Iron-reducing Bacteria Research Articles

Mineral transformation of poorly crystalline ferrihydrite to hematite and goethite facilitated by an acclimated microbial consortium in electrodes of soil microbial fuel cells

In this study, we investigated the biogenic mineral transformation of poorly crystalline ferrihydrite in the presence of an acclimated microbial consortium after confirming successful soil microbial fuel cell optimization. The acclimated microbial consortia in the electrodes distinctly transformed amorphous ferrihydrite into crystallized hematite (cathode) and goethite (anode) under ambient culture conditions (30 °C). Serial analysis, including transmission/scanning electron microscopy and X-ray/selected area electron diffraction, confirmed that the biogenically synthesized nanostructures were iron nanospheres (~100 nm) for hematite and nanostars (~300 nm) for goethite. Fe(II) ion production with acetate oxidation via anaerobic respiration was much higher in the anode electrode sample (3.2- to 17.8-fold) than for the cathode electrode or soil samples. Regarding the culturable bacteria from the acclimated microbial consortium, the microbial isolates were more abundant and diverse at the anode. These results provide new insights into the biogeochemistry of iron minerals and microbial fuel cells in a soil environment, along with physiological characters of microbes (i.e., iron-reducing bacteria), for in situ applications in sustainable energy research.

Hydrogel bioreactor drives Feammox and synergistically removes composite pollutants: Performance optimization, microbial communities and functional genetic differences

Mixed pollutant wastewater has been a difficult problem due to the high toxicity of water bodies and the difficulty of treatment. Rice husk biochar modified with nano-iron tetroxide (RBC-nFe3O4) by polyvinyl alcohol cross-linking internal doping was used to introduce iron-reducing bacteria Klebsiella sp. FC61 to construct a bioreactor. The results of the long-term operation of the bioreactor showed that the removal efficiency of ammonia nitrogen (NH4+-N) and chemical oxygen demand best reached 90.18 and 98.49%, respectively. In addition, in the co-presence of Ni2+, Cd2+, and ciprofloxacin, the bioreactor was still able to remove pollutants efficiently by RBC-nFe3O4 and bio-iron precipitation inside the biocarrier. During the long-term operation, Klebsiella was always the dominant species in the bioreactor. And the sequencing data for functional prediction showed that the biocarrier contained a variety of enzymes and proteins involved in Feammox-related activities to ensure the stable and efficient operation of the bioreactor.

Evaluation of microbiologically influenced corrosion and biofouling in a nuclear storage basin

Biofouling and microbiologically influenced corrosion are major concerns to the long-term integrity of nuclear waste storage basins. The results of long-term microbial monitoring of nuclear storage at the Savannah River Site L-Basin nuclear material storage facility were examined to determine corrosion potential and biofouling. The densities of specific microbial species that can impact microbial corrosion and biofouling, including sulfate-reducing bacteria (SRB) and acid-producing (e.g., iron-oxidizing) bacteria (APB), were quantified by colony forming units (CFU). Several trends in microbial activity were observed during this time period. Overall microbial densities decreased slightly between 2000 and 2012. Metabolic diversity of microorganisms as measured by BIOLOG™ also decreased dramatically during this time. Aerobic microbial densities decreased from 2001 to 2010. Aerobes were most prevalent at 3.23 average CFU/mL and APB densities were lower at 0.80 average CFU/mL. From 2017 to present, iron-reducing bacteria were most prevalent at 3.41 average CFU/mL and APB were least prevalent at 0.44 average CFU/mL. All bacterial densities decreased except that of low-nutrient bacteria, which averaged 2.90 CFU/mL, and SRB averaged 0.19 CFU/mL. No distinct correlations between microbial concentrations, temperature, and either water chemistry parameters (pH and conductivity) or radiological conditions (19–30 disintegrations per minute (DPM) beta-gamma/mL; the equivalent to 0.32–0.50 Bq per mL) were determined. The occurrence of microbial biofilm formation on storage cannisters created biofouling issues in recent years. Although cleaning the biofouled surfaces provided temporary relief, the biofouling returned. Based on these results and physical observations of coupons, there has been minimal evidence of corrosion to date.

Bioenergetics of aerobic and anaerobic growth of Shewanella putrefaciens CN32.

