Dissimilatory Reduction Research Articles

Geobacter-associated prophages confer beneficial effect on dissimilatory reduction of Fe(III) oxides

The dissimilatory reduction of Fe(III) oxides driven by Fe(III)-reducing bacteria (FRB) is an important biogeochemical process that influences not only iron cycling but also the biogeochemical cycles of carbon, trace metals, nutrients and contaminants. Phages have central roles in modulating the population and activity of FRB, but the mechanism for phage-involved Fe(III) oxide reduction is still unclear. This work used a common FRB, Geobacter soli, to explore the roles and underlying mechanisms of FRB-harboring prophages in the dissimilatory reduction of Fe(III) oxides. Bioinformatic analysis predicted 185 phage-related genes in the G. soli genome, comprising functional prophages that were verified to be induced to form tailed phage particles. Ferrihydrite reduction was facilitated as prophage induction was stimulated and declined as prophage induction was inhibited, which indicated a positive role of G. soli-harboring prophages in Fe(III) oxide reduction. A comparison of gene expression and released phage particles in the cells grown with Fe(III)-citrate and ferrihydrite suggested that microbial ferrihydrite reduction would activate the SOS response and consequently induce the prophages to enter lytic cycles. The prophage-mediated lysis of the subpopulation resulted in an increased release of extracellular DNA and membrane vesicles that were conducive to Fe(III) oxide reduction, which might explain the positive role of prophages in ferrihydrite reduction. In summary, our results revealed the functional roles and underlying mechanisms of FRB-associated prophages in facilitating the dissimilatory reduction of Fe(III) oxides, which will advance our understanding of iron cycling in natural ecosystems.

Continuously feeding fenton sludge into anaerobic digesters: Iron species change and operating stability

Fenton sludge generated from the Fenton process contains a large number of ferric species and organic pollutants, which need to be properly treated before discharge. In this study, Fenton sludge as an Fe(III) source for dissimilatory iron reduction (DIR) was continuously added with increasing dosage into an anaerobic digester to enhance the treatment. Results showed continuously feeding Fenton sludge to the anaerobic digester did not deteriorate the performance and increased methane production and COD removal rate by 2.2 folds and 14.0%, respectively. The Fe content of sludge in the digester increased from 40.25 mg/g (dry weight) to 131.53 mg/g after continuously feeding for 77days, and then declined to 109.17 mg/g when the feeding was stopped. Mass balance analysis showed that 20.5 to 48.4% of Fe in the Fenton sludge was released to the effluent. After experiment, the ratio of reducible Fe species to the total Fe was 75.1%, which maintained the high activity in DIR. Microbial community analysis showed that iron-reducing bacteria were enriched with the addition of Fenton sludge and the sludge in the digester had a higher conductivity and capacitance to strengthen the electron transfer of DIR. All results suggested that feeding Fenton sludge into anaerobic digesters was a feasible method to dispose of Fenton sludge as well as to enhance the performance of anaerobic digestion.

Anaerobic ammonium oxidation driven by dissimilatory iron reduction in autotrophic Anammox consortia

Feammox has been applied to wastewater biological nitrogen removal. However, few studies have reported that Fe(III)(hydr)oxides induced Anammox consortia to remove NH4+ via the Feammox pathway. In this study, Fe(OH)3 was added to Anammox systems to investigate its effect on nitrogen removal via Feammox. The specific Anammox activity increased by 39 % by Fe(OH)3. Ammonia oxidation was observed to occur along with Fe(III) reduction and Fe(II) generation, which was further confirmed by the isotope test with feeding 15NH4+-N to detect 30N2. The cyclic voltammetry test showed that electron-storage capacity of Anammox sludge increased with Fe(OH)3. In situ Fourier transform infrared spectroscopy suggested that Fe(OH)3 enhanced the polarization of functional groups of outer membrane cytochrome of Anammox consortia to benefit extracellular electron transfer. This study demonstrated that Fe(OH)3 could induce Anammox consortia to perform extracellular respiration to enhance NH4+-N removal in the Anammox sludge system.

