Effect of sulfide on growth of marine bacteria

Sulfide in engineered methanogenic systems - Friend or foe?

Sulfide ions are regarded to be toxic to microorganisms in engineered methanogenic systems (EMS), where organic substances are anaerobically converted to products such as methane, hydrogen, alcohols, and carboxylic acids. A vast body of research has addressed solutions to mitigate process disturbances associated with high sulfide levels, yet the established paradigm has drawn the attention away from the multifaceted sulfide interactions with minerals, organics, microbial interfaces and their implications for performance of EMS. This brief review brings forward sulfide-derived pathways other than toxicity and with potential significance for anaerobic organic matter degradation. Available evidence on sulfide reactions with organic matter, interventions with key microbial metabolisms, and interspecies electron transfer are critically synthesized as a guidance for comprehending the sulfide effects on EMS apart from the microbial toxicity. The outcomes identify existing knowledge gaps and specify future research needs as a step forward towards realizing the potential of sulfide-derived mechanisms in diversifying and optimizing EMS applications.

Chemistry of Hydrogen Sulfide-Pathological and Physiological Functions in Mammalian Cells

Hydrogen sulfide (H2S) was recognized as a gaseous signaling molecule, similar to nitric oxide (-NO) and carbon monoxide (CO). The aim of this review is to provide an overview of the formation of hydrogen sulfide (H2S) in the human body. H2S is synthesized by enzymatic processes involving cysteine and several enzymes, including cystathionine-β-synthase (CBS), cystathionine-γ-lyase (CSE), cysteine aminotransferase (CAT), 3-mercaptopyruvate sulfurtransferase (3MST) and D-amino acid oxidase (DAO). The physiological and pathological effects of hydrogen sulfide (H2S) on various systems in the human body have led to extensive research efforts to develop appropriate methods to deliver H2S under conditions that mimic physiological settings and respond to various stimuli. These functions span a wide spectrum, ranging from effects on the endocrine system and cellular lifespan to protection of liver and kidney function. The exact physiological and hazardous thresholds of hydrogen sulfide (H2S) in the human body are currently not well understood and need to be researched in depth. This article provides an overview of the physiological significance of H2S in the human body. It highlights the various sources of H2S production in different situations and examines existing techniques for detecting this gas.

In situ formation of ferrous sulfide in glycyrrhizic acid hydrogels to promote healing of multi-drug resistant Staphylococcus aureus-infected diabetic wounds

Diabetic wound treatment faces great challenges in clinic. Staphylococcus aureus (S. aureus) is one of the most frequently isolated pathogens from the diabetic infections, which can severely impede wound healing time. Herein, ferrous sulfide (FeS) nanoparticles were fabricated through an in situ reaction between Fe2+ and S2- in glycyrrhizic acid (GA) solution. As the FeS nanoparticles aged, the solution gradually transformed into a gel, exhibiting excellent mechanical strength, injectability, and biocompatibility as a wound dressing. In addition to its own pharmacological effects, GA could act as the protector for FeS from oxidation of air. It also provided a weak acidic microenvironment, facilitating the pH-dependent dissolution reaction of FeS to release H2S and Fe2+. Notably, the effective antibacterial performance of the FeS/GA hydrogels towards S. aureus and multi-drug resistant S. aureus (MRSA) was achieved via the degradedly released Fe2+ and H2S through combination of ferroptosis damage and energy metabolism disruption. Moreover, FeS/GA hydrogels effectively modulated the proportion of M1/M2 macrophages, reduced the secretion of inflammatory cytokines, and significantly enhanced the proliferation and migration of fibroblasts in vitro. Importantly, in an MRSA-infected diabetic wound model, the FeS/GA hydrogels efficiently eradicated bacteria and regulated the inflammatory microenvironment, thereby promoting the diabetic wound repair. Overall, our study establishes a novel strategy for developing multifunctional hydrogels that serve as an effective therapeutic platform for managing bacteria-infected diabetic wounds.

