Sulphate-Reducing Bacteria’s Response to Extreme pH Environments and the Effect of Their Activities on Microbial Corrosion

Iron pipe corrosion enhanced the transformation of iopamidol, a precursor of iodinated disinfection byproducts: The role of sulfate-reducing bacteria

Long-term use of iron pipes leads to inevitable corrosion due to chemical and biological processes, with sulfate-reducing bacteria (SRB) playing a significant role. The corrosion products generated will affect the transformation of micropollutants in pipe networks. This study investigated the effect of SRB-influenced corrosion (SIC) on the transformation of iodine-containing micropollutants, using iopamidol (IPM) as a model compound. The degradation rate of IPM in the presence of Febio (with SIC) was 2.3 times higher than that with Feabio (without SIC). This enhancement was primarily attributed to accelerated and selective electron transfer facilitated by FeSx formation in the SIC process. The enhancement was more pronounced in presence of an appropriate amount of SO42 (120 mg L-1), or under a weakly acidic condition (pH 6). The enhancement was further validated in real water, where the released iodide was converted into iodinated disinfection by-products (I-DBPs) and/or iodate (IO3-), depending on the disinfectant used. This study offers an insight into the interplay between SRB-driven iron corrosion and iodine-containing pollutant transformation, contributing to a deeper understanding of micropollutant fate in corroded iron pipe networks.

pH-dependent genotypic and phenotypic variability in Oleidesulfovibrio alaskensis G20

Sulfate-reducing bacteria (SRB) exhibit versatile metabolic adaptability with significant flexibility influenced by pH fluctuations, which play a critical role in biogeochemical cycles. In this study, we used a model SRB, Oleidesulfovibrio alaskensis G20, to determine the temporal effects of pH variations (pH 6, 7, and 8) on both growth dynamics and metabolic gene expressions. The specific growth rate at pH 6 (0.014 h-1) closely matched that at pH 7 (0.016 h-1), while pH 8 exhibited a lower growth rate (0.010 h-1). Lactate consumption peaked at pH 7 (0.35 mM lactate.h-1) and declined at pH 8 (0.09 mM lactate.h-1). Significant hydrogen production was evident under both acidic and alkaline conditions. Gene expression studies revealed that ATPases function as proton pumps, while hydrogenases mediate reversible proton-to-hydrogen conversion. Sulfate and energy metabolism act as electron acceptors and donors, while amino acid synthesis regulates basic and acidic amino acids to mitigate pH stress. Downregulation of FtsZ at pH 6 suggests impaired division, correlating with slightly longer lengths (~2 µm), while upregulation of divisome proteins at pH 8 suggests efficient division processes, aligning with shorter lengths (~1.8 µm). This study will facilitate the employment of O. alaskensis G20 in extreme pH environments, enhancing its effectiveness in optimizing bioremediation and anaerobic digestion processes.

IMPORTANCE

Sulfate-reducing bacteria (SRB) play essential roles in global sulfur and carbon cycling and are critical for bioremediation and anaerobic digestion processes. However, detailed studies on the genotypic and phenotypic responses of SRB under varying pH conditions are limited. This study addresses this gap by examining the pH-dependent genetic and metabolic adaptations of Oleidesulfovibrio alaskensis G20, revealing key mechanisms regulating hydrogenase and ATPase activities, cell division, and extracellular polymeric substance formation. These findings provide new insights into how SRB maintains pH homeostasis, showcasing their ability to survive and function in both acidic and alkaline environments. Furthermore, this study reveals critical genetic and phenotypic characteristics that will directly aid to engineer industrial effluent management systems, bioremediation, and dissolved heavy metal recovery. By elucidating the dynamic response of O. alaskensis G20 to varied pH environments, the research provides a foundation for enhancing the resilience and performance of SRB-based systems, paving the way for improved environmental and industrial applications.

Revealing the effect of Al2O3 on sulfur transformation in anaerobic sludge process

Al2O3, one multifunctional adsorbent and dehydrator, was widely recognized as a practical and environmentally friendly additive that enhances fermentation efficiency and facilitates the recovery of resources from waste-activated sludge (WAS). However, its potential harmful effects on WAS fermentation, such as the generation of hydrogen sulfide (H2S), have been previously overlooked. This study found that with the increase of Al2O3 dosage from 0 to 60 mg/g VSS, the maximum production of H2S decreased from 371.60 ± 3.72 × 10-4 to 303.36 ± 3.03 × 10-4 mg/g VSS. The study on the transformation of sulfur-containing compounds has identified that the primary cause for lowering the formation of hydrogen sulfide (H2S) is the inhibitory effect of aluminium oxide (Al2O3) on sulfate reduction. The mechanism analysis discovered that Al2O3 initially stimulated the functional groups and hydrogen bonding networks present in sludge EPS. This resulted in a 2.04 % rise in the content of C-C groups, a 7.78 % increase in the content of C-O-C groups, and a 4.24 % increase in the content of β-turn and α-Helix structures. This resulted in the fracturing of sludge EPS and the release of soluble metal ions such as aluminium, magnesium, and iron. The liberated metal ions facilitated the conversion of H2S gas and dissolved sulfide into metal sulfide, hence contributing significantly to the reduction of H2S gas emissions. Microbial community research revealed that the inclusion of Al2O3 enhanced the performance of methanogens (e.g., Methanothrix), but inhibited sulfate reducing bacteria (e.g., unclassified_c__Deltaproteobacteria). Additional examination of functional genes demonstrated that Al2O3 decreases the amount of functional genes involved in the hydrolysis of organic sulfur (such as MetQ, pepD, CDO1, yhdR, etc.). and sulfate reduction processes (sat, cysC, aprAB, dsrAB, etc.). These findings offer novel perspectives on the treatment of sludge using Al2O3 and could have substantial consequences for sludge treatment.

