Iron-reducing Bacteria Research Articles

Comparative transcriptome and gut microbiota analysis of Exopalaemon carinicauda with different growth rates from a full-sib family

In the breeding process of Exopalaemon carinicauda from the same family, noticeable differences often occur in growth characteristics under the same conditions. To investigate this issue, we performed a comparative transcriptome analysis to identify the critical genes involved in weight gain and compared the intestinal flora to screen for potential intestinal probiotics. In total, we identified 1311 differentially expressed genes (DEGs), of which 735 genes, including troponin C, chitinase, cathepsin B, cathepsin L, and trypsin, were upregulated exclusively in the fast growth group. Several DEGs were validated by quantitative real-time PCR and assigned to the ribosome, phagosome, apoptosis, purine metabolism, and Hippo signaling pathways. The microbiome community richness and diversity of the fast-growing individuals (FGIs) were higher than those of the slow-growing individuals (SGIs). In the current study, the intestinal microflora was mainly distributed in the Proteobacteria, Firmicutes, and Bacteroidota. The species with significant differences (P < 0.05) between the FGI and SGI groups included the iron-reducing bacteria, Nitrospira moscoviensis, Sulfuritalea hydrogenivorans, and Alpha proteobacterium. Our results provided insights towards revealing the mechanism underlying the growth differences in E. carinicauda.

Water Management Impacts on Chromium Behavior and Uptake by Rice in Paddy Soil with High Geological Background Values.

Chromium (Cr) is an expression toxic metal and is seriously released into the soil environment due to its extensive use and mining. Basalt is an important Cr reservoir in the terrestrial environment. Cr in paddy soil can be enriched by chemical weathering. Therefore, basalt-derived paddy soils contain extremely high concentrations of Cr and can enter the human body through the food chain. However, the water management conditions' effect on the transformation of Cr in basalt-derived paddy soil with high geological background values was less recognized. In this study, a pot experiment was conducted to investigate the effects of different water management treatments on the migration and transformation of Cr in a soil-rice system at different rice growth stages. Two water management treatments of continuous flooding (CF) and alternative wet and dry (AWD) and four different rice growth stages were set up. The results showed that AWD treatment significantly reduced the biomass of rice and promoted the absorption of Cr in rice plants. During the four growth periods, the root, stem and leaf of rice increased from 11.24-16.11 mg kg-1, 0.66-1.56 mg kg-1 and 0.48-2.29 mg kg-1 to 12.43-22.60 mg kg-1, 0.98-3.31 mg kg-1 and 0.58-2.86 mg kg-1, respectively. The Cr concentration in roots, stems and leaves of AWD treatment was 40%, 89% and 25% higher than CF treatment in the filling stage, respectively. The AWD treatment also facilitated the potential bioactive fractions conversion to the bioavailable fraction, compared with the CF treatment. In addition, the enrichment of iron-reducing bacteria and sulfate-reducing bacteria with AWD treatment also provided electron iron for the mobilization of Cr, thus affecting the migration and transformation of Cr in the soil. We speculated that the reason for this phenomenon may be the bioavailability of Cr was affected by the biogeochemical cycle of iron under the influence of alternating redox. This indicates that AWD treatment may bring certain environmental risks in contaminated paddy soil with high geological background, and it is necessary to be aware of this risk when using water-saving irrigation to plant rice.

Dynamic variations of oil components and microbial communities during indigenous microbial stimulation pilot study in low-permeability reservoirs

Indigenous microbial stimulation is considered as a highly promising technology for enhanced oil recovery (EOR) of low-permeability reservoirs. In this paper, oil components and microbial communities of indigenous microorganisms before and after bio-stimulation in the largest low-permeability oil field of China were discussed. The results showed that Pseudomonas aeruginosa was dominant in the original samples, followed by some sulfate-reducing bacteria (SRB) and iron-reducing bacteria (IRB), such as Desulfovibrio oxyclinae, and Methylopila capsulata, Deferribacter abyssi. After bio-stimulation, the species of microorganisms gradually decreased, the content of Pseudomonas aeruginosa reached 2∼3 times than that of the original samples. The harmful bacteria, such as SRB and IRB, gradually disappeared. The Pr/Ph of the oil decreased, whereas the Pr/nC 17, Ph/nC 18, and ∑nC 21−/∑nC 22+ increased. The average molecular weight of oil decreased after the microorganisms were stimulated, in which the contents of N1-containing compounds increased, and that of O1-containing compounds decreased. The contents of biphenyls, naphthalene, and its derivatives decreased. Whereas those of aromatic compounds, such as phenanthrene, quaternary, fluorene, and their homologs increased. Pilot study was applied in LD field block, the average water cut of 27–47 well group decreased from 87.60% to 74.86%, the oil production increased from 12.18 t/d to 29.58 t/d.