Dissimilatory and Cytoplasmic Antimonate Reductions in a Hydrogen-Based Membrane Biofilm Reactor.

A hydrogen-based membrane biofilm reactor (H2-MBfR) was operated to investigate the bioreduction of antimonate [Sb(V)] in terms of Sb(V) removal, the fate of Sb, and the pathways of reduction metabolism. The MBfR achieved up to 80% Sb(V) removal and an Sb(V) removal flux of 0.55 g/m2·day. Sb(V) was reduced to Sb(III), which mainly formed Sb2O3 precipitates in the biofilm matrix, although some Sb(III) was retained intracellularly. High Sb(V) loading caused stress that deteriorated performance that was not recovered when the high Sb(V) loading was removed. The biofilm community consisted of DSbRB (dissimilatory Sb-reduction bacteria), SbRB (Sb-resistant bacteria), and DIRB (dissimilatory iron-reducing bacteria). Dissimilatory antimonate reduction, mediated by the respiratory arsenate reductase ArrAB, was the main reduction route, but respiratory reduction coexisted with cytoplasmic Sb(V)-reduction mediated by arsenate reductase ArsC. Increasing Sb(V) loading caused stress that led to increases in the expression of arsC gene and intracellular accumulation of Sb(III). By illuminating the roles of the dissimilatory and cytoplasmic Sb(V) reduction mechanism in the biofilms of the H2-MBfR, this study reveals that the Sb(V) loading should be controlled to avoid stress that deteriorates Sb(V) reduction.

Crab bioturbation affects competition between microbial nitrogen removal and retention in estuarine and coastal wetlands

As the important benthic animal in coastal wetlands, crab bioturbation may significantly affect the nitrogen (N) budgets by regulating microbial N transformation processes. However, the response of interaction between different microbial N processes to crab bioturbation remains poorly understood. Here, a 30-day microcosmic experiment was conducted using sediment collected from the Yangtze Estuary wetland, followed by the determination of temporal variations of physicochemical parameters, N removal (denitrification plus anammox, which is defined as N2 production) and retention rates (nitrate dissimilatory reduction to ammonium, DNRA) as well as relevant gene abundances in response to different crabs densities. The results showed that crab bioturbation simultaneously promoted the rates of N2 production and DNRA processes. These two process rates were positively associated with the intensity of crab bioturbation, which was supported by molecular analysis of relevant functional gene abundance. Crab bioturbation was more beneficial to DNRA than N2 production. Due to this disproportionate stimulation, crab bioturbation increased the importance of DNRA, indicating that N retention was becoming more significant under crab bioturbation in estuarine and coastal wetlands. The variations of sediment total organic carbon and oxygen availability driven by crab bioturbation were the critical factors mediating the changes in microbial N removal and retention. Overall, our findings highlighted that crab bioturbation can affect the N budgets in estuarine and coastal wetlands by altering the competition between microbial N removal and retention.

Microbial Pb(II)-bioprecipitation: Characterising responsible biotransformation mechanisms

The research aimed to facilitate the scalability of a lead bioremediation process through improved understanding of the dominant mechanisms present. The process utilises a local microbial consortium which previously demonstrated highly efficient bioremoval and -recovery of aqueous lead. To this end the project investigated lead bioremoval, microbial growth, and the effects of two different complementary anions (nitrates from lead nitrate and perchlorate from lead perchlorate) on the resulting precipitate composition and structure. The experiments were conducted anaerobically to facilitate dissimilatory metal reduction with Luria Bertani broth in the presence of different lead concentrations. Analyses included growth, lead removal, nitrate, perchlorate and sulphate measurements, transmission and scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. A maximum lead removal rate of 4.71 ppm/h and a maximum specific growth rate of 0.76 μ/h were observed. Both the presence of nitrate, perchlorate, as well as different lead concentrations had significant effects on the precipitate. This contrasted with the growth that was solely affected by the lead concentrations present. Lead sulphide, elemental lead, elemental sulphur, and pyromorphite were present in the precipitate at varying ratios dependent on the conditions. The anoxic biotransformation of lead sulphide to pyromorphite was established, with the production of elemental sulphur in solid-state. A consistent amount of elemental lead was detected throughout, indicating dissimilatory reduction. A symbiotic relationship between sulphate reducing, lead reducing, sulphur oxidizing, and denitrifying bacteria was found to be responsible for biotransformation and bioprecipitation. The improved understanding of the Pb bioremoval and bioprecipitation mechanisms presented in the current study provides much needed insights crucial to future scaling of the technology and consequent cleaner production of lead. To further elucidate the bioremediation processes involved in the system, it is recommended to conduct genomic and transcriptomic research into the microbiome to assess its adaptability under continuous operation.

