Distinct gene clusters drive formation of ferrosome organelles in bacteria.

Cellular iron homeostasis is vital and maintained through tight regulation of iron import, efflux, storage and detoxification1-3. The most common modes of iron storage use proteinaceous compartments, such as ferritins and related proteins4,5. Although lipid-bounded iron compartments have also been described, the basis for their formation and function remains unknown6,7. Here we focus on one such compartment, herein named the 'ferrosome', that was previously observed in the anaerobic bacterium Desulfovibrio magneticus6. Using a proteomic approach, we identify three ferrosome-associated (Fez) proteins that are responsible for forming ferrosomes in D. magneticus. Fez proteins are encoded in a putative operon and include FezB, a P1B-6-ATPase found in phylogenetically and metabolically diverse species of bacteria and archaea. We show that two other bacterial species, Rhodopseudomonas palustris and Shewanella putrefaciens, make ferrosomes through the action of their six-gene fez operon. Additionally, we find that fez operons are sufficient for ferrosome formation in foreign hosts. Using S. putrefaciens as a model, we show that ferrosomes probably have a role in the anaerobic adaptation to iron starvation. Overall, this work establishes ferrosomes as a new class of iron storage organelles and sets the stage for studying their formation and structure in diverse microorganisms.

Sulfate-reducing bacteria unearthed: ecological functions of the diverse prokaryotic group in terrestrial environments.

Sulfate-reducing prokaryotes (SRPs) are essential microorganisms that play crucial roles in various ecological processes. Even though SRPs have been studied for over a century, there are still gaps in our understanding of their biology. In the past two decades, a significant amount of data on SRP ecology has been accumulated. This review aims to consolidate that information, focusing on SRPs in soils, their relation to the rare biosphere, uncultured sulfate reducers, and their interactions with other organisms in terrestrial ecosystems. SRPs in soils form part of the rare biosphere and contribute to various processes as a low-density population. The data reveal a diverse range of sulfate-reducing taxa intricately involved in terrestrial carbon and sulfur cycles. While some taxa like Desulfitobacterium and Desulfosporosinus are well studied, others are more enigmatic. For example, members of the Acidobacteriota phylum appear to hold significant importance for the terrestrial sulfur cycle. Many aspects of SRP ecology remain mysterious, including sulfate reduction in different bacterial phyla, interactions with bacteria and fungi in soils, and the existence of soil sulfate-reducing archaea. Utilizing metagenomic, metatranscriptomic, and culture-dependent approaches will help uncover the diversity, functional potential, and adaptations of SRPs in the global environment.

Characterization of the Bottlenecks and Pathways for Inhibitor Dissociation from [NiFe] Hydrogenase.

[NiFe] hydrogenases can act as efficient catalysts for hydrogen oxidation and biofuel production. However, some [NiFe] hydrogenases are inhibited by gas molecules present in the environment, such as O2 and CO. One strategy to engineer [NiFe] hydrogenases and achieve O2- and CO-tolerant enzymes is by introducing point mutations to block the access of inhibitors to the catalytic site. In this work, we characterized the unbinding pathways of CO in the complex with the wild-type and 10 different mutants of [NiFe] hydrogenase from Desulfovibrio fructosovorans using τ-random accelerated molecular dynamics (τRAMD) to enhance the sampling of unbinding events. The ranking provided by the relative residence times computed with τRAMD is in agreement with experiments. Extensive data analysis of the simulations revealed that from the two bottlenecks proposed in previous studies for the transit of gas molecules (residues 74 and 122 and residues 74 and 476), only one of them (residues 74 and 122) effectively modulates diffusion and residence times for CO. We also computed pathway probabilities for the unbinding of CO, O2, and H2 from the wild-type [NiFe] hydrogenase, and we observed that while the most probable pathways are the same, the secondary pathways are different. We propose that introducing mutations to block the most probable paths, in combination with mutations to open the main secondary path used by H2, can be a feasible strategy to achieve CO and O2 resistance in the [NiFe] hydrogenase from Desulfovibrio fructosovorans.

Mitigation of Desulfovibrio ferrophilus IS5 degradation of X80 carbon steel mechanical properties using a green biocide.

