Sulfur Transformation Research Articles

Effects of filling substrates on remediation performance and sulfur transformation of sulfate reducing packed-bed bioreactors treating acid mine drainage

The filling substrate is one of key factors influencing effectiveness of sulfate reducing packed-bed bioreactor (SRPB) treating acid mine drainage (AMD). The effects of four substrates (i.e. quartz sand, steel residue, biochar, and peanut shell) on remediation performance and sulfur transformation of SRPB treating AMD was studied. The results showed that steel residue and biochar improved sulfate reduction efficiency (61% and 49%) compared to quartz sand (32%), whereas peanut shell inhibited sulfate reduction efficiency (19%), attributed to its decomposition process leading to a severe accumulation of acetic acid. More amounts of sulfides generated in steel residue bioreactor were converted into acid volatile sulfide and elemental sulfur, resulting in a significant decrease in dissolved sulfide in the effluent. Metals (Fe, Al, Zn, Cd and Cr) except for Mn were effectively immobilized in the bioreactors, particularly for Al and Cd. Sulfate reducing bacteria and sulfide oxidizing bacteria lived symbiotically in all bioreactors which exhibited similar heterogeneity in microbial distribution and function, i.e. bacterial sulfate reduction mainly occurring in bottom-middle layers and photoautotrophic sulfide oxidation in upper layer close to outlet. The microbial response mechanism to various substrate environments was revealed through co-occurrence networks analysis. This study suggests that attention should be paid to the inhibitory effect of acetic acid accumulation on sulfate reduction when using sole lignocellulosic waste (peanut shell), and steel residue and biochar could be utilized as filling substances to promote sulfate reduction.

Diversity and ecology of microbial sulfur metabolism.

Sulfur plays a pivotal role in interactions within the atmosphere, lithosphere, pedosphere, hydrosphere and biosphere, and the functioning of living organisms. In the Earth's crust, mantle, and atmosphere, sulfur undergoes geochemical transformations due to natural and anthropogenic factors. In the biosphere, sulfur participates in the formation of amino acids, proteins, coenzymes and vitamins. Microorganisms in the biosphere are crucial for cycling sulfur compounds through oxidation, reduction and disproportionation reactions, facilitating their bioassimilation and energy generation. Microbial sulfur metabolism is abundant in both aerobic and anaerobic environments and is interconnected with biogeochemical cycles of important elements such as carbon, nitrogen and iron. Through metabolism, competition or cooperation, microorganisms metabolizing sulfur can drive the consumption of organic carbon, loss of fixed nitrogen and production of climate-active gases. Given the increasing significance of sulfur metabolism in environmental alteration and the intricate involvement of microorganisms in sulfur dynamics, a timely re-evaluation of the sulfur cycle is imperative. This Review explores our understanding of microbial sulfur metabolism, primarily focusing on the transformations of inorganic sulfur. We comprehensively overview the sulfur cycle in the face of rapidly changing ecosystems on Earth, highlighting the importance of microbially-mediated sulfur transformation reactions across different environments, ecosystems and microbiomes.

Mechanism of Intracellular Elemental Sulfur Oxidation in Beggiatoa leptomitoformis, Where Persulfide Dioxygenase Plays a Key Role.

Representatives of the colorless sulfur bacteria of the genus Beggiatoa use reduced sulfur compounds in the processes of lithotrophic growth, which is accompanied by the storage of intracellular sulfur. However, it is still unknown how the transformation of intracellular sulfur occurs in Beggiatoa representatives. Annotation of the genome of Beggiatoa leptomitoformis D-402 did not identify any genes for the oxidation or reduction of elemental sulfur. By searching BLASTP, two putative persulfide dioxygenase (PDO) homologs were found in the genome of B. leptomitoformis. In some heterotrophic prokaryotes, PDO is involved in the oxidation of sulfane sulfur. According to HPLC-MS/MS, the revealed protein was reliably detected in a culture sample grown only in the presence of endogenous sulfur and CO2. The recombinant protein from B. leptomitoformis was active in the presence of glutathione persulfide. The crystal structure of recombinant PDO exhibited consistency with known structures of type I PDO. Thus, it was shown that B. leptomitoformis uses PDO to oxidize endogenous sulfur. Additionally, on the basis of HPLC-MS/MS, RT-qPCR, and the study of PDO reaction products, we predicted the interrelation of PDO and Sox-system function in the oxidation of endogenous sulfur in B. leptomitoformis and the connection of this process with energy metabolism.

