Variation in the condition of marine sediments provides selective preservation milieus, which act as a key determinant for the abundance and distribution of dinoflagellate resting cysts in natural sediments. Microbial degradation is an understudied biological factor of potential importance in the processes. However, gaps remain in our knowledge about the fundamental information of the bacterial consortia associated with dinoflagellate resting cysts both in laboratory cultures and in the field. Here we used Scrippsiella acuminata as a representative of cyst-producing dinoflagellates to delineate the diversity and composition of bacterial microbiomes co-existing with the laboratory-cultured resting cysts, and to explore possible impacts of low temperature, darkness, and anoxia (the mock conditions commonly observed in marine sediments) on the associated bacterial consortia. Bacterial microbiome with high diversity were revealed associated with S. acuminata at resting stage. The mock conditions could significantly shift bacterial community structure and exert notably inhibitory effects on growth-promoting bacteria. Resting cysts under conditions typically observed in marine sediments fostered bacterial microbiomes with more diverse trophic strategies, characteristic of prominently enriched anaerobic chemotrophic bacteria generating energy via respiration with several different terminal electron acceptors, which yielded more acidic milieu unfavorable for the preservation of calcareous resting cysts. Our findings suggest that there is complex and dynamic interaction between dinoflagellates resting cysts and the associated bacterial consortia in natural sediments. This intrinsic interaction may influence the maintenance and/or accumulation of dinoflagellate resting cysts with potential of germination and initiation blooms in the field.

The gut microbiota-brain axis allows for bidirectional communication between the microbes in our gastrointestinal (GI) tract and the central nervous system. Psychological stress has been known to disrupt the gut microbiome (dysbiosis) leading to anxiety-like behavior. Pathogens administered into the gut have been reported to cause anxiety. Whether commensal bacteria affect the gut-brain axis is not well understood. In this study, we examined the impact of a commensal sulfate-reducing bacteria (SRB) and its metabolite, hydrogen sulfide (H2S), on anxiety-like behavior. We found that mice gavaged with SRB had increased anxiety-like behavior as measured by the open field test. We also tested the effects of magnesium oxide (MgO) on SRB growth both in vitro and in vivo using a water avoidance stress (WAS) model. We found that MgO inhibited SRB growth and H2S production in a dose-dependent fashion. Mice that underwent psychological stress using the WAS model were observed to have an overgrowth (bloom) of SRB (Deferribacterota) and increased anxiety-like behavior. However, WAS-induced overgrowth of SRB and anxiety-like behavioral effects were attenuated in animals fed a MgO-enriched diet. These findings supported a potential MgO-reversible relationship between WAS-induced SRB blooms and anxiety-like behavior.

The production of short-chain fatty acids (SCFAs) is constrained by substrate availability and the increased fractional pressure of H2 emitted by acidogenic/fermentative bacteria during anaerobic fermentation of waste activated sludge (WAS). This study introduced a novel approach employing zero-valent iron (ZVI)-activated sulfite pretreatment combined with H2-consuming sulfate-reducing bacteria (SRB) mediation to improve SCFAs, especially acetate production from WAS fermentation. Experimental results showed that the combined ZVI-activated sulfite and incomplete-oxidative SRB (io-SRB) process achieved a peak SCFAs production of 868.11 mg COD/L, with acetate accounting for 80.55 %, which was 7.90- and 2.18-fold higher than that obtained from raw WAS fermentation, respectively. This could be firstly attributed to the SO4- and OH generated by ZVI-activated sulfite, which significantly promoted WAS decomposition, e.g., soluble proteins and carbohydrates increased 14.3- and 10.8-fold, respectively, over those in raw WAS. The biodegradation of dissolved organic matter was subsequently enhanced by the synergistic interaction and H2 transfer between anaerobic fermentation bacteria (AFB) and io-SRB. The positive and negative correlations among AFB, nitrate-reducing bacteria (NRB) and the io-SRB consortia were revealed by molecular ecological network (MEN) and Mantel test. Moreover, the expression of functional genes was also improved, for instance, in relation to acetate formation, the relative abundances of phosphate acetyltransferase and acetate kinase was 0.002 % and 0.005 % higher than that in the control test, respectively. These findings emphasized the importance of sulfate radicals-based oxidation pretreatment and the collaborative relationships of multifunctional microbes on the value-added chemicals and energy recovery from sludge fermentation.