Synthesis of biochar@α-Fe2O3@Shewanella loihica complex for remediation of soil contaminated by hexavalent chromium: Optimization of conditions and mechanism.

The reduction of hexavalent chromium combined with the process of dissimilatory iron reduction is an important strategy for microbial remediation of chromium-contaminated soil. However, its applicability is limited by the slow speed of bacterial bioreduction and the toxic effect of heavy metals on bacteria. Here, biochar (BC) was used as a substrate and was loaded with iron oxide in the form of hematite and Shewanella loihica to synthesize a BC@α-Fe2O3@S. loihica complex and thus achieve combined microbial-chemical remediation. After optimization by a Box-Behnken design, the optimal dosages of the complex, humic acid (as an electron shuttle), and sodium lactate (as an electron donor) were found to be 1.38mL/g, 33.94mg/g, and 12.95%, respectively. The Cr(VI) reduction rate in soil contaminated with 1000mg/kg Cr(VI) reached 98.26%, and remediation could be achieved within 7 days. Characterization of the BC@α-Fe2O3@S. loihica complex before and after it was used for remediation by energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy proved that the oxygen-containing functional groups and aromatic compounds on the surface of the BC participated in the adsorption and reduction of Cr(VI) and that the loaded hematite particles were fully utilized by microorganisms. Therefore, the BC@α-Fe2O3@S. loihica complex has great potential for the remediation of Cr(VI)-contaminated soil.

In-situ untilization of nitrogen-rich wastewater discharged from a biotrickling filter as a moisture conditioning agent for composting: Effect of nitrogen composition

Although the composting-biotrickling filter coupled system removed ammonia-based odor pollution, other pollutants (nitrogen-rich wastewater) arose. This study intended to determine the effect of in-situ disposal of different kinds of nitrogen-rich wastewater [i.e., multi-nitrogen (NH4+, NO2–, and NO3–)-rich (STL1), NO2–-rich (STL2), and NO3–-rich (STL3)] as a moisture adjustment agent during the composting thermophilic period on nitrogen transformation. Results indicated that nitrogen-rich wastewater addition did not impair the compost maturation, whereas raised the total nitrogen content of fertilizer by 15.8%-46.7% compared to the control group (i.e., tap water group). Moreover, adding STL1 has the potential to reduce CO2 and NH3 emissions and avoid incomplete organic nitrogen decomposition. Furthermore, nitrogen flow analysis unveiled that STL1 addition increased nitrogen content by strengthening ammonification, dissimilatory nitrite reduction to ammonium, and high-temperature nitrification pathways. Thus, in-situ disposal of STL1 from biotrickling filters via composting is a suitable technique for coupled systems to achieve zero discharge.

Soil metatranscriptome demonstrates a shift in C, N, and S metabolisms of a grassland ecosystem in response to elevated atmospheric CO2.

