Sulfide Oxidation Processes Research Articles

Evaluating the Sulfur Oxidation Capability of a Rhodopseudomonas palustris Strain by Gene and Enzyme Analyses for Potential Applications in Environmental Bioremediation

Sulfur-oxidizing bacteria are capable of oxidizing various sulfur compounds including sulfide and thiosulfate in the environment. Hydrogen sulfide (H2S), a product of anaerobic decomposition, is highly corrosive. With the typical smell of rotten eggs, the toxic gas H2S causes many harmful effects on the environment and human health. Sulfide:quinone oxidoreductase enzyme (SQR) produced by sulfur-oxidizing bacteria plays an important role in the sulfide oxidation process, contributing to minimizing sulfide toxicity in the environment. In this study, the presence of sqr gene and SQR enzyme in the photosynthetic purple bacterium Rhodopseudomonas palustris (R. palustris) isolated from domestic wastewater was determined by gene amplification (PCR) using specific primer pairs following by sequencing and denaturing SDS-PAGE method combined with sulfide oxidase assay that measures BaSO4 turbidity, respectively. The results showed that the sqr gene has 1254 bp in length, encoding for the SQR protein containing 417 amino acids with a molecular weight of 45.87 kDa and locating on the cell membrane. The enzyme operated optimally under the condition of pH 6.5 and temperature at 30 °C with sulfide oxidation activity recorded up to 20-21 U/ml. The study has initially shown the ability of the R. palustris bacterial strain to oxidize sulfide for further research using sulfur-oxidizing bacteria applied in environmental treatment.

Synergistic Electrocatalysis and Spatial Nanoconfinement to Accelerate Sulfur Conversion Kinetics in Aqueous Zn−S Battery

AbstractAqueous zinc batteries based on the conversion‐type sulfur cathodes are promising in energy storage system due to the high theoretical energy density, low cost, and good safety. However, the multi‐electron solid‐state intermediate conversion reaction of sulfur cathodes generally possess sluggish kinetics, which leads to lower discharge voltage and inefficient sulfur utilization, thus suppressing the practical energy density. Herein, sulfur nanoparticles derived from metal–organic frameworks confined in situ within electrospun fibers derived sulfur and nitrogen co‐doped carbon nanofibers (S@S,N−CNF) composite, which possesses yolk–shell S@C nanostructure, is fabricated through successive sulfidation, pyrolysis, and sulfide oxidation processes, and served as a high‐performance cathode material for Zn−S battery. The S and N dopants on carbon can collectively catalyse sulfur reduction reaction (SRR) by lowering energy barrier and accelerating kinetics to increase discharge voltage and specific capacity. Meanwhile, the yolk–shell S@C structure with spatially confined S nanoparticle yolks is beneficial to improve charge transfer and lower activation energy, thus further expediting SRR kinetics. Furthermore, extensive density functional theory (DFT) calculations reveal that S and N dual‐doping can thermodynamically and dynamically reduce the energy barrier of rate‐determining step (i.e., the transformation of *ZnS4 into *ZnS2) for the overall SRR, thereby significantly accelerating SRR kinetics.

Synergistic Electrocatalysis and Spatial Nanoconfinement to Accelerate Sulfur Conversion Kinetics in Aqueous Zn-S Battery.

Aqueous zinc batteries based on the conversion-type sulfur cathodes are promising in energy storage system due to the high theoretical energy density, low cost, and good safety. However, the multi-electron solid-state intermediate conversion reaction of sulfur cathodes generally possess sluggish kinetics, which leads to lower discharge voltage and inefficient sulfur utilization, thus suppressing the practical energy density. Herein, sulfur nanoparticles derived from metal-organic frameworks confined in situ within electrospun fibers derived sulfur and nitrogen co-doped carbon nanofibers (S@S,N-CNF) composite, which possesses yolk-shell S@C nanostructure, is fabricated through successive sulfidation, pyrolysis, and sulfide oxidation processes, and served as a high-performance cathode material for Zn-S battery. The S and N dopants on carbon can collectively catalyse sulfur reduction reaction (SRR) by lowering energy barrier and accelerating kinetics to increase discharge voltage and specific capacity. Meanwhile, the yolk-shell S@C structure with spatially confined S nanoparticle yolks is beneficial to improve charge transfer and lower activation energy, thus further expediting SRR kinetics. Furthermore, extensive density functional theory (DFT) calculations reveal that S and N dual-doping can thermodynamically and dynamically reduce the energy barrier of rate-determining step (i.e., the transformation of *ZnS4 into *ZnS2) for the overall SRR, thereby significantly accelerating SRR kinetics.