Enrichment and response of iron-metabolizing microorganisms and metabolic genes in the contaminated area of stratified stacking coal gangue dumps, Northern China.

In the Xishan coalfield of northern China, the stratified stacking of soil and gangue was applied to limit the acid pollution from high-sulfur coal gangue. In this study, we found that stratified stacking can effectively neutralize the acidity, with the pH value of gangue-leaching water being 6.02-8.13. In contrast to the acidic contaminated area, most of the microorganisms in the study area sediment were neutrophilic, with the main genera being Arthrobacter, Pseudorhodobacter, Pseudomonas, and Rhodoferax. A variety of iron- and sulfur-metabolizing bacteria was discovered in the gangue-leaching sediment, with the total relative abundance ranging from 4.20 to 23.75%, of which the iron-reducing bacteria (FeRB) accounted for the highest percentage. The distributions of these functional microorganisms in the samples were significantly influenced by Fe and S. The co-occurrence network analysis revealed a significant positive correlation between the iron- and sulfur-metabolizing bacteria in the sediment (93.75%), indicating a strong reciprocal symbiotic relationship between these bacteria. The iron and sulfur metabolism genes in the sediment were predicted and compared based on the Tax4Fun functional prediction method. Results showed that functional genes related to iron metabolism were highly expressed in the gangue-leaching sediment. This study enhances the understanding of iron and sulfur metabolism in gangue-leaching contaminated areas.

Microbial reduction and alteration of Fe(III)-containing smectites in the presence of biochar-derived dissolved organic matter

Clay minerals are important components of solid-phase iron pools in soils, and the redox state of structurally-coordinated iron in clay minerals can significantly influence soil physicochemical properties. Due to increasing use of biochar in agriculture, the dissolved organic matter derived from biochar (BDOM) has become an unignorable fraction of dissolved organic carbon in soil systems. However, our knowledge regarding the effect of BDOM on soil biogeochemical processes (particularly on iron redox cycling) is still very limited. To examine the role of BDOM in the microbial reduction of Fe(III) in clays, BDOM was extracted from wheat straw biochar and selectively added to laboratory reactors in which lactate, Fe(III)-containing smectite (montmorillonite SWy-2 or nontronite NAu-2), and a typical iron-reducing bacterium Shewanella oneidensis strain MR-1 were used as the respective electron donor, electron acceptor, and reaction mediator. The results demonstrated that BDOM contained bio-reactive quinone moieties. BDOM amendment increased the initial rate and final extent of Fe(III) bioreduction by strain MR-1. Such promotion effect of BDOM might be ascribed to its quinone moieties functioning as electron shuttles between MR-1 cells and structural Fe(III) in smectite. Structural changes were observed in the bioreduced smectite systems, especially for NAu-2 reactors in which obvious dissolution and illitization occurred. These observations suggest that BDOM is bio-reactive and is able to stimulate the microbial reduction of Fe(III) in clay minerals, and may offer new insights into the effects of biochar application in elemental cycles in soils.

Unveiling the mechanisms of Fe(III)-loaded chitosan composite (CTS-Fe) in enhancing anaerobic digestion of waste activated sludge