Effects of the low molecular compounds from methanol extraction on the transformation of organic sulfur during coal pyrolysis

Effects of the low molecular compounds from methanol extraction on the transformation of organic sulfur during coal pyrolysis

The construction of double short-cut sulfur autotrophic denitrification and PN/Anammox partition and its effect on the coupling performance of nitrogen and sulfur removal

How to reduce NO3--N from partial nitrification /Anammox (PN/Anammox) for low carbon emissions, thus achieve deep nitrogen removal, is a significant issue when applying PN/Anammox to treatment inorganic high-ammonia wastewater. This study designed a prepositioned double short-cut sulfur autotrophic denitrification (DSSADN) system integrated with PN/Anammox, achieving simultaneous sulfur recovery and complete autotrophic denitrification. It also examined the impact of reflux changes on the nitrogen and sulfur transformation characteristics in the coupled system when treating ammonia and sulfur-containing wastewater. Results indicate that the coupling of DSSADN zone (zone C1) enhanced TN removal by PN/Anammox, with the TN removal rate (TNRRT), TN removal efficiency (TNRET), and S2- removal rate reaching 0.54 kg/(m³·d), 95.1%, and 100%, respectively. The NO2--N accumulation efficiency (NiAEC1) of DSSADN reached 87.1%, with ΔSO42--S consistently less than 11.8 mg/L, and the S0 accumulation efficiency (S0AEC1) reaching 82.4%. A small amount of O2 carried in the reflux can effectively reduce residual S2- in zone C1, preventing its entry into the PN/Anammox zone (zone C2) and mitigating its toxic effects on Anammox. However, O2 also increases the expression of soxB in zone C1, causing more S2- to be oxidized to SO42-, and reducing S0AEC1. When DOC1 was between 0.05 mg/L and 0.34 mg/L, nirK expression was significantly increased, and the abundance of related functional microorganisms changed, led to more NO3--N being reduced to N2. When DOC1 exceeds 0.34 mg/L, it inhibits the denitrification process, leading to elevated NiAE. Therefore, when regulating reflux in DSSADN+PN/Anammox partitioned integrated coupling system, attention should be given to changes in DOC1, controlling it within 0.05 mg/L.

How Does Triclocarban Affect Sulfur Transformation in Anaerobic Systems?

Triclocarban (TCC), as a typical antimicrobial agent, accumulates at substantial levels in natural environments and engineered systems. This work investigated the impact of TCC on anaerobic sulfur transformation, especially toxic H2S production. Experimental findings revealed that TCC facilitated sulfur flow from the sludge solid phase to liquid phase, promoted sulfate reduction and sulfur-containing amino acid degradation, and largely improved anaerobic H2S production, i.e., 50-600 mg/kg total suspended solids (TSS) TCC increased the cumulative H2S yields by 24.76-478.12%. Although TCC can be partially biodegraded in anaerobic systems, the increase in H2S production can be mainly attributed to the effect of TCC rather than its degradation products. TCC was spontaneously adsorbed by protein-like substances contained in microbe extracellular polymers (EPSs), and the adsorbed TCC increased the direct electron transfer ability of EPSs, possibly due to the increase in the content of electroactive polymer protein in EPSs, the polarization of the amide group C═O bond, and the increase of the α-helical peptide dipole moment, which might be one important reason for promoting sulfur bioconversion processes. Microbial analysis showed that the presence of TCC enriched the organic substrate-degrading bacteria and sulfate-reducing bacteria and increased the abundances of functional genes encoding sulfate transport and dissimilatory sulfate reduction.