Shewanella putrefaciens is a model dissimilatory iron-reducing bacterium that can use Fe(III) and O2 as terminal electron acceptors. Consequently, it has the ability to influence both aerobic and anaerobic groundwater systems, making it an ideal microorganism for improving our understanding of facultative anaerobes with iron-based metabolism. In this work, we examine the bioenergetics of O2 and Fe(III) reduction coupled to lactate oxidation in Shewanella putrefaciens CN32. Bioenergetics were measured directly via isothermal calorimetry and by changes to the chemically defined growth medium. We performed these measurements from 25 to 36°C. Modeling metabolism with macrochemical equations allowed us to define a theoretical growth stoichiometry for the catabolic reaction of 1.00 O2:lactate and 1.33 Fe(III):lactate that was consistent with the observed ratios of O2:lactate (1.20 ± 0.23) and Fe(III):lactate (1.46 ± 0.15) consumption. Aerobic growth showed minimal variation with temperature and minimal variation in thermodynamic potentials of incubation. Fe(III)-based growth showed a strong temperature dependence. The Gibbs energy and enthalpy of incubation was minimized at ≥30°C. Energy partitioning modeling of Fe(III)-based calorimetric incubation data predicted that energy consumption for non-growth associate maintenance increases substantially above 30°C. This prediction agrees with the data at 33 and 35°C. These results suggest that the effects of temperature on Shewanella putrefaciens CN32 are metabolism dependent. Gibbs energy of incubation above 30°C was 3-5 times more exergonic with Fe(III)-based growth than with aerobic growth. We compared data gathered in this study with predictions of microbial growth based on standard-state conditions and based on the thermodynamic efficiency of microbial growth. Quantifying the growth requirements of Shewanella putrefaciens CN32 has advanced our understanding of the thermodynamic constraints of this dissimilatory iron-reducing bacterium.

Biomagnetism: Insights Into Magnetic Minerals Produced by Microorganisms

Biomagnetism describes the biological origin of magnetism within living organisms. This phenomenon occurs due to the formation of iron-based minerals that exhibit magnetic ordering at room temperature. Perhaps the most studied form of biomagnetism originates in bacteria, especially magnetotactic bacteria that produce internal magnetite and greigite grains and iron-reducing bacteria that produce magnetite nanoparticles externally as a byproduct of iron respiration. These bacteria likely contribute to a significant proportion of environmental magnetite. The emergence of biomagnetism remains unclear, although it is thought that magnetotactic bacteria evolved this mechanism several billion years ago. Understanding how and why micro-organisms generate biomagnetism is helping to shed light on the origin of life on Earth and potentially on other planets. Biomagnetism is also of broad interest to industrial and environmental applications.

Coupled pyrite and sulfur autotrophic denitrification for simultaneous removal of nitrogen and phosphorus from secondary effluent: feasibility, performance and mechanisms

The discharge standards of nitrogen (N) and phosphorus (P) in wastewater treatment plants (WWTPs) have become increasingly strict to reduce water eutrophication. Further reducing N and P in effluent from municipal WWTPs need to be achieved effectively and eco-friendly. In this study, a carbon independent pyrite and sulfur autotrophic denitrification (PSAD) system using pyrite and sulfur as electron donor was developed and compared with pyrite autotrophic denitrification (PAD) and sulfur autotrophic denitrification (SAD) systems through batch and continuous flow biofilter experiments. Compare to PAD and SAD, PSAD was more effective in simultaneous removal in N and P. At hydraulic retention time (HRT) 3 h, average effluent concentrations of total nitrogen (TN) and total phosphate (TP) of 1.40 ± 0.03 and 0.19 ± 0.02 mg/L were achieved when treating real secondary effluent with 20.65 ± 0.24 mg/L TN and 1.00 ± 0.24 mg/L TP. The improvement in simultaneous removal of N and P was attributed to the coupling of PAD and SAD in enhancing the transformation of sulfur and iron and enlarging the reaction zone in the pyrite and sulfur autotrophic denitrification biofilter (PSADB) system. Therefore, more biomass was accumulated and the microbial denitrification functional stability, including electrons transfer and consumption was enhanced on the surface of pyrite and sulfur particles in the PSADB system. Moreover, autotrophic denitrifiers (Thiobacillus and Ferritrophicum), sulfate-reducing bacteria (Desulfocapsa) and iron reducing bacteria (Geothrix), acting as contributors to microbial nitrogen, sulfur and iron cycle, were specially enriched. In addition, the leaching of iron ions was promoted, which facilitated the removal of phosphate in the form of Fe3(PO4)2·8H2O and Fe3PO4. PSADB has proven to be an efficient technology for simultaneous removal of N and P, which could meet increasingly stringent discharge standards effectively and eco-friendly.

