Autotrophic induced heterotrophic bioreduction of bromate in use of elemental sulfur or zerovalent iron as electron donor

Robust Activity and Stability of P-Doped Fe-Carbon Composites Derived from MOF for Bromate Reduction

Iron-based materials are effective for the reductive removal of the disinfection byproduct bromate in water, while the construction of highly stable and active Fe-based materials with wide pH adaptability remains greatly challenging. In this study, highly dispersed iron phosphide-decorated porous carbon (Fe2P(x)@P(z)NC-y) was prepared via the thermal hydrolysis of Fe@ZIF-8, followed by phosphorus doping (P-doping) and pyrolysis. The reduction performances of Fe2P(x)@P(z)NC-y for bromate reduction were evaluated. Characterization results showed that the Fe, P, and N elements were homogeneously distributed in the carbonaceous matrix. P-doping regulated the coordination environment of Fe atoms and enhanced the conductivity, porosity, and wettability of the carbonaceous matrix. As a result, Fe2P(x)@P(1.0)NC-950 exhibited enhanced reactivity and stability with an intrinsic reduction kinetic constant (kint) 1.53-1.85 times higher than Fe(x)@NC-950 without P-doping. Furthermore, Fe2P(0.125)@P(1.0)NC-950 displayed superior reduction efficiency and prominent stability with very low Fe leaching (4.53-22.98 μg L-1) in a wide pH range of 4.0-10.0. The used Fe2P(0.125)@P(1.0)NC-950 could be regenerated by phosphating, and the regenerated Fe2P(0.125)@P(1.0)NC-950 maintained 85% of its primary reduction activity after five reuse cycles. The study clearly demonstrates that Fe2P-decorated porous carbon can be applied as a robust and stable Fe-based material in aqueous bromate reduction.

Independent and synergistic bio-reductions of uranium (VI) driven by zerovalent iron in aquifer

Zerovalent iron [Fe(0)] can donate electron for bioprocess, but microbial uranium (VI) [U(VI)] reduction driven by Fe(0) is still poorly understood. In this study, Fe(0) supported U(VI) bio-reduction was steadily achieved in the 160-d continuous-flow biological column. The maximum removal efficiency and capacity of U(VI) were 100% and 46.4 ± 0.52 g/(m³·d) respectively, and the longevity of Fe(0) increased by 3.09 times. U(VI) was reduced to solid UO₂, while Fe(0) was finally oxidized to Fe(III). Autotrophic Thiobacillus achieved U(VI) reduction coupled to Fe(0) oxidation, verified by pure culture. H₂ produced from Fe(0) corrosion was consumed by autotrophic Clostridium for U(VI) reduction. The detected residual organic intermediates were biosynthesized with energy released from Fe(0) oxidation and utilized by heterotrophic Desulfomicrobium, Bacillus and Pseudomonas to reduce U(VI). Metagenomic analysis found the upregulated genes for U(VI) reduction (e.g., dsrA and dsrB) and Fe(II) oxidation (e.g., CYC1 and mtrA). These functional genes were also transcriptionally expressed. Cytochrome c and glutathione responsible for electron transfer also contributed to U(VI) reduction. This study reveals the independent and synergistic pathways for Fe(0)-dependent U(VI) bio-reduction, providing promising remediation strategy for U(VI)-polluted aquifers.

Novel microbial consortia facilitate metalliferous immobilization in non-ferrous metal(loid)s contaminated smelter soil: Efficiency and mechanisms