Anaerobic digestion (AD) of waste activated sludge (WAS) is usually limited by the low generation efficiency of methane. Fe(III)-loaded chitosan composite (CTS-Fe) have been reported to effectively enhanced the digestion of WAS, but its role in promoting anaerobic sludge digestion remains unclear. In present study, the effects of CTS-Fe on the hydrolysis and methanogenesis stages of WAS anaerobic digestion were investigated. The addition of CTS-Fe increased methane production potential by 8%–23% under the tested conditions with the addition of 5–20 g/L CTS-Fe. Besides, the results demonstrate that the addition of CTS-Fe could effectively promote the hydrolysis of WAS, evidenced by lower protein or polysaccharides concentration, higher soluble organic carbon in rector adding CTS-Fe, as well as the increased activity of extracellular hydrolase with higher CTS-Fe concentration. Meanwhile, the enrichment of Clostridia abundance (iron-reducing bacteria (IRBs)) was observed in CTS-Fe adding reactor (8.9%–13.8%), which was higher than that in the control reactor (7.9%). The observation further suggesting the acceleration of hydrolysis through dissimilatory iron reduction (DIR) process, thus providing abundant substrates for methanogenesis. However, the presence of CTS-Fe was inhibited the acetoclastic and hydrogenotrophic methanogenesis process, which could be ascribed to the Fe(III) act as electron acceptor coupled to methane for anaerobic oxidation. Furthermore, coenzyme F420 activity in the CTS-Fe added reactor was 34.9% lower than in the blank, also abundance of microorganisms involved in hydrogenotrophic methanogenesis was decreased. Results from this study could provide theoretical support for the practical applications of CTS-Fe.

Simultaneous partial nitrification, Anammox and nitrate-dependent Fe(II) oxidation (NDFO) for total nitrogen removal under limited dissolved oxygen and completely autotrophic conditions

Sustainable nitrogen removal from wastewater at reduced energy and/or chemical consumptions is challenging. This paper investigated, for the first time, the feasibility of coupled partial nitrification, Anammox and nitrate-dependent Fe(II) oxidation (NDFO) for sustainable autotrophic nitrogen removal. With NH4+-N as the only nitrogen-containing compound in the influent, near-complete nitrogen removal (a total of 97.5 % with a maximal total nitrogen removal rate of 6.64 ± 2.68 mgN/L/d) was achieved in a sequencing batch reactor for a 203-d operation without organic carbon source addition and forced aeration. Anammox (predominated by Candidatus Brocadia) and NDFO bacteria (such as Denitratisoma) were successfully enriched, with total relative abundances up to 11.54 % and 10.19 %, respectively. Dissolved oxygen (DO) concentration was a key factor affecting the coupling of multi (ammonia oxidization, Anammox, NDFO, iron-reduction, etc.) bacterial communities, resulting in different total nitrogen removal efficiencies and rates. In batch tests, the optimal DO concentration was 0.50–0.68 mg/L with a maximal total nitrogen removal efficiency of 98.7 %. Fe(II) in the sludge not only competed with nitrite oxidizing bacteria for DO to prevent complete nitrification, but promoted the transcription of NarG and NirK genes (10.5 and 3.5 times higher than the group without Fe(II) addition) as indicated by the reverse transcription quantitative polymerase chain reaction (RT-qPCR), resulting in increased NDFO rate (by 2.7 times) and promoted NO2−-N generated from NO3−-N, which back fed the Anammox process, achieving near-complete nitrogen removal. The reduction of Fe(III) by iron-reducing bacteria (IRB) and hydrolytic and fermentative anaerobes enabled a sustainable Fe(II)/Fe(III) recycling, avoiding the need in continuous Fe(II) or Fe (III) dosage. The coupled system is expected to benefit the development of novel autotrophic nitrogen removal processes with neglectable energy and material consumptions for the treatment of wastewater with low organic carbon and NH4+-N contents in underdeveloped regions, such as decentralized rural wastewaters.

Promoting vivianite recovery: Crucial role of tightly-bound extracellular polymeric substances

Vivianite is an important bio-induced product of dissimilated iron reduction (DIR), which exists widely in activated sludge and digested sludge of wastewater treatment plants (WWTPs). Extracellular polymeric substances (EPS) surrounding dissimilatory iron-reducing bacteria (DIRB) were reported to be transient media for microbial extracellular electron transfer (EET) and DIR. However, what happens when a layer of EPS envelops microbial cells during vivianite recovery? This study tried to assess the relationship between iron reduction and electron transfer by stripping EPS layer-by-layer, then clarified the delamination of different EPS layers on the performance of vivianite recovery. After stripping total EPS (PC-EPS batches) of DIRB, the Fe (III) reduction efficiencies (RFe), Fe (III) reduction rate (VFe), and vivianite formation efficiency (RV) decreased by 33%, 37%, and 30%, respectively. Tightly bound-EPS (TB-EPS) was confirmed to play a crucial role in vivianite formation, which contributed 28–51% to vivianite recovery and 34–55% to iron reduction. Electronic shuttle substances were contained in TB-EPS, which enhanced the EET rate and efficiency between cells and Fe (III). The polysaccharide content of TB-EPS was positively related to adhesiveness between cells and mineral, as well as the iron reduction efficiency. Furthermore, redox proteins (PpcA, OmcB) were embedded in EPS, which shortened the distance of electron hopping to across the EPS layer and further accelerated vivianite recovery from wastewater. Long-term operation of anaerobic reactors confirmed that TB-EPS played critical roles in bio-induced vivianite formation.