Active Nitrogen Fixation by Iron-Reducing Bacteria in Rice Paddy Soil and Its Further Enhancement by Iron Application

In rice paddy soil, biological nitrogen fixation is important for sustaining soil nitrogen fertility and rice growth. Anaeromyxobacter and Geobacteriaceae, iron-reducing bacteria belonging to Deltaproteobacteria, are newly discovered nitrogen-fixing bacteria dominant in paddy soils. They utilize acetate, a straw-derived major carbon compound in paddy soil, as a carbon and energy source, and ferric iron compounds as electron acceptors for anaerobic respiration. In our previous paddy field experiments, a significant increase in soil nitrogen-fixing activity was observed after the application of iron powder to straw-returned paddy field soil. In addition, combining iron application with 60–80% of the conventional nitrogen fertilizer rate could maintain rice yields similar to those with the conventional nitrogen fertilization rate. It was thus suggested that iron application to paddy soil increased the amount of nitrogen fixed in the soil by enhancing nitrogen fixation by diazotrophic iron-reducing bacteria. The present study was conducted to directly verify this suggestion by 15N-IRMS analysis combined with 15N-DNA-stable isotope probing of iron-applied and no-iron-applied plot soils in an experimental paddy field. In no-iron-applied native paddy soil, atmospheric 15N2 was incorporated into the soil by biological nitrogen fixation, in which diazotrophic iron-reducing bacteria were the most active drivers of nitrogen fixation. In iron-applied paddy soil, the amount of 15N incorporated into the soil was significantly higher due to enhanced biological nitrogen fixation, especially via diazotrophic iron-reducing bacteria, the most active drivers of nitrogen fixation in the soil. Thus, our previous suggestion was verified. This study provided a novel picture of active nitrogen-fixing microorganisms dominated by diazotrophic iron-reducing bacteria in paddy soil, and directly proved the effectiveness of iron application to enhance their nitrogen fixation and increase the incorporation of atmospheric nitrogen into soil. The enhancement of biological nitrogen fixation in paddy fields by iron application may lead to novel and unique paddy soil management strategies to increase soil nitrogen fertility and ensure rice yields with reduced nitrogen fertilizer input and lower environmental nitrogen burdens.

Potential relevance between soybean nitrogen uptake and rhizosphere prokaryotic communities under waterlogging stress

Waterlogging in soil can limit the availability of nitrogen to plants by promoting denitrification and reducing nitrogen fixation and nitrification. The root-associated microorganisms that determine nitrogen availability at the root-soil interface can be influenced by plant genotype and soil type, which potentially alters the nitrogen uptake capacity of plants in waterlogged soils. In a greenhouse experiment, two soybean genotypes with contrasting capacities to resist waterlogging stress were grown in Udic Argosol and Haplic Alisol soils with and without waterlogging, respectively. Using isotope labeling, high-throughput amplicon sequencing and qPCR, we show that waterlogging negatively affects soybean yield and nitrogen absorption from fertilizer, atmosphere, and soil. These effects were soil-dependent and more pronounced in the waterlogging-sensitive than tolerant genotype. The tolerant genotype harbored more ammonia oxidizers and less nitrous oxide reducers. Anaerobic, nitrogen-fixing, denitrifying and iron-reducing bacteria such as Geobacter/Geomonas, Sphingomonas, Candidatus Koribacter, and Desulfosporosinus were proportionally enriched in association with the tolerant genotype under waterlogging. These changes in the rhizosphere microbiome might ultimately help the plant to improve nitrogen uptake under waterlogged, anoxic conditions. This research contributes to a better understanding of the adaptability of soybean genotypes under waterlogging stress and might help to formulate fertilization strategies that improve nitrogen use efficiency of soybean.Schematic representation of the effects of waterlogging on nitrogen uptake and rhizosphere microbiota in dependence of soil type and soybean genotype.