Most microbiologically influenced corrosion (MIC) studies focus on the threat of pinhole leaks caused by MIC pitting. However, microbes can also lead to structural failures. Tetrakis hydroxymethyl phosphonium sulfate (THPS) biocide mitigated the microbial degradation of mechanical properties of X80 steel pipeline by Desulfovibrio ferrophilus (IS5 strain), a very corrosive sulfate reducing bacterium. It was found that 100 ppm (w/w) THPS added to the enriched artificial seawater (EASW) culture medium before incubation resulted in 2.8-log reduction in sessile cell count after a 7-d incubation at 28 °C under anaerobic conditions, leading to 94% uniform corrosion rate reduction (from 1.3 to 0.07 mm/a), and 84% pitting corrosion rate reduction (from 0.70 to 0.11 mm/a). The X80 dogbone coupon incubated with 100 ppm THPS for 7 d suffered 3% loss in ultimate tensile strain and 0% loss in ultimate tensile strength compared with the abiotic control in EASW. In comparison, the no-treatment X80 dogbone coupon suffered losses of 13% in ultimate tensile strain and 6% in ultimate tensile stress, demonstrating very good THPS efficacy.

Sulfate reduction behavior in response to landfill dynamic pressure changes.

During the long-term stabilization process of landfills, the pressure field undergoes constant changes. This study constructed dynamic pressure changes scenarios of high-pressure differentials (0.6 MPa) and low-pressure differentials (0.2 MPa) in the landfill pressure field at 25 °C and 50 °C, and investigated the sulfate reduction behavior in response to landfill dynamic pressure changes. The results showed that the pressurization or depressurization of high-pressure differentials caused more significant differences in sulfate reduction behavior than that of low-pressure differentials. The lowest hydrogen sulfide (H2S) release peak concentration under pressurization was only 29.67% of that under initial pressure condition; under depressurization, the highest peak concentration of H2S was up to 21,828 mg m-3, posing a serious risk of H2S pollution. Microbial community and correlation analysis showed that pressure had a negative impact on the sulfate-reducing bacteria (SRB) community, and the SRB community adjusted its structure to adapt to pressure changes. Specific SRBs were further enriched with pressure changes. Differential H2S release behavior under pressure changes in the 25 °C pressure environments were mediated by Desulfofarcimen (ASV343) and Desulfosporosinus (ASV1336), while Candidatus Desulforudis (ASV24) and Desulfohalotomaculum (ASV94) played a key role at 50 °C. This study is helpful in the formulation of control strategies for the source of odor pollution in landfills.

Superwettable surfaces and factors impacting microbial adherence in microbiologically-influenced corrosion: a review.

Microbiologically-influenced corrosion (MIC) is a common operational hazard to many industrial processes. The focus of this review lies on microbial corrosion in the maritime industry. Microbial metal attachment and colonization are the critical steps in MIC initiation. We have outlined the crucial factors influencing corrosion caused by microorganism sulfate-reducing bacteria (SRB), where its adherence on the metal surface leads to Direct Electron Transfer (DET)-MIC. This review thus aims to summarize the recent progress and the lacunae in mitigation of MIC. We further highlight the susceptibility of stainless steel grades to SRB pitting corrosion and have included recent developments in understanding the quorum sensing mechanisms in SRB, which governs the proliferation process of the microbial community. There is a paucity of literature on the utilization of anti-quorum sensing molecules against SRB, indicating that the area of study is in its nascent stage of development. Furthermore, microbial adherence to metal is significantly impacted by surface chemistry and topography. Thus, we have reviewed the application of super wettable surfaces such as superhydrophobic, superhydrophilic, and slippery liquid-infused porous surfaces as "anti-corrosion coatings" in preventing adhesion of SRB, providing a potential avenue for the development of practical and feasible solutions in the prevention of MIC. The emerging field of super wettable surfaces holds significant potential for advancing efficient and practical MIC prevention techniques.

The electron-bifurcating FeFe-hydrogenase Hnd is involved in ethanol metabolism in Desulfovibrio fructosovorans grown on pyruvate.