Pelosinus baikalensis sp. nov., an Iron-Reducing Bacterium Isolated from a Cold Freshwater Lake

Pelosinus baikalensis sp. nov., an Iron-Reducing Bacterium Isolated from a Cold Freshwater Lake

Direct extracellular electron transfer to an indium tin doped oxide electrode via heme redox reactions in Desulfovibrio ferrophilus IS5

Soluble redox mediators have been hypothesized to play a major role in cellular electron transportation to extracellular insoluble electron acceptors in sulfate-reducing bacteria (SRB) through a diffusion-based electron shuttle mechanism. Herein, in vivo electrochemistry shows that outer-membrane cytochromes (OMCs) directly mediated extracellular electron transfer (EET) in Desulfovibrio ferrophilus IS5. Anodic current production by IS5, coupled with lactate oxidation, was detected on indium-tin-doped oxide electrodes poised at +400 mV (vs. standard hydrogen electrode), which was the sole electron acceptor. Subsequent electrolyte replacement experiments with a fresh one showed that cells attached to the electrode contributed to 73% of current production by direct EET, while the electron shuttle mechanism may have contributed to the rest. Differential pulse voltammetry detected two redox species at E = −180 and 20 mV, with the former being most likely assignable to cell-surface cytochromes because nitric oxide decreased the peak current at −180 mV, as previously demonstrated with OMCs in iron-reducing bacteria. The EET onset potential at −200 mV further supports the notion that OMCs mediated EET in IS5, and that EET is thermodynamically favorable for reducing Fe(III) oxide. These results suggest that the direct EET mechanism regulates the reduction rate of insoluble substrates in SRB.

Electrokinetic-Enhanced Bioremediation of Trichloroethylene-Contaminated Low-Permeability Soils: Mechanistic Insight from Spatio-Temporal Variations of Indigenous Microbial Community and Biodehalogenation Activity.

Electrokinetic-enhanced bioremediation (EK-Bio), particularly bioaugmentation with injection of biodehalogenation functional microbes such as Dehalococcoides, has been documented to be effective in treating a low-permeability subsurface matrix contaminated with chlorinated ethenes. However, the spatio-temporal variations of indigenous microbial community and biodehalogenation activity of the background matrix, a fundamental aspect for understanding EK-Bio, remain unclear. To fill this gap, we investigated the variation of trichloroethylene (TCE) biodehalogenation activity in response to indigenous microbial community succession in EK-Bio by both column and batch experiments. For a 195 day EK-Bio column (∼1 V/cm, electrolyte circulation, lactate addition), biodehalogenation activity occurred first near the cathode (<60 days) and then spread to the anode (>90 days), which was controlled by electron acceptor (i.e., Fe(III)) competition and microbe succession. Amplicon sequencing and metagenome analysis revealed that iron-reducing bacteria (Geobacter, Anaeromyxobacter, Geothrix) were enriched within initial 60 d and were gradually replaced by organohalide-respiring bacteria (versatile Geobacter and obligate Dehalobacter) afterward. Iron-reducing bacteria required an initial long time to consume the competitive electron acceptors so that an appropriate reductive condition could be developed for the enrichment of organohalide-respiring bacteria and the enhancement of TCE biodehalogenation activity.

Simultaneous removal of NOx− and NH4+ driven by Fe(II)/Fe(III) cycle under the continuously-feeding mode