Pressure up to 60 bar has no major effect on the overall hydrogen consumption of the sulfate reducer Oleidesulfovibrio alaskensis

AIMS

Subsurface environments found in geological aquifers or reservoirs are not sterile, but harbor diverse microbial communities for which hydrogen (H2) is a ubiquitous electron donor, especially for sulfate-reducing bacteria (SRB). Most studies investigating SRB have been conducted through consumption experiments at near-atmospheric pressure. However, pressures are significantly higher in subsurface formations. It remains a crucial question whether high H2 partial pressure influences microbial consumption. Therefore, we tested a relevant SRB under increased H2-pressure to investigate changes in H2-consumption behavior.

METHODS AND RESULTS

We cultured the H2-consuming SRB Oleidesulfovibrio alaskensis G20 under 1, 30, and 60 bar of H2 overpressure and quantified consumption over time. Data were compared to sterile incubations. After 16 days, the total amount of consumed H2, sulfate, and acetate was similar for all pressure conditions and pH ended over 9, which is beyond the described pH limit. While the maximum H2 consumption rate was found higher at atmospheric pressures (0.20 mmol per day) compared to 30 and 60 bar (0.13 and 0.11 mmol per day), the maximum rate per surface area was comparable (0.02, 0.03, 0.02 mmol per day per cm2). The total rate of H2 consumption per cm2 was higher with increasing pressure, which is probably related to the increased solubility of H2 in the brine phase due to pressure.

CONCLUSIONS

The data show that pressures up to 60 bar have no significant effect on the overall activity of O. alaskensis. The governing factor for the H2 consumption rate is contact area between brine and gas phase and the concentration of dissolved H2.

Synergistic effects of indigenous bacterial consortia on heavy metal tolerance and reduction

Heavy metal contamination represents a critical environmental and public health challenge, necessitating effective remediation approaches. This study examines the bioremediation potential of three indigenous bacterial strains Aeromonas caviae KQ_21, Aeromonas hydrophila AUoR_24, and Shewanella putrefaciens SUoR_24 evaluated both individually and in consortia for their capacity to remove heavy metals. Tolerance assessments demonstrated that the coculture of these strains exhibited superior resistance to copper (Cu), zinc (Zn), and nickel (Ni), with optimal growth observed up to 6 mM for Cu, 9 mM for Zn, and 5 mM for Ni, outperforming the monocultures. The co-culture system also achieved higher metal reduction efficiencies, with reductions of 47.02% for Cu, 61.49% for Ni, and 61.93% for Zn, in contrast to lower reductions observed in individual strains. The study further explored the impact of environmental conditions on bioremediation efficiency. Optimal temperature for both monoculture and coculture setups was found to be 30 °C. pH and salt concentration variations significantly affected bacterial growth and metal reduction, highlighting the necessity of tailored conditions for enhanced bioremediation. In terms of metal removal mechanisms, the results demonstrated that nickel (Ni) removal occurred primarily through bioaccumulation, while copper (Cu) removal involved both biosorption and bioaccumulation. Zinc (Zn) removal was facilitated through biosorption, bioaccumulation, and biotransformation. These findings underscore the effectiveness of bacterial consortia, particularly indigenous strains, in improving heavy metal tolerance and reduction through synergistic interactions and cooperative metabolic processes. This research offers valuable insights into optimizing bacterial consortia for environmental cleanup and advances the application of indigenous bacteria in bioremediation strategies. Future investigations should focus on exploring additional microbial species and further elucidating the molecular mechanisms that contribute to enhanced bioremediation efficacy.