S(-II) reactivates Cd2+-stressed Shewanella oneidensis via promoting low-molecular-weight thiols synthesis and activating antioxidant defense

Efficient remedies for living organisms including bacteria to counteract cadmium (Cd²⁺) toxicity are still highly needed. Plant toxicity studies have showed that exogenous S(-II) (including hydrogen sulfide and its ionic forms, i.e., H₂S, HS^-, and S^2-) application can effectively alleviate adverse effects of Cd stress, but whether S(-II) could mitigate bacterial Cd toxicity remains unclear. In this study, S(-II) was applied exogenously to Cd-stressed Shewanella oneidensis MR-1 and the results showed that S(-II) can significantly reactivate impaired physiological processes including growth arrest and enzymatic ferric (Fe(III) reduction inhibition. The efficacy of S(-II) treatment is negatively correlated with the concentration and time length of Cd exposure. Energy-dispersive X-ray (EDX) analysis suggested the presence of cadmium sulfide inside cells treated with S(-II). Both compared proteomic analysis and RT-qPCR showed that enzymes associated with sulfate transport, sulfur assimilation, methionine, and glutathione biosynthesis were up-regulated in both mRNA and protein levels after the treatment, indicating S(-II) may induce the biosynthesis of functional low-molecular-weight (LMW) thiols to counteract Cd toxicity. Meanwhile, the antioxidant enzymes were positively modulated by S(-II) and thus the activity of intracellular reactive oxygen species was attenuated. The study demonstrated that exogenous S(-II) can effectively alleviate Cd stress for S. oneidensis likely through inducing intracellular trapping mechanisms and modulating cellular redox status. It suggested that S(-II) may be a highly effective remedy for bacteria such as S. oneidensis under Cd-polluted environments.

Continuous H2/CO2 fermentation for acetic acid production under transient and continuous sulfide inhibition

Waste gas fermentation powered by renewable H₂ is reaching kiloton scale. The presence of sulfide, inherent to many waste gases, can cause inhibition, requiring additional gas treatment. In this work, acetogenesis and methanogenesis inhibition by sulfide were studied in a 10-L mixed-culture fermenter, supplied with CO₂ and connected with a water electrolysis unit for electricity-powered H₂ supply. Three cycles of inhibition (1.3 mM total dissolved sulfide (TDS)) and recovery were applied, then the fermenter was operated at 0.5 mM TDS for 35 days. During operation at 0.5 mM TDS the acetate production rate reached 7.1 ± 1.5 mmol C L^-1 d^-1. Furthermore, 43.7 ± 15.6% of the electrons, provided as H₂, were distributed to acetate and 7.7 ± 4.1% to butyrate, the second most abundant fermentation product. Selectivity of sulfide as inhibitor was demonstrated by a 7 days lag-phase of methanogenesis recovery, compared to 48 h for acetogenesis and by the less than 1% electrons distribution to CH₄, under 0.5 mM TDS. The microbial community was dominated by Eubacterium, Proteiniphilum and an unclassified member of the Eggerthellaceae family. The taxonomic diversity of the community decreased and conversely the phenotypic diversity increased, during operation. This work illustrated the scale-up potential of waste gas fermentations, by elucidating the effect of sulfide as a common gas impurity, and by demonstrating continuous, potentially renewable supply of electrons.

Coastal riverine wetland biogeochemistry follows soil organic matter distribution along a marsh-to-mangrove gradient (Florida, USA)

Many subtropical coastal wetland vegetation communities are transitioning from herbaceous marsh to woody mangrove, often facilitated by sea-level rise. This study investigated the relationships between vegetation community (upstream marsh, ecotone/transition, and downstream mangrove), salinity (S), and soil biogeochemistry in wetlands along three rivers on the Florida Gulf coast (the Little Manatee, Peace, and Fakahatchee Rivers). Vegetation was surveyed, and soil and water samples were collected during both the dry and the wet season and analyzed for biogeochemical properties (soil: bulk density, pH, organic matter, extractable inorganic and total nutrients, dissolved organic carbon (DOC), and microbial biomass carbon; water: inorganic nutrients and DOC) and processes (greenhouse gas production) while salinity and water level were continuously monitored in the field. Results indicated landscape-scale patterns in soil biogeochemistry differed significantly by river and were most strongly correlated with soil organic matter content, regardless of vegetation community or salinity regime. Contrary to expectations, soil organic matter content gradients were not always inversely related to salinity gradients, and methane production was observed in moderate- (S = 12) and high- (S = 34) salinity mangrove communities. The vegetation ecotone experienced seasonally variable salinity and did not serve as a true biogeochemical intermediate between the marsh and mangrove communities. This study demonstrates the need for site-specific studies of biogeochemical gradients in coastal wetlands and indicates the marsh-to-mangrove ecotone is not a proxy for salinity or biogeochemical tipping points. Instead, soil organic matter content is suggested as the most relevant indicator of biogeochemical properties and processes in wetlands along coastal rivers, superseding vegetation community or salinity.