Light-Induced Ring-to-Chain Transformations of Elemental Sulfur: Nonadiabatic Dynamics Simulations.

The emergence of high-sulfur content polymeric materials and their diverse applications underscore the need for a comprehensive understanding of the ring-to-chain transformation of elemental sulfur. In this study, we delve into the ultrafast transformation of the elemental sulfur S8 ring upon photoexcitation employing advanced nonadiabatic dynamics simulations. Our findings reveal that the bond breaking of the S8 ring occurs within tens of femtoseconds. At the time of bond breaking, most molecules are in the lowest singlet excited state S1. S1 survives for 40-450 fs before relaxing to the quasi-degenerate manifolds formed by the T1 and S0 states of the S8 chain. This suggests that upon photoexcitation the polymerization of the S8 chains might proceed before the chains relax to their lowest energy states. The derived temporal resolution provides a detailed perspective on the dynamics of S8 rings upon photoexcitation, shedding light on the intricate processes involved in its excited-state transformations.

Molecular understanding of speciation transformation of phosphorus and sulfur in food waste digestate during hydrothermal treatment

Recovering phosphorus (P) and sulfur (S) from biowaste is a key strategy to address the current P resources shortage and soil S deficiency. Food waste digestate (FWD) contains high contents of P and S, while its direct application is severely limited by available nutrient leaching loss and pollutant exposure. Hydrothermal treatment (HT) is an effective technique for biowaste disposal, enabling detoxification and resource recovery. The study systematically investigated the speciation transformation of P and S in FWD during HT, using chemical extraction and in-situ X-ray absorption near-edge structure (XANES) spectroscopy. The results revealed that up to 98% of P in FWD was enriched in the solid product (hydrochar) after HT, with organic P and labile P being converted into stable Ca-bound forms, predominantly hydroxyapatite. This transformation reduced the risk of P leakage loss compared to untreated FWD. Interestingly, the S speciation evolution exhibited more complexity. The highest S proportion in hydrochar of 73.6% was observed at 140 °C under HT. As the temperature increased from 140 °C to 180 °C, S in the hydrochar gradually dissolved into the liquid phase, attributed to unstable aliphatic compounds (mercaptan) and the sulfides oxidizing to sulfates. Above 180 °C, intermediate oxidation states and sulfates were reduced and formed metal sulfides. These findings have important implications for understanding the viability of HT for FWD disposal and the value-added utilization of FWD.

Transformation and control of organic sulfur during pyrolysis of sludge under conditions relevant to smoldering combustion: Role of oxygen and CaO

This study focused on the effect of oxygen (0–15 %) and 5 % CaO addition on the organic-S control and transformation behavior during pyrolysis (400–600 °C) of sludge under the conditions relevant to smoldering combustion. The results show that oxygen inhibits the total emission of gaseous sulfur (decreased by 25.6–36.9 %). At low temperatures (<500 °C), oxygen enhances the oxidation of aliphatic-S, aromatic-S/thiophene-S, and sulfide-S, leading more sulfur retains in the form of sulfone-S and sulfate-S in char products, also migrates to water-soluble products (especially sulfone-S). At high temperatures (>500 °C), the formed sulfur species in char products mainly further decompose into water-soluble sulfone-S, and partially generate SO2. After the addition of CaO during oxidative pyrolysis, the synergistic promotion effect on the sulfur fixation in char products is found, mainly due to the generation of more amount of stable sulfone-S and sulfate-S in char products. This leads to a decrease in gaseous sulfur by 12.4–14.6 % and an increase in sulfur content of char products by 31.3–202.9 %.

Combustion-explosion suppression and environmental protection of typical sulfur-containing hazardous chemicals.