Biodesulfurization of high-sulfur oil from the Karazhanbas field of Kazakhstan with deep eutectic solvents

The Karazhanbas oil field in the Mangystau region of Kazakhstan contains high-sulfur oil (1.6-2.2 %). It is known that sulfur negatively affects the operational properties of petroleum products, causes the corrosion of pipelines, and adversely affects the environment and the human body. Therefore, the development of biodesulfurization technology, taking into account local features, is relevant for this field. The purpose of the study is to develop biodesulfurization of high-sulfur oil from the Karazhanbas field in Kazakhstan using deep eutectic solvents. Research objectives: isolation of sulfate-oxidizing and sulfate-reducing bacteria from the studied oils; identification of isolated bacteria; study of the effect of heavy metal Cr(VI) and sulfur on microbial activity; testing of native strains for the potential for desulfurization of crude oil. The research methodology was based on the application of the Koch methods to determine the total number of microorganisms; light microscopy - for the study of microbiological preparations; genetic identification of bacteria based on the analysis of the nucleotide sequence of a fragment of the 16S rRNA gene; synthesis of deep eutectic solvents; testing of isolated bacteria - for sensitivity to Cr (VI), for the ability of microorganisms to use hydrocarbons of high-sulfur oil, for activity in sulfur-containing crude oil, for determination of the mass fraction of sulfur. From 12 aerobic bacterial cultures isolated from oil samples, 9 strains with active and moderate growth in a medium with high-sulfur oil were selected during testing, followed by two strains (Bacillus paramycoides SFN-1, Bacillus cereus SFN-2), which were the most resistant to Cr (VI) and two strains (Bacillus cereus SFN2, Bacillus thuringiensis SFN3), which have shown sulfur-oxidizing abilities. The native bacterial strains selected during the study showed high disulfurization activity without the addition of deep eutectic solvents (hereinafter referred to as DES) (Bacillus thuringiensis SFN3), with the addition of DES-1 (Bacillus cereus SFN2) and with the addition of DES-2 (Bacillus thuringiensis SFN3). As a result of a comparative analysis of microbial desulfurization processes, it was found that the highest biodesulfurization rate at the end of the experiment was recorded in cultures of Pseudomonas aeruginosa B-5807 (96.3 %), Bacillus thuringiensis SFN-3 (96.1 %), and Rhodococcus erythropolis AC 1039 (96 %).

Mechanisms of thermal, acid, desiccation and osmotic tolerance of Cronobacter spp

Cronobacter spp. exhibit remarkable resilience to extreme environmental stresses, including thermal, acidic, desiccation, and osmotic conditions, posing significant challenges to food safety. Their thermotolerance relies on heat shock proteins (HSPs), thermotolerance genomic islands, enhanced DNA repair mechanisms, and metabolic adjustments, ensuring survival under high-temperature conditions. Acid tolerance is achieved through internal pH regulation, acid efflux pumps, and acid tolerance proteins, allowing survival in acidic food matrices and the gastrointestinal tract. Desiccation tolerance is mediated by the accumulation of protective osmolytes like trehalose, stabilizing proteins and membranes to withstand dryness, especially in dry food products. Similarly, osmotic stress resilience is supported by compatible solutes such as trehalose and glycine betaine, along with metabolic adaptations to balance osmotic pressures. These mechanisms highlight the adaptability of Cronobacter spp. to diverse environments. Moreover, exposure to sublethal stresses, including heat, osmotic, dry, and pH stresses, may induce homologous or cross-resistance, complicating control strategies. Understanding these survival mechanisms is essential to mitigate the risks of Cronobacter spp., especially in powdered infant formula (PIF), and ensure food safety.

Two novel triazine-based quaternary ammonium salt Gemini surfactants as potential corrosion inhibitors for carbon steel in a sulfate-reducing bacteria solution: Experimental and theoretical studies

In this paper, two triazine ring-containing quaternary ammonium salt Gemini surfactants (C12-2-C12 and C14-2-C14) were synthesized. The minimum inhibitory concentrations against sulfate-reducing bacteria (SRB) of C12-2-C12, C14-2-C14 and dodecyl dimethyl benzyl ammonium chloride (1227) were determined using the double-dilution method. The performance of C12-2-C12 and C14-2-C14 in inhibiting carbon steel corrosion in the presence of SRB was examined, with 1227 serving as a control sample. The corrosion inhibition properties were assessed through static weight loss, electrochemical testing, and surface analysis. The interface adsorption behaviour of the corrosion inhibitor was explored via molecular dynamics simulations. Results indicate that the minimum inhibitory concentrations (MIC) of C12-2-C12 (0.021 mM) and C14-2-C14 (0.005 mM) are lower than that of 1227 (0.300 mM). The results of static weightlessness measurement reveal that the corrosion inhibition effects of the three surfactants on carbon steel soaked in SRB solution follow the order of C14-2-C14 > C12-2-C12 > 1227, with inhibition rates of 93.23 %, 88.45 %, and 76.49 % at a concentration of 0.2 mM, respectively. The adsorption behavior of these surfactants (1227, C12-2-C12, and C14-2-C14) on carbon steel surface in the presence of SRB conforms the Langmuir isotherm adsorption model. The outcomes of electrochemical experiments align with the static weight loss data. Furthermore, surface analysis results suggest that the surfactants can adsorb onto the carbon steel surface to form a protective film, thereby inhibiting SRB-induced corrosion.