Soil organisms play an important role in the equilibrium and cycling of nutrients. Because elevated CO2 (eCO2) affects plant metabolism, including rhizodeposition, it directly impacts the soil microbiome and microbial processes. Therefore, eCO2 directly influences the cycling of different elements in terrestrial ecosystems. Hence, possible changes in the cycles of carbon (C), nitrogen (N), and sulfur (S) were analyzed, alongside the assessment of changes in the composition and structure of the soil microbiome through a functional metatranscriptomics approach (cDNA from mRNA) from soil samples taken at the Giessen free-air CO2 enrichment (Gi-FACE) experiment. Results showed changes in the expression of C cycle genes under eCO2 with an increase in the transcript abundance for carbohydrate and amino acid uptake, and degradation, alongside an increase in the transcript abundance for cellulose, chitin, and lignin degradation and prokaryotic carbon fixation. In addition, N cycle changes included a decrease in the transcript abundance of N2O reductase, involved in the last step of the denitrification process, which explains the increase of N2O emissions in the Gi-FACE. Also, a shift in nitrate () metabolism occurred, with an increase in transcript abundance for the dissimilatory reduction to ammonium () (DNRA) pathway. S metabolism showed increased transcripts for sulfate () assimilation under eCO2 conditions. Furthermore, soil bacteriome, mycobiome, and virome significantly differed between ambient and elevated CO2 conditions. The results exhibited the effects of eCO2 on the transcript abundance of C, N, and S cycles, and the soil microbiome. This finding showed a direct connection between eCO2 and the increased greenhouse gas emission, as well as the importance of soil nutrient availability to maintain the balance of soil ecosystems.

Comparison of different small molecular weight alcohols for sustaining sulfidogenic bioreactors maintained at moderately low pH.

Sulfate-reducing bacteria (SRB) catalyse the dissimilatory reduction of sulfate to hydrogen sulfide using a wide range of small molecular weight organic compounds, and hydrogen, as electron donors. Here we report the effects of different combinations of small molecular weight alcohols on the performance and bacterial composition of a moderately low pH sulfidogenic bioreactor (pH 4.0–5.5) operated at 35°C in continuous flow mode. Ethanol alone and methanol or ethanol used in combination with glycerol were evaluated based on their equivalent amounts of carbon. Although evidenced that methanol was utilised as electron donor to fuel sulfidogenesis at pH 5.5, rates of sulfate reduction/sulfide production were negatively impacted when this alcohol was first introduced to the system, though these rates increased in subsequent phases as a result of adaptation of the microbial community. Further increased dosage of methanol again caused rates of sulfidogenesis to decrease. Methanol addition resulted in perturbations of the bioreactor microbial community, and species not previously detected were present in relatively large abundance, including the sulfate-reducer Desulfovibrio desulfuricans. Ethanol utilization was evidenced by the increase in rates of sulfidogenesis as the dosage of ethanol increased, with rates being highest when the bioreactor was fed with ethanol alone. Concentrations of acetate in the effluent liquor also increased (up to 8 mM) as a result of incomplete oxidation of ethanol. This alcohol continued to be used as the electron donor for sulfate reduction when the bioreactor pH was decreased incrementally (to pH 4.0), but rates of sulfidogenesis decreased. The relative abundance of Dv. desulfuricans diminished as the bioreactor pH was lowered, while that of the acidophilic Firmicute Desulfosporosinus acididurans increased. This study has shown that all three alcohols can be used to fuel microbial sulfidogenesis in moderately acidic liquors, though the cost-effectiveness, availability and toxicity to the microbial community will dictate the choice of substrate.

Impact of sulfamethoxazole and organic supplementation on mixotrophic denitrification process: Nitrate removal efficiency and the response of functional microbiota