Desulfovibrio fructosovorans, a sulfate-reducing bacterium, possesses six gene clusters encoding six hydrogenases catalyzing the reversible oxidation of H2 into protons and electrons. Among them, Hnd is an electron-bifurcating hydrogenase, coupling the exergonic reduction of NAD+ to the endergonic reduction of a ferredoxin with electrons derived from H2 . It was previously hypothesized that its biological function involves the production of NADPH necessary for biosynthetic purposes. However, it was subsequently demonstrated that Hnd is instead a NAD+ -reducing enzyme, thus its specific function has yet to be established. To understand the physiological role of Hnd in D. fructosovorans, we compared the hnd deletion mutant with the wild-type strain grown on pyruvate. Growth, metabolite production and consumption, and gene expression were compared under three different growth conditions. Our results indicate that hnd is strongly regulated at the transcriptional level and that its deletion has a drastic effect on the expression of genes for two enzymes, an aldehyde ferredoxin oxidoreductase and an alcohol dehydrogenase. We demonstrated here that Hnd is involved in ethanol metabolism when bacteria grow fermentatively and proposed that Hnd might oxidize part of the H2 produced during fermentation generating both NADH and reduced ferredoxin for ethanol production via its electron bifurcation mechanism.

DsrC is involved in fermentative growth and interacts directly with the FlxABCD-HdrABC complex in Desulfovibrio vulgaris Hildenborough.

DsrC is a key protein in dissimilatory sulfur metabolism, where it works as co-substrate of the dissimilatory sulfite reductase DsrAB. DsrC has two conserved cysteines in a C-terminal arm that are converted to a trisulfide upon reduction of sulfite. In sulfate-reducing bacteria, DsrC is essential and previous works suggested additional functions beyond sulfite reduction. Here, we studied whether DsrC also plays a role during fermentative growth of Desulfovibrio vulgaris Hildenborough, by studying two strains where the functionality of DsrC is impaired by a lower level of expression (IPFG07) and additionally by the absence of one conserved Cys (IPFG09). Growth studies coupled with metabolite and proteomic analyses reveal that fermentation leads to lower levels of DsrC, but impairment of its function results in reduced growth by fermentation and a shift towards more fermentative metabolism during sulfate respiration. In both respiratory and fermentative conditions, there is increased abundance of the FlxABCD-HdrABC complex and Adh alcohol dehydrogenase in IPFG09 versus the wild type, which is reflected in higher production of ethanol. Pull-down experiments confirmed a direct interaction between DsrC and the FlxABCD-HdrABC complex, through the HdrB subunit. Dissimilatory sulfur metabolism, where sulfur compounds are used for energy generation, is a key process in the ecology of anoxic environments, and is more widespread among bacteria than previously believed. Two central proteins for this type of metabolism are DsrAB dissimilatory sulfite reductase and its co-substrate DsrC. Using physiological, proteomic and biochemical studies of Desulfovibrio vulgaris Hildenborough and mutants affected in DsrC functionality, we show that DsrC is also relevant for fermentative growth of this model organism and that it interacts directly with the soluble FlxABCD-HdrABC complex that links the NAD(H) pool with dissimilatory sulfite reduction.

Sulfur-oxidizing bacteria (SOB) and sulfate-reducing bacteria (SRB) in oil reservoir and biological control of SRB: a review.

Sulfur-oxidizing bacteria (SOB) and sulfate-reducing bacteria (SRB) inhabit oilfield production systems. Sulfur oxidation driven by SOB and dissimilatory sulfate reduction driven by SRB play important roles in sulfur cycle of oil reservoirs. More importantly, hydrogen sulfide produced by SRB is an acidic, flammable, and smelly toxic gas associated with reservoir souring, corrosion of oil-production facilities, and personnel safety. Effective control of SRB is urgently needed for the oil industry. This depends on an in-depth understanding of the microbial species that drive sulfur cycle and other related microorganisms in oil reservoir environments. Here, we identified SOB and SRB in produced brines of Qizhong block (Xinjiang Oilfield, China) from metagenome sequencing data based on reported SOB and SRB, reviewed metabolic pathways of sulfur oxidation and dissimilatory sulfate reduction, and ways for SRB control. The existing issues and future research of microbial sulfur cycle and SRB control are also discussed. Knowledge of the distribution of the microbial populations, their metabolic characteristics and interactions can help to develop an effective process to harness these microorganisms for oilfield production.

