Comparative analysis of microbial communities from different full-scale haloalkaline biodesulfurization systems

Modelling anaerobic sulfide removal by sulfide shuttling bacteria

Sulfide oxidizing bacteria are used in industrial biodesulfurization processes to convert sulfide to sulfur. These bacteria can spatially separate sulfide removal from terminal electron transfer, thereby acting as sulfide shuttles. The mechanisms underlying sulfide shuttling are not yet clear. In this work, newly obtained sulfide removal data were used to develop a new model for anaerobic sulfide removal and this model was shown to be an improvement over two previously published models. The new model describes a fast chemical step and a consecutive slow enzymatic step. The improved model includes the effect of pH, with higher total sulfide removal at increasing pH, as well as partial sulfide removal at higher sulfide concentrations. The two-stage model is supported by recent developments in anaerobic sulfide removal research and contributes to a better understanding of the underlying mechanisms. The model is a step toward accurately modelling anaerobic sulfide removal in industrial systems.

Harnessing the potential of the microbial sulfur cycle for environmental biotechnology

The sulfur cycle is a complex biogeochemical cycle characterized by the high variability in the oxidation states of sulfur. While sulfur is essential for life processes, certain sulfur compounds, such as hydrogen sulfide, are toxic to all life forms. Micro-organisms facilitate the sulfur cycle, playing a prominent role even in extreme environments, such as soda lakes, acid mine drainage sites, hot springs, and other harsh habitats. The activity of these micro-organisms presents unique opportunities for mitigating sulfur-based pollution and enhancing the recovery of sulfur and metals. This review highlights the application of sulfur-oxidizing and -reducing micro-organisms in environmental biotechnology through three illustrative examples. Additionally, it discusses the challenges, recent trends, and prospects associated with these applications.

Biodesulfurization of landfill biogas by a pilot-scale bioscrubber: Operational limits and microbial analysis

Biogas serves as a crucial renewable energy vector to ensure a more sustainable energy future. However, the presence of hydrogen sulfide (H2S) limits its application in various sectors, emphasizing the importance of effective H2S removal techniques for maximizing its potential. In the present study, the limits of a pilot-scale bioscrubber for biogas desulfurization was study in a real scenario. An increase in the superficial liquid velocity resulted in significant improvements in the H2S removal efficiency, increasing from 76 ± 8% (elimination capacity of 6.2 ± 0.5 gS-H2S m-3 h-1) to 97.7 ± 0.5% (elimination capacity of 8 ± 1 gS-H2S m-3 h-1) as the superficial liquid velocity increased from 50 ± 3 m h-1 to 200 ± 8 m h-1. A USL of 161.4 ± 0.5 m h-1 was able to achieve outlet H2S concentrations as low as 3 ± 1 ppmv (H2S removal efficiency of 97 ± 1%) for 7 days. High superficial liquid velocity favoured the aerobic H2S oxidation reducing the nitrate demand. The maximum EC reached throughout the operation was 50.8 ± 0.6 gS-H2S m-3 h-1 (H2S removal efficiency of 96 ± 1%) and a sulfur production of 60%. Studies in batch flocculation experiments showed sulfur removal rates up to 97.6 ± 0.9% with a cationic flocculant dose of 75 mg L-1. Microbial analysis revealed that the predominant genus with sulfo-oxidant capacity during periods of low H2S inlet load was Thioalkalispira-sulfurivermis (61-69%), while in periods of higher H2S inlet load, family Arcobacteraceae was the most prevalent (11%).

Process conditions affect microbial diversity and activity in a haloalkaline biodesulfurization system

Biodesulfurization (BD) systems that treat sour gas employ mixtures of haloalkaliphilic sulfur-oxidizing bacteria to convert sulfide to elemental sulfur. In the past years, these systems have seen major technical innovations that have led to changes in microbial community composition. Different studies have identified and discussed the microbial communities in both traditional and improved systems. However, these studies do not identify metabolically active community members and merely focus on members' presence/absence. Therefore, their results cannot confirm the activity and role of certain bacteria in the BD system. To investigate the active community members, we determined the microbial communities of six different runs of a pilot-scale BD system. 16S rRNA gene-based amplicon sequencing was performed using both DNA and RNA. A comparison of the DNA- and RNA-based sequencing results identified the active microbes in the BD system. Statistical analyses indicated that not all the existing microbes were actively involved in the system and that microbial communities continuously evolved during the operation. At the end of the run, strains affiliated with Alkalilimnicola ehrlichii and Thioalkalivibrio sulfidiphilus were confirmed as the most active key bacteria in the BD system. This study determined that microbial communities were shaped predominantly by the combination of hydraulic retention time (HRT) and sulfide concentration in the anoxic reactor and, to a lesser extent, by other operational parameters.IMPORTANCEHaloalkaliphilic sulfur-oxidizing bacteria are integral to biodesulfurization (BD) systems and are responsible for converting sulfide to sulfur. To understand the cause of conversions occurring in the BD systems, knowing which bacteria are present and active in the systems is essential. So far, only a few studies have investigated the BD system's microbial composition, but none have identified the active microbial community. Here, we reveal the metabolically active community, their succession, and their influence on product formation.