Controls of H2S, Fe2 +, and Mn2 + on Microbial NO3 --Reducing Processes in Sediments of an Eutrophic Lake

Understanding the biogeochemical controls on the partitioning between nitrogen (N) removal through denitrification and anaerobic ammonium oxidation (anammox), and N recycling via dissimilatory nitrate (NO3 -) reduction to ammonium (DNRA) is crucial for constraining lacustrine N budgets. Besides organic carbon, inorganic compounds may serve as electron donors for NO3 - reduction, yet the significance of lithotrophic NO3 - reduction in the environment is still poorly understood. Conducting incubation experiments with additions of 15N-labeled compounds and reduced inorganic substrates (H2S, Fe2+, Mn2+), we assessed the role of alternative electron donors in regulating the partitioning between the different NO3 --reducing processes in ferruginous surface sediments of Lake Lugano, Switzerland. In sediment slurry incubations without added inorganic substrates, denitrification and DNRA were the dominant NO3 --reducing pathways, with DNRA contributing between 31 and 46% to the total NO3 - reduction. The contribution of anammox was less than 1%. Denitrification rates were stimulated by low to moderate additions of ferrous iron (Fe2+ ≤ 258 μM) but almost completely suppressed at higher levels (≥1300 μM). Conversely, DNRA was stimulated only at higher Fe2+ concentrations. Dissolved sulfide (H2S, i.e., sum of H2S, HS- and S2-) concentrations up to ∼80 μM, strongly stimulated denitrification, but did not affect DNRA significantly. At higher H2S levels (≥125 μM), both processes were inhibited. We were unable to find clear evidence for Mn2+-supported lithotrophic NO3 - reduction. However, at high concentrations (∼500 μM), Mn2+ additions inhibited NO3 - reduction, while it did not affect the balance between the two NO3 - reduction pathways. Our results provide experimental evidence for chemolithotrophic denitrification or DNRA with Fe2+ and H2S in the Lake Lugano sediments, and demonstrate that all tested potential electron donors, despite the beneficial effect at low concentrations of some of them, can inhibit NO3 - reduction at high concentration levels. Our findings thus imply that the concentration of inorganic electron donors in lake sediments can act as an important regulator of both benthic denitrification and DNRA rates, and suggest that they can exert an important control on the relative partitioning between microbial N removal and N retention in lakes.

Occurrence and biosynthesis of 3-mercaptopropionic acid in Methanocaldococcus jannaschii

In a non-targeted analysis of thiol-containing compounds in the hyperthermophilic methanogen Methanocaldococcus jannaschii, we discovered three unexpected metabolites: 3-mercaptopropionic acid (MPA), 2-hydroxy-4-mercaptobutyric acid (HMBA) and 4-mercapto-2-oxobutyric acid (MOB). HMBA and MOB have never been reported as natural products, while MPA is highly prevalent in aquatic environments as a result of biotic and abiotic processing of sulfur-containing compounds. This report provides evidence that HMBA and MOB are part of a biosynthetic pathway to generate MPA in M. jannaschii We show that HMBA can be biosynthesized from malate semialdehyde and hydrogen sulfide, likely using a mechanism similar to that proposed for coenzyme M, coenzyme B and homocysteine biosynthesis in methanogens, where an aldehyde is converted to a thiol. The L-sulfolactate dehydrogenase, derived from the MJ1425 gene, is shown to catalyze the NAD-dependent oxidation of HMBA to MOB. Finally, we demonstrate that HMBA can be used as a biosynthetic precursor to MPA in M. jannaschii cell extracts. This proposed pathway may contribute to the wide occurrence of MPA in marine environments and indicates that MPA must serve some important function in M. jannaschii.