Metagenomics and Stable Isotopes Uncover the Augmented Sulfide-Driven Autotrophic Denitrification in a Seasonally Hypoxic, Sulfate-Abundant Reservoir.

The mechanism governing sulfur cycling in nitrate reduction within sulfate-rich reservoirs during seasonal hypoxic conditions remains poorly understood. This study employs nitrogen and oxygen isotope fractionation in nitrate, along with metagenomic sequencing to elucidate the intricacies of the coupled sulfur oxidation and nitrate reduction process in the water column. In the Aha reservoir, a typical seasonally stratified water body, we observed the coexistence of denitrification, bacterial sulfide oxidation, and bacterial sulfate reduction in hypoxic conditions. This is substantiated by the presence of abundant N/S-related genes (nosZ and aprAB/dsrAB) and fluctuations in N/S species. The lower 15εNO3/18εNO3 ratio (0.60) observed in this study, compared to heterotrophic denitrification, strongly supports the occurrence of sulfur-driven denitrification. Furthermore, we found a robust positive correlation between the metabolic potential of bacterial sulfide oxidation and denitrification (p < 0.05), emphasizing the role of sulfide produced via sulfate reduction in enhancing denitrification. Sulfide-driven denitrification relied on ∑S2- as the primary electron donor preferentially oxidized by denitrification. The pivotal genus, Sulfuritalea, emerged as a central player in both denitrification and sulfide oxidation processes in hypoxic water bodies. Our study provides compelling evidence that sulfides assume a critical role in regulating denitrification in hypoxic water within an ecosystem where their contribution to the overall nitrogen cycle was previously underestimated.

Geochemical and Isotopic Characteristics of the Emir Geothermal Waters in Kula Area, Western Anatolia

In this study, we investigate chemical and isotopic characteristics of thermal waters of the Emir geothermal field in the Kula region, which hosts the youngest volcanism in Turkey. Studied thermal waters with temperature and electrical conductivity values of 21–63 °C and 3840 to 5210 μS/cm are of Na–HCO3 type and have neutral character. δ18O and δD of thermal waters are − 9.40 to − 8.41‰ and − 64.16 to − 56.38‰ (VSMOW) and indicate a meteoric source with local recharge. Tritium values of thermal waters in the Emir geothermal field are mostly < 1 TU signifying a deep circulation. Positive δ13C values (1.32–4.46‰ VPDB) imply that carbon is derived dominantly from marine limestone and dominantly from endogenic CO2. δ18O and δ34S of dissolved sulfate yield that marine limestone is the source of sulfur in thermal waters, which are partly affected by sulfide oxidation and bacterial reduction processes. At discharge temperatures, Emir thermal waters are oversaturated with respect to albite, aragonite, calcite, α-cristobalite, dolomite, gibbsite, illite, K-feldspar, kaolinite, muscovite and quartz but undersaturated for anhydrite and wairakite. The activity diagrams suggest that high Na+ and K+ concentrations in waters are attributed to dissolution of muscovite, K-feldspar and albite. Chemical and isotopic compositions of the Emir thermal waters are controlled by a combination of processes including water–rock interaction, dissolution/precipitation and ion exchange. Various chemical and isotopic geothermometers applied to the thermal waters yielded reservoir temperatures in the range of 80–125 °C. Paleo-temperatures estimated from δ18O values of travertines and thermal waters (isotope fractionation) are consistent with modern discharge temperatures.

Possibilities for improving the technology of roasting zinc concentrates

The paper presents an investigation into the oxidation process of zinc sulfide concentrate. A common challenge encountered during the fluidized calcination process is the high concentration of sulfide sulfur in the condensed products, such as the mixture collected at the furnace threshold and in the dust. This scientific work reports the results of laboratory studies aimed at improving the technology of roasting zinc concentrates. The study's objective was to obtain zinc cinders with increased solubility in aqueous solutions by roasting sulfide zinc concentrates. The results show that the optimal composition of the charge for roasting was determined using limestone and wastewater from the processing plant, which contains alkaline earth metal oxides. This composition helped reduce the formation of ferrites and silicates by 1.5-1.7 times.

