Iron-oxidizing Bacteria Research Articles

The Accumulation of the REE by Bacterial Fe Oxyhydroxide

The current study was focused on Fe oxyhydroxides from the north-western part of the East-European platform. Modern-day Fe oxyhydroxides of bacterial origin demonstrate an enhanced concentration of rare earth elements (up to 1200 ppm), compared to samples without iron bacteria. The 143Nd/144Nd ratio in bacterial Fe oxyhydroxide has the value from 0.511532 to 0.512588 and corresponds to the geochemical signature of the waters, oxyhydroxides precipitated from. Samples of iron hydroxides from Quaternary and recent continental ore deposits with different Nd and Sr isotope composition were used for the laboratory reduction of Fe3+ up to emergence of magnetite (T ~ 1000°C). 143Nd/144Nd and 87Sr/86Sr ratios in the newly formed mineral phases show insignificant discrepancy with parent iron ore. The persistency of Sm–Nd and Rb–Sr isotope systems in the process of bog iron ore experimental melting permits it’s applying to paleoenvironment reconstructions and archaeometry.

Effect of Anthropogenic Disturbances on the Microbial Relationship during Bioremediation of Heavy Metal-Contaminated Sediment.

Soil, sediment, and waters contaminated with heavy metals pose a serious threat to ecosystem function and human health, and microorganisms are an effective way to address this problem. In this work, sediments containing heavy metals (Cu, Pb, Zn, Mn, Cd, As) were treated differently (sterilized and unsterilized) and bio-enhanced leaching experiments were carried out with the addition of exogenous iron-oxidizing bacteria A. ferrooxidans and sulfur-oxidizing bacteria A. thiooxidans. The leaching of As, Cd, Cu, and Zn was higher in the unsterilized sediment at the beginning 10 days, while heavy metals leached more optimally in the later sterilized sediment. The leaching of Cd from sterilized sediments was favored by A. ferrooxidans compared to A. thiooxidans. Meanwhile, the microbial community structure was analyzed using 16S rRNA gene sequencing, which revealed that 53.4% of the bacteria were Proteobacteria, 26.22% were Bacteroidetes, 5.04% were Firmicutes, 4.67% were Chlamydomonas, and 4.08% were Acidobacteria. DCA analysis indicated that microorganisms abundance (diversity and Chao values) increased with time. Furthermore, network analysis showed that complex networks of interactions existed in the sediments. After adapting to the acidic environmental conditions, the growth of some locally dominant bacteria increased the microbial interactions, allowing more bacteria to participate in the network, making their connections stronger. This evidence points to a disruption in the microbial community structure and its diversity following artificial disturbance, which then develops again over time. These results could contribute to the understanding of the evolution of microbial communities in the ecosystem during the remediation of anthropogenically disturbed heavy metals.

Remediation of arsenic-contaminated calcareous agricultural soils by iron-oxidizing bacteria combined with organic fertilizer.

In arid soil with low-iron and high-calcium carbonate contents, the fate of arsenic (As) is mainly controlled by the contents of calcium and organic matter in the soil. However, there is still a lack of knowledge about their interaction and that effect on their absorption by maize. The purpose of this study was to explore the long-term immobilization and repair mechanism of in situ As-contaminated farmland. We designed three treatments: iron-oxidizing bacteria (FeOB), organic fertilizer, FeOB and organic fertilizer added in combination. After 140-day field farmland remediation trial, the results showed that the FeOB can effectively immobilize the water-soluble As (FS1) in soil, and the organic fertilizer promoted the remediation of FeOB. In addition, the content of As in maize grains was reduced after treatment by FeOB and organic fertilizer. The XRD and XPS analysis of the topsoil showed that the combined treatment of FeOB and organic fertilizer promoted the formation of calcium arsenate mineral with low solubility and high stability; As(III) would gradually transform into As(V). The biological iron (hydr)oxide can increase the contents of Fe and As in the rhizosphere and form iron plaques on the surface of the roots by SEM-EDS analysis of maize root. Collectively, these results clarify the main biogeochemical ways to control the fate of As in calcareous soils with low-iron and low-organic matter contents and provide a basis for in situ remediation of As.