Desalination of the power plant salty wastewater by use of an algae-based photosynthetic microbial desalination cell

In this research the possibility of using a photosynthetic microbial desalination cell (PhMDC) is investigated for desalination of power plant salty wastewater (PPSWW), along with power generation and organic load removal. The PhMDC was operated with anaerobic sludge in the anode chamber, microalgae in the cathode chamber, and different conductivities of PPSWW (10, 20, 40, and 55 mS cm-1) in the desalination chamber under different illumination modes (continuous light mode and light/dark mode). The highest power density (285.5 mW m-2), desalination efficiency (60.9%), and COD removal (74.8%) was achieved at conductivity of 55 mS cm-1 under continuous light mode. The highest algal growth (900 mg. L-1) was also observed at this conductivity. The applied system demonstrated effective removal of different presented cations and anions in PPSWW with removal efficiencies of more than 58%. Dynamic shift of microbial community in the anode chamber showed notable increase in sulfate-reducing bacteria and some specific genera such as Desulfovibrio, Pseudomonas, Rhodobacter, Rhodopseudomonas, and Desulfuromonas due to their potential for electricity generation and adaptation to saline and acidic conditions.

Effects of anthropogenic activities on the microbial community diversity of Ologe Lagoon sediment in Lagos State, Nigeria

The impact of pollution on the Ologe Lagoon was assessed by comparing physicochemical properties, hydrocarbon concentrations and microbial community structures of the sediments obtained from distinct sites of the lagoon. The locations were the human activity site (OLHAS), industrial-contaminated sites (OLICS) and relatively undisturbed site (OLPS). The physicochemical properties, heavy metal concentrations and hydrocarbon profiles were determined using standard methods. The microbial community structures of the sediments were determined using shotgun next-generation sequencing (NGS), taxonomic profiling was performed using centrifuge and statistical analysis was done using statistical analysis for metagenomics profile (STAMP) and Microsoft Excel. The result showed acidic pH across all sampling points, while the nitrogen content at OLPS was low (7.44 ± 0.085 mg/L) as compared with OLHAS (44.380 ± 0.962 mg/L) and OLICS (59.485 ± 0.827 mg/L). The levels of the cadmium, lead and nickel in the three sites were above the regulatory limits. The gas chromatography flame ionization detector (GC-FID) profile revealed hydrocarbon contaminations with nC14 tetradecane > alpha xylene > nC9 nonane > acenaphthylene more enriched at OLPS. Structurally, the sediments metagenomes consisted of 43 phyla,75 classes each, 165, 161, 166 orders, 986, 927 and 866 bacterial genera and 1476, 1129, 1327 species from OLHAS, OLICS and OLPS, respectively. The dominant phyla in the sediments were Proteobacteria, Firmicutes, Actinobacteria, and Chloroflexi. The principal component ordination (PCO) showed that OLPS microbial community had a total variance of 87.7% PCO1, setting it apart from OLHAS and OLICS. OLICS and OLHAS were separated by PCO2 accounting for 12.3% variation, and the most polluted site is the OLPS.

Adaptive strategies and ecological roles of phages in habitats under physicochemical stress

Bacteriophages (phages) play a vital role in ecosystem functions by influencing the composition, genetic exchange, metabolism, and environmental adaptation of microbial communities. With recent advances in sequencing technologies and bioinformatics, our understanding of the ecology and evolution of phages in stressful environments has substantially expanded. Here, we review the impact of physicochemical environmental stress on the physiological state and community dynamics of phages, the adaptive strategies that phages employ to cope with environmental stress, and the ecological effects of phage-host interactions in stressful environments. Specifically, we highlight the contributions of phages to the adaptive evolution and functioning of microbiomes and suggest that phages and their hosts can maintain a mutualistic relationship in response to environmental stress. In addition, we discuss the ecological consequences caused by phages in stressful environments, encompassing biogeochemical cycling. Overall, this review advances an understanding of phage ecology in stressful environments, which could inform phage-based strategies to improve microbiome performance and ecosystem resilience and resistance in natural and engineering systems.

Recent advances in microbial fuel cell-based self-powered biosensors: a comprehensive exploration of sensing strategies in both anode and cathode modes

With the rapid development of society, it is of paramount importance to expeditiously assess environmental pollution and provide early warning of toxicity risks. Microbial fuel cell-based self-powered biosensors (MFC-SPBs) have emerged as a pivotal technology, obviating the necessity for external power sources and aligning with the prevailing trends toward miniaturization and simplification in biosensor development. In this case, vigorous advancements in MFC-SPBs have been acquired in past years, irrespective of whether the target identification event transpires at the anode or cathode. The present article undertakes a comprehensive review of developed MFC-SPBs, categorizing them into substrate effect and microbial activity effect based on the nature of the target identification event. Furthermore, various enhancement strategies to improve the analytical performance like accuracy and sensitivity are also outlined, along with a discussion of future research trends and application prospects of MFC-SPBs for their better developments.