Recirculating aquaculture systems (RAS) effluent is characterized by low COD to total inorganic nitrogen ratio (C/N), excessive nitrate, and the presence of traces of antibiotics. Hence, it urgently needs to be treated before recycling or discharging. In this study, four denitrification bioreactors at increasing C/N ratios (0, 0.7, 2, and 5) were started up to treat mariculture wastewater under the sulfamethoxazole (SMX) stress, during which the bioreactors performance and the shift of mixotrophic microbial communities were explored. The result showed that during the SMX exposure, organic supplementation enhanced nitrate and thiosulfate removal, and eliminated nitrite accumulation. The denitrification rate was accelerated by increasing C/N from 0 to 2, while it declined at C/N of 5. The decline was ascribed to which SMX reduced the relative abundance of denitrifiers, but improved the capability of dissimilatory nitrogen reduction to ammonia (DNRA) and sulfide production. The direct evidence was the relative abundance of sulfidogenic populations, such as Desulfuromusa, Desulfurocapsa, and Desulfobacter increased under the SMX stress. Moreover, high SMX (1.5 mg L−1) caused the obvious accumulation of ammonia at C/N of 5 due to the high concentration of sulfide (3.54 ± 1.08 mM) and the enhanced DNRA process. This study concluded that the mixotrophic denitrification process with the C/N of 0.7 presented the best performance in nitrate and sulfur removal and indicated the maximum resistance to SMX.

Genome analysis of the candidate phylum MBNT15 bacterium from a boreal peatland predicted its respiratory versatility and dissimilatory iron metabolism.

Uncultured bacteria of the candidate phylum MBNT15, distantly related to Desulfobacterota, have been identified in a broad range of mostly organic-rich aquatic environments. We assembled a near-complete genome of a member of MBNT15 from a boreal peatland metagenome and used genomic data to analyze the metabolic pathways of this bacterium and its ecological role. This bacterium, designated SHF-111, was predicted to be rod shaped, it lacks flagellar machinery but twitching motility is encoded. Genome-based phylogenetic analysis supported the phylum-level classification of the MBNT15 lineage. Genome annotation and metabolic reconstruction revealed the presence of the Embden–Meyerhof, Entner–Doudoroff and pentose phosphate pathways, as well as the complete tricarboxylic acid (TCA) cycle, and suggested a facultatively anaerobic chemoheterotrophic lifestyle with the ability to ferment peptides, amino acids, fatty acids and simple sugars, and completely oxidize these substrates through aerobic and anaerobic respiration. The SHF-111 genome encodes multiple multiheme c-type cytochromes that probably enable dissimilatory iron reduction. Consistently, the relative abundance of MBNT15 in peatlands positively correlated with iron concentration. Apparently, in the wetland ecosystem, MBNT15 representatives play the role of scavengers, carrying out the complete mineralization of low molecular weight organic substances formed as a result of microbial degradation of complex polymeric substrates. Comparative genome analysis of the MBNT15 phylum revealed that vast majority of its members are capable of aerobic respiration and dissimilatory iron reduction and some species also can reduce sulfur and nitrogen compounds, but not sulfate. Based on phylogenetic and genomic analyses, the novel bacterium is proposed to be classified as Candidatus Deferrimicrobium borealis, within a candidate phylum Deferrimicrobiota.

Effect of humic acid on bioreduction of facet-dependent hematite by Shewanella putrefaciens CN-32

Interfacial reactions between iron (Fe) (hydr)oxide surfaces and the activity of bacteria during dissimilatory Fe reduction affect extracellular electron transfer. The presence of organic matter (OM) and exposed facets of Fe (hydr)oxides influence this process. However, the underlying interfacial mechanism of facet-dependent hematite and its toxicity toward microbes during bioreduction in the presence of OM remains unknown. Herein, humic acid (HA), as typical OM, was selected to investigate its effect on the bioreduction of hematite {100} and {001}. When HA concentration was increased from 0 to 500 mg L−1, the bioreduction rates increased from 0.02 h−1 to 0.04 h−1 for hematite {100} and from 0.026 h−1 to 0.05 h−1 for hematite {001}. Since hematite {001} owned lower resistance than hematite {100} irrespective of the HA concentration, and hematite {100} was less favorable for reduction. Microscopy-based analysis showed that more hematite {001} nanoparticles adhered to the cell surface and were bound more closely to the bacteria. Moreover, less cell damage was observed in the HA-hematite {001} treatments. As the reaction progressed, some bacterial cells died or were inactivated; confocal laser scanning microscopy showed that bacterial survival was higher in the HA-hematite {001} treatments than in the HA-hematite {100} treatments after bioreduction. Spectroscopic analysis revealed that facet-dependent binding was primarily realized by surface complexation of carboxyl functional groups with structural Fe atoms, and that the binding order of HA functional groups and hematite was affected by the exposed facets. The exposed facets of hematite could influence the electrochemical properties and activity of bacteria, as well as the binding of bacteria and Fe oxides in the presence of OM, thereby governing the extracellular electron transfer and concomitant bioreduction of Fe (hydr)oxides. These results provide new insights into the interfacial reactions between OM and facet-dependent Fe oxides in anoxic, OM-rich soil and sediment environments.