Sulfur, as a crucial chemical raw, poses increased combustion-explosion risks when mixed with other hazardous substances due to its dual nature as both an oxidant and a reducing agent. Additionally, sulfur-induced combustion and explosions can result in environmental pollution. Combustion-explosion suppression technology plays a crucial role in industrial production by effectively preventing hazardous chemical explosion incidents. This research investigates the combustion-explosion suppression of black powder, a common hazardous chemical containing sulfur, by utilizing two solid-based blast suppressants, NH4H2PO4 and NaHCO3. On this basis, examining changes in the oxidation states of sulfur and explaining the mechanisms of combustion-explosion suppression through the examination of combustion-explosion products. Additionally, numerical calculations are employed to analyze the evolution patterns of gaseous and solid-phase products throughout the entire combustion-explosion process. Research indicates that NaHCO3 exhibits a more effective combustion-explosion suppression effect on black powder compared to NH4H2PO4, which attributed to the valence state transformation of sulfur and the reduction of carbon oxidation. Furthermore, with the enhancement of combustion-explosion suppression effect, K2S, which a pollutes the environment, is gradually transform converted into potassium fertilizer K2SO4, which benefits plants. These results offer new insights into the research of combustion-explosion suppression of sulfur-containing substances and environmental protection strategies.

The sewer advances: How to select eco-friendly pipe materials for environmental protection

Sewer pipe materials exhibit diverse inner-surface features, which can affect the attachment of biofilm and influence microbial metabolic processes. To investigate the role of the type of pipe material on the composition and metabolic capabilities of the adhering microorganisms, three sets of urban sewers (High-Density Polyethylene Pipe (HDPE), Ductile Iron Pipe (DIP), and Concrete Pipe (CP)) were constructed. Measurements of biofilm thickness and environmental factors revealed that the thickest biofilm in CP pipes reached 2000 μm, with ORP values as low as −325 mV, indicating a more suitable anaerobic microbial habitat. High-throughput sequencing showed similar relative abundances of genera related to carbon and sulfur metabolism in the DIP and CP pipes, whereas HDPE exhibited only half the relative abundance compared to that found in the other pipes. To explore the impact of pipe materials on the mechanisms of microbial response, a metagenomic approach was used to investigate the biological transformation of carbon and sulfur in wastewater. The annotations of the crucial enzyme-encoding genes related to methyl coenzyme M and sulfite reductase in DIP and CP were 50 and 110, respectively, whereas HDPE exhibited lower counts (25 and 70, respectively). This resulted in significantly lower carbon and sulfur metabolism capabilities in the HDPE biofilm than in the other two pipes. The stability of wastewater quality during the transmission process in HDPE pipes reduces the metabolic generation of toxic and harmful gases within the pipes, favoring the preservation of carbon sources for sewer systems. This study reveals the variations in carbon and sulfur metabolism in wastewater pipe systems influenced by pipe materials and provides insights for designing future sewers.

Optimization of product distribution during co-pyrolysis of furfural residues and waste tyres via response surface method and infrared heating

Co-pyrolysis technique has proved to be an available way to recycle the energy of biomass waste and improve bio-oil quality. In this work, the co-pyrolysis behaviors and product distribution of waste tyres (WT) and furfural residues (FR) were studied by TG-FTIR/GC–MS and infrared heating fixed reactor. TG-FTIR/GC–MS results show that a large amount of CH4 and aromatics were produced at the co-pyrolysis temperature of 410°C. The response surface methodology (RSM) was utilized to optimize the yields of co-pyrolysis products, including oil, aromatic hydrocarbon (AH) in oil, and CH4 in gas. It was found that the highest oil production of 39.24 wt% was obtained at 550 °C and 10 °C/s, with the highest AH content of 35.02 % and the highest CH4 yield of 17.65 wt% at 700 °C and 40 °C/s. Co-pyrolysis oil and char characteristics were analyzed by SIMDIS, GC–MS, XPS, and the ultimate analysis. It was found that there was a high D-limonene content in oil (up to 25.79 %). With increasing co-pyrolysis temperature, AH content gradually increased and that of acid in oil declined. As the temperature elevated from 400 to 700 °C at 10 °C/s, the content of AH rose from 6.48 to 31.56 % and that of acid decreased from 19.74 to 11.73 %. In addition, the transformation of organic sulfur into metal sulfides was facilitated by raising the temperature.