Clay-associated microbial communities and their relevance for a nuclear waste repository in the Opalinus Clay rock formation.

Microorganisms are known to be natural agents of biocorrosion and mineral transformation, thereby potentially affecting the safety of deep geological repositories used for high-level nuclear waste storage. To better understand how resident microbial communities of the deep terrestrial biosphere may act on mineralogical and geochemical characteristics of insulating clays, we analyzed their structure and potential metabolic functions, as well as site-specific mineralogy and element composition from the dedicated Mont Terri underground research laboratory, Switzerland. We found that the Opalinus Clay formation is mainly colonized by Alphaproteobacteria, Firmicutes, and Bacteroidota, which are known for corrosive biofilm formation. Potential iron-reducing bacteria were predominant in comparison to methanogenic archaea and sulfate-reducing bacteria. Despite microbial communities in Opalinus Clay being in majority homogenous, site-specific mineralogy and geochemistry conditions have selected for subcommunities that display metabolic potential for mineral dissolution and transformation. Our findings indicate that the presence of a potentially low-active mineral-associated microbial community must be further studied to prevent effects on the repository's integrity over the long term.

Iron reduction as a viable metabolic pathway in Enceladus’ ocean

AbstractRecent studies postulated the viability of a suite of metabolic pathways in Enceladus’ ocean motivated by the detection of H2 and CO2 in the plumes – evidence for available free energy for methanogenesis driven by hydrothermal activity at the moon's seafloor. However, these have not yet been explored in detail. Here, a range of experiments were performed to investigate whether microbial iron reduction could be a viable metabolic pathway in the ocean by iron-reducing bacteria such as Geobacter sulfurreducens. This study has three main outcomes: (i) the successful reduction of a number of crystalline Fe(III)-bearing minerals predicted to be present at Enceladus was shown to take place to differing extents using acetate as an electron donor; (ii) substantial bacterial growth in a simulated Enceladus ocean medium was demonstrated using acetate and H2(g) separately as electron donors; (iii) microbial iron reduction of ferrihydrite was shown to partially occur at pH 9, the currently accepted value for Enceladus’ ocean, whilst being severely hindered at the ambient ocean temperature of 0°. This study proposes the possibilities for biogeochemical iron cycling in Enceladus’ ocean, suggesting that a strain of iron-reducing bacteria can effectively function under Enceladus-like conditions.

Iron reduction in composting environment synergized with quinone redox cycling drives humification and free radical production from humic substances

The aim of this paper was to investigate the influence of Fe (III) on humification and free radicals evolution. The experimental data showed that the experimental group (CT) with Fe2(SO4)3 had a better degree of humification than the control group (CK). The humic substances (HS) content was 10% higher in CT (23.94 mg·g−1) than in CK (21.54 mg·g−1) in the final. Fe (III) contributed significantly to the formation of free radicals in HS. The amount of H2O2 in CT increased to 74.8 mmol·kg−1, while CK was only 46.5 mmol·kg−1. The content of semiquinone free radical was 10.32 × 1011 spins/mm3 in CT, 5.11 × 1011 spins/mm3 in CK in the end. Several iron-reducing bacteria were detected in composting, among which Paenibacillus was dominant. The above findings suggested that the application of Fe2(SO4)3 enhanced the iron reduction synergistic quinone redox cycling and promoted the generation of free radicals during the humification of composting.

A study on the microbial biocorrosion behavior of API 5 L X65 carbon steel exposed to seawater