The influence of shellfish farming on sedimentary organic carbon mineralization: A case study in a coastal scallop farming area of Yantai, China

This study quantified the rate and relative contribution of each sedimentary organic carbon (OC) mineralization pathway in the Yantai coastal area. The results showed that scallop farming activities with raft-breeding facilities led to increased accumulation of OC and reactive Fe(III), which in turn promoted OC aerobic mineralization, Fe reduction, and competitively inhibited sulfate reduction. In the scallop farming area (SFA), O2 reduction, dissimilatory Fe reduction, and sulfate reduction contributed 32.17 %, 27.77 %, and 30.18 % of the total OC mineralization, 1.6 times, 1.2 times, and 0.6 times those of the non-farming area, respectively. Nevertheless, scallop harvesting and resuspension by water currents will increase the short-term risk of dissolved inorganic carbon accumulation in the water column. The OC budget showed that the Yantai coastal area exhibited more OC mineralization than storage, with only 5.0–7.2 % of the net settled OC being permanently buried in the sediment.

Biochar facilitates ferrihydrite reduction by Shewanella oneidensis MR-1 through stimulating the secretion of extracellular polymeric substances

Biochar can mediate extracellular electron transfer (EET) of Shewanella oneidensis MR-1 and subsequently facilitate dissimilatory reduction of iron(III) minerals. Previous studies mainly focused on the interaction of biochar and membrane cytochrome complexes to reveal the mediating mechanisms between biochar and S. oneidensis MR-1. However, the influence of biochar on the production and activity of extracellular polymeric substances (EPS) has long been neglected, despite the fact that EPS are commonly exudated by S. oneidensis MR-1 and can participate in a variety of electron transfer processes due to their redox activity. Here, we performed a series of microbial ferrihydrite reduction experiments in combination with electrochemical voltametric and impedance analyses to investigate the role of biochar in the formation and transformation of cell EPS during EET. Results showed that the added biochar not only functioned as an electron shuttle facilitating electron transfer, but also induced the secretion of five times more EPS by S. oneidensis MR-1, leading to a 1.4-fold faster ferrihydrite reduction in comparison with biochar-free setups. We further extracted the secreted EPS and found that the proportion of redox-active exoproteins was significantly (p < 0.05) increased in the EPS and resulted in a higher electron exchange capacity in secreted EPS. Such increased exoprotein content also induced a higher ratio of exoprotein to exopolysaccharide, which largely dropped diffusion and electron transfer impedance of EPS to 1.1 and 18 Ω, respectively, and accelerated the EET and thus the ferrihydrite reduction. Overall, our findings revealed the interactions between biochar and EPS matrices, which could potentially play a critical role in EET processes in both environmental or biotechnological systems.

New insight into mechanisms of ferroferric oxide enhancing medium-chain fatty acids production from waste activated sludge through anaerobic fermentation

Medium chain fatty acids (MCFAs) production from waste activated sludge (WAS) is restricted by poor biodegradability of WAS and low electron transfer efficiency. Herein, a novel ferroferric oxide (Fe3O4) technique was proposed. Results indicated that the MCFAs yield and selectivity were respectively enhanced by 155.4% and 66.7% in the Fe3O4-mediated WAS. Mechanistic studies disclosed that Fe3O4 promoted substrates degradation through conducting dissimilatory iron reduction (DIR) and stimulating hydrolase activity, providing precursors for chain elongation (CE). Generally, Fe3O4 improved the key processes for MCFA production at different degrees, i.e., hydrolysis, acidification and CE. Interestingly, MCFAs yield enhancement was primarily ascribed to facilitated electron transfer rather than DIR or produced ferrous iron, which could be supported by the analyses of electrochemical properties, electron transfer system activity and morphology. Further, Fe3O4 shifted the key microorganisms in favor of MCFAs production. Overall, this strategy could improve MCFAs production, sludge dewatering and phosphorus removal, concurrently.

Refining the early Cambrian marine redox profile by using pyrite sulfur and iron isotopes

It is widely accepted that the emergence of metazoans in the Ediacaran-Cambrian transition might be triggered by oxygenation of the atmosphere-ocean system. However, some Ediacaran and early Cambrian macroscopic fossils (such as multicellular algae) were preserved under sulfidic conditions, challenging the conventional view of the prohibition of eukaryotes in the presence of H2S. It was proposed that organisms might have lived in some episodic non-sulfidic intervals although the ocean was predominantly sulfidic. However, the hypothesized short-lived non-sulfidic intervals were hardly identified by traditional bulk sample analyses, which cannot provide sufficiently high temporal resolution to resolve the short-term oxygenation events. In this study, we analyzed pyritized sponge spicules and disseminated pyrites from black shales of the early Cambrian Shuijingtuo Formation in South China. We conducted in situ pyrite sulfur (δ34Spy) and iron (δ56Fepy) isotopes as well as bulk sample pyrite sulfur isotope analyses. The intra-crystal or intra-spicule δ34Spy variations reflect the evolution of seawater and porewater geochemistry during pyrite formation, providing a higher temporal resolution of redox fluctuation in the early Cambrian ocean. Our study indicates: (1) The bulk sample pyrite sulfur isotope and pyrite content data suggest diagenetic pyrite precipitation in sediment porewater with H2S diffusion from the overlying sulfidic seawater; (2) Limited intra-crystal and intra-spicule δ34Spy variations imply that both spicule and disseminate pyrites had a homogenous S source from sulfidic seawater, and dissimilatory sulfate reduction (DSR) in sediment porewater was negligible; (3) The in situ iron isotope analyses indicate active dissimilatory iron reduction (DIR) in sediment that generated excessive ferrous iron (Fe2+) to compensate for Fe2+ consumption by pyrite precipitation, allowing Fe2+ to accumulate in ferruginous porewater. Therefore, the early Cambrian ocean was characterized by active DSR in sulfidic seawater and DIR in ferruginous sediment porewater. In addition, our study demonstrates that the seawater might be persistently sulfidic, and does not support the presence of intermittent non-sulfidic intervals for the survival of organisms. If correct, it is hypothesized that some primitive sponges might have survived in sulfidic seawater, although the seawater H2S concentration remains unknown.

Transcriptome analysis provides new insights into the tolerance and aerobic reduction of Shewanella decolorationis Ni1-3 to bromate.

As a possible human carcinogen, bromate is easily formed in drinking water and wastewater treatments using advanced oxidation technology. Microbial reduction is a promising method to remove bromate, but little is known about aerobic bromate reduction as well as the molecular mechanism of tolerance and reduction to bromate in bacteria. Herein, bromate reduction by isolate under aerobic conditions was reported for the first time. Shewanella decolorationis Ni1-3, isolated from an activated sludge recently, was identified to reduce bromate to bromide under both aerobic and anaerobic conditions. RNA-Seq together with differential gene expression analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis was performed to identify that bromate triggered the expression of genes for oxidative stress protection (e.g., ohr, msrQ, dsbC, gpo, gorA, and gst), DNA damage repair (e.g., dprA, parA, and recJ), and sulfur metabolism (e.g., cysH, cysK, and cysP). However, the genes for lactate utilization (e.g., lldF and dld), nitrate reduction (e.g., napA and narG), and dissimilatory metal reduction (e.g., mtrC and omcA) were down-regulated in the presence of bromate. The results contribute to revealing the molecular mechanism of resistance and reduction in S. decolorationis Ni1-3 to bromate under aerobic conditions and clarifying the biogeochemical cycle of bromine. KEY POINTS: • Aerobic bromate reduction by pure culture was observed for the first time • Strain Ni1-3 effectively reduced bromate under both aerobic and anaerobic conditions • ROS and SOS response genes were strongly induced in the presence of bromate.

Sediment Nitrate Dissimilatory Reduction Processes along a Salinity Gradient in an Estuarine and Coastal Wetland, China

Nitrate (NO3−) dissimilatory reduction processes (denitrification, anammox and dissimilatory NO3− reduction to ammonium (DNRA)) in estuarine and coastal ecosystems play a crucial role in regulating reactive nitrogen loadings. However, nitrate reduction process rates and relative proportions along the estuarine salinity gradient remain poorly understood. Here, denitrification, anammox and DNRA were explored simultaneously along a salinity gradient in Yangtze Estuary based on nitrogen isotope-tracing experiments. Measured denitrification, anammox and DNRA process rates were in the range of 2.33–28.21 nmol g−1 h−1, 0.43–1.87 nmol g−1 h−1 and 0.28–0.74 nmol g−1 h−1, respectively, with a large spatio-temporal variation. The changes in these nitrate reduction process rates were mainly affected by the TOC, TN, NH4+ and NOx− concentrations, rather than salinity and related functional gene abundance. Denitrification dominated the total NO3− reduction process (67.52 to 93.85%), while anammox (3.67 to 25.01%) and DNRA (2.48 to 11.21%) also played a substantially important role in nitrate reduction. The proportions of denitrification to gross nitrate reduction in high-salinity areas were generally lower than those in freshwater, but the opposite was true for DNRA. Overall, our study reported the simultaneous observation of nitrate dissimilatory reduction processes along the salinity gradient of the estuary and highlighted that changes in sediment environmental variables affected by human activities can alter the distribution patterns of NO3− reduction processes.

Reductive dissolution of jarosite by inorganic sulfur compounds catalyzed by Acidithiobacillus thiooxidans

The adsorption of jarosite and the resulting passivation of mineral surfaces can negatively influence metal extraction from sulfidic ores as well as the fate of other elements in biohydrometallurgical processes. Some bioleaching microorganisms mediate dissimilatory iron reduction coupled to sulfur oxidation (DIRSO), a process utilized predominantly in continuously enhanced leaching of metals from sulfide and/or oxidized ores. In this study, the reductive dissolution of jarosite (biosynthesized by the iron-oxidizing archaeon Acidianus manzaensis) catalyzed by the mesophilic acidophilic bacterium Acidithiobacillus (At.) thiooxidans oxidizing different inorganic sulfur compounds was investigated. Kinetic measurements of pH, ORP, iron concentrations, and planktonic cell counts were performed to describe the reductive dissolution of jarosite. Moreover, the solid leaching residues were analyzed using X-ray absorption near edge structure (XANES), Inductively coupled plasma - optical emission spectrometry (ICP-OES), scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy. The dissolution rates of jarosite after 34 days of bioleaching by At. thiooxidans with S0, Na2S2O3, and Na2SO3 were 41.7, 76.3, and 98.4%, respectively, while negligible jarosite dissolution was detected in abiotic controls. The presence of Na2S2O3 and Na2SO3 resulted in structural modifications on the jarosite surfaces, but the dissolution of jarosite was not promoted in the absence of At. thiooxidans. In the biotic assays with Na2SO3, jarosite was completely dissolved, indicating that Na2SO3 was the most suitable electron donor (out of those tested) for DIRSO by At. thiooxidans. The findings obtained in this study can contribute to designing suitable bioleaching strategies for oxidized ores. They also highlight the potential of microbially catalyzed DIRSO to mitigate jarosite formation that often hinders bioleaching of sulfidic ores.