Unlocking the Gut's Treasure: Lipase-Producing Bacillus subtilis Probiotic from the Intestine of Microstomus kitt (Lemon sole)

The main objective of this research was to identify potential probiotic candidates belonging to the Bacillus species that could demonstrate tolerance to bile salt and acidic conditions. The study focused on isolating Bacillus strains from the intestine of marine fish-Microstomus kitt. The isolation process involved the use of selective MRS media through the pour plate method. After 24 h, one particular isolate was identified based on its morphological and biochemical traits as Bacillus species. To confirm the identity, molecular characterization of the 16S RNA from the isolated strain was performed, and the sequence analysis verified it as Bacillus subtilis strain ACL_BS 001. With the molecular confirmation, the next step was to assess the probiotic characteristics of this B. subtilis strain. Various tests were conducted to evaluate its acid/pH tolerance, NaCl tolerance, and bile salt tolerance. The results indicated that B. subtilis exhibited high viability percentages even under acidic pH, in the presence of 1.5% bile salt, and at high salt concentrations. Subsequently, we investigated the strain's ability to produce lipase, an important enzyme with potential industrial applications. B. subtilis was grown in MRS agar amended with olive oil as a lipase substrate. After incubation, the presence of lipase activity was confirmed, and the enzymatic assay revealed a significant lipase enzyme activity of 100.23 µmoles/ml of the sample. In conclusion, the study successfully isolated and identified B. subtilis from the intestine of Microstomus kitt, and the strain exhibited promising probiotic characteristics, including resistance to bile salt and acidic conditions. Furthermore, the strain was found to produce lipase, which opens up possibilities for future research focusing on isolating and purifying the lipase from this potential probiotic B. subtilis strain.

Extremophiles and their expanding biotechnological applications

Microbial life is not restricted to any particular setting. Over the past several decades, it has been evident that microbial populations can exist in a wide range of environments, including those with extremes in temperature, pressure, salinity, and pH. Bacteria and Archaea are the two most reported types of microbes that can sustain in extreme environments, such as hot springs, ice caves, acid drainage, and salt marshes. Some can even grow in toxic waste, organic solvents, and heavy metals. These microbes are called extremophiles. There exist certain microorganisms that are found capable of thriving in two or more extreme physiological conditions simultaneously, and are regarded as polyextremophiles. Extremophiles possess several physiological and molecular adaptations including production of extremolytes, ice nucleating proteins, pigments, extremozymes and exopolysaccharides. These metabolites are used in many biotechnological industries for making biofuels, developing new medicines, food additives, cryoprotective agents etc. Further, the study of extremophiles holds great significance in astrobiology. The current review summarizes the diversity of microorganisms inhabiting challenging environments and the biotechnological and therapeutic applications of the active metabolites obtained as a response to stress conditions. Bioprospection of extremophiles provides a progressive direction with significant enhancement in economy. Moreover, the introduction to omics approach including whole genome sequencing, single cell genomics, proteomics, metagenomics etc., has made it possible to find many unique microbial communities that could be otherwise difficult to cultivate using traditional methods. These findings might be capable enough to state that discovery of extremophiles can bring evolution to biotechnology.

Anti-staphylococcal activity of soilless cultivated cannabis across the whole vegetation cycle under various nutritional treatments in relation to cannabinoid content

Antibiotic resistance in staphylococcal strains and its impact on public health and agriculture are global problems. The development of new anti-staphylococcal agents is an effective strategy for addressing the increasing incidence of bacterial resistance. In this study, ethanolic extracts of Cannabis sativa L. made from plant parts harvested during the whole vegetation cycle under various nutritional treatments were assessed for in vitro anti-staphylococcal effects. The results showed that all the cannabis extracts tested exhibited a certain degree of growth inhibition against bacterial strains of Staphylococcus aureus, including antibiotic-resistant and antibiotic-sensitive forms. The highest antibacterial activity of the extracts was observed from the 5th to the 13th week of plant growth across all the nutritional treatments tested, with minimum inhibitory concentrations ranging from 32 to 64 µg/mL. Using HPLC, Δ9-tetrahydrocannabinolic acid (THCA) was identified as the most abundant cannabinoid in the ethanolic extracts. A homolog of THCA, tetrahydrocannabivarinic acid (THCVA), reduced bacterial growth by 74%. These findings suggest that the cannabis extracts tested in this study can be used for the development of new anti-staphylococcal compounds with improved efficacy.