AbstractDespite much progress achieved, corrosion in oil and gas pipelines remains a concern due to industrial failures, and environmental and economic damages. Oil and gas pipeline failures are very common as a result of the natural degradation of carbon steel exposed to the marine environment. It has been reported that the presence of microorganisms in seawater contributes to the intensification of corrosion and subsequent biofilm formation on metal surfaces. Few scientific publications have investigated the effects of seawater containing natural microorganisms on the internal corrosion of pipelines, which is the motivation for this study. The present study aims to report the corrosion behavior of carbon steel American Petroleum Institute (API) 5 L X65 exposed to seawater collected from the Persian Gulf containing microorganisms such as sulfate‐reducing bacteria (SRB), iron‐reducing bacteria (IRB), and acid‐producing bacteria (APB). Microorganisms were detected, segregated, colonized, and finally injected into autoclaved seawater to investigate their effect on the corrosion behavior of carbon steel. Nondestructive electrochemical techniques were performed to study the corrosion behavior and field emission electron microscope images and energy dispersive x‐ray analysis (EDS) were also utilized to characterize the corrosion products. The results confirmed the amounts of oxygen and iron presented of FeO as the main corrosion product in abiotic conditions. Corrosion products and electrochemical properties of steel have been influenced by microbial activity. The variation of the open circuit potentials (OCP) and Electrochemical Impedance Spectroscopy (EIS) demonstrated that SRB and APB could not only significantly harm an alloy, but also could alter its electrochemical behavior from uniform to local damage. The outcomes proved that biofilm formation and bacterial activity can cause serious degradation.

Co-digestion of sulfur-rich vegetable waste with waste activated sludge enhanced phosphorus release and hydrogenotrophic methanogenesis

Anaerobic co-digestion of sulfur-rich vegetable waste (SVW) with waste activated sludge (WAS) and the underlying mechanisms associated with methane production and phosphorus (P) release were investigated. Four types of SVW (Chinese cabbage, cabbage, rapeseed cake, and garlic) were utilized for co-digestion with WAS, and the methane yield increased by 7.3%–35.3%; in the meantime, the P release amount from WAS was enhanced by 9.8%–24.9%. The organic carbon in SVW promoted methane production, while organic sulfur and the formation of FeS facilitated P release. Among the four types of SVW, rapeseed cake was identified as the most suitable co-digestion substrate for enhancing both methane production and P release due to its balanced nutrients and relatively high sulfur content. Syntrophic bacteria working with hydrogenotrophic methanogens, iron-reducing bacteria, sulfate-reducing bacteria, and hydrogenotrophic methanogens were enriched. Metabolic pathways related to sulfate reduction and methanogenesis were facilitated, especially hydrogenotrophic methanogenesis. Enzymes involved in hydrogenotrophic methanogenesis were promoted by 76.05%–407.98% with the addition of Chinese cabbage, cabbage, or rapeseed cake. This study provides an eco-friendly technology for promoting P resource and energy recovery from WAS and an in-depth understanding of the corresponding microbial mechanisms.

Remediation of Cr(VI)-contaminated soil mixed with chromite ore processing residue by ferrous sulfate and enzyme residue

In this study, Cr(VI)-contaminated soil mixed with COPR by using ferrous sulfate (FeSO4), enzyme residue (ER), and their combination under aerobic or anaerobic condition were investigated. The concentration of Cr(VI) decreased from 1498.05 to 104.63 mg kg−1 after the simultaneous addition of FeSO4 (30 %, w/w as FeSO4·7H2O) and ER (30 %, w/w) at 45 d under the anaerobic condition with a reduction efficiency of 93.02 %, which is higher than that by single FeSO4 (72.39 %) or ER (75.47 %) under the anaerobic condition. XRD, XPS, FTIR, and fluorescence spectroscopy were conducted to characterize soil and ER composition. Metagenomic analysis was performed to reveal the reduction mechanisms of FeSO4 and ER. The anaerobic condition with lower Eh was beneficial for Cr(VI) reduction than aerobic condition, and Eh was the main driver for the evolution of Cr(VI) reduction-related microorganisms. Moreover, the addition of ER enriched the organic matter and microbials in the soil. During the decomposition of organic matter under the anaerobic condition, organic acids were generated, leading to a decrease in pH and promoting the release of Cr(VI) from minerals. They also served as electron donors in Cr(VI) reduction. Additionally, the addition of excess FeSO4 stimulated the growth of iron-reducing bacteria and sulfate-reducing bacteria, facilitating to Cr(VI) reduction. Metagenomic analysis showed that Acinetobacter, related to the nemA and nfsA genes, was the dominant Cr(VI) reduction genus. Thus, the combination of FeSO4 and ER is a promising method for the remediation of Cr(VI)-contaminated soils mixed with COPR.