Pollution characteristics and microbial community succession of a rural informal landfill in an arid climate

Informal landfills pose potential threats to the environment and human health due to the lack of anti-seepage measures. However, little research has been conducted on the distribution of pollutants in informal landfill sites situated in arid climates, as well as the underlying interaction mechanisms between environmental factors and microbial structure. In this study, we sought to investigate the pollution characteristics and microbial community succession of the landfill in northern China. The results revealed that heavy metals in the landfill showed poor mobility and migration. The lower layers of the garbage samples had higher water-soluble contents of heavy metals compared to the upper layers. The landfill-derived dissolved organic matter (DOM) was found to originate from microbial production, and four fluorescent components were identified, including fulvic acid-like substances, humus-like substances, and protein-like components. Fluorescence intensity and humification degree increased with increasing depth. The microbial diversity and richness decreased with sampling depth. The most abundant phyla in the samples were Proteobacteria, unidentified_Bacteria, Bacteroidota, Firmicutes, Myxococcota, Gemmatimonadota, Actinobacteria, and Deinococcota. As the sampling depth increased, Proteobacteria decreased, while Bacteroidota and Firmicutes showed a remarkable increase, with little variation observed in the other phyla. The partial least-squares path model (PLS-PM) results indicated that pH had the most significant effect on microbial abundance and diversity (direct effect value = -5.560), while DOM and heavy metals had the opposite effect, with direct effects of 1.838 and 3.231, respectively. DOM was identified as the driving factor for the variation in other environmental factors. The redundancy analysis (RDA) showed that the dominant genera were greatly influenced by Cu, humic-like substances, and protein-like substances. Among them, Bacillus, Alcanivorax, Devosia, and Chryseolinea may play important roles in the remediation of landfills. Our study not only gains a deeper understanding of the pollution risk of informal landfills in arid climates, but also provides a scientific basis for the future treatment and restoration of contaminated sites associated with landfills.

Synergistic between autotrophic and heterotrophic microorganisms for denitrification using bio-S as electron donor

In recent years, biological sulfur (bio-S) was employed in sulfur autotrophic denitrification (SAD) in which autotrophic Thiobacillus denitrificans and heterotrophic Stenotrophomonas maltophilia played a key role. The growth pattern of T.denitrificans and S.maltophilia exhibited a linear relationship between OD₆₀₀ and CFU when OD₆₀₀ < 0.06 and <0.1, respectively. When S.maltophilia has applied alone, the NorBC and NosZ were undetected, and denitrification was incomplete. The DsrA of S.maltophilia could produce sulfide as an alternative electron donor for T.denitrificans. Even though T.denitrificans had complete denitrification genes, its efficiency was low when used alone. The interaction of T.denitrificans and S.maltophilia reduced nitrite accumulation, leading to complete denitrification. A sufficient quantity of S.maltophilia may trigger the autotrophic denitrification activity of T.denitrificans. When the colony-forming units (CFU) ratio of S.maltophilia to T.denitrificans was reached at 2:1, the highest denitrification performance was achieved at 2.56 and 12.59 times higher than applied alone. This research provides a good understanding of the optimal microbial matching for the future application of bio-S.

Bacterial Biological Factories Intended for the Desulfurization of Petroleum Products in Refineries

The removal of sulfur by deep hydrodesulfurization is expensive and environmentally unfriendly. Additionally, sulfur is not separated completely from heterocyclic poly-aromatic compounds. In nature, several microorganisms (Rhodococcus erythropolis IGTS8, Gordonia sp., Bacillus sp., Mycobacterium sp., Paenibacillus sp. A11-2 etc.) have been reported to remove sulfur from petroleum fractions. All these microbes remove sulfur from recalcitrant organosulfur compounds via the 4S pathway, showing potential for some organosulfur compounds only. Activity up to 100 µM/g dry cell weights is needed to meet the current demand for desulfurization. The present review describes the desulfurization capability of various microorganisms acting on several kinds of sulfur sources. Genetic engineering approaches on Gordonia sp. and other species have revealed a variety of good substrate ranges of desulfurization, both for aliphatic and aromatic organosulfur compounds. Whole genome sequence analysis and 4S pathway inhibition by a pTeR group inhibitor have also been discussed. Now, emphasis is being placed on how to commercialize the microbes for industrial-level applications by incorporating biodesulfurization into hydrodesulfurization systems. Thus, this review summarizes the potentialities of microbes for desulfurization of petroleum. The information included in this review could be useful for researchers as well as the economical commercialization of bacteria in petroleum industries.