Disentangling the effects of sulfate and other seawater ions on microbial communities and greenhouse gas emissions in a coastal forested wetland

Seawater intrusion into freshwater wetlands causes changes in microbial communities and biogeochemistry, but the exact mechanisms driving these changes remain unclear. Here we use a manipulative laboratory microcosm experiment, combined with DNA sequencing and biogeochemical measurements, to tease apart the effects of sulfate from other seawater ions. We examined changes in microbial taxonomy and function as well as emissions of carbon dioxide, methane, and nitrous oxide in response to changes in ion concentrations. Greenhouse gas emissions and microbial richness and composition were altered by artificial seawater regardless of whether sulfate was present, whereas sulfate alone did not alter emissions or communities. Surprisingly, addition of sulfate alone did not lead to increases in the abundance of sulfate reducing bacteria or sulfur cycling genes. Similarly, genes involved in carbon, nitrogen, and phosphorus cycling responded more strongly to artificial seawater than to sulfate. These results suggest that other ions present in seawater, not sulfate, drive ecological and biogeochemical responses to seawater intrusion and may be drivers of increased methane emissions in soils that received artificial seawater addition. A better understanding of how the different components of salt water alter microbial community composition and function is necessary to forecast the consequences of coastal wetland salinization.

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.

Microbial Characterization of Arctic Glacial Ice Cores with a Semiautomated Life Detection System

The search for extant microbial life will be a major focus of future astrobiology missions; however, no direct extant life detection instrumentation is included in current missions to Mars. In this study, we developed the semiautomated MicroLife detection platform that collects and processes environmental samples, detects biosignatures, and characterizes microbial activity. This platform is composed of a drill for sample collection, a redox dye colorimetric system for microbial metabolic activity detection and assessment (μMAMA [microfluidics Microbial Activity MicroAssay]), and a MinION sequencer for biosignature detection and characterization of microbial communities. The MicroLife platform was field-tested on White Glacier on Axel Heiberg Island in the Canadian high Arctic, with two extracted ice cores. The μMAMA successfully detected microbial metabolism from the ice cores within 1 day of incubation. The MinION sequencing of the ice cores and the positive μMAMA card identified a microbial community consistent with cold and oligotrophic environments. Furthermore, isolation and identification of microbial isolates from the μMAMA card corroborated the MinION sequencing. Together, these analyses support the MicroLife platform's efficacy in identifying microbes natively present in cryoenvironments and detecting their metabolic activity. Given our MicroLife platform's size and low energy requirements, it could be incorporated into a future landed platform or rovers for life detection.

Photocatalytic deactivation of sulphate reducing bacteria using visible light active CuO/TiO2 nanocomposite photocatalysts synthesized by ultrasonic processing

Sulphate-reducing bacteria wreaks havoc to oil pipelines, as it is an active agent for scale formation in the oil production tubing, and plugging of reservoir rock around the oil wells, and this leads to the degradation of oil quality. In this work, we synthesized copper oxide/titanium dioxide nanocomposite photocatalysts with three different mass contents of copper oxide (10%, 20% and 30%) and used them as an effective photo-catalyst in the process of photo-catalytic deactivation of sulphate-reducing bacteria. The anchoring of copper oxide on titanium dioxide brought about the following positive attributes in copper oxide/titanium dioxide nanocomposite pertained to the photo-catalyst: (i) the material transformed to visible light active with the potential to harness the more efficient visible spectral region of the solar radiation, (ii) increased surface area on the photo-catalyst enhanced the number of active reaction sites in the material, and (iii) efficiently retarded the undesired photo-generated electron hole recombination to promote the photo-catalytic activity. Although, the photo-catalyst effective under both UV and visible light, the deactivation was found to be higher in visible radiation, particularly the nanocomposite with 20%- copper oxide on titanium dioxide showed the highest photocatalytic degradation with of Sulphate-reducing bacteria with a decay constant as high as 1.38 min ^-1 and the total depletion time as low as 8 min. It was confirmed that the bacterial deactivation was neither due to the bactericidal effect of the nanocomposite nor due to the light mediated deactivation.

Functional Microbial Communities in Hybrid Linear Flow Channel Reactors for Desulfurization of Tannery Effluent

Recent research has demonstrated that hybrid linear flow channel reactors (HLFCRs) can desulfurize tannery effluent via sulfate reduction and concurrent oxidation of sulfide to elemental sulfur. The reactors can be used to pre-treat tannery effluent to improve the efficiency of downstream anaerobic digestion and recover sulfur. This study was conducted to gain insight into the bacterial communities in HLFCRs operated in series and identify structure-function relationships. This was accomplished by interpreting the results obtained from amplicon sequencing of the 16S rRNA gene and quantification of the dissimilatory sulfite reducing (dsrB) gene. In an effort to provide a suitable inoculum, microbial consortia were harvested from saline estuaries and enriched. However, it was found that bioaugmentation was not necessary because native communities from tannery wastewater were selected over exogenous communities from the enriched consortia. Overall, Dethiosulfovibrio sp. and Petrimonas sp. were strongly selected (maximum relative abundances of 29% and 26%, respectively), while Desulfobacterium autotrophicum (57%), and Desulfobacter halotolerans (27%) dominated the sulfate reducing bacteria. The presence of elemental sulfur reducing genera such as Dethiosulfovibrio and Petrimonas is not desirable in HLFCRs, and strategies to counter their selection need to be considered to ensure efficiency of these systems for pre-treatment of tannery effluent.