Heterotrophic bacteria dominate the sulfide oxidation process in coastal sediments

Sulfate reduction and sulfur oxidation are very active in coastal sediments. Together they shape the biogeochemistry and microbial ecology at hot places of organic matter metabolism. Compared to the well-studied sulfate reduction process, sulfur oxidation process is relatively lack of investigation. For a long time, autotrophic/mixotrophic bacteria were thought to be the main sulfur oxidation strains in sediments. Herein, we investigated the distribution of reduced sulfur compounds in differently layers of coastal sediments at the Yellow sea. We found that sulfide (H2S), sulfane sulfur (S0), and thiosulfate mainly accumulated in deep anaerobic sediments and were mostly oxidized in surface sediments (∼3 cm in depth). Bacterial community analysis indicated that heterotrophic bacteria were dominating species in surface sediments. Metatranscriptome analysis showed that transcripts of flavocytochrome c sulfide dehydrogenase (FCC), persufide dioxygenase (PDO), and sulfite-oxidizing enzyme (SOE) were abundant in surface sediments. In addition, using a Roseobacterium (Ruegeria pomeroyi DSS-3) as the model strain, we investigated how FCC, PDO, and SOE work together to oxidize H2S to sulfate. This study clarified that heterotrophic bacteria are the main sulfur oxidation strains in coastal sediments.

Species' functional traits and interactions drive nitrate-mediated sulfur-oxidizing community structure and functioning.

Understanding the processes and mechanisms governing microbial community assembly and their linkages to ecosystem functioning has long been a core issue in microbial ecology. An in-depth insight still requires combining with analyses of species' functional traits and microbial interactions. Our study showed how species' functional traits and interactions determined microbial community structure and functions by a well-controlled laboratory experiment with nitrate-mediated sulfur oxidation systems using high-throughput sequencing and culture-dependent technologies. The results provided solid evidences that species' functional traits and interactions were the intrinsic factors determining community structure and function. More importantly, our study established quantitative links between community structure and function based on species' functional traits and interactions, which would have important implications for the design and synthesis of microbiomes with expected functions.

New insight into the pyrophoricity and mechanism of ironic sulfide from synergistic effect of FeS and FeS2

The pyrophoricity of ironic sulfide of sulfur corrosion products in oil tanks is a critical safety and environment concern that may trigger fire and explosion accidents. This paper focused on mixtures of FeS with FeS2 and aimed to systematically investigate their influence on the pyrophoricity of ironic sulfide. The results showed that the mixtures’ oxidation spontaneous combustion processes are generally similar, including low-temperature heating, oxidation decomposition, and burning-out stages. The more unstable molecular configuration and uneven surface morphology of FeS made it more prone to spontaneous combustion than FeS2. As the proportion of FeS2 in the sample increased, it absorbed the energy used to activate FeS during the early stages of oxidation and decomposition, causing the sample’s activation energy to increase and its pyrophoricity to weaken. When the proportion of FeS2 reached a certain level, the reaction may produce a large amount of elemental sulfur, which further oxidized and released heat, thus promoting the sample’s pyrophoricity. The study results suggest that the oxidation process of ironic sulfide involved a spontaneous, multistage exothermic reaction and produced intermediate products such as elemental sulfur, leading to a synergistic effect that influenced the reaction process.

Underlying mechanisms for natural organic matters mediated aerobic ciprofloxacin transformation by sulfide

Natural organic matters (NOMs), sulfide and organic pollutants such as antibiotics might all coexist in natural water environments. However, the impact of NOMs on aerobic organic pollutants transformation by sulfide is still poor understood. In this study, it observed that 50 ppm (14.55–23.05 mg C L−1) of various NOMs could facilitate the aerobic transformation of antibiotic ciprofloxacin (CIP) by sulfide, and the pseudo first order reaction rate k ranged from 3.24 × 10−4 to 27.6 × 10−4 min−1 for different sources of NOMs compared with 1.36 × 10−4 min−1 for control one at pH 6.5. Moreover, sulfide oxidation process would play important roles for the aerobic CIP transformation, while transformation of other intermediate sulfur species did not directly promote CIP transformation. Electron paramagnetic resonance (EPR) and quenching experiments indicated that singlet oxygen (1O2) was the main active specie playing important roles in the process of aerobic CIP transformation with presence of sulfide and NOMs. Furthermore, carbonyl groups of the NOMs, especially the quinones, were demonstrated to play a critical role to promote the transformation of intermediate H2O2 to 1O2. This study provides a better understanding for the NOMs-mediated aerobic organic pollutants transformation by sulfide in aqueous environments.