Bacterial diversity of an acid mine drainage beside the Xichú River (Mexico) accessed by culture-dependent and culture-independent approaches.

Xichú River is a Mexican river located in an environmental preservation area called Sierra Gorda Biosphere Reserve. Around it, there are tons of abandoned mine residues that represent a serious environmental issue. Sediment samples of Xichú River, visibly contaminated by flows of an acid mine drainage, were collected to study their prokaryotic diversity. The study was based on both cultural and non-cultural approaches. The analysis of total 16S rRNA gene by MiSEQ sequencing allowed to identify 182 Operational Taxonomic Units. The community was dominated by Pseudomonadota, Bacteroidota, "Desulfobacterota" and Acidobacteriota (27, 21, 19 and 16%, respectively). Different culture conditions were used focusing on the isolation of anaerobic bacteria, including sulfate-reducing bacteria (SRB) and arsenate-reducing bacteria (ARB). Finally, 16 strains were isolated. Among them, 12 were phylogenetically identified, with two strains being SRB, belonging to the genus Solidesulfovibrio ("Desulfobacterota"), while ten are ARB belonging to the genera Azospira (Pseudomonadota), Peribacillus (Bacillota), Raineyella and Propionicimonas (Actinomycetota). The isolate representative of Raineyella genus probably corresponds to a new species, which, besides arsenate, also reduces nitrate, nitrite, and fumarate.

Coexistence of Psychrophilic, Mesophilic, and Thermophilic Sulfate-Reducing Bacteria in a Deep Subsurface Aquifer Associated with Coal-Bed Methane Production.

The microbial community of subsurface environments remains understudied due to limited access to deep strata and aquifers. Coal-bed methane (CBM) production is associated with a large number of wells pumping water out of coal seams. CBM wells provide access to deep biotopes associated with coal-bed water. Temperature is one of the key constraints for the distribution and activity of subsurface microorganisms, including sulfate-reducing prokaryotes (SRP). The 16S rRNA gene amplicon sequencing coupled with in situ sulfate reduction rate (SRR) measurements with a radioactive tracer and cultivation at various temperatures revealed that the SRP community of the coal bed water of the Kuzbass coal basin is characterized by an overlapping mesophilic-psychrophilic boundary. The genus Desulfovibrio comprised a significant share of the SRP community. The D. psychrotolerans strain 1203, which has a growth optimum below 20 °C, dominated the cultivated SRP. SRR in coal bed water varied from 0.154 ± 0.07 to 2.04 ± 0.048 nmol S cm-3 day-1. Despite the ambient water temperature of ~ 10-20 °C, an active thermophilic SRP community occurred in the fracture water, which reduced sulfate with the rate of 0.159 ± 0.023 to 0.198 ± 0.007 nmol S cm-3 day-1 at 55 °C. A novel moderately thermophilic "Desulforudis audaxviator"-clade SRP has been isolated in pure culture from the coal-bed water.

Hydrogen Availability Is Dependent on the Actions of Both Hydrogen-Producing and Hydrogen-Consuming Microbes.

Hydrogen gas (H2) is produced by H2-producing microbes in the gut during polysaccharide fermentation. Gut microbiome also includes H2-consuming microbes utilizing H2 for metabolism: methanogens producing methane, CH4, and sulfate-reducing bacteria producing hydrogen sulfide, H2S. H2S is not measured in the evaluation of gaseous byproducts of microbial fermentation. We hypothesize that the availability of measured H2 depends on both hydrogen producers and hydrogen consumers by measuring H2 in vitro and in vivo. In the in vitro study, groups were Bacteroides thetaiotaomicron (B. theta, H2 producers), Desulfovibrio vulgaris (D. vulgaris, H2 consumers), and D. vulgaris + B. theta combined. Gas samples were collected at 2 h and 24 h after incubation and assayed for H2, CH4, and H2S. In the in vivo study Sprague-Dawley rats were gavaged with suspended bacteria in four groups: B. theta, D. vulgaris, combined, and control. Gas was analyzed for H2 at 60 min. In the in vitro experiment, H2 concentration was higher in the combined group (188 ± 93.3 ppm) compared with D. vulgaris (27.17 ± 9.6 ppm) and B. theta groups (34.2 ± 29.8 ppm; P < 0.05); H2S concentration was statistically higher in the combined group (10.32 ± 1.5 ppm) compared with B. theta (0.19 ± 0.03 ppm) and D. vulgaris group (3.46 ± 0.28 ppm; P < 0.05). In the in vivo study, H2 concentrations were significantly higher in the B. theta group (44.3 ± 6.0 ppm) compared with control (31.8 ± 4.3) and the combined group (34.2 ± 8.7, P < 0.05). This study shows that sulfate-reducing bacteria could convert available H2 to H2S, leading to measured hydrogen levels that are dependent on the actions of both H2 producers and H2 consumers.

