy soil and how its phase transformation changes the soil microbial processes that impact the accumulation of iAs and DMA in grains. Here, we found that amending As-contaminated paddy soil with 0.5%–1% (w/w) schwertmannite decreased the accumulation of iAs and DMA in grains by 37.41%–43.29% and 50.60%–73.89%, respectively, even though schwertmannite has transformed to goethite and secondary FeS was formed in both rhizosphere and bulk soils. The phase transformation of schwertmannite released a considerable amount of SO42− into porewater, thereby increasing the abundances of both sulfate-reducing bacteria and the dsrB gene but decreasing the abundance of iron-reducing bacteria. This result suggested that schwertmannite phase transformation has promoted sulfate-reducing process and weakened iron-reducing process in flooded soil. Such promoted sulfate-reducing process and weakened iron-reducing process in paddy soil can decrease the reductive dissolution of As-bearing (oxyhydr)oxides, increase the formation of secondary FeS mineral for decreasing porewater As concentration, and strengthen the role of Fe plaque as a barrier for As absorption by rice. Additionally, the application of schwertmannite has decreased the abundance of arsM gene and weakened As methylation process in soil. Therefore, the effective decrease of iAs and DMA accumulation in rice grains by schwertmannite can not only be ascribed to the adsorption capacity of schwertmannite for As and the adsorption or incorporation of As by transformation products, but also contributed by the promoted sulfate-reducing process and the weakened iron-reducing process in flooded paddy soil.

Biogenic amorphous FeOOH activated additional intracellular electron flow pathways for accelerating reductive dechlorination of tetrachloroethylene

Dissimilatory iron-reducing bacteria (DIRB) with extracellular electron transfer (EET) capabilities have shown significant potential for bioremediating halogenated hydrocarbon contaminated sites rich in iron and humic substances. However, the role and microbial molecular mechanisms of iron-humic acid (Fe-HA) complexes in the reductive dehalogenation process of DIRB remains inadequately elucidated. In this study, we developed a sustainable carbon cycling approach using Fe-HA complexes to modulate the electron flux from sawdust (SD), enabling almost complete reductive dechlorination by most DIRB (e.g., Shewanella oneidensis MR-1) that lack complex iron-sulfur molybdo enzymes. The SD-Fe-HA/MR-1 system achieved a 96.52% removal efficiency of tetrachloroethylene (PCE) at concentrations up to 250 μmol/L within 60 days. Material characterization revealed that DIRB facilitated the hydrolysis of macromolecular carbon sources by inducing the formation of amorphous ferrihydrite (FeOOH) in Fe-HA complexes. More importantly, the bioavailable FeOOH activated additional intracellular electron flow pathways, increasing the activity of potential dehalogenases. Transcriptome further highlight the innovative role of biogenic amorphous FeOOH in integrating intracellular redox metabolism with extracellular charge exchange to facilitate reductive dechlorination in DIRB. These findings provide novel insights into accelerating reductive dechlorination in-situ contaminated sites lacking obligate dehalogenating bacteria.

Mobilization of phosphorus in sediments of eutrophic lakes induced by elevated sulfate levels

Elevated sulfate levels in eutrophic lakes have been observed to induce the release of endogenous phosphorus. While previous studies have predominantly examined its impact on iron-bound phosphorus (FeP), the influence on organic phosphorus (OP), a crucial active phosphorus component in sediments, remains poorly understood. In this study, mesocosms were established with lactate supplementation and varying sulfate concentrations to explore sulfate reduction and its impacts on phosphorus mobilization in freshwater sediments. Lactate addition induced hypoxia and provided substrates, thereby stimulating sulfate reduction with a decline of sulfate levels, an increase of sulfide concentrations, and fluctuations of sulfate-reducing bacteria. Meanwhile, concentrations of total dissolved phosphorus and phosphate were dramatically promoted during lactate decomposition, with a higher sulfate concentration associated with greater phosphorus elevation, correlating with the decrease of total phosphorus in sediment. The increase in phosphorus of the overlying water was partly attributed to FeP release from the sediment, confirmed by a decrease in its sediment content. FeP release was ascribed to dissimilatory reduction of iron oxides or chemical reduction mediated by sulfides in anoxic sediments, leading to the desorption and subsequent release of phosphorus. Evidences included the proliferation of iron-reducing bacteria, a decrease in Fe(II) concentrations in sediment pore- water, and the continuous accumulation of solid iron sulfides in surface sediments. Furthermore, OP mineralization in sediment also contributed to the increase in phosphorus in water columns, confirmed by a reduction in its content and the abundance of fermentation bacteria in surface sediment. Notably, the decrease in OP content accounted for >80 % of the total phosphorus reduction in surface sediment in the end. Thus, sulfur cycling plays a critical role in iron and phosphorus cycling, significantly stimulating not only the mobilization of FeP but also OP in sediments, with OP mineralization potentially being the primary contributor to endogenous phosphorus release.

Biogenic Origin of Fe-Mn Crusts from Hydrothermal Fields of the Mid-Atlantic Ridge, Puy de Folles Volcano Region

Ferromanganese formations are widespread in the Earth’s aquatic environment. Of all the mechanisms of their formation, the biogenic one is the most debatable. Here, we studied the Fe-Mn crusts of hydrothermal fields near the underwater volcano Puy de Folles (rift valley of the Mid-Atlantic Ridge). The chemical and mineralogical composition (optical and electron microscopy with EDX, X-ray powder diffraction, X-ray fluorescence analysis, Raman and FTIR spectroscopy, gas chromatography—mass spectrometry (GC-MS)) and the magnetic properties (static and resonance methods, including at cryogenic temperatures) of the samples of Fe-Mn crusts were investigated. In the IR absorption spectra, based on hydrogen bond stretching vibrations, it was concluded that there were compounds with aliphatic (alkane) groups as well as compounds with double bonds (possibly with a benzene ring). The GC-MS analysis showed the presence of alkanes, alkenes, hopanes, and steranes. Magnetically, the material is highly coercive; the blocking temperatures are 3 and 13 K. The main carriers of magnetism are ultrafine particles and X-ray amorphous matter. The analysis of experimental data allows us to conclude that the studied ferromanganese crusts, namely in their ferruginous phase, were formed as a result of induced biomineralization with the participation of iron-oxidizing and iron-reducing bacteria.