Physiological suitability of sulfate reducing granules for the development of bioconcrete

Regular monitoring and timely repair of concrete cracks are required to minimise further deterioration. Self-healing of cracks has been proposed as an alternative to the crack maintenance procedures. One of the proposed techniques is to use axenic cultures to exploit microbial induced calcite precipitation (MICP). However, such healing agents are not cost-effective for in situ use. As the market for bio-based self-healing concrete necessitates a low-cost bio-agent, non-axenic sulfate reducing bacterial (SRB) granules were investigated in this study through cultivation in an upflow anaerobic sludge blanket (UASB) reactor. The compact granules can protect the bacteria from adverse conditions without encapsulation. This study investigated the microbial activities of SRB granules at different temperatures, pH, and COD concentrations which the microbes would experience during the concrete casting and curing process. The attenuation and recovery of microbial activities were measured before and after the exposure. Moreover, the MICP yield was also tested for a possible use in self-healing bioconcrete. The results consistently showed that SRB granules were able to survive starvation, high temperature (50-60 ^o C), and high pH (12), together with SEM/EDS/XRD evidence. Microbial staining analysis demonstrated the formation of spores in the granules during their exposure to the harsh conditions. SRB granule was thus demonstrated to be a viable self-healing non-axenic agent for low-cost bioconcrete. This article is protected by copyright. All rights reserved.

Inhibition of Sulfate Reduction and Cell Division by Desulfovibrio desulfuricans Coated in Palladium Metal

The growth of sulfate-reducing bacteria (SRB) and associated hydrogen sulfide production can be problematic in a range of industries such that inhibition strategies are needed. A range of SRB can reduce metal ions, a strategy that has been utilized for bioremediation, metal recovery, and synthesis of precious metal catalysts. In some instances, the metal remains bound to the cell surface, and the impact of this coating on bacterial cell division and metabolism has not previously been reported. In this study, Desulfovibrio desulfuricans cells (1g dry weight) enabled the reduction of up to 1500 mmol (157.5 g) palladium (Pd) ions, resulting in cells being coated in approximately 1 μm of metal. Thickly coated cells were no longer able to metabolize or divide, ultimately leading to the death of the population. Increasing Pd coating led to prolonged inhibition of sulfate reduction, which ceased completely after cells had been coated with 1200 mmol Pd g-1 dry cells. Less Pd nanoparticle coating permitted cells to carry out sulfate reduction and divide, allowing the population to recover over time as surface-associated Pd diminished. Overcoming inhibition in this way was more rapid using lactate as the electron donor, compared to formate. When using formate as an electron donor, preferential Pd(II) reduction took place in the presence of 100 mM sulfate. The inhibition of important metabolic pathways using a biologically enabled casing in metal highlights a new mechanism for the development of microbial control strategies. IMPORTANCE Microbial reduction of sulfate to hydrogen sulfide is highly undesirable in several industrial settings. Some sulfate-reducing bacteria are also able to transform metal ions in their environment into metal phases that remain attached to their outer cell surface. This study demonstrates the remarkable extent to which Desulfovibrio desulfuricans can be coated with locally generated metal nanoparticles, with individual cells carrying more than 100 times their mass of palladium metal. Moreover, it reveals the effect of metal coating on metabolism and replication for a wide range of metal loadings, with bacteria unable to reduce sulfate to sulfide beyond a specific threshold. These findings present a foundation for a novel means of modulating the activity of sulfate-reducing bacteria.

The role of organic acid metabolites in geo-energy pipeline corrosion in a sulfate reducing bacteria environment

The dominant factors in Microbial Influenced Corrosion (MIC) are hard to determine because normally several individual species and their metabolites are involved, and, moreover, different metabolites may cause opposing effects. To address this problem, the effects of individual metabolites from different species should be elucidated when at the same time other metabolites are held constant. In this study, the role is investigated of simulated organic acid metabolites, namely, acetic and L–ascorbic acids, on corrosion of geo-energy pipelines (carbon steel) in a simulated Sulfate Reducing Bacteria (SRB) environment. The SRB environment is simulated using a calcium alginate biofilm, abiotic sulfide, CO₂, and NaCl brine. The electrochemical results show that both simulated organic acid metabolites accelerate corrosion in a simulated SRB environment. The results are further supported by electrochemical weight losses, kinetic corrosion activation parameters, multiple linear regression, ICP-OES, pH, and XRD. However, a comparison of electrochemical results with those published in the literature for a simulated SRB environment without acetic or L-ascorbic acid under similar experimental conditions shows that the presence of acetic in this study results in lower corrosion current densities while in presence of L-ascorbic acid results into higher corrosion current densities. This implies that acetic and L-ascorbic acids inhibit and accelerate corrosion, respectively. In addition, the results highlight that H₂S is a key role of corrosion in the presence of organic acid. The results of this study are important new and novel information on the role of acetic and L-ascorbic acids in corrosion of geo-energy pipelines in the SRB environment.