The link between increased Desulfovibrio and disease severity in Parkinson's disease.

Parkinson's disease (PD), a progressive and incurable neurodegenerative disease, has taken a huge economic toll and medical burden on our society. Increasing evidence has shown a strong link between PD and the gut microbiome, but studies on the relationship between the gut microbiome and the severity of PD are limited. In this study, 90 fecal samples were collected from newly diagnosed and untreated patients with PD (n = 47) and matched healthy control subjects (n = 43). The 16S rRNA amplicon and shotgun metagenomic sequencing was performed, aiming to uncover the connection between the gut microbiome and disease severity in PD. The results showed that Desulfovibrio was significantly increased in PD compared to healthy controls and positively correlated with disease severity. The increase in Desulfovibrio was mainly driven by enhanced homogeneous selection and weakened drift. Moreover, through metagenome-assembled genomes (MAGs) analysis, a Desulfovibrio MAG (MAG58) was obtained which was also positively correlated with disease severity. MAG58 possesses a complete assimilatory sulfate reduction pathway and a near-complete dissimilatory sulfate reduction pathway to produce hydrogen sulfide which may influence the development of PD. Based on these results, a potential pathogenic mechanism was presented to illustrate how the increased Desulfovibrio accelerates the development of PD by producing excessive hydrogen sulfide. The present study highlighted the vital role of Desulfovibrio in the development of PD, which may provide a new target for the diagnosis and treatment of PD. KEY POINTS: • The evidence for the link between increased Desulfovibrio and disease severity in PD • A Desulfovibrio MAG was obtained which was correlated with PD • A model was presented to illustrate how increased Desulfovibrio causes PD.

Optimization of antimicrobial peptides for the application against biocorrosive bacteria.

Microbiologically influenced corrosion is a common problem in the industrial field due to the deterioration of metals in the presence of various microorganisms, in particular sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB). A common method to reduce microbiologically influenced corrosion is the application of biocides. The limited number of suitable biocides and the resulting development of resistance, high dosage, and high application rate hinder an effective application. An environmentally friendly alternative could be the application of antimicrobial peptides (AMP), which have already been established in the field of medical devices for a while. Here, the successful treatment of different AMPs against 3 SRB and 1 SOB was demonstrated. The peptide L5K5W was favored due to its broad activity, high stability, and simple structure resulting in low synthesis costs. An alanine scan showed that substitution of leucine with tryptophan increased the activity of this peptide twofold compared to the original peptide against D. vulgaris, the main representative of SRB. Additional optimization of this modified peptide through changes in amino acid composition and lipidations significantly increased the effectiveness, finally resulting in a minimum inhibitory concentration (MIC) of 15.63 µg/mL against Desulfovibrio vulgaris. Even against the marine SRB Desulfovibrio indonesiensis with a required salt concentration of min. 2%, an activity of the peptides can be observed (MIC: 31.25 µg/mL). The peptides also remained stable and active for 7 days in the supernatant of the bacterial culture. KEY POINTS: • Antimicrobial peptides provide an alternative to combat biocorrosive bacteria. • Optimization of the peptide sequence leads to a significant increase in activity. • The investigated peptides exhibit high stability, both in the medium and in the bacterial supernatant.

Desulfovibrio mangrovi sp. nov., a sulfate-reducing bacterium isolated from mangrove sediments: a member of the proposed genus "Psychrodesulfovibrio".