Deciphering the biodesulfurization pathway employing marine mangrove Bacillus aryabhattai strain NM1-A2 according to whole genome sequencing and transcriptome analyses

In the biogeochemical cycle, sulfur oxidation plays a vital role and is typically referred to as the elemental sulfur or reductive sulfide oxidation process. This study aimed to characterize a subtropical mangrove-isolated bacterial strain using biochemical, whole-genome, and transcriptome sequencing analyses to enhance our understanding of sulfur metabolism and biodegradation from a molecular genetic perspective. Strain NM1-A2 was characterized as Gram-positive and found to have a close molecular phylogenetic relationship with Bacillus aryabhattai. NM1-A2 efficiently converted dibenzothiophene (DBT) into 2-hydroxybiphenyl (2-HBP) via a 4S pathway with 95% efficiency, using enzymes encoded by the dsz operon (dszA, dszB, and dszC), which determine monooxygenases (DszA & DszC) and desulfinase (DszB). The whole-genome sequence of NM1-A2 had a length of approximately 5,257,678 bp and included 16 sulfur metabolism-related genes, featuring the ABC transport system, small subunit (ssu) and cysteine (cys) gene families, and adenosine 5′-phosphosulfate (APS) and 3′-phosphoadenosine-5′-phosphosulfate (PAPS) biosynthesis-related genes. Transcriptomic analysis of NM1-A2 using three sulfur groups—magnesium sulfate (MS), sulfur powder (SP), and sodium thiosulfate (ST) resulted in a significant number of differentially expressed genes (1200, 2304, and 2001, respectively). This analysis revealed that intracellular cysteine concentration directly regulated the expression of cys and ssu genes. Sulfate did not directly affect cys gene expression but repressed ssu gene expression. The cys gene expression levels decreased during the conversion of sulfate to sulfide and cysteine. The transcriptomic data was validated by analyzing the expression patterns of NM1-A2 using real-time quantitative PCR validation analysis. The expression levels of cysl, mccB, and nrnA were significantly upregulated, while cysH, metB, and sat were downregulated in the SP, ST, and MS groups, respectively. This research contributes to our understanding of marine mangrove microorganisms' bacterial efficiency through characterization, whole-genome, and transcriptome sequencing-based molecular degradation of organic compounds in the mangrove ecosystem, which may enhance nutrient availability.

Riverine sulfate sources and behaviors in arid environment, Northwest China: Constraints from sulfur and oxygen isotopes

The fate of riverine sulfate ion (SO42-) and its environmental effects in arid environment are difficult to evaluate due to its complicated sources and strongly coupled behaviors with water cycle which is significantly modified by humans. To understand the sulfur cycle in aquatic systems in arid environment, the chemical and sulfur and oxygen isotopic compositions (δ34SSO4 and δ18OSO4) of major rivers around the Badain Jaran Desert, northwestern China, were investigated. These rivers had averaged SO42- content at 1336 µmol/L, over 10 times higher than the global average. The δ34SSO4 and δ18OSO4 values ranged from -5.3‰ to +11.8‰ and +1.6‰ to +12.8‰, respectively. The end-member analysis and the inverse model showed that riverine sulfate was mainly derived from evaporites dissolution (0-87%), sulfide oxidation (13%-100%) and precipitation (0-33%), indicating heterogeneity in sulfur sources and behaviors along the river drainage with the lithology variations and climate gradients. Multiple isotopic tools combining with hydro-chemistry compositions could be applied to reveal sulfur cycle in arid environment. Based on the calculation, sulfide oxidation plays the primary role in the headwater and upstream in the Qilian-Mountains area, where sulfide is widely exposed. While the proportion of evaporites dissolution contributing to riverine sulfate is much higher in downstream in a drier environment. Besides, less precipitation and higher temperature can lead to more intensive evaporation, affecting the process of sulfide oxidation and enhancing the rates of evaporites dissolution and sulfate precipitation in the basin.