In view of water and soil getting polluted by Pb(II), Zn(II), and other heavy metals in tailings and acid mine drainage (AMD), we explored the removal effect of sulfate-reducing bacteria (SRB) on Pb(II), Zn(II), and other pollutants in solution and tailings based on the microbial treatment technology. We used the scanning electron microscope-energy dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), and X-ray fluorescence (XRF), to reveal the mechanism of SRB treatment of tailings. The results showed that SRB had a strong removal capacity for Zn(II) at 0-40 mg/L; however, Zn(II) at 60-100 mg/L inhibited the growth of SRB. Similarly, SRB exhibited a very strong ability to remove Pb(II) from the solution. At a Pb(II) concentration of 10-50 mg/L, its removal percentage by SRB was 100%. SRB treatment could effectively immobilize the pollutants leached from the tailings. With an increase in the amount of tailings added to each layer, the ability of SRB to treat the pollutants diminished. When 1 cm of tailingssand was added to each layer, SRB had the best effect on tailing sand treatment. After treatment, the immobilization rates of SO42-, Fe(III), Mn(II), Pb(II), Zn(II), Cu(II), and total Cr in the leachate of #1 tailing sand were 95.44%, 100%, 90.88%, 100%, 96.20%, 86.23%, and 93.34%, respectively. After the tailings were treated by SRB, although the tailings solidified into a cohesive mass from loose granular particles, their mechanical strength was <0.2 MPa. Desulfovibrio and Desulfohalotomaculum played the predominant roles in treating tailings by mixing SRB. The S2- and carbonate produced by mixing SRB during the treatment of tailings could metabolize sulfate by combining with the heavy metal ions released by the tailings to form FeS, MnS, ZnS, CuS, PbS, Cr2S3, CaCO3, MnCO3, and other precipitated particles. These particles were attached to the surface of the tailings, reducing the environmental pollution of the tailings in the water and soil around the mining area.

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Boosting acetate production from waste activated sludge (WAS) fermentation is often hindered by the inefficient solubilization in the hydrolysis step and the high hydrogen pressure ( [Formula: see text] ) during the acidogenesis of C3-C5 short-chain fatty acid (SCFAs), i.e., propionate (HPr), butyrate (HBu) and valerate (HVa). Therefore, this study employed persulfate (PS) oxidation and C3-C5 incomplete-oxidative sulfate reducing bacteria (io-SRB) metabolizers to tailor SCFAs conversion from WAS fermentation. The decomposition efficiency, performance of SCFAs production was investigated. Results showed that the PS significantly promoted WAS decomposition, with a dissolution rate of 39.4%, which is 26.0% higher than the un-treated test. Furthermore, SCFAs yields were increased to 462.7 ± 42 mg COD/g VSS in PS-HBu-SRB, which was 7.4 and 2.2 times higher than that of un-treated and sole PS tests, respectively. In particular, the sum of acetate and HPr reached the peak value of 85%, indicating that HBu-SRB mediation promoted the biotransformation of HBu and macromolecular organics by reducing the [Formula: see text] restriction. Meanwhile, sulfate radical (SO4∙-)-based oxidation (SR-AOPs) was effective in the decomposition of WAS, the oxidative product, i.e., sulfate served the necessary electron acceptor for the metabolism of io-SRB. Further analysis of Mantel test revealed the cluster of the functional genus and their interaction with environmental variables. Additionally, molecular ecological network analysis explored the potential synergistic and competitive relationships between critical genera. Additionally, the potential synergistic and competitive relationships between critical genera was explored by molecular ecological network analysis. This study provides new insights into the integration of SR-AOPs with microbial mediation in accelerating SCFAs production from WAS fermentation.