Hydrothermal carbonization of sewage sludge for hydrochar valorization: Role of feedwater pH on sulfur removal and transformation

Adjusting the pH value is a useful method to improve the hydrochar properties during hydrothermal carbonization (HTC). The distribution of various sulfur species in hydrochar is considered as an important parameter affecting its further utilization. Nevertheless, the detailed effects of pH on the redistribution of different sulfur forms are still unknown. This study investigated the sulfur transformation pathways during HTC of sewage sludge with different feedwater pH (0–14) at 220 °C. Both acidic and alkaline feedwater facilitate the conversion of organic sulfur from the hydrochar into the stable species in aqueous products (i.e., sulfate-S). The latter especially leads to a decreased sulfur retention ratio of 31.97 % at pH=0 and 60.13 % at pH=14. Under acidic conditions, organic sulfur species such as sulfone-S and aliphatic-S undergo enhanced cyclization to form aromatic-S/thiophene-S in aqueous and hydrochar products; additionally, the oxidation of sulfone-S predominates the generation of sulfate-S in aqueous products at pH < 1. Under alkaline conditions, the aromatic-S/thiophene-S can be further oxidized into sulfate-S in aqueous products at pH>13. Furthermore, the interaction between water-soluble sulfate-S and hydrolytic intermediates (i.e., glucose, heterocyclic compounds) is intensified at pH=14, resulting in increased formation of sulfone-S and sulfite-S in aqueous products. The insights gained from this study can offer guidance for controlling sulfur distribution during HTC by adjusting the feedwater pH.

Formation of Inorganic Sulfate and Volatile Nonsulfated Products from Heterogeneous Hydroxyl Radical Oxidation of 2-Methyltetrol Sulfate Aerosols: Mechanisms and Atmospheric Implications.

Chemical transformation of 2-methyltetrol sulfates (2-MTS), key isoprene-derived secondary organic aerosol (SOA) constituents, through heterogeneous hydroxyl radical (•OH) oxidation can result in the formation of previously unidentified atmospheric organosulfates (OSs). However, detected OSs cannot fully account for the sulfur content released from reacted 2-MTS, indicating the existence of sulfur in forms other than OSs such as inorganic sulfates. This work investigated the formation of inorganic sulfates through heterogeneous •OH oxidation of 2-MTS aerosols. Remarkably, high yields of inorganic sulfates, defined as the moles of inorganic sulfates produced per mole of reacted 2-MTS, were observed in the range from 0.48 ± 0.07 to 0.68 ± 0.07. These could be explained by the production of sulfate (SO4 •-) and sulfite (SO3 •-) radicals through the cleavage of C-O(S) and (C)O-S bonds, followed by aerosol-phase reactions. Additionally, nonsulfated products resulting from bond cleavage were likely volatile and evaporated into the gas phase, as evidenced by the observed aerosol mass loss (≤25%) and concurrent size reduction upon oxidation. This investigation highlights the significant transformation of sulfur from its organic to inorganic forms during the heterogeneous oxidation of 2-MTS aerosols, potentially influencing the physicochemical properties and environmental impacts of isoprene-derived SOAs.

Cooperative Sulfur Transformations at a Dinickel Site: A Metal Bridging Sulfur Radical and Its H-Atom Abstraction Thermochemistry.

Starting from the dinickel(II) dihydride complex [ML(Ni-H)2] (1M), where L3- is a bis(tridentate) pyrazolate-bridged bis(β-diketiminato) ligand and M+ is Na+ or K+, a series of complexes [KLNi2(S2)] (2K), [MLNi2S] (3M), [LNi2(SMe)] (4), and [LNi2(SH)] (5) has been prepared. The μ-sulfido complexes 3M can be reversibly oxidized at E1/2 = -1.17 V (in THF; vs Fc+/Fc) to give [LNi2(S•)] (6) featuring a bridging S-radical. 6 has been comprehensively characterized, including by X-ray diffraction, SQUID magnetometry, EPR and XAS/XES spectroscopies, and DFT calculations. The pKa of the μ-hydrosulfido complex 5 in THF is 30.8 ± 0.4, which defines a S-H bond dissociation free energy (BDFE) of 75.1 ± 1.0 kcal mol-1. 6 reacts with H atom donors such as TEMPO-H and xanthene to give 5, while 5 reacts with 2,4,6-tri(tert-butyl)phenoxy radical in a reverse H atom transfer to generate 6. These findings provide the first full characterization of a genuine M-(μ-S•-)-M complex and provide insights into its proton-coupled electron transfer (PCET) reactivity, which is of interest in view of the prominence of M-(μ-SH/μ-S)-M units in biological systems and heterogeneous catalysis.