Disturbance and restoration of soil microbial communities after in-situ thermal desorption in a chlorinated hydrocarbon contaminated site

Thermal desorption technology has been widely used for the remediation of organic contaminated soil, but the heating process may alter the soil properties and its safety reutilization. After thermal remediation, the target pollutants including chloroform, 1,2-dichloroethane, 1,1,2-trichloroethane, 1,2,3-trichloropropane and vinyl chloride in the chlorinated hydrocarbon contaminated site were reduced significantly. The soil microbial α-diversity was also reduced by more than half. Notably, the relative abundance of Chloroflexi decreased by 9.0%, while Firmicutes had a 9.0% increase after thermal remediation. By water regulation and exogenous microorganism addition, the soil microbial community could not be restored to its initial state before thermal remediation in a relatively short time (30 days). The relative abundance of Proteobacteria increased from 25.4% to 41.7% and 51.0% by water regulation and exogenous microorganism addition, respectively. The modularity of the microbial co-occurrence network was strengthened after microbial restoration, but the interaction among microorganisms was weakened. Thermal remediation might be conducive to the C- and N-cycle related processes, but severely weakened the sulfide oxidation processes. Notably, microbial restoration would benefit the recovery of the S-cycle functional groups. These results provided a new perspective for the safety reutilization of soil after thermal remediation.

Biogeochemical impacts of fish farming on coastal sediments: Insights into the functional role of cable bacteria.

Fish farming in sea cages is a growing component of the global food industry. A prominent ecosystem impact of this industry is the increase in the downward flux of organic matter, which stimulates anaerobic mineralization and sulfide production in underlying sediments. When free sulfide is released to the overlying water, this can have a toxic effect on local marine ecosystems. The microbially-mediated process of sulfide oxidation has the potential to be an important natural mitigation and prevention strategy that has not been studied in fish farm sediments. We examined the microbial community composition (DNA-based 16S rRNA gene) underneath two active fish farms on the Southwestern coast of Iceland and performed laboratory incubations of resident sediment. Field observations confirmed the strong geochemical impact of fish farming on the sediment (up to 150 m away from cages). Sulfide accumulation was evidenced under the cages congruent with a higher supply of degradable organic matter from the cages. Phylogenetically diverse microbes capable of sulfide detoxification were present in the field sediment as well as in lab incubations, including cable bacteria (Candidatus Electrothrix), which display a unique metabolism based on long-distance electron transport. Microsensor profiling revealed that the activity of cable bacteria did not exert a dominant impact on the geochemistry of fish farm sediment at the time of sampling. However, laboratory incubations that mimic the recovery process during fallowing, revealed successful enrichment of cable bacteria within weeks, with concomitant high sulfur-oxidizing activity. Overall our results give insight into the role of microbially-mediated sulfide detoxification in aquaculture impacted sediments.

Formation of mine drainage in the Far Eastern region and its impact on the ecosphere and public health