Fe(III) (hydr)oxides have been reported to serve as the extracellular electron acceptor of iron-reducing bacteria to oxidize NH4+, and the resulted Fe(II) may be oxidized by NOx− to Fe(III) that continuously participates to the next round of NH4+ removal, but whether such the Fe(II)/Fe(III) cycle can simultaneously remove NOx− and NH4+ under continuously feeding modes remains unknown. In this study, a NH4+-containing wastewater with and without NO2− or NO3− was fed into anaerobic reactors continuously to investigate the nitrogen removal with the Fe(II)/Fe(III) cycle. The results showed that, under a hydraulic retention time (HRT) of 48 h, the NH4+-N removal efficiencies in the NO3−-fed and NO2−-fed reactors reached about 50.3 % and 42.7 % respectively, accompanied with the complete removal of NO3− and NO2−. The experiment of intermittent addition of 14NOx− into the serum bottle containing 15NH4+ showed that the Fe(II) content decreased rapidly after NOx− addition, and then gradually increased, indicating the occurrence of iron cycle. The isotope experiment also demonstrated that 29N2 and 30N2 were generated after adding NOx−, and the Anammox microorganisms were undetected in all groups. The above results indicated that NOx− and NH4+ could be simultaneously removed under the continuously-feeding mode, in which Fe(II)/Fe(III) cycle was the essential reason for the nitrogen removal.

Geothrix oryzisoli sp. nov., a ferric iron-reducing bacterium isolated from paddy soil.

An anaerobic, Gram-staining-negative, rod-shaped, Fe(III)-reducing strain, designated SG189T, was isolated from paddy soil in Fujian Province, China. Growth occurred at 20-35 ℃ (optimum 30 ℃), pH 6.5-8.0 (optimum 7.0) and 0-0.2% (w/v) NaCl (optimum 0%). The strain SG189T showed the highest 16S rRNA sequences similarities to the type strains of Geothrix fermentans DSM 14018T (98.9%), "Geothrix terrae" SG184T (99.0%) and "Geothrix alkalitolerans" SG263T (99.3%). ANI and dDDH values between strain SG189T and the most closely related Geothrix species were 86.5-87.1% and 31.5-32.9%, which lower than the cut-off values (ANI 95-96% and dDDH 70%) for prokaryotic species delineation. Further, genome-based phylogenomic trees constructed using 81 core genes (UBCG2) and 120 conserved genes (GTDB) showed that strain SG189T formed a clade with members of the genus Geothrix. The menaquinone was shown to be MK-8, and the major fatty acids were iso-C15:0 and iso-C13:0 3OH. The genomic DNA G + C content was 68.2%. Additionally, we found that strain SG189T possessed ability to reduce ferric iron, and strain SG189T could reduce 10mM of ferric citrate in 10days with lactate as the sole electron donor. Based on the observed physiological and biochemical properties, chemotaxonomic characteristics, ANI and dDDH values, SG189T represents a novel species of the genus Geothrix, for which the name Geothrix oryzisoli sp. nov. is proposed. The type strain is SG189T (= GDMCC 1.3408T = JCM 39324T).

Seasonal and Spatial Variations in Functional Genes and Microbial Community of Feammox and Its Associated Processes in Urban Green Heart Soil

Research on Fe3+ reduction coupled to anaerobic ammonium oxidation (Feammox) and its associated processes in the moderately low-dissolved oxygen (DO) urban natural environment is lacking. To clarify seasonal and spatial variations in Feammox, iron-reducing, and anaerobic ammonium oxidation (anammox) in urban green spaces, we examined the physicochemical indices and functional genes acd, acm, Geo, and hszA in topsoils and wetland soils across four seasons. Further, we performed 16S rRNA high-throughput sequencing. The Feammox-related gene acm was detected in all topsoil samples. Season and habitat affected soil physicochemical indices influencing gene distributions. Moisture content (45.3%) and Fe3+ (13.3%) mediated genetic changes. Competition between Feammox and iron-reducing bacteria (IRB) lowered the distributions of acd and acm in summer and increased these in winter. The acd and acm distributions were higher in wetland soil than in forestland soil. The dominant phyla, Nitrospirota, Actinobacteriota, and Desulfobacterota, correlated positively. Network analysis revealed that the relative abundances of acd, Geo, and hszA correlated positively with Flavobacterium and Thermomonas, Subgroup_2, and Candidatus_Solibacter, respectively. Feammox, iron-reducing, and anammox microorganisms correlated positively but competition existed between certain taxa. Candidatus, Sphingomonas, and Geobacter are linked to Feammox, iron reduction, and anammox. Here, we demonstrated the theoretical feasibility of developing Feammox-based nitrogen removal technology under moderately low-DO conditions, providing a reference for elucidating the ecological contribution of Feammox in an urban green heart.

Effects of Different Nanoparticles on Microbes.