Exposure to toxic metals from nonferrous metal(loid) smelter soils can pose serious threats to the surrounding ecosystems, crop production, and human health. Bioremediation using microorganisms is a promising strategy for treating metal(loid)-contaminated soils. Here, a native microbial consortium with sulfate-reducing function (SRB1) enriched from smelter soils can tolerate exposures to mixtures of heavy metal(loid)s (e.g., As and Pb) or various organic flotation reagents (e.g., ethylthionocarbamate). The addition of Fe²⁺ greatly increased As³⁺ immobilization compared to treatment without Fe²⁺, with the immobilization efficiencies of 81.0% and 58.9%, respectively. Scanning electronic microscopy-energy dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy confirmed that the As³⁺ immobilizing activity was related to the formation of arsenic sulfides (AsS, As₄S₄, and As₂S₃) and sorption/co-precipitation of pyrite (FeS₂). High-throughput 16S rRNA gene sequencing of SRB1 suggests that members of Clostridium, Desulfosporosinus, and Desulfovibrio genera play an important role in maintaining and stabilizing As³⁺ immobilization activity. Metal(loid)s immobilizing activity of SRB1 was not observed at high and toxic total exposure concentrations (220-1181 mg As/kg or 63-222 mg Pb/kg). However, at lower concentrations, SRB1 treatment decreased bioavailable fractions of As (9.0%) and Pb (28.6%) compared to without treatment. Results indicate that enriched native SRB1 consortia exhibited metal(loid) transformation capacities under non-toxic concentrations of metal(loid)s for future bioremediation strategies to decrease mixed metal(loid)s exposure from smelter polluted soils.

Comparative analysis of the endophytic bacteria inhabiting the phyllosphere of aquatic fern Azolla species by high-throughput sequencing

BACKGROUND

Azolla is a small floating fern living in symbiosis with nitrogen-fixing cyanobacteria and provides a variety of important ecosystem benefits. Previous studies have presented that Azolla harbors diverse bacteria that may play a key role in host fitness and productivity. However, the characteristics of endophytic bacteria inhabiting the phyllosphere of different species of Azolla have not yet been fully understood.

RESULTS

In this study, the 16S ribosomal DNA (rDNA) V5-V7 region of bacteria was determined by Illumina high-throughput sequencing platform to study the diversity and richness of endophytic bacterial communities in the phyllosphere of five Azolla species collected from different countries. A total of 1150 operational taxonomic units (OTUs) were detected for the endophytic bacteria community. According to the α diversity indices, the diversity of bacteria was ordered as Azolla imbricata > A. pinnata > A. filiculoides > A. mexicana > A. caroliniana. The PCoA results displayed that the bacterial communities of A. mexicana and A. caroliniana shared the highest similarity, followed by the similarity between A. pinnata and A. imbricata, and they were significantly distinct from the community of A. filiculoides. The dominant bacteria of Azolla mainly belonged to the phylum of Proteobacteria, followed by Actinobacteria, Chlorobillobacteria, and Firmicutes. In detail, the relative abundance of Proteobacteria in A. imbricata was 52.23%, whereas it was more than 80.00% in the other four species of Azolla. Notably, Herbaspirillum (45.91%, 44.08%) and Methylophilus (29.97%, 37.96%) were the main genera inhabiting A. mexicana and A. caroliniana respectively. Ferrovibrio (18.54%) and Rhizobium (16.68%) were the dominant genera inhabiting A. filiculoides. The group of unidentified genera (41.63%, 44.92%) consisted most of the bacteria in A. imbricata and A. pinnata respectively. Further analysis suggested that the significant different bacteria identified in LDA Effect Size analysis existed Azolla species-specific patterns.

CONCLUSIONS

In summary, all results suggested that the diversity and composition of the endophytic bacterial communities were different in Azolla species.

A new LDH based sustained-release carbon source filter media to achieve advanced denitrogenation of low C/N wastewater at low temperature

Advanced denitrogenation of wastewater is now facing major challenges brought by low C/N ratio and low temperature. The development of sustained-release materials with good and stable carbon release properties was an effective countermeasure. FeNi-Layered double-metal hydroxides (LDH)- sodium carboxymethyl cellulose (CMC) filter media and its potential use in heterotrophic and sulfur-based mixotrophic denitrification biological filter (DNBF), was firstly reported. It demonstrated stable structure and good carbon release performance with a mass transfer coefficient (K) of 4.40 mg·L^-1·s^-1. When the influent NO₃^--N of 50 mg/L with the C/N ratio of 3 at 10 °C, the maximum nitrogen loading rate of 0.22 kg·N/(m³·d) and effluent TN close to 5 mg/L (nitrogen removal of almost 90 %) could be achieved. The slowly released carbon source and the leached iron increased the abundance of denitrifying bacteria and functional genes, and the augmentation of Sulfuritalea and the secretion of biofilm protein stimulated by sulfur also played a synergistic role. This study provided a new potentially effective strategy to enhance advanced denitrification of wastewater of low C/N wastewater at low temperature.