The long-term development of the mining industry in the Komsomolsky, Kavalerovsky and Dalnegorsky districts of the Far East of Russia caused origination of large-scale mining technogenic systems. During the period of socalled “perestroika”, mining production in the region was suspended, while mine workings (pits, adits) and tailings dumps were not subjected to any kind of preservation or reclamation. Only the boron and lead-zinc mining sectors in the Dalnegorsk district are currently in operation. The purpose of this paper is to assess the composition of mine waters, reveal the conditions of their formation, the presence of various aqueous species (coordination compounds and ions) of different elements and establish the parameters of precipitation of a number of hypergenic natural and technogenic minerals from these waters. This paper provides the hydrochemical characteristics of mine waters in the mining technogenic systems of tin-sulfide, copper-tin, tin-polymetallic, and polymetallic deposits, indicates the conditions of their formation and describes the adverse impact on the hydrosphere, as well as on human health in these districts. The studies of sulfide oxidation and mine water formation processes were carried out by the method of physicochemical simulation involving the use of the Selektor software package. The Eh–pH parameters of solutions, their composition with respect to stable aqueous species (complex compounds and simple ions), paragenetic associations (paragenesis) of precipitating hypergenic minerals with respect to the primary composition of ores and host rocks were established in a wide temperature range (from −25 to +45 °С). It has been established that the simulated micropore solutions participating in the formation of mine waters exhibit a wide range of Eh–pH parameters: Eh from 0.55 to 1.24 V and pH from 0.3 to 13.8. The technogenic minerals Fe, Cu, Zn, Pb and Sb belonging to oxide and hydroxide, sulphate, and arsenate classes are precipitated from them. Mine waters of high concentration, prior to and after the precipitation of technogenic minerals (weight of which reaches the hundreds of grams), are released into the hydrosphere. The simulated solutions contain all the elements of sulfide ores: Cu, Zn, Pb, Fe, Ag, As, Sb and S, whereas their concentrations in the form of aqueous species reach the tens of grams, while under cryogenic conditions the concentrations are by one or two orders of magnitude higher as a result of ice formation. The forms of migration of the elements depend on the temperature conditions. The negative impact of mine waters on the region hydrosphere and human health was demonstrated. In the districts under consideration, obvious trend of increasing morbidity (for almost all types of diseases) by 2 times both in adults and in children as compared to other Far Eastern regions was revealed. In addition, the morbidity of the child population for almost all the diseases under consideration proved much higher than in adults.

Enhanced electro-activity of nickel phosphide by pre-treatment for efficient hydrogen sulfide elimination

Electrochemical sulfide oxidation is a promising approach for sulfide removal from wastewater or biogas due to low energy and chemical consumption. In this work, nickel phosphide was facilely electrodeposited on stainless steel (SS/Ni-P) and comprehensively evaluated as anode catalyst for sulfide oxidation. Electrochemical property analysis suggested that SS/Ni-P had low polarization resistance (109.10 Ω) and high electrochemical active surface area (Cdl = 1.3 mF/cm2). The sulfide removal efficiency of SS/Ni-P achieved 95.00 ± 3.55 % at 1.42 V vs RHE within 48 h, which was 2.60 times and 3.62 times of that by SS/Ni and SS anodes, respectively. The first order kinetic rate constant of SS/Ni-P for sulfide removal was 0.0315 ± 0.0061 h-1, superior than that of the reported single nickel atom based catalyst with stainless steel substrate. Pre-treating SS/Ni-P under a constant external potential for 10 s further improved the electroactivity on sulfide oxidation due to the enhancement of the electrochemical active surface area by 46.56%. Further analysis of the chemical state changes during the sulfide oxidation process revealed that the Ni from Ni-P was the real active center, which formed Ni-S precursors to promote polysulfide formation. This work provided a highly efficient sulfide oxidation anode material for sulfide containing wastewater and biogas treatment.

Comparative studies of novel biooxidation process to low-grade sulphide gold ores

ABSTRACT The Sand Farming is one of novel biooxidation processes suitable for sulphide oxidation of low-grade refractory gold ores. It has been previously proven to be feasible and more efficient compared to other conventional sulphide oxidation processes. In this study, the Sand Farming was compared with conventional tank biooxidation to investigate biooxidation behaviors on ores with different mineralogy and compare the ultimate gold recovery. Ore samples were tested for Sand Farming biooxidation. Conventional tank biooxidation was also compared as the baseline. After each biooxidation was completed, cyanidation was conducted for gold extraction. The Sand Farming achieved the gold recovery of 75% from high grade with higher sulphur content sample (Sample A) and 68% from low grade with lower sulphur content sample (Sample B), slightly lower than tank biooxidation of 83% and 85%, respectively. Sand Farming can be an alternative to several sulphide oxidation processes with better overall economics.

Bioelectrocatalytic sulfide oxidation by a haloalkaliphilic electroactive microbial community dominated by Desulfobulbaceae

