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Abstract: Mesophilic iron and sulfur-oxidizing acidophiles are readily found in acid mine drainage sites and bioleaching operations, but relatively little is known about their activities at suboptimal temperatures and in cold environments. The purpose of this work was to characterize the oxidation of elemental sulfur (S0), tetrathionate (S4O6 2−) and ferrous iron (Fe2+) by the psychrotolerant Acidithiobacillus strain SS3. The rates of elemental sulfur and tetrathionate oxidation had temperature optima of 20° and 25°C, respectively, determined using a temperature gradient incubator that involved narrow (1.1°C) incremental increases from 5° to 30°C. Activation energies calculated from the Arrhenius plots were 61 and 89kJmol−1 for tetrathionate and 110kJmol−1 for S0 oxidation. The oxidation of elemental sulfur produced sulfuric acid at 5°C and decreased the pH to approximately 1. The low pH inhibited further oxidation of the substrate. In media with both S0 and Fe2+, oxidation of elemental sulfur did not commence until all available ferrous iron was oxidized. These data on sequential oxidation of the two substrates are in keeping with upregulation and downregulation of several proteins previously noted in the literature. Ferric iron was reduced to Fe2+ in parallel with elemental sulfur oxidation, indicating the presence of a sulfur:ferric iron reductase system in this bacterium. [Copyright &y& Elsevier]

Natural organic matter (NOM) removal is the main objective of artificial groundwater recharge (AGR) for drinking water production and biodegradation plays a substantial role in this process. This study focused on the biodegradation of NOM and nutrient availability for microorganisms in AGR by the determination of extracellular enzyme activities (EEAs) and nutrient concentrations along a flow path in an AGR aquifer (Tuusula Water Works, Finland). Natural groundwater in the same area but outside the influence of recharge was used as a reference. Determination of the specific α-d-glucosidase (α-Glu), β-d-glucosidase (β-Glu), phosphomonoesterase (PME), leucine aminopeptidase (LAP) and acetate esterase (AEST) activities by fluorogenic model substrates revealed major increases in the enzymatic hydrolysis rates in the aquifer within a 10m distance from the basin. The changes in the EEAs along the flow path occurred simultaneously with decreases in nutrient concentrations. The results support the assumption that the synthesis of extracellular enzymes in aquatic environments is up and down regulated by nutrient availability. The EEAs in the basin sediment and pore water samples (down to 10cm) were in the same order of magnitude as in the basin water, suggesting similar nutritional conditions. Phosphorus was likely to be the limiting nutrient at this particular AGR site. Furthermore, the extracellular enzymes functioned in a synergistic and cooperative way. [Copyright &y& Elsevier]

Abstract: Iron oxidation in bioleaching systems commonly produces mixtures of hydroxysulfate minerals. The purpose of this study was to characterize iron precipitates formed in liquid media inoculated with iron-oxidizing acidophiles (Acidithiobacillus ferrooxidans). Air-dried precipitates were characterized by X-ray diffraction (XRD), elemental analysis, specific surface area, color, and scanning electron microscopy. The Fe(III)-hydroxysulfates produced in this study included schwertmannite (Fe8O8(OH)6SO4) and various solid solution jarosites (K,Na,NH4,H3O)Fe3(SO4)2(OH)6). The precipitates were composed entirely of schwertmannite in the presence of insufficient concentrations of monovalent ions. The levels of NH4 +, K+, and Na+ were determined for the formation of the corresponding jarosites. The levels varied depending on the jarosite type and were the lowest for K+ and highest for Na+. With natrojarosite especially, when synthesized with 500 mM Na+, the highest level tested in this study, the precipitate still contained poorly ordered schwertmannite as a major phase. [Copyright &y& Elsevier]

Abstract: Pyritic sludge spilled from the 1998 dam failure in Aznalcóllar, Spain, was subjected to chemical and microbiological leaching tests in shake flasks. The sample contained pyrite as the main sulfide mineral and sphalerite and arsenopyrite in minor amounts. The experiments were carried out at ambient and elevated temperatures (22, 45, and 65 °C) using iron-oxidizing bacteria and thermophilic archaea for inocula. The leaching was monitored by chemical analysis of solution samples and by X-ray diffraction analysis of solids. Elevated temperature accelerated the oxidation of sulfide minerals and the solubilization of Fe, Zn and As. The overall reaction was acid-producing and jarosite was the final sink of precipitated ferric iron formed upon pyrite oxidation. The results demonstrate that sludge oxidation is greatly accelerated by acidophilic microorganisms, leading to dissolution of potentially toxic metals such as As. [Copyright &y& Elsevier]

Abstract: Microbial fuel cells (MFCs) are a promising technology for sustainable production of alternative energy and waste treatment. The performance of microbial fuel cells is severely affected by limitations based on irreversible reactions and processes in the anode and the cathode compartments. The purpose of this paper is to review the cathodic limitations MFCs and provide an overview on cathodic activation, ohmic and mass transport losses and substrate crossover. Recent studies that have addressed these limitations and explored approaches for improvement are also discussed. MFCs still face many challenges but with consistent advances, especially with respect to the cathode, performance can continue to improve. [Copyright &y& Elsevier]

Abstract: Ammoniojarosite [(NH4,H3O)Fe3(OH)6(SO4)2], a poorly soluble basic ferric sulfate, was produced by microbiological oxidation of ferrous sulfate at pH 2.0–3.0 over a range of concentrations (5.4–805mM) and temperatures (22–65°C). Ammoniojarosites were also produced by chemical (abiotic) procedures in parallel thermal (36–95°C) experiments. At 36°C, schwertmannite [ideally Fe8O8(OH)6(SO4)] was the only solid product formed at <10mM concentrations. Between 11.5 and 85.4mM , a mixed product of ammoniojarosite and schwertmannite precipitated, as identified by X-ray diffraction. In excess of 165mM , ammoniojarosite was the only solid phase produced. An increase in the incubation temperature using thermoacidophiles at 45 and 65°C accelerated the formation of ammoniojarosite in culture solutions containing 165mM . Both the biogenic and chemical ammoniojarosites were yellow (2Y–4Y in Munsell hue), low surface area (<1m2/g), well crystalline materials with average c o and a o unit cell parameters of 17.467±0.048Å and 7.330±0.006Å, respectively. Strong positive correlations were observed between unit cell axial ratios (c o/a o) and increasing synthesis temperature in both biotic and abiotic systems. All samples were N deficient compared to stoichiometric ammoniojarosite, and both chemical and X-ray data indicated partial replacement of by H3O+ to form solid solutions with 0.14–0.24mole H3O+ per formula unit. The morphology of the biogenic jarosites included aggregated discs, pseudo-cubic crystals and botryoidal particles, whereas the chemical specimens prepared at 36–95°C were composed of irregular crystals with angular edges. Morphological information may thus be useful to evaluate environmental parameters and mode of formation. The data may also have application in predicting phase boundary conditions for Fe(III) precipitation in biogeochemical processes and treatment systems involving acid sulfate waters. [Copyright &y& Elsevier]

The purpose of this study was to assess the weathering of finely ground phlogopite, a trioctahedral mica, by placing it in contact with heterotrophic (Bacillus cereus) and acidophilic (Acidithiobacillus ferrooxidans) cultures. X-ray diffraction analyses of the phlogopite sample before and after 24 weeks of contact in B. cereus cultures revealed a decrease in the characteristic peak intensities of phlogopite, indicating destruction of individual structural planes of the mica. No new solid phase products or interlayer structures were detected in B. cereus cultures. Acidithiobacillus ferrooxidans cultures enhanced the chemical dissolution of the mineral and formed partially weathered interlayer structures, where interlayer K was expelled and coupled with the precipitation of K-jarosite [KFe3(SO4)2(OH)6]. [ABSTRACT FROM AUTHOR]

The purpose of this study was to characterize the phylogenetic and phenotypic traits of M91-3, a soil bacterium capable of mineralizing atrazine (2-chloro-4-N-isopropyl-6-N-ethyl-s-triazine). The isolate was identified as Ralstonia basilensis based on 99.5% homology of the 16S rRNA sequence and various chemotaxonomic data. The isolate used atrazine as the sole source of energy, carbon, and nitrogen. It could also use several other s-triazines as nitrogen sources. Ralstonia basilensis M91-3 was capable of denitrification, which was confirmed by gas chromatographic analysis of nitrous oxide under acetylene blockage conditions.Key words: atrazine biodegradation, denitrification, herbicide degrader, Ralstoniabasilensis, triazine degradation.L'objectif de cette étude fut de caractériser les traits phylogénétiques et phénotypiques de M91-3, une bactérie du sol capable de minéraliser l'atrazine (2-chloro-4-N-isopropyle-6-N-éthyle-s-triazine). Sur la base d'une homologie de 99,5% de la séquence de l'ARNr 16S et de diverses données chimiotaxonomiques, l'isolat a été identifié comme étant Ralstonia basilensis. L'isolat a utilisé l'atrazine comme seule source d'énergie, de carbone et d'azote. Il a également pu utiliser un certain nombre d'autres s-triazines en tant que sources d'azote. Ralstonia basilensis M91-3 fut capable de dénitrification, fait confirmé par l'analyse par chromatographie en phase gazeuse de l'oxyde nitreux dans des conditions de blocage à l'acétylène.Mots clés : biodégradation de l'atrazine, dénitrification, dégradateur d'herbicide, Ralstonia basilensis, dégradation des triazines.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Evaluates the mineralization of atrazine in wetlands in Ohio. Evolution of carbon dioxide from atrazine; Levels of mineralization; Effect of seasonality of atrazine runoff on the level of mineralization; Kinetic parameters of atrazine mineralization.

The purpose of this study was to determine whether there was an association between kinetics of atrazine mineralization, the number and type of atrazine-degrading microorganisms, and the presence of three genes representing different steps in the degradative pathway of atrazine in three soils with different histories of atrazine application. Composite soil samples were collected from two agricultural fields and one riparian zone soil. The samples were amended with atrazine, and mineralization was measured in biometers as 14CO2 evolution in samples spiked with [ring-U-14C]-labeled atrazine. Atrazine-degrading microorganisms were enumerated by a most-probable-number (MPN) method, which was based on loss of atrazine (HPLC assay) in acetate media. Dot-blot hybridization assays were performed on total DNA extracted from the MPN samples. The DNA probes used in dot-blot assays were the genes atzA (atrazine chlorohydrolase from Pseudomonas ADP), atrA (cytochrome P-450 from Rhodococcus TE1), and trzD (cyanuric acid amidohydrolase from Pseudomonas NRRLB-12228). The herbicide amendment enhanced the subsequent rate of mineralization of atrazine in all three soil samples. The MPN numbers were in the range of 100–102 cells g−1 dry wt. soil, indicating that atrazine-degrading microorganisms could not be quantitatively enumerated by this technique. Positive hybridization signals of DNA extracted from MPN samples were frequent with the atzA probe; the atrA dot blots had fewer positive signals. The trzD signals were negligible or undetectable, although the parallel mineralization studies showed fast and extensive 14CO2 evolution from [ring-U-14C]-atrazine. The results suggested that trzD, the only gene known to encode s-triazine ring-cleavage, is not dominant among the atrazine-degrading populations of these soils. Streptomycin and cycloheximide were added to soil samples in biometers to determine the relative contributions of bacteria and fungi in the soils to the mineralization of atrazine. The relative suppression of mineralization in the presence of the bacterial or fungal specific inhibitor was approximately the same, indicating that both groups contributed to the mineralization of atrazine. [Copyright &y& Elsevier]

Cobaltite (CoAsS) is a strategically important mineral. This work investigated the bioleaching of cobaltite-bearing magnetite-rich ore. The bioleaching of cobaltite was carried out with mixed mesophilic and moderately thermophilic cultures at 4, 8, and 12% pulp densities in shake flasks. The bioleaching with mesophiles at 8% pulp dissolved up to 89% of the cobalt content, higher than the bioleaching of 4% pulp and abiotic control test. Additional Fe3+ in the leach solution increased cobalt dissolution in the control test. The bioleaching by moderate thermophiles reached 97% cobalt dissolution in 16 d contact time. Kinetic modeling indicated that the controlling step of bioleaching with moderate thermophiles was the chemical reaction, while the diffusion was the rate-limiting factor for the bioleaching with mesophiles. [Display omitted] • Cobaltite leaching was tested with mesophilic and moderately thermophilic cultures. • Moderate thermophiles extracted 97% Co and 85% As from the ore sample. • Cobalt dissolution by moderate thermophiles was under chemical reaction control. • Kinetics of cobalt dissolution by mesophiles was under diffusion control. • Direct addition of Fe3+ to the leach solution increased the cobalt recovery. [ABSTRACT FROM AUTHOR]

As a recurrent climatic phenomenon in the context of climate change, extreme rainstorms induce vertical translocation of organic matter and increase moisture content in terrestrial ecosystems. However, it remains unclear whether heavy rainstorms can impact microbial communities in the deep biosphere by modulating organic matter input. In this study, we present findings on the different responses of bacterial and fungal communities in a subsurface cave to