Nanoparticles widely exist in nature and may be formed through inorganic or organic pathways, exhibiting unique physical and chemical properties different from those of bulk materials. However, little is known about the potential consequences of nanomaterials on microbes in natural environments. Herein, we investigated the interactions between microbes and nanoparticles by performing experiments on the inhibition effects of gold, ludox and laponite nanoparticles on Escherichia coli in liquid Luria-Bertani (LB) medium at different nanoparticle concentrations. These nanoparticles were shown to be effective bactericides. Scanning electron microscopy (SEM) images revealed the distinct aggregation of cells and nanoparticles. Transmission electron microscopy (TEM) images showed considerable cell membrane disruption due to nanoparticle accumulation on the cell surfaces, resulting in cell death. We hypothesized that this nanoparticle accumulation on the cell surfaces not only disrupted the cell membranes but also physically blocked the microbes from accessing nutrients. An iron-reducing bacterium, Shewanella putrefaciens, was tested for its ability to reduce the Fe (III) in solid ferrihydrite (HFO) or aqueous ferric citrate in the presence of laponite nanoparticles. It was found that the laponite nanoparticles inhibited the reduction of the Fe (III) in solid ferrihydrite. Moreover, direct contact between the cells and solid Fe (III) coated with the laponite nanoparticles was physically blocked, as confirmed by SEM images and particle size measurements. However, the laponite particles had an insignificant effect on the extent of aqueous Fe (III) bioreduction but slightly enhanced the rate of bioreduction of the Fe (III) in aqueous ferric citrate. The slightly increased rate of bioreduction by laponite nanoparticles may be due to the removal of inhibitory Fe (II) from the cell surface by its sorption onto the laponite nanoparticle surface. This result indicates that the scavenging of toxic heavy metals, such as Fe (II), by nanoparticles may be beneficial for microbes in the environment. On the other hand, microbial cells are also capable of detoxifying nanoparticles by coagulating nanoparticles with extracellular polymeric substances or by changing nanoparticle morphologies. Hence, the interactions between microbes and nanoparticles in natural environments should receive more attention.

Iron plaque crystallinity, heavy metal toxicity, and metal translocation in Kandelia obovata seedlings as altered by an iron-reducing bacterium under different flooding regimes

Iron plaque crystallinity, heavy metal toxicity, and metal translocation in Kandelia obovata seedlings as altered by an iron-reducing bacterium under different flooding regimes

Short-chain fatty acid production and phosphorous recovery from waste activated sludge via anaerobic fermentation: A comparison of in-situ and ex-situ thiosulfate-assisted Fe2+/persulfate pretreatment

Recently, increasing attention is given on the resource and energy recovery (e.g. short-chain fatty acids (SCFAs) and phosphorus (P)) from waste active sludge (WAS) under the “Dual carbon goals”. This study compared four thiosulfate-assisted Fe2+/persulfate (TAFP) pretreatments of WAS, i.e. in-situ TAFP pretreatment (R1), ex-situ TAFP pretreatment (R2), in-situ TAFP pretreatment + pH adjustment (R3) and ex-situ TAFP pretreatment + pH adjustment (R4), followed by anaerobic fermentation over 20 days for SCFA production and P recovery. The results showed that the maximal SCFA yields in R1–4 were 730.2 ± 7.0, 1017.4 ± 13.9, 860.1 ± 40.8, and 1072.0 ± 33.2 mg COD/L, respectively, significantly higher than Control (365.2 ± 17.8 mg COD/L). The findings indicated that TAFP pretreatments (particularly ex-situ TAFP pretreatment) enhanced WAS disintegration and provided more soluble organics and subsequently promoted SCFA production. The P fractionation results showed the non-apatite inorganic P increased from 11.6 ± 0.2 mg P/g TSS in Control to 11.8 ± 0.5 (R1), 12.4 ± 0.3 (R2), 13.2 ± 0.7 (R3) and 12.7 ± 0.7 mg P/g TSS (R4), suggesting TAFP pretreatments improved P bioavailability due to formation of Fe-P mineral (Fe(H2PO4)2·2H2O), which could be recycled through magnetic separators. These findings were further strengthened by the analysis of microbial community and related marker genes that fermentative bacteria containing SCFA biosynthesis genes (e.g. pyk, pdhA, accA and accB) and iron-reducing bacteria containing iron-related proteins (e.g. feoA and feoB) were enriched in R1–4 (dominant in ex-situ pretreatment systems, R2 and R4). Economic evaluation further verified ex-situ TAFP pretreatment was cost-effective and a better strategy over other operations to treat WAS for SCFA production and P recovery.