"Psychrodesulfovibrio", a proposed genus within the family Desulfovibrionaceae, is a group of sulfate-reducing bacteria with biogeochemical significance but restricted child taxa availability. In this study, a strictly anaerobic bacterium, designed strain FT415T, was isolated from mangrove sediments in Futian Mangrove Nature Reserve in Shenzhen, China. The strain was Gram-stain-negative, motile, and vibrio-shaped with a single polar flagellum, which grew at the temperature range of 15-42 °C (optimum 37 °C), pH range of 6.0-7.5 (optimum 6.8), and in the presence of 0-36 g l-1 NaCl (optimum 6 g l-1 NaCl). In the presence of sulfate, electron donors including lactate, ethanol, pyruvate, malate, fumarate, succinate, cysteine, and glycerol were incompletely oxidized to acetate, and H2 and formate were used as electron donors with acetate as the carbon source by strain FT415T. Sulfate, thiosulfate, sulfide, and anthraquinone-2,6-disulfonate were reduced in the presence of lactate. Fe(III) oxide was reduced without cell growth. Fermentative growth was observed with pyruvate and cysteine. Vitamins were not required for growth. The major cellular fatty acids (> 10%) were C16:0, summed feature 10 (C18:1 c11/t9/t6 and/or unknown ECL 17.834), C16:1 cis 9, and C18:0. The major polar lipids were phosphatidylethanolamine, phospholipids, and aminolipids. The predominant menaquinone was MK-6(H2). The genomic DNA G+C content was 56.7%. Phylogenetic analysis showed that strain FT415T shared a 98.1% similarity in 16S rRNA gene sequence, an average nucleotide identity value of 84.0%, an average amino-acid identity value of 85.4%, and a digital DNA-DNA hybridization value of 25.7% with its closest relative Desulfovibrio subterraneus HN2T, which has been proposed to be transferred to the genus "Psychrodesulfovibrio". Based on phenotypic, phylogenetic, and genotypic evidence, a new species of the family Desulfovibrionaceae, Desulfovibrio mangrovi sp. nov. was proposed with the type strain FT415T (=GDMCC 1.3410T=KCTC 25525T).

Bacterial sulfidogenic community from the surface of technogenic materials in vitro: composition and biofilm formation.

Microbial biofilms of sulfate-reducing bacteria Desulfovibrio oryzae SRB1 and SRB2 were evaluated on polyethylene terephthalate in mono- and associative bacterial cultures. Bacillus velesensis strains C1 and C2b suppressed both the formation of biofilm and reduced the number of sulfate-reducing bacteria in the biofilm on the polyethylene terephthalate during the 50-day experiment. A decrease in the number of sulfate-reducing bacteria compared to the monoculture was also noted in association of D. oryzae SRB1 + Sat1 (bacterium-satellite of the sulfate-reducing bacteria). The strain Sat1 was identified as Anaerotignum (Clostridium) propionicum based on some microbiological, physiological and biochemical, genetic features. The importance of studying existing interactions between microorganisms in the ferrosphere and plastisphere is emphasized.

Biofilms and beyond: a comprehensive review of the impact of Sulphate Reducing Bacteria on steel corrosion.

Sulphate-reducing bacteria (SRB) are known to cause severe corrosion of steel structures in various industries, resulting in significant economic and environmental consequences. This review paper critically examines the impact of SRB-induced corrosion on steel, including the formation of SRB biofilms, the effect on different types of steel, and the various models developed to investigate this phenomenon. The role of environmental factors in SRB-induced corrosion, molecular techniques for studying SRBs, and strategies for mitigating corrosion are discussed. Additionally, the sustainability implications of SRB-induced corrosion and the potential use of alternative materials were explored. By examining the current state of knowledge on this topic, this review aims to provide a comprehensive understanding of the impact of SRB-induced corrosion on steel and identify opportunities for further research and development.

Magnetic genes: Studying the genetics of biomineralization in magnetotactic bacteria.