Dithionite promoted microbial dechlorination of hexachlorobenzene while goethite further accelerated abiotic degradation by sulfidation in paddy soil

It is of great scientific and practical importance to explore the mechanisms of accelerated degradation of Hexachlorobenzene (HCB) in soil. Both iron oxide and dithionite may promote the reductive dechlorination of HCB, but their effects on the microbial community and the biotic and abiotic mechanisms behind it remain unclear. This study investigated the effects of goethite, dithionite, and their interaction on microbial community composition and structure, and their potential contribution to HCB dechlorination in a paddy soil to reveal the underlying mechanism. The results showed that goethite addition alone did not significantly affect HCB dechlorination because the studied soil lacked iron-reducing bacteria. In contrast, dithionite addition significantly decreased the HCB contents by 44.0–54.9%, while the coexistence of dithionite and goethite further decreased the HCB content by 57.9–69.3%. Random Forest analysis suggested that indicator taxa (Paenibacillus, Acidothermus, Haliagium, G12-WMSP1, and Frankia), Pseudomonas, richness and Shannon’s index of microbial community, and immobilized Fe content were dominant driving factors for HCB dechlorination. The dithionite addition, either with or without goethite, accelerated HCB anaerobic dechlorination by increasing microbial diversity and richness as well as the relative abundance of the above specific bacterial genera. When goethite and dithionite coexist, sulfidation of goethite with dithionite could remarkably increase FeS formation and then further promote HCB dechlorination rates. Overall, our results suggested that the combined application of goethite and dithionite could be a practicable strategy for the remediation of HCB contaminated soil.

Corrosion behavior on carbon steel affected by iron-reducing bacteria via dissimilatory Fe(Ⅲ) reduction in simulated marine atmospheric environment

The corrosion behavior of carbon steel in simulated marine atmospheric environment combined with microorganisms was investigated. Results demonstrated that weight loss was increased, pitting corrosion was aggravated and the velocity of charge transfer and ionic migration were accelerated in media with bacteria. 16S rDNA sequencing revealed that iron-reducing bacteria (IRB) grew into a dominant population in the biofilm. The compact and protective corrosion product film in the inner layer was disrupted locally in presence of IRB. The corrosion mechanism of carbon steel in marine atmospheric environment influenced by IRB via dissimilatory Fe(Ⅲ) reduction had been discussed.

Nano iron tetroxide-modified rice husk biochar promoted Feammox performance of Klebsiella sp. FC61 and synergistically removed Ni2+ and ciprofloxacin

The iron reduction coupled with ammonia oxidation process (Feammox) is a biological reaction process associated with the nitrogen cycle that has been discovered in recent years. In this study, the iron-reducing bacterium Klebsiella sp. FC61 was attached by synthesizing nano-loadings of iron tetroxide (nFe3O4) onto rice husk biochar (RBC), and the RBC-nFe3O4 was used as an electron shuttle to participate in the biological iron reduction process of soluble and insoluble Fe3+ to improve the ammonia oxidation efficiency to 81.82%. This acceleration of electron transfer increased the carbon consumption rate and further tuned up the COD removal efficiency to 98.00%. The Feammox could be coupled with iron denitrification for internal nitrogen/iron cycling to reduce the accumulation of nitrate by-products and achieve the recycling of iron. In addition, pollutants such as Ni2+, ciprofloxacin, and formed chelates could be removed by pore adsorption and π-π interactions using bio-iron precipitates produced by iron-reducing bacteria.

Preparation and mechanism of carbon felt supported iron trioxide and zero-valent iron for enhancing anaerobic digestion performance