Acquiring Iron-Reducing Enrichment Cultures: Environments, Methods and Quality Assessments

Lateritic duricrusts cover iron ore deposits and form spatially restricted, unique canga ecosystems endangered by mining. Iron cycling, i.e., the dissolution and subsequent precipitation of iron, is able to restitute canga duricrusts, generating new habitats for endangered biota in post-mining landscapes. As iron-reducing bacteria can accelerate this iron cycling, we aim to retrieve microbial enrichment cultures suitable to mediate the large-scale restoration of cangas. For that, we collected water and sediment samples from the Carajás National Forest and cultivated the iron-reducing microorganisms therein using a specific medium. We measured the potential to reduce iron using ferrozine assays, growth rate and metabolic activity. Six out of seven enrichment cultures effectively reduced iron, showing that different environments harbor iron-reducing bacteria. The most promising enrichment cultures were obtained from environments with repeated flooding and drying cycles, i.e., periodically inundated grasslands and a plateau of an iron mining waste pile characterized by frequent soaking. Selected enrichment cultures contained iron-reducing and fermenting bacteria, such as Serratia and Enterobacter. We found higher iron-reducing potential in enrichment cultures with a higher cell density and microorganism diversity. The obtained enrichment cultures should be tested for canga restoration to generate benefits for biodiversity and contribute to more sustainable iron mining in the region.

New insights into the microbial-driven metal reductive dissolution for enhanced phosphorus release from iron-rich sludge

The extraction of phosphorus (P) from iron-rich sludge is a critical step for P recovery process. The acidogenic phosphorus release (APR) process was proved as a cost-effective and environmental-friendly method to separate and release Fe–P from iron-rich sludge, including primary sludge and activated sludge. However, the role of bacteria in this microbial-driven metal reductive dissolution approach was not clear. This study aimed to reveal the mechanism of microbial cooperation during APR process. The P release fraction could achieve as high as 63.2% from iron-rich primary sludge. High-throughput sequencing of 16S rRNA gene amplicon was conducted to characterize the functional microorganisms participating in APR process, including hydrolytic bacteria Prevotella, acidogens Selenomonas, Bacteroides, Lactococcus, Tolumonas, and iron-reducing bacteria Aeromonas and Sulfurospirillum. Microbial iron reduction and acidogenic fermentation were identified as two critical biological reactions in APR process. A two-phase temporal succession of bacterial community was characterized in batch APR process. The strong positive relationship between iron-reducing bacteria and acidogens was revealed by network analysis. This study successfully proved that bacteria-mediating metal reductive dissolution approach could efficiently release the reducible metal compounds (such as Fe–P) from complex mixture, which can be extended to many other scenarios regarding resource extraction and recovery.

Enhanced benzofluoranthrene removal in constructed wetlands with iron- modified biochar: Mediated by dissolved organic matter and microbial response.

Polycyclic aromatic hydrocarbons (PAHs) pose a high risk to ecosystems owing to their adverse environmental effects. The use of biochar in constructed wetlands (CWs) to remove PAH has received increased interest, but is frequently challenging because of saturation adsorption. To enhance the microbial degradation, electron acceptors are provided. This study aimed to remove a representative PAH, benzofluoranthrene (BbF), using iron-modified biochar as a supplement to the CW substrate. Results revealed that iron-mediated biochar based CWs increased the removal of BbF by 20.4 % and ammonium by 25.6 %. The BbF retained in substrate with biochar (36.6 % higher content) and further removed with iron modification (40.6 % lower content). Iron-modified biochar increased dissolved organic carbon content, particularly low-aromaticity, and low-molecular-weight organic matters (25.7 % higher tryptophan-like material), which contributed to PAH degradation by microorganisms. Microbial analysis confirmed that iron-mediated biochar enriched the abundance of microbes (e.g., Cellulomonas, Actinotalea, and Sphingomonas) and key enzymes (e.g., catA, lipV, and sdhA) that are involved in PAH degradation. Higher proportion of iron-reducing bacteria (e. g., Thiobacillus, Rhodobacter) played a significant role in driving microbial iron cycle, which was beneficial for PAHs removal. Based on the results, we confirmed that the use of iron-modified biochar in CWs enhance PAH removal.