Enhancement of nitrogen removal in constructed wetlands through boron mud and elemental sulfur addition: Regulation of sulfur and oxygen cycling

Constructed wetlands (CWs) utilizing elemental sulfur (S0) as an electron donor are effective for nitrate (NO3–-N) removal from low C/N wastewater. However, the limited bioavailability of chemical S0 (chem-S0) due to low water solubility and inadequate mass transfer impedes complete denitrification. In this study, boron mud waste and S0 (S0&BM) were processed and combined to convert chem-S0 to biological S0 (bio-S0) in CWs. The employment of S0&BM improved NO3–-N and total nitrogen (TN) removal rates by 15.36 % and 10.55 % compared to S0 alone. The 15N isotope tracing experiment unveiled the pathways of N2O production and demonstrated that S0&BM facilitated full denitrification, resulting in a higher percentage of nitrogen being degraded in a non-polluting form (54.70 %). Releasing trace amounts of boron and magnesium in S0&BM mitigated the excessive acidification caused by the sulfur autotrophic process and promoted biofilm formation, thereby pronouncing vertical oxygen fluctuations. Meanwhile, oxygen vacancies generated in the S0&BM promoted the closed-loop sulfur cycle, starting from the oxidation of chem-S0 to sulfate (SO42-), the important process of SO42--reducing bacteria using partial organic compounds as electron donors to reduce SO42- to sulfide (S2-) was realized, and finally the S2- was oxidized to bio-S0 with better properties. S0&BM enriched functional microbial communities in the biofilm related to nitrogen and sulfur transformation. Functional gene analysis showed an increase in the narG, nirS, norB, and nosZ genes supporting denitrification. The dsrA and sqr genes responsible for the sulfur cycle exhibited the highest abundance. This realization allowed for the utilization of waste materials for treatment, enhancing the energy efficiency of carbon reduction and pollution reduction in CWs.

Synergistic effect of Ca(NO3)2 - CaO2 on the improvement of sediment microecology: Transformation of sulfur and ferrous iron, and improvement mechanism

The synergy of Ca(NO3)2 and CaO2 can effectively reduce the risks of secondary pollution caused by nitrate escape and release. However, the timing and suitable dosage of Ca(NO3)2 and CaO2 during the synergistic interaction have not been fully investigated. In this work, we separated acid volatile sulfides (AVS) oxidation and ferrous iron oxidation by controlling the dosage of Ca(NO3)2. Results indicated that at a low RN/1.6S2−ratio, there was an obvious competitive relationship between AVS oxidation and ferrous iron oxidation, and sulfide was oxidized prior to ferrous iron. More efficient AVS and ferrous iron oxidation was achieved using Ca(NO3)2 to oxidize AVS and CaO2 to oxidize ferrous iron. After the treatment with Ca(NO3)2 and CaO2, the anaerobic reduction environment of the sediment was modified, and the metabolic pathways dominated by sulfate respiration and methanogenic metabolism in the sediment were gradually converted to nitrate-reduction and dissimilatory iron reduction. The synergy of Ca(NO3)2 and CaO2 could reduce 99.61 % CH4 compared with control check and could reduce 81.66 % N2O compared with adding Ca(NO3)2 only. Furthermore, the biodegradability of organic matter was improved due to the transformation of stubborn organic matter. These results provide valuable guidance for applying Ca(NO3)2 and CaO2 in sediment remediation.