The effect of aboveground long-term low-dose ionizing radiation on soil microbial diversity and structure

Studies investigating the diversity and structure of soil microbial systems in response to ionizing radiation are scarce. In particular, effects of long-term low-dose radiation is rarely studied because of its unique conditions. In this study, an area in Chengdu, China, which has been irradiated by the radionuclide thorium-232 for more than 10 years was investigated. Four groups of samples with absorbed dose rates ranging from 192.906 ± 5.05 to 910.964 ± 41.09 nGy/h were collected to analyze the compositional and functional changes of the soil microbial systems in the region. The diversity and structure of the soil microbial systems were determined using high-throughput sequencing. Our results showed that long-term low-dose ionizing radiation had no significant effect on soil bacterial diversity, but had a great impact on fungal diversity. Long-term ionizing radiation strongly affected soil microbial community structure. Long-term low-dose ionizing radiation was shown to have a promoting effect on iron-oxidizing bacteria and ectomycorrhizal fungi and have an inhibiting effect on predatory or parasitic fungi, further affecting the soil C/N ratio. This study is of great reference significance for future research on the impact of long-term low-dose ionizing radiation on soil ecosystems.

Synergistic enhancement of corrosion protection of carbon steels using corrosion inhibitors and biocides: Molecular adsorption studies, DFT calculations and long-term corrosion performance evaluation

Corrosion of carbon steel (CS) water pipelines is a major concern worldwide today, which causes leakage of precious water, damage valuable assets, interruption of the water supply, and pose the danger of contamination. In the present work, we demonstrate synergistic enhancement of corrosion protection of CS using biocides (BC) and corrosion inhibitor (CI) combinations of zinc chloride (ZnCl2), phosphoric acid (H3PO4), sodium molybdate (Na2MoO4) and an ionic liquid, 1-Butyl-3-methylimidazolium chloride (IL). 25 ppm of biocides (BC) such as benzalkonium chloride, bronopol, and isothiazoline showed excellent antimicrobial activity against the slime formers and manganese and iron-oxidizing bacteria (Mn/IOB). Electrochemical analysis showed nearly 98% corrosion inhibition efficiency of mixed CI and the anticorrosion mechanism of these CI on iron was further studied by quantum chemical calculations and adsorption studies. Molecular adsorption of the inhibitors onto the Fe(110) surface, modeled from first principle calculations, showed that adsorption energies of the ZnCl2, H3PO4, Na2MoO4 and the IL inhibitor molecules were − 1.94 eV, − 9.73 eV, − 2.14 eV and − 2.46 eV, respectively, in the order of H3PO4 >IL>Na2MoO4 >ZnCl2 indicating thermodynamically favorable interactions which was in good agreement with the experimental data. The long term efficiency of these BC and CI combinations was also tested under accelerated conditions in a pilot scale cooling tower. Nearly 92% corrosion inhibition efficiency was shown by a combination of all CI and BC when compared to corrosion inhibitors alone (81%). These findings are very promising for addressing the corrosion issues in carbon steel water pipelines.

Introducing heterotrophic iron ore bacteria as new candidates in promoting the recovery of e-waste strategic metals.

Electrical instruments are an integral part of human life resulting in a vast electronic waste generation (74.7 Mt by 2030), threatening human life and the environment due to its hazardous nature. Therefore, proper e-waste management is a necessity. Currently, bio-metallurgy is a sustainable process and an emerging research field. Simultaneous leaching of metals using two groups of indigenous heterotrophs and autotrophs was an exciting work done in this study. Bioleaching experiments using pre-adapted cultures were investigated at three e-waste densities: 5, 10, and 15g/L. Statistical analysis was done using two-way ANOVA. Copper (93%), zinc (21.5%), and nickel (10.5%) had the highest recovery efficiencies. There was a significant difference between copper, nickel, tin, and zinc concentrations and the bacterial group (P < 0.05); Iron-oxidizing bacteria showed the most weight decrease and recovered 46-47% of total metals, mainly copper and nickel, while sulfur oxidizers were more capable of zinc leaching. The heterotrophs solubilized tin preferably and substantially decreased e-waste weight. Using heterotrophs alongside autotrophs is proposed to promote metal recovery.