A wastewater treatment system has been established based on sulfate-reducing and sulfide-oxidizing processes for treating organic wastewater containing high sulfate/sulfide. The influence of COD/SO42- ratio and hydraulic retention time (HRT) on removal efficiencies of sulfate, COD, sulfide and electricity generation was investigated. The continuous operation of the treatment system was carried out for 63 days with the optimum COD/SO42- ratio and HRT. The result showed that the COD and sulfate removal efficiencies were stable, reaching 94.8 ± 0.6 and 93.0 ± 1.3% during the operation. A power density level of 18.0 ± 1.6 mW/m2 was obtained with a sulfide removal efficiency of 93.0 ± 1.2%. However, the sulfide removal efficiency and power density decreased gradually after 45 days. The results from scanning electron microscopy (SEM) with an energy dispersive X-ray (EDX) show that sulfur accumulated on the anode, which could explain the decline in sulfide oxidation and electricity generation. This study provides a promising treatment system to scale up for its actual applications in this type of wastewater.

Sulfate-reducing bacteria (SRB) can immobilize heavy metals in soils through biomineralization, and the parent rock and minerals in the soil are critical to the immobilization efficiency of SRB. To date, there is little knowledge about the fate of Cd associated with the parent rocks and minerals of soil during Cd immobilized by SRB. In this study, we created a model system using clay-size fraction of soil and SRB to explore the role of SRB in immobilizing Cd in soils from stratigraphic successions with high geochemical background. In the system, clay-size fractions (particle size < 2 µm) with concentration of Cd (0.24-2.84 mg/kg) were extracted from soils for bacteria inoculation. After SRB reaction for 10 days, the Cd fraction tended to transform into iron-manganese bound. Further, two clay-size fractions, i.e., the non-crystalline iron oxide (Fe-OX) and the crystalline iron oxide (Fe-CBD), were separated by extraction. The reaction of SRB with them verified the transformation of primary iron-bearing minerals into secondary iron-bearing minerals, which contributed to Cd redistribution. This study shows that SRB could exploit the composition and structure of minerals to induce mineral recrystallization, thereby aggravating Cd redistribution and immobilization in clay-size fractions from stratigraphic successions with high geochemical background.

The increased demand for rare earth resources has led to an increase in the development of rare earth mines (REMs). However, the production of high-concentration leaching agents (SO4 2-) and heavy metals as a result of rare earth mining has increased, necessitating the removal of contaminants. Here, a series of experiments with different remediation measures, including control (CK), sulfate-reducing bacteria (SRB) alone (M), chemicals (Ca(OH)2, 1.5 g/kg) plus SRB (CM-L), chemicals (Ca(OH)2, 3.0 g/kg) plus SRB (CM-M), and chemicals (Ca(OH)2, 4.5 g/kg) plus SRB (CM-H), were conducted to investigate the removal effect of SO4 2-, Pb, Zn, and Mn from the REM soil. Then, a high-throughput sequencing technology was applied to explore the response of bacterial community diversity and functions with different remediation measures. The results indicated that CM-M treatment had a more efficient removal effect for SO4 2-, Pb, Zn, and Mn than the others, up to 94.6, 88.3, 98.7, and 91%, respectively. Soil bacterial abundance and diversity were significantly affected by treatments with the inoculation of SRB in comparison with CK. The relative abundance of Desulfobacterota with the ability to transform SO4 2- into S2- increased significantly in all treatments, except for CK. There was a strong correlation between environmental factors (pH, Eh, SO4 2-, Pb, and Zn) and bacterial community structure. Furthermore, functional prediction analysis revealed that the SRB inoculation treatments significantly increased the abundance of sulfate respiration, sulfite respiration, and nitrogen fixation, while decreasing the abundance of manganese oxidation, dark hydrogen oxidation, and denitrification. This provides good evidence for us to understand the difference in removal efficiency, bacterial community structure, and function by different remediation measures that help select a more efficient and sustainable method to remediate contaminants in the REM soil.

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.