Sulfur release behavior and sulfur fixation mechanism during biomass microwave co-pyrolysis of Ascophyllum and rice straw

Co-pyrolysis with low-sulfur biomass is expected to improve the yield and quality of bio-fuels, without the usage of calcium-based desulfurizer. Sulfur transformation during microwave fluidized-bed co-pyrolysis between terrestrial and marine biomass (Ascophyllum, AS; Rice straw, RS) was investigated. Sulfur release was promoted during biomass co-pyrolysis, but it was inhibited during pyrolysis between AS and low-sulfur char. Thermal cracking of biomass was promoted during co-pyrolysis between biomass, accelerating the combination of H atoms and −SH radicals. Introduction of low-sulfur bio-char (CA) inhibited the generation of bio-char and the release of sulfur. Released sulfur was captured by –OH/C = C functional groups on bio-char through dehydration reactions/addition reactions, forming mercaptan in bio-char. Furthermore, introduction of microwave and bio-char promoted the cyclization and aromatization reaction, converting mercaptan to thiophene and improving the thermal stability of solid sulfur, and thus increasing in-situ sulfur fixation rate.

Thallium spill shifts the structural and functional characteristics of viral communities with different lifestyles in river sediments

Thallium (Tl), a highly toxic heavy metal, can affect microbial community, while little is known about its effect on viral community. The present study investigated the variation of viral communities, as well as their interactions with microbial hosts under Tl stress. Tl in sediments significantly altered the composition and diversity of the viral communities, but showed no significant links with the prokaryotic communities, which may reveal a potential discrepancy in the sensitivity of the viral and prokaryotic communities to heavy metal stress. Auxiliary metabolic genes (AMGs) involved in denitrification, methane oxidation and organic sulfur transformation were enriched at T1-contaminated sites, while the abundance of AMGs related to methanogenesis and sulfate reduction were higher at pristine sites. Specially, the enrichment of AMGs involved in assimilatory sulfate reduction in Tl-contaminated sites could possibly reduce Tl bioavailability by enhancing the microbially-driven sulfur cycling to generate sulfides that could be complexed with Tl. Moreover, there was a significantly positive correlation between virus-carrying metal resistant genes and the sedimentary Tl concentration, implying that Tl contamination might enhance the metal resistant potential of the viruses. Serving as the functional gene reservoir, the response of viral AMGs to Tl stress could represent a potential pathway for microorganisms to be adapted to the metal-polluted environments. Our study provided novel insights into the impact of Tl spill on viral communities, shedding light on functional characteristics and the links of virus-host interaction with Tl level.

Integrating experiments with modeling to understand key bacterial taxa dynamics after episodic mixing of a stratified water column

Hydraulic mixing of stratified reservoirs homogenizes physicochemical gradients and microbial communities. This has potential repercussions for microbial metabolism and water quality, not least in dams and hydraulically controlled waters. A better understanding of how key taxa respond to mixing of such stratified water bodies is needed to understand and predict the impact of hydraulic operations on microbial communities and nutrient dynamics in reservoirs. We studied taxa transitions between cyanobacteria and sulfur-transforming bacteria following mixing of stratified water columns in bioreactors and complemented the experimental approach with a biogeochemical model. Model predictions were consistent with experimental observations, suggesting that stable stratification of DO is restored within 24 h after episodic and complete mixing, at least in the absence of other more continuous disturbances. Subsequently, the concentration of S2− gradually return to pre-mixing states, with higher concentration at the surface and lower in the bottom waters, while the opposite pattern was seen for SO42−. The total abundance of sulfate-reducing bacteria and phototrophic sulfur bacteria increased markedly after 24h of mixing. The model further predicted that the rapid re-oxygenation of the entire water column by aeration will effectively suppress the water stratification and the growth of sulfur-transforming bacteria. Based on these results, we suggest that a reduction of thermocline depth by optimal flow regulation in reservoirs may also depress sulfur transforming bacteria and thereby constrain sulfur transformation processes and pollutant accumulation. The simulation of microbial nutrient transformation processes in vertically stratified waters can provide new insights about effective environmental management measures for reservoirs.