Promoting direct interspecies electron transfer (DIET) for methanogenesis via conductive materials is an effective strategy to enhance anaerobic digestion (AD) for methane production. In situ growth of iron trioxide (ITO) and zero-valent iron (ZVI) on carbon felts (CF) was first prepared as composite CF@ITO and CF@ZVI for AD application in this study via hydrothermal deposition and co-precipitation, respectively. The optimal preparation conditions of 2-fold concentration and 120℃ for CF@ITO and of 1-fold concentration for CF@ZVI were determined via batch AD tests adding different iron-carbon composites. Methane production was increased by 47.73% and 34.98%, respectively, for the optimally prepared CF@ITO and CF@ZVI compared to the control. The mechanisms behind were further explored in a more systematic and profound way. Cyclic voltammetry measurements showed that CF@ITO and CF@ZVI had around 10 times higher double-layer capacitance than CF, demonstrating the enhanced conductivity of iron-carbon composites. Fe and fluorescence analysis revealed that both composites increased Fe bioavailability and sludge conductivity potentially via enriching electrochemically active microorganisms and stimulating the secretion of protein-like substances, which enhanced microbial activity for methanogensis. Metagenomic sequencing analysis indicated that both composites enriched the functional genes associated with energy production and conversion, carbon and methane metabolism, and polysaccharide lyase activity. Iron reducing bacteria enhancing carbohydrate metabolic activity were more enriched in sludge after adding composites. Methanothrix capable of undertaking DIET for methanogenesis and electron carrier proteins associated genes were significantly enriched in biofilm on CF@ITO and CF@ZVI, implying the mediation of DIET via both composites and electron carrier proteins. Methanocorpusculum and Methanobacterium via interspecific hydrogen transfer (IHT) for methanogenesis were only significantly enriched in biofilm on CF@ZVI, demonstrating both enhanced DIET and IHT by CF@ZVI.

Vertical distribution of dissimilatory iron reducing communities in the sediments of Taihu Lake

The reduction of Fe(III) coupled with the oxidation of organic matter, primarily stimulated by dissimilatory iron-reducing bacteria (DIRB) under anoxic conditions, is a critical biogeochemical process in lacustrine sediments. Many single strains have been recovered and investigated, however, the changes in the diversity of culturable DIRB communities with sedimentary depth have not been fully revealed. In this study, 41 DIRB strains affiliated to ten genera of phylum Firmicutes, Actinobacteria, and Proteobacteria were isolated from the sediments of Taihu Lake at three depths (0–2 cm, 9–12 cm, and 40–42 cm), referring to distinct nutrient conditions. Fermentative metabolisms were identified in nine genera (except genus Stenotrophomonas). The DIRB community diversity and the microbial iron reduction (MIR) patterns vary in vertical profiles. The community abundance varied with the TOC contents in vertical profiles. The DIRB communities, containing 17 strains of 8 genera, were most diverse in the surface sediments (0–2 cm), where organic matter was most abundant among the three depths. 11 DIRB strains of five genera were identified in the 9–12 cm sediments with the lowest content of organic matter, while 13 strains of seven genera were identified in deep sediments (40–42 cm). Among the isolated strains, phylum Firmicutes dominated the DIRB communities at three depths, while its relative abundance increased with depth. Fe2+ ion was recognized as the dominant microbial ferrihydrite-reducing product of DIRB from 0 to 12 cm sediments. Instead, lepidocrocite and magnetite were the main MIR products of DIRB retrieved from 40 to 42 cm. The results indicate that the MIR driven by fermentative DIRB is crucial in lacustrine sediments and that the distribution of nutrients and iron (minerals) likely influences the diversity of DIRB communities in the lacustrine sediments.

Synthesis and Enhanced Oil Recovery Potential of the Bio-Nano-Oil Displacement System.

Nanoparticles (NPs) have attracted great attention in the tertiary oil recovery process due to their unique properties. As an economical and efficient green synthesis method, biosynthesized nanoparticles have the advantages of low toxicity, fast preparation, and high yield. In this study, with the theme of biotechnology, for the first time, the bio-nanoparticles reduced by iron-reducing bacteria were compounded with the biosurfactant produced by Bacillus to form a stable bio-nano flooding system, revealing the oil flooding mechanism and enhanced oil recovery (EOR) potential of the bio-nano flooding system. The interfacial properties of the bio-nano-oil displacement system were studied by interfacial tension and wettability change experiments. The enhanced oil recovery potential of the bio-nano-oil displacement agent was measured by microscopic oil displacement experiments and core flooding experiments. The bio-nano-oil displacement system with different nanoparticle concentrations can form a stable dispersion system. The oil-water interfacial tension and contact angle decreased with the increase in concentration of the bio-nano flooding system, which also has a high salt tolerance. Microscopic oil displacement experiments proved the efficient oil displacement of the bio-nano-oil displacement system and revealed its main oil displacement mechanism. The effects of concentration and temperature on the recovery of the nano-biological flooding system were investigated by core displacement experiments. The results showed that the recovery rate increased from 4.53 to 15.26% with the increase of the concentration of the system. The optimum experimental temperature was 60 °C, and the maximum recovery rate was 15.63%.