Sulfide-oxidizing microorganisms (SOMs) play a vital role in biogeochemical sulfur cycling and are useful for the bioremediation of sulfide-rich wastewaters and environments. The electroactive SOMs remain poorly explored from extreme environments. This study presents the autotrophic electroactive microbial biofilm capable of sulfide oxidation under haloalkaline conditions (pH – 9.5; salinity – 20 g/L). It was obtained through electrochemical microbial enrichment from sub-surface sediments of the haloalkaline Lonar lake at an applied anode potential of -330 mV vs. Ag/AgCl in microbial electrolysis cells (MECs). The sulfide-oxidizing electroactive biofilm achieved a maximum average current density of 315±23 µA/cm2 with 87±10% coulombic efficiency and 34±8% sulfide oxidation to sulfate. The bioelectrocatalytic sulfide oxidation at the anode facilitated 0.16±0.02 mM/day hydrogen production at the cathode of MECs. Low current densities and neither sulfate nor hydrogen production were observed in abiotic electrochemical controls suggesting the bioelectrocatalytic role of anodic microbial biofilm in the sulfide to sulfate oxidation process. The sulfide oxidation process was faster in bioelectrochemical (0.94±0.2 mM/day) than the abiotic reactors (0.49±0.01 mM/day), confirming the microbial role in the enhanced sulfide oxidation bioelectrocatalysis. Sulfur was detected at the anode surface in both abiotic and biotic electrochemical experiments, suggesting the occurrence of electrochemical sulfide oxidation to sulfur process under here-tested conditions. The bio-anode analysis through scanning electron microscopic imaging confirmed the microbial growth at the anode surface, and 16S-rRNA based amplicon sequencing revealed the dominance of unclassified Desulfobulbaceace at a relative sequence abundance of 61.8 ± 9.9% in anodic biofilm. This work on electroactive SOMs from a natural haloalkaline habitat contributes to the limited understanding of extreme electroactive microorganisms and their role in sulfur cycling in such environments.

Caracterización del proceso biológico de sulfuro oxidación: un enfoque de respirometría de pulsos in situ y microrespirometria de pulsos ex situ

During the optimization of environmental biotechnology processes, it is important to count on proper and reliable information about the kinetic and stoichiometric parameters of the microorganisms. In this work, the biological sulfide oxidation process was assessed under two novel dynamic pulse respirometric approaches: in-situ pulse respirometry conducted in airlift bioreactor and ex-situ pulse respirometry carried out in microreactors (microrespirometry) with samples taken from the airlift bioreactor. The process was characterized in terms of the growth yield, substrate oxidation yield, maximum oxygen uptake rate, affinity constant, and mass transfer coefficient. The in-situ pulse respirometry showed to be a reproducible technique that allowed the determination of the kinetic and stoichiometric parameters besides the detection of mass transfer limitations in the airlift bioreactor, however, its use in biological sulfide oxidation is limited to a few experiments and experimental conditions with significant time investment. On the other hand, the ex-situ pulse microrespirometry allowed the acquisition of a higher amount of information under a broader range of sulfide concentrations (from 5 to 60 mg H2S L-1) and experimental conditions such as different pH values. The results obtained showed that the ex-situ microrespirometry technique would be preferable over in-situ pulse respirometry for the proper and reliable characterization of the sulfide oxidation process.

DNA microarray for detection and identification of sulfur oxidizing bacteria in Biogas Clean-up System

Knowledge of gene function and coexistence in the sulfur oxidizing bacteria (SOB) communities plays a significant role in driving the sulfide oxidation process in biogas clean-up process, including the stability and balance within the system. Microarray techniques can be responding to achieve as specific-detection, quantitative-identification, and high-throughput tools for microbial characterization in various environments. This research designed the microarray for monitoring SOB bacteria based on the entire genome and functional genes: soxAXBYZ and fccAB, using genome sequencing of non-SOB as a negative control, and then SOB microarray used to detect and identify SOB species-strain in the starch industry. The design of the DNA microarray revealed 61,788 probes which covered 722 strains of SOB and 35 strains of non-SOB. The quality test results demonstrated the DNA concentration, specific activity (28-36 pmol/μg), and yield (6-7 μg) of the genomic DNA had high-quality and could be repeated in the future with little noise signal. The expression level of recirculating sludge has increased in level of expression than the starting sludge. Thiothrix, Syntrophomonas, Paracoccus Magnetospirillum, Arcobacter, Sulfuricurvum, Acinetobacter, and Hydrogenophaga gained the gene expression level that involved with sulfide oxidation. The overexpression could be due to the biotrickling filter have more nutrients and optimal conditions for SOB growth to synthesize the necessary proteins for cell adaptation, such as SoxXA, SoxYZ, SoxB, and FccAB related to bacterial activity that oxidized the H2S in biogas.