Many species of bacteria can manufacture materials on a finer scale than those that are synthetically made. These products are often produced within intracellular compartments that bear many hallmarks of eukaryotic organelles. One unique and elegant group of organisms is at the forefront of studies into the mechanisms of organelle formation and biomineralization. Magnetotactic bacteria (MTB) produce organelles called magnetosomes that contain nanocrystals of magnetic material, and understanding the molecular mechanisms behind magnetosome formation and biomineralization is a rich area of study. In this Review, we focus on the genetics behind the formation of magnetosomes and biomineralization. We cover the history of genetic discoveries in MTB and key insights that have been found in recent years and provide a perspective on the future of genetic studies in MTB.

Study on the treatment of sulfite wastewater by Desulfovibrio.

In the wet flue gas desulfurization (WFGD) process, SO2 is adsorbed by alkaline liquor to produce alkaline wastewater containing sulfate and sulfite. Although the traditional chemical treatment method can achieve a high removal rate, it consumes a large number of chemicals and yields a large number of low-value by-products. The biological treatment process is a greener and more environmentally friendly treatment method. The current work studies microbial flue gas desulfurization directly using sulfite as the electron acceptor in the reduction process. Desulfovibrio were obtained by isolation and purification, and their growth conditions in sulfite wastewater and desulfurization process conditions were investigated by intermittent and continuous experiments. The results of intermittent experiments indicated that the optimal growth conditions of Desulfovibrio were a temperature of 38 °C, a pH value of 8.0, a COD/SO32- of 2 and that the growth of bacteria would be inhibited at a pH above 9.0 or below 7.3. Furthermore, Desulfovibrio could grow in simulated wastewater with a high SO32- concentration of 8000 mg/L. The results of continuous experiments showed that the removal of sulfite and the recovery of elemental sulfur was realized by a micro-oxygen depletion process, and the removal rate of sulfite of 99%, the yield of elemental sulfur is more than 80% and can reach 90% under the condition of low influent concentration. The bacteria grew well at a temperature of 40 °C and a pH value of the influent water of 7.5. To ensure the treatment effect, the hydraulic retention time (HRT) should be more than doubled for each 1000 mg/L increase in the influent sulfite concentration under the same reflux ratio. When the influent sulfite concentration was 1000 mg/L, 2000 mg/L, 3000 mg/L, and 4000 mg/L, the corresponding HRT was 3.01 h, 6.94 h, 17.4 h, and 31.9 h, respectively. The dominant species in the reactor was Desulfovibrio bacteria at 63.9% abundance. This study demonstrated the feasibility of using sulfite as an electron acceptor for microbial desulfurization, which can optimize the initial process and provide the possibility of treating high-concentration sulfite wastewater.

Effects of organic substrates on sulfate-reducing microcosms treating acid mine drainage: Performance dynamics and microbial community comparison.

Bioremediation techniques utilizing sulfate-reducing bacteria (SRB) for acid mine drainage (AMD) treatment have attracted growing attention in recent years, yet substrate bioavailability for SRB is a key factor influencing treatment effectiveness and long-term stability. This study investigated the effects of external organic substrates, including four complex organic wastes (i.e., sugarcane bagasse, straw compost, shrimp shell (SS), and crab shell (CS)) and a small-molecule organic acid (i.e., propionate), on AMD removal performance and associated microbial communities during the 30-day operation of sulfate-reducing microcosms. The results showed that the pH values increased in all five microcosms, while CS exhibited the highest neutralization ability and a maximum alkalinity generation of 1507 mg/L (as CaCO3). Sulfate reduction was more effective in SS and CS microcosms, with sulfate removal efficiencies of 95.6% and 86.0%, respectively. All sulfate-reducing microcosms could remove heavy metals to different degrees, with the highest removal rate of >99.0% observed for aluminum. The removal efficiency of manganese, the most recalcitrant metal, was the highest (96%) in the CS microcosm. Correspondingly, SRB was more abundant in the CS and SS microcosms as revealed by sequencing analysis, while Desulfotomaculum was the dominant SRB in the CS microcosm, accounting for 10.8% of total effective bacterial sequences. Higher abundances of functional genes involved in fermentation and sulfur cycle were identified in CS and SS microcosms. This study suggests that complex organic wastes such as CS and SS could create and maintain preferable micro-environments for active growth and metabolism of functional microorganisms, thus offering a cost-efficient, stable, and environmental-friendly solution for AMD treatment and management.