Impact of Tannery Effluent on the Self-purification Capacity and Biodiversity Level of a River

The present study investigates the impact of tannery effluents on the self-purification capacity and the local macroinvertebrate community of one natural stream. As the concentration of chromium and sulfide increased from up- to downstream sites, the reduction of suspended solids, 5-days biological oxygen demand (BOD5), chemical oxygen demand and nitrification capacity decreased by 61 %, 21 %, 30 % and 74 %, respectively. Similarly, the share of Ephemeroptera, Plecoptera, and Trichoptera on the macroinvertebrate community decreased from 24 % to 0 %. Also the diversity (Simpson's) index and the correlation between the physicochemical parameters, BOD5 reduction, the macroinvertebrate abundance and the chromium concentration underpin the importance of the contamination by tannery effluents for the degradation of the stream habitat quality. In conclusion, although the physicochemical parameters indicate that the self-purification of the river can be maintained for a certain stream section, the biodiversity of the river is severely compromised.

A Matter of Timing: Contrasting Effects of Hydrogen Sulfide on Oxidative Stress Response in Shewanella oneidensis

Hydrogen sulfide (H2S), well known for its toxic properties, has recently become a research focus in bacteria, in part because it has been found to prevent oxidative stress caused by treatment with some antibiotics. H2S has the ability to scavenge reactive oxygen species (ROS), thus preventing oxidative stress, but it is also toxic, leading to conflicting reports of its effects in different organisms. Here, with Shewanella oneidensis as a model, we report that the effects of H2S on the response to oxidative stress are time dependent. When added simultaneously with H2O2, H2S promoted H2O2 toxicity by inactivating catalase, KatB, a heme-containing enzyme involved in H2O2 degradation. Such an inhibitory effect may apply to other heme-containing proteins, such as cytochrome cbb3 oxidase. When H2O2 was supplied 20 min or later after the addition of H2S, the oxidative-stress-responding regulator OxyR was activated, resulting in increased resistance to H2O2. The activation of OxyR was likely triggered by the influx of iron, a response to lowered intracellular iron due to the iron-sequestering property of H2S. Given that Shewanella bacteria thrive in redox-stratified environments that have abundant sulfur and iron species, our results imply that H2S is more important for bacterial survival in such environmental niches than previously believed.

IMPORTANCE

Previous studies have demonstrated that H2S is either detrimental or beneficial to bacterial cells. While it can act as a growth-inhibiting molecule by damaging DNA and denaturing proteins, it helps cells to combat oxidative stress. Here we report that H2S indeed has these contrasting biological functions and that its effects are time dependent. Immediately after H2S treatment, there is growth inhibition due to damage of heme-containing proteins, at least to catalase and cytochrome c oxidase. In contrast, when added a certain time later, H2S confers an enhanced ability to combat oxidative stress by activating the H2O2-responding regulator OxyR. Our data reconcile conflicting observations about the functions of H2S.

Enriching distinctive microbial communities from marine sediments via an electrochemical-sulfide-oxidizing process on carbon electrodes

Sulfide is a common product of marine anaerobic respiration, and a potent reactant biologically and geochemically. Here we demonstrate the impact on microbial communities with the removal of sulfide via electrochemical methods. The use of differential pulse voltammetry revealed that the oxidation of soluble sulfide was seen at +30 mV (vs. SHE) at all pH ranges tested (from pH = 4 to 8), while non-ionized sulfide, which dominated at pH = 4 was poorly oxidized via this process. Two mixed cultures (CAT and LA) were enriched from two different marine sediments (from Catalina Island, CAT; from the Port of Los Angeles, LA) in serum bottles using a seawater medium supplemented with lactate, sulfate, and yeast extract, to obtain abundant biomass. Both CAT and LA cultures were inoculated in electrochemical cells (using yeast-extract-free seawater medium as an electrolyte) equipped with carbon-felt electrodes. In both cases, when potentials of +630 or +130 mV (vs. SHE) were applied, currents were consistently higher at +630 then at +130 mV, indicating more sulfide being oxidized at the higher potential. In addition, higher organic-acid and sulfate conversion rates were found at +630 mV with CAT, while no significant differences were found with LA at different potentials. The results of microbial-community analyses revealed a decrease in diversity for both CAT and LA after electrochemical incubation. In addition, some bacteria (e.g., Clostridium and Arcobacter) not well-known to be capable of extracellular electron transfer, were found to be dominant in the electrochemical cells. Thus, even though the different mixed cultures have different tolerances for sulfide, electrochemical-sulfide removal can lead to major population changes.