Anaerobic sulphide removal by haloalkaline sulphide oxidising bacteria

Sulphide is a toxic and corrosive compound and requires removal from waste streams. Recent discoveries show that sulphide oxidising bacteria (SOB) from modern desulphurisation plants are able to spatially separate sulphide removal and oxygen reduction when exposed to intermittent anaerobic and aerobic environments. Here, SOB act as electron shuttles between electron donor and acceptor. The underlying mechanisms for electron shuttling are of yet unknown. To investigate the anaerobic sulphide removal of SOB, batch experiments and mathematical models were applied. The sulphide removal capacity decreased at increasing biomass concentrations. At 0.6 mgN/L SOB could remove up to 8 mgS/mgN in 30 min. It was found that biological activity determines sulphide removal, alongside chemical processes. Anaerobic oxidation of electron carriers was determined to only explain 0.1% of charge storage, where irreversible cleavage of long chain polysulphides could explain full sulphide storage. Different sulphide removal and intracellular storage processes are postulated.

Lingguizhugan decoction improves non-alcoholic steatohepatitis partially by modulating gut microbiota and correlated metabolites

Background

Lingguizhugan decoction is a traditional Chinese medicine prescription that has been used to improve non-alcoholic fatty liver disease and its progressive form, non-alcoholic steatohepatitis (NASH). However, the anti-NASH effects and underlying mechanisms of Lingguizhugan decoction remain unclear.

Methods

Male Sprague-Dawley rats were fed a methionine- and choline-deficient (MCD) diet to induce NASH, and then given Lingguizhugan decoction orally for four weeks. NASH indexes were evaluated by histopathological analysis and biochemical parameters including serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), liver triglycerides (TG), etc. Fecal samples of rats were subjected to profile the changes of gut microbiota and metabolites using 16S rRNA sequencing and ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS). Bioinformatics was used to identify Lingguizhugan decoction reversed candidates, and Spearman's correlation analysis was performed to uncover the relationship among gut microbiota, fecal metabolites, and NASH indexes.

Results

Four-week Lingguizhugan decoction treatment ameliorated MCD diet-induced NASH features, as evidenced by improved hepatic steatosis and inflammation, as well as decreased serum AST and ALT levels. Besides, Lingguizhugan decoction partially restored the changes in gut microbial community composition in NASH rats. Meanwhile, the relative abundance of 26 genera was significantly changed in NASH rats, and 11 genera (such as odoribacter, Ruminococcus_1, Ruminococcaceae_UCG-004, etc.) were identified as significantly reversed by Lingguizhugan decoction. Additionally, a total of 99 metabolites were significantly altered in NASH rats, and 57 metabolites (such as TDCA, Glutamic acid, Isocaproic acid, etc.) enriched in different pathways were reversed by Lingguizhugan decoction. Furthermore, Spearman's correlation analyses revealed that most of the 57 metabolites were significantly correlated with 11 genera and NASH indexes.

Conclusion

Lingguizhugan decoction may exert protective effects on NASH partially by modulating gut microbiota and correlated metabolites.

Deep Subsurface Hypersaline Environment as a Source of Novel Species of Halophilic Sulfur-Oxidizing Bacteria

The sulfur cycle participates significantly in life evolution. Some facultatively autotrophic microorganisms are able to thrive in extreme environments with limited nutrient availability where they specialize in obtaining energy by oxidation of reduced sulfur compounds. In our experiments focused on the characterization of halophilic bacteria from a former salt mine in Solivar (Presov, Slovakia), a high diversity of cultivable bacteria was observed. Based on ARDRA (Amplified Ribosomal DNA Restriction Analysis), at least six groups of strains were identified with four of them showing similarity levels of 16S rRNA gene sequences lower than 98.5% when compared against the GenBank rRNA/ITS database. Heterotrophic sulfur oxidizers represented ~34% of strains and were dominated by Halomonas and Marinobacter genera. Autotrophic sulfur oxidizers represented ~66% and were dominated by Guyparkeria and Hydrogenovibrio genera. Overall, our results indicate that the spatially isolated hypersaline deep subsurface habitat in Solivar harbors novel and diverse extremophilic sulfur-oxidizing bacteria.