Preparation of biologically activated lignite immobilized SRB particles and their AMD treatment characteristics

In response to the insufficient supply of carbon sources and the toxicity of heavy metal ions when using sulfate reducing bacteria (SRB) to treat acid mine wastewater (AMD), the immobilized particles are prepared with Rhodopseudomonas, SRB and lignite as the main raw materials. And based on single factor test and orthogonal test to determine the optimal ratio of biologically activated lignite fixed SRB particles. The adsorption characteristics of immobilized particles were studied under the optimal ratio, and the reaction kinetics and adsorption capacity of SRB particles immobilized on biologically activated lignite to different ions were analyzed. The results show that: lignite not only has good adsorption performance, but also can be used as the carbon source of SRB after being degraded by Rhodopseudomonas, solving the problems of low removal efficiency of SRB treatment of AMD and insufficient carbon source supply. When the dosage of lignite (particle size is 200 mesh), Rhodopseudomonas, and SRB are 3%, 10%, and 10% mesh, the prepared biologically activated lignite-immobilized SRB particles have the best effect on AMD treatment. The removal rates of SO₄²⁻, Zn²⁺, and Cu²⁺ were 83.21%, 99.59%, and 99.93%, respectively, the pH was increased to 7.43, the COD release was 523 mg/L, and the ORP value was − 134 mV. The reduction process of SO₄²⁻ by the biologically activated lignite-immobilized SRB particles conforms to the pseudo-first-order kinetics, and the adsorption of Zn²⁺ is more in line with the Freundlich isotherm adsorption equation and the pseudo-second-order kinetic model. And it does not spread in a single form, both internal and external diffusion occur. SEM, FT-IR, and BET analysis of biologically activated lignite immobilized SRB particles showed that the pore structure is developed, has a large number of adsorption sites, and some activated groups participate in the reaction. The adsorption process of Zn²⁺ and Cu²⁺ in AMD meets the multi-layer adsorption theory.

Hydrogen sulphide management in anaerobic digestion: A critical review on input control, process regulation, and post-treatment

Hydrogen sulphide (H₂S) in biogas is a problematic impurity that can inhibit methanogenesis and cause equipment corrosion. This review discusses technologies to remove H₂S during anaerobic digestion (AD) via: input control, process regulation, and post-treatment. Post-treatment technologies (e.g. biotrickling filters and scrubbers) are mature with >95% removal efficiency but they do not mitigate H₂S toxicity to methanogens within the AD. Input control (i.e. substrate pretreatment via chemical addition) reduces sulphur input into AD via sulphur precipitation. However, available results showed <75% of H₂S removal efficiency. Microaeration to regulate AD condition is a promising alternative for controlling H₂S formation. Microaeration, or the use of oxygen to regulate the redox potential at around -250 mV, has been demonstrated at pilot and full scale with >95% H₂S reduction, stable methane production, and low operational cost. Further adaptation of microaeration relies on a comprehensive design framework and exchange operational experience for eliminating the risk of over-aeration.

Haloalkaliphilic denitrifiers-dependent sulfate-reducing bacteria thrive in nitrate-enriched environments

As bridge in global cycles of carbon, nitrogen, and sulfur, sulfate-reducing bacteria (SRB) play more and more important role under various environments, especially the saline-alkali environments with significant increase in area caused by human activities. Sulfate reduction can be inhibited by environmental nitrate. However, how SRB cope with environmental nitrate stress in these extreme environments still remain unclear. Here, after a long-term enrichment of sediment from saline-alkali Qinghai Lake of China using anaerobic filter reactors, nitrate was added to evaluate the response of SRB. With the increase in nitrate concentrations, the inhibition on sulfate reduction was gradually observed. Interestingly, extension of hydraulic retention time can relieve the inhibition caused by high nitrate concentration. Mass balance analysis showed that nitrate reduction is prior to sulfate reduction. Further metatranscriptomic analysis shows that, genes of nitrite reductase (periplasmic cytochrome c nitrite reductase gene) and energy metabolisms (lactate dehydrogenase, formate dehydrogenase, pyruvate:ferredoxin-oxidoreductase, and fumarate reductase genes) in SRB was down-regulated, challenging the long-held opinion that up-regulation of these genes can relieve the nitrate inhibition. Most importantly, the nitrate addition activated the denitrification pathway in denitrifying bacteria (DB) via significantly up-regulating the expression of the corresponding genes (nitrite reductase, nitric oxide reductase c subunit, nitric oxide reductase activation protein and nitrous oxide reductase genes), quickly reducing the environmental nitrate and relieving the nitrate inhibition on SRB. Our findings unravel that in response to environmental nitrate stress, haloalkaliphilic SRB show dependency on DB, and expand our knowledge of microbial relationship during sulfur and nitrogen cycles.