Structure and Seasonal Variability of Groundwater Microbial Communities in the City of Moscow

Abstract—Groundwater, which appears on the surface in the form of springs, is an important ecologically significant component of the aquatic ecosystem, sensitive to changes in environmental conditions. The anthropogenic impact associated with urbanization leads to a change in the characteristics of groundwater, which in turn affects the composition of microbial communities in spring waters. Using high-throughput sequencing of the 16S ribosomal RNA gene fragments, we characterized the composition of microbial communities in five natural springs in the city of Moscow in the spring, summer, and winter seasons. The microbial communities of each spring in different seasons were similar to each other and clearly differed from the microbiomes of other springs. Among the Archaea, which averaged about 20% of microbial communities, ammonium-oxidizing Crenarchaeota predominated, as well as Nanoarchaeota. Most of the Bacteria belonged to the phyla Proteobacteria, Patescibacteria, Verrucomicrobiota, Chloroflexi, and Bacteroidota. Autotrophic bacteria, including iron-oxidizing bacteria of the family Gallionellaceae and nitrifiers, as well as methanotrophs, accounted for significant proportions in microbial communities in the springs with a presumably deeper water source. Chemical and molecular analyzes did not reveal contamination of spring waters with toxic substances and oil-derived products, as well as the presence of pathogenic microorganisms and indicators of fecal pollution. However, during the spring season, the proportions of halophilic and hydrocarbon-oxidizing bacteria increased in water microbiomes, which may reflect entry into groundwater after snow thawing of deicin reagents and hydrocarbons, which are successfully biodegraded in the soil.

Microbiological Characteristics of Three Stratified Lakes in the Nizhny Novgorod Region

Abstract—Three karst lakes were investigated in the Nizhny Novgorod region: Staropustynskie lakes Svyato and Nekrasov Bay and Lake Svetloyar. The studied lakes belonged to the mesotrophic-eutrophic polyhumous type and were characterized by stable stratification with signs of meromixia. Their water columns were divided into aerobic and anaerobic zones, with the bottom water containing sulfide. Fe(II) compounds were also present in the Staropustynskie lakes. In the Lake Nekrasov Bay, the mixolimnion showed a high rate of oxygenic photosynthesis, up to 1.2 µg С L–1 day–1, as well as a maximum of anoxygenic photosynthesis in the chemocline (0.030–0.706 µg С L–1 day–1) at a depth of 1.5–2.5 m. The peak of dark CO2 assimilation (0.146 µg С L–1 day–1) occurred at a depth of 1.5 m in the oxycline zone. Anoxygenic phototrophic bacteria (APB) were found in the Lakes Zaliv Nekrasova and Svyato at the boundary of light penetration. Green sulfur bacteria with short cell prosthecate outgrowths, “Ancalochloris sp.,” predominated. Consortia “Chlorochromatium aggregatum” and filamentous chlorobacteria “Chloronema giganteum” were also found, their cell sheaths accumulated ferric iron salts. In the Staropustynskie lakes, various morphotypes of iron bacteria formed clusters in the microaerobic zone. In Lake Svetloyar the chemocline was located at a depth of 16 m, outside the photic zone, and the conditions were unfavorable for APB growth. In the studied lakes, heterotrophic aerobic bacteria played the main role in the aerobic oxidation of sulfur compounds in the chemocline zone.

Comparación de índices de calidad de agua para consumo humano en pozos profundos del municipio miranda (Zulia, Venezuela)

Groundwater can be an inexhaustible source for various human activities; but also, very vulnerable to chemical and microbiological contamination, so it must be constantly monitored to know its quality in relation to the different uses made of the aquifers. In turn, the water quality indices (WQI) allow the transmission of information on the quality of the water resource, both to the competent authorities and to the general public, in a simple and concise manner. In the present investigation, three different ICA (weighted Arithmetic ICA, ICA-CCME and ICA-Bhargava) were compared in 32 deep wells in a rural area of the Miranda municipality (Zulia, Venezuela), taking into account the parameters: pH, turbidity, color, total dissolved solids, chloride, sulfate, sodium, total hardness, nitrate+nitrite, total iron, total manganese, total and fecal coliform bacteria. The results highlight that, with respect to the ICA-CCME, 22% of the wells have a "fair" quality, while for the ICA-Bhargava 100% were "average", due to the presence of coliform bacteria. In addition, for the weighted ICA-Arithmetic, 25.0% exhibited a "poor" classification. In general, the weighted ICA-Arithmetic and ICA-CCME revealed that 75% and approximately 16% of the wells, respectively, have adequate conditions for human consumption, while for the ICA-Bhargava, none is suitable for said purpose. This discrepancy between the results of the different ICAs is due to the number and type of parameters considered. However, none of the wells fully accomplished with the permissible limits established by the World Health Organization for human consumption, being unsuitable for this use, therefore, the ICA that best adjusted to the water quality of the area of study was the ICA-Bhargava, since it corresponds to the results shown by the referred norms.

Sulfur enhancement effects for uranium bioleaching in column reactors from a refractory uranium ore.

The feasibility of sulfur enhancement for uranium bioleaching in column reactors was assessed with a designed mixed Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferriphilum from a refractory uranium ore. The uranium extraction reached 86.2% with the sulfur enhancement (1 g/kg) in 77 days leaching process, increased by 12.6% vs. the control without sulfur addition. The kinetic analysis showed that uranium bioleaching with sulfur enhancement in columns followed an internal diffusion through the product layer-controlled model. Ore residue characteristics indicated that sulfur enhancement could strengthen the porosity of passivation layer, improving the ore permeability. Notably, bacterial community analysis showed that sulfur enhancement at 1 g/kg could make the iron-oxidizing and sulfur-oxidizing bacteria on the ore surface maintain a good balance (approx. 1:1), and thus decomposing ore more effectively. Lastly, a possible mechanism model for uranium bioleaching with sulfur enhancement was proposed.

High-rate iron sulfide and sulfur-coupled autotrophic denitrification system: Nutrients removal performance and microbial characterization

Iron sulfides-based autotrophic denitrification (IAD) is a promising technology for nitrate and phosphate removal from low C:N ratio wastewater due to its cost-effectiveness and low sludge production. However, the slow kinetics of IAD, compared to other sulfur-based autotrophic denitrification (SAD) processes, limits its engineering application. This study constructed a co-electron-donor (FeS and S0 with a volume ratio of 2:1) iron sulfur autotrophic denitrification (ISAD) biofilter and operated at as short as 1 hr hydraulic retention time (HRT). Long-term operation results showed that the superior total nitrogen and phosphate removals of the ISAD biofilter were 90–100% at 1–12 h HRT, with the highest denitrification rate up to 960 mg/L/d. Considering low sulfate production, HRT of 3 h could be the optimal condition. Such superior performance in the ISAD biofilter was achieved due to the interactions between FeS and S0, which accelerated the denitrification process and maintained the acidity-alkalinity balance. Metagenomic analysis found that the enriched nitrate-dependent iron-oxidizing (NDFO) bacteria (Acinetobacter and Acidovorax), sulfur-oxidizing bacteria (SOB), and dissimilatory nitrate reduction to ammonia (DNRA) bacteria likely supported stable nitrate reduction. The metabolic pathway analysis showed that completely denitrification and DNRA, coupled with sulfur oxidation, disproportionation, iron oxidation and phosphate precipitation with FeS and S0 as co-electron donors, were responsible for the high-rate nitrate and phosphate removal. This study provides the potential of ISAD as a highly efficient post-denitrification technology and sheds light on the balanced microbial S-N-Fe transformation.

Enhancing sludge dewatering efficiency through bioleaching facilitated by increasing reactive oxygen species

Bioleaching facilitated by iron-oxidizing bacteria is regarded as a promising sludge dewatering method due to excellent dewaterability and low cost. However, a two-days bioleaching time for sludge conditioning decreased its daily treatment capacity. In fact, Fe2+ easily reacts with O2 to produce reactive oxygen species (ROS) with high oxidizing activity. Can bioleaching performed in Fe2+-rich system generate ROS to decompose sludge extracellular polymeric substances (EPS)? Here both contribution of ROS produced in bioleaching to improve sludge dewaterability and the increase of ROS content to shorten sludge bioleaching treatment time were investigated. The introduction of H2O2 in sludge bioleaching treatment (BS+H2O2) to increase ROS could simultaneously improve sludge dewaterability and decrease bioleaching time. Specific resistance to filtration (SRF) and capillary suction time (CST) reduction ratios (90.3% and 80.9%) in BS+H2O2 process were much higher than those in other processes after only 30 min reaction. Mechanisms of improving sludge dewaterability in BS+H2O2 mainly included ROS oxidation and Fe3+ flocculation by analysis of the contribution factors. These findings not only provide an effectively method to promote sludge dewatering efficiency of bioleaching, but also give new sights into the design of cost-efficient processes for improving the sludge dewatering.

Effect of Microbial Community on Iron Release under Low Velocity in Drinking Water Supply Pipes

Iron release from water supply network affects water quality safety. To investigate the change of microbial community structure and its effect on iron release in water supply pipes under leakage condition, the research was carried out based on the pilot platform used in actual water supply system. Microbial community structure was analyzed using high-throughput sequencing and the total iron index was measured by atomic flame absorption spectroscopy. The results showed that Proteobacteria had a large competitive advantage in the laminar flow rate, the average relative content increased more than 60%. At the level of class, the relative content of Alphaproteobacteria, Gammaproteobacteria, Betaproteobacteria increased larger than others. When the velocity was close to the critical flow rate, the microbial community was gradually stabilized. The total iron concentration decreased with the increase of flow rates, when the flow rate was 40% of the critical flow rate, the total iron concentration tended to be stable, and the promotion of total iron release was mainly iron-oxidizing bacteria and sulfate reducing bacteria, and the inhibition effect was mainly nitrate reducing bacteria. It has important reference significance for further controlling the microbial community and iron release in the water at the end of the pipe network.

Nitrogen and phosphorusas major factors shaping microbial community structures in surface sediments in Xiangxi River, Three Gorges Reservoir

香溪河是三峡库区最大的入库支流,目前关于香溪河沉积物微生物群落结构特征及其主要影响因素尚不明确。本研究监测香溪河上、中、下游上覆水及沉积物的主要理化指标,通过16S rDNA高通量测序研究香溪河表层沉积物中微生物群落结构特征,使用统计学软件分析细菌与理化指标间的关系。结果表明,上覆水中氨氮(NH₃-N)、叶绿素a(Chl.a)浓度自下游向上游逐渐升高,其中NH₃-N浓度从下游的2.04 mg/L升高到上游的3.14 mg/L。不同点位上覆水中磷酸盐(PO^3-₄)浓度在0.14~0.18 mg/L之间波动;同一点位间隙水中NH₃-N、PO^3-₄浓度明显高于上覆水,10~15 cm沉积物间隙水中NH₃-N与PO^3-₄浓度分别是0~5 cm沉积物间隙水的3.4倍和1.7倍。沉积物中Fe(Ⅱ)、Fe(Ⅲ)、酸可挥发性硫化物和铬还原性硫化物含量均表现为上游点位高于中游、下游,底层沉积物含量高于中层和表层。香溪河中游沉积物的微生物多样性和丰富度高于下游和上游,其中变形菌门(Proteobacteria)是表层沉积物中的优势菌门,鞘脂单胞菌属(Sphingomonas)为主要菌属。不同代谢功能的微生物在空间分布上存在差异,比如具有降解多环芳烃能力的外新鞘脂菌属(Novosphingobium)和土生单胞菌属(Terrimonas)在下游点位的相对丰度最高,分别达到5.8%和5.4%,硝化螺旋菌属(Nitrospira)和黄杆菌属(Flavobacterium)在中游的相对丰度最高,而铁氧化菌水杆菌属(Aquabacterium)主要分布在上游点位。冗余分析(RDA)表明总有机碳、硫酸根、Fe(Ⅱ)、氨氮和总磷是影响香溪河沉积物中微生物群落结构的主要环境因子。本研究有助于进一步了解周边环境和人为活动对香溪河水质稳定及沉积物中微生物的影响,为三峡库区水环境改善和管理提供参考。;Xiangxi River is the largest inflow tributary in the Three Gorges Reservoir area. Structural characteristics and influence factors of the microbial communities in sediments of Xiangxi River are not clear so far. This study investigated the main physical and chemical parameters of the overlying water (i.e., surface, middle and bottom layers) and sediments of the Xiangxi River. 16S rDNA high-throughput sequencing was used to reveal the characteristics of microbial community structures in the sediments. In addition, the relationship between bacteria and physicochemical parameters were analyzed statistically. Chlorophyll.a (Chl.a), concentrations of ammonia nitrogen (NH₃-N) in the overlying water increased gradually from the downstream (2.04 mg/L) to the upstream (3.14 mg/L). The concentrations of phosphate (PO^3-₄) in overlying water fluctuated between 0.14 and 0.18 mg/L at different sampling sites. In addition, the concentrations of NH₃-N and PO^3-₄ in the pore-water at the same site were significantly higher than those in the overlying water. Pore-water NH₃-N and PO^3-₄ concentrations at 10-15 cm depth were 3.4 and 1.7 times higher than those at 0-5 cm depth in sediments, respectively. Higher contents of Fe (Ⅱ), Fe (Ⅲ), acid volatile sulfide and chromium reducing sulfide were observed in the upstream sampling sites and bottom layers of the sediments. The microbial diversity and richness in the sediments of midstream were higher compared to the sediments of downstream and upstream. Proteobacteria was the dominant phylum in the surface sediments, and Sphingomonas was the main genus. The spatial distributions of microorganisms for different metabolic activities varied. Typical bacteria with the ability to degrade polycyclic aromatic hydrocarbons, such as Novosphingobium and Terrimonas, were mainly observed in the sediments of downstream sites with percentage reaching 5.8% and 5.4%, respectively. The percentages of Nitrospira and Flavobacterium were highest in the midstream. The iron-oxidizing bacteria (i.e., Aquabacterium) were rich in the upstream sites. Redundancy analysis (RDA) showed that total organic carbon (TOC), sulfate (SO^2-₄), Fe (Ⅱ), NH₃-N and total phosphorus (TP) were the main environmental factors shaping the microbial community structures in sediments of Xiangxi River. This study will help to further understand the impacts of surrounding environment and human activities on the stability of water quality and the microorganisms in the sediments of Xiangxi River, and provide a reference for the improvement and management of the water environment in the Three Gorges Reservoir area.

Root cause analysis of the Circular hole corrosion failure of N80 tubing

During well repair operations in an oil field, a Φ73.02 mm×5.51 mm N80 grade flat oil pipe with a circular hole was found. The depth of the well is between 550 meters to 2100 meters, with a usage cycle of 120 days. In order to figure out the root cause of the circular hole failure, a series of experiments were carried out. The chemical composition, yield strength, tensile strength, and elongation of the oil pipe meet the requirements of API SPEC 5CT-2018 standard. The microstructure of the oil pipe matrix consists of ferrite and pearlite, and there are no obvious cracks. The grain size of the material is all above 8.5 levels, and there are no coarse grains or non-metallic inclusions exceeding the standard. The perforation of the oil pipe is caused by internal corrosion, mainly due to CO2 corrosion and dissolved oxygen corrosion. The coexistence of Ca2+ and Mg2+ ions, iron bacteria, and corrosive bacteria in the wellbore fluid can lead to scale deposition inside the pipe, causing under-deposit corrosion, and the accelerating effect of Cl ions on corrosion ultimately leads to perforation of the pipe.

Application of Acidithiobacillus ferrooxidans VKM B-3655 for bioleaching silicate ore

Acid metal bioleaching is common and classical for nickel recovery from the sulfide refractory ores: various microorganisms can oxidize sulfides as energetic substrates. Silicate nickel ores are widespread in the world but their bioleaching is more problematic because silicates cannot serve as energetic substrates. Meanwhile iron in the silicate nickel ores presents a significant part and can be used by some acidophilic autotrophic microorganisms for the ore destruction. In model experiments, we studied application of acidophilic autotrophic sulfur-/ iron-oxidizing bacteria Acidithiobacillus ferrooxidans VKM B-3655 for the nickel recovery from the nickel-bearing silicate ore with high content of iron. The strain was selected by its ability of iron oxidation and resistance to arsenic which also presented in the ore. We also evaluated possibility to stimulate the bioleaching with formate as additional energetic substrates or with persulfate for increasing the medium redox. It was shown that low concentrations of sodium formate (0.3%) and persulfate (0.1%) stimulated growth of A. ferrooxidans while higher persulfate concentration (1.0%) stimulated the ore bioleaching.

Diversity of Mixotrophic Neutrophilic Thiosulfate- and Iron-Oxidizing Bacteria from Deep-Sea Hydrothermal Vents

At deep-sea hydrothermal vents, sulfur oxidation and iron oxidation are of the highest importance to microbial metabolisms, which are thought to contribute mainly in chemolithoautotrophic groups. In this study, 17 mixotrophic neutrophilic thiosulfate- and iron-oxidizing bacteria were isolated from hydrothermal fields on the Carlsberg Ridge in the Indian Ocean, nine to the γ-proteobacteria (Halomonas (4), Pseudomonas (2), Marinobacter (2), and Rheinheimera (1)), seven to the α-proteobacteria (Thalassospira, Qipengyuania, Salipiger, Seohaeicola, Martelella, Citromicrobium, and Aurantimonas), and one to the Actinobacteria (Agromyces), as determined by their 16S rRNA and genome sequences. The physiological characterization of these isolates revealed wide versatility in electron donors (Fe(II) and Mn(II), or thiosulfate) and a variety of lifestyles as lithotrophic or heterotrophic, microaerobic, or anaerobic. As a representative strain, Pseudomonas sp. IOP_13 showed its autotrophic gowth from 105 cells/ml to 107 cells/ml;carbon dioxide fixation capacity with the δ13CVPDB in the biomass increased from -27.42‱ to 3460.06‱; the thiosulfate-oxidizing ability with produced SO42- increased from 60 mg/L to 287 mg/L; and the iron-oxidizing ability with Fe(II) decreased from 10 mM to 5.2 mM. In addition, iron-oxide crust formed outside the cells. Gene coding for energy metabolism involved in possible iron, manganese, and sulfur oxidation, and denitrification was identified by their genome analysis. This study sheds light on the function of the mixotrophic microbial community in the iron/manganese/sulfur cycles and the carbon fixation of the hydrothermal fields.

Role of Indigenous Bacteria in Corrosion of Two Types of Carbon Steel.

This study aimed to investigate the presence of both aerobic and anaerobic bacteria in a water sample collected from a nuclear power plant and establish if the indigenous bacteria or the products of their metabolic activities could initiate the corrosion of two different types of carbon steel (i.e., A570, 1045). The aerobic (heterotrophic, iron-oxidizing) and anaerobic (sulfate-reducing) bacteria were detected in low numbers in the water sample. Three bacterial strains were isolated by the enrichment procedure from this sample. Based on phenotypic and genotypic characteristics, the isolated bacteria were identified as Stenotrophomonas maltophilia IBBCn1 (MT893712), Stenotrophomonas maltophilia IBBCn2 (MT893713), and Bacillus thuringiensis IBBCn3 (MT893714). The bacteria existing in the water sample were able to initiate the corrosion of carbon steel A570 and 1045. The sulfate-reducing bacteria were detected in higher numbers than the heterotrophic bacteria and iron-oxidizing bacteria at the end of the biocorrosion experiments. The carbon steel coupons revealed macroscopic and microscopic changes in the surface characteristics, and these changes could be due to biofilm formation on their surfaces and the accumulation of the corrosion products. The corrosion rate varied from one type of carbon steel to another, depending on the incubation conditions and the chemical composition of the coupons.

Modeling the process of biological deferrization of underground waters in contact loading of bioreactor

The conducted analysis of modern biotechnologies in the field of groundwater treatment showed that one of the development trends is the direction of biological iron removal, which has not only a long history and fundamentality of research into the physiology, ultrastructure and life mechanisms of ferrobacteria, but also a wide implementation of the method at water treatment plants in Europе, Australia, Canada, USA, Japan. The introduction of modern technological equipment at such stations calls for the need to forecast their work using methods of mathematical modeling of processes with their subsequent computer implementation. The work provides a brief analysis of existing mathematical models, most of which are based on the kinetics of enzymatic reactions and are presented as modifications of the Michaelis-Menten and Monod equations.&#x0D; Despite the large number of studies on this topic, until now there is no comprehensive model that would take into account all the processes that take place in the contact loading of bioreactors, in contrast to the physicochemical mechanisms in the filtering process, for which modern multicomponent mathematical models have been developed.&#x0D; The aim of the work is to development of a mathematical model of the kinetics of the process of biological iron removal groundwater in bioreactors and verification of its computer implementation with the data of experimental studies. The mathematical model is represented by the Cauchy problem for a nonlinear system of differential equations in partial derivatives of the first order. The system of the Cauchy problem consists of five equations with five unknown functions, which describe the distribution the concentration of ferrum cations, bacteria and the matrix structures in two phases (movable and immobilized) both in space and time The inverse influence of the characteristics of the process, in particular, the concentration of matrix structures in the inter-pore space, as well as characteristics of the medium with the help of coefficients of mass exchange and porosity, were taken into account. The model makes it possible to predict changes in cleaning efficiency depending on the duration of the filter cycle, filtration speed, Fe2+ concentration, the content of iron bacteria and their matrix structures in the interpore space, and to determine the optimal time of operation of the bioreactor between washings&#x0D;

Mixotrophic denitrification improvement in ecological floating bed: Interaction between iron scraps and plant biomass

In this study, an iron scrap (IS)-based ecological floating bed was constructed to couple with plant biomass (FeB-EFB) for treating low-polluted water, and the nitrogen removal performance and mechanism were explored. The results showed that the nitrogen could be effectively removed in FeB-EFB, and the nitrate removal efficiency was 29.14 ± 8.06% even at a low temperature (13.9 ± 2.2 °C). After the temperature rose to 20.0 ± 0.9 °C, the denitrification rate was increased by 0.63 ± 0.16–0.81 ± 0.27 g/(m2 d) due to the synergistic effect of ISs and plant biomass. Plant biomass could promote the ISs release efficiency, while ISs could facilitate plant biomass availability by promoting cellulose decomposition. High-throughput sequencing analysis revealed that the iron-oxidizing bacteria Pseudomonas were the dominant genus in FeB-EFB. Meanwhile, the existence of plant biomass could increase the abundance of iron-related bacteria and enrich heterotrophic and facultative denitrifying bacteria (e.g., Hydrogenophaga, Comamonas) as well, improving iron-mediated denitrification and heterotrophic denitrification simultaneously. Therefore, mixotrophic denitrification improvement played a major role in promoting nitrogen removal of FeB-EFB. These results indicated that coupling iron scraps with plant biomass may be an effective way to improve the nitrogen removal performance of EFB.