Bromate reduction by Shewanella oneidensis MR-1 is mediated by dimethylsulfoxide reductase

Microbial bromate reduction plays an important role in remediating bromate-contaminated waters as well as biogeochemical cycling of bromine. However, little is known about the molecular mechanism of microbial bromate reduction so far. Since the model strain Shewanella oneidensis MR-1 is capable of reducing a variety of oxyanions such as iodate, which has a high similarity to bromate, we hypothesize that S. oneidensis MR-1 can reduce bromate. Here, we conducted an experiment to investigate whether S. oneidensis MR-1 can reduce bromate, and report bromate reduction mediated by a dimethylsulfoxide reductase encoded with dmsA. S. oneidensis MR-1 is not a bromate-respiring bacterium but can reduce bromate to bromide under microaerobic conditions. When exposed to 0.15, 0.2, 0.25, 0.5, and 1 mM bromate, S. oneidensis MR-1 reduced bromate by around 100, 75, 64, 48, and 23%, respectively, within 12 h. In vivo evidence from gene deletion mutants and complemented strains of S. oneidensis MR-1 indicates that MtrB, MtrC, CymA, GspD, and DmsA are involved in bromate reduction, but not NapA, FccA, or SYE4. Based on our results as well as previous findings, a proposed molecular mechanism for bromate reduction is presented in this study. Moreover, a genomic survey indicates that 9 of the other 56 reported Shewanella species encode proteins highly homologous to CymA, GspD, and DmsA of S. oneidensis MR-1 by sequence alignment. The results of this study contribute to understanding a pathway for microbial bromate reduction.

Enhanced biological antimony removal from water by combining elemental sulfur autotrophic reduction and disproportionation

Antimony (Sb), a toxic metalloid, has serious negative effects on human health and its pollution has become a global environmental problem. Bio-reduction of Sb(V) is an effective Sb-removal approach. This work, for the first time, demonstrates the feasibility of autotrophic Sb(V) bio-reduction and removal coupled to anaerobic oxidation of elemental sulfur (S⁰). In the S⁰-based biological system, Sb(V) was reduced to Sb(III) via autotrophic bacteria by using S⁰ as electron donor. Meanwhile, S⁰ disproportionation reaction occurred under anaerobic condition, generating sulfide and SO₄^2- in the bio-systems. Subsequently, Sb(III) reacted with sulfide and formed Sb(III)-S precipitate, achieving an effective total Sb removal. The precipitate was identified as Sb₂S₃ by SEM-EDS, XPS, XRD and Raman spectrum analyses. In addition, it was found that co-existing nitrate inhibited the Sb removal, as nitrate is the favored electron acceptor over Sb(V). In contrast, the bio-reduction of co-existing SO₄^2- enhanced sulfide generation, followed by promoting Sb(V) reduction and precipitation. Illumina high-throughput sequencing analysis revealed that Metallibacterium, Citrobacter and Thiobacillus might be responsible for Sb(V) reduction and S⁰ disproportionation. This study provides a promising approach for the remediation of Sb(V)-contaminated water.

Iron carriers promote biofilm formation and p-nitrophenol degradation

Vertical baffled biofilm reactors (VBBR) equipped with Plastic-carriers and Fe-carriers were employed to explore the effect of biofilm carriers on biofilm formation and p-nitrophenol (PNP) degradation. The results showed that Fe-carriers enhanced biofilm formation and PNP degradation. The maximum thickness of biofilm grown on the Fe-carriers was 1.5-fold higher than that on the Plastic-carriers. The Fe-VBBR reached a maximum rate of PNP removal at 13.02 μM L^-1 h^-1 with less sodium acetate addition (3 mM), while the maximum rate of PNP removal was 11.53 μM L^-1 h^-1 with more sodium acetate addition (6 mM) in the Plastic-based VBBR. High-throughput sequencing suggested that the Fe-VBBR had a higher biodiversity of the bacterial community in evenness, and the Achromobacter genus and Xanthobacteraceae family were as main PNP degraders. Kyoto Encyclopedia of Genes and Genomes (KEGG) Orthology analysis suggested more abundances of iron uptake genes were expressed to transport iron into the cytoplasm under an iron-limited condition in two VBBRs, and the metabolic pathway of PNP degradation went through 4-nitrocatechol and 1,2,4-benzenetriol. Our results provide a new insight for iron enhancing biofilm formation and PNP degradation.

Cultivation of sulfide-driven partial denitrification granules for efficient nitrite generation from nitrate-sulfide-laden wastewater

Sulfide partial denitrification (SPD) is an alternative pathway for nitrite production accompanied with elemental sulfur (S⁰) production for nitrate removal from wastewater with anammox. In this study, the SPD granular sludge was cultivated for the first time in an upflow anaerobic sludge bed (UASB) reactor to reach the efficacy of maximum nitrate-to-nitrite transformation ratio of 92% and an in-situ maximum NO₃^--N reduction rate of 2.46 kg-N/m³-d, both much higher than literature results. Mature granules had an average particle size of 2.52 mm and hold smooth surface with excess rod bacteria. The elements Ca and S, and proteins in extracellular polymeric substances contributed to granule structure's stability. Enriched Thiobacillus genus was proposed to accumulate nitrite at moderate HRT (2-6 h). The immobilized functional strains assist efficient partial nitrification reactions to be realized with formed S⁰ as byproduct.

Synergistic bioreduction of Te(Ⅳ) using S(0) as electron donor

This study for the first time bioreduced Te(IV) using elemental sulfur (S⁰) as electron donor, achieving 91.17%±0.8% conversion with reaction rate of 0.77 ± 0.01 mg/L/h in a 60-day cultivation. Characterization using X-ray photoelectron spectroscopy and X-ray power diffraction analyses confirmed that most removed Te(IV) was reduced to elemental Te(0) deposits, while ion chromatogram analysis showed that most S(0) was oxidized to sulfite and sulfate. High-throughput 16S rRNA gene sequencing indicated that the Te(IV) reduction coupled to S(0) oxidation was mediated synergistically by a microbial consortia with S(0)-oxidizing bacteria (Thiobacillus) to generate volatile fatty acids as metabolites and Te(IV)-reducing bacteria (Rhodobacter) to consume formed volatile fatty acids to yield Te(0). The synergy between these two strains presents a novel bioremediation consortium to efficiently treat Te(IV) wastewaters.

Responses of Root Endophytes to Phosphorus Availability in Peach Rootstocks With Contrasting Phosphorus-Use Efficiencies

Phosphorus (P) is an important macronutrient for all lives, but it is also a finite resource. Therefore, it is important to understand how to increase the P availability and plant uptake. The endophytes can help host plants to improve P uptake and will be apparently affected by plant genotypes. To investigate the mechanism of root endophytes in promoting P uptake of peach rootstocks, we analyzed the variations of the root endophytic fungal and bacterial communities of peach rootstocks with different P efficiencies under high or low level of P addition. Results showed that Proteobacteria was the dominant bacterial phylum in the roots of all rootstocks under the two levels of P addition. At low P level, the abundance of Actinoplanes in phosphorus-inefficiency root system was apparently higher than that at high P level. Actinoplanes produced important secondary metabolites, improving the stress resistance of plants. Under high P condition, the abundance of Ferrovibrio was higher in Qing Zhou Mi Tao than in Du Shi. Fe oxides considerably reduced the availability of applied P, which partially explained why the P utilization in Qing Zhou Mi Tao is inefficient. Further, Ascomycota was the dominant fungal phylum in the roots of all rootstocks under different levels of P addition. The fungi community of roots varied in different rootstocks at each P level, but was similar for the same rootstock at different P levels, which indicated that genotype had a greater effect than P addition on the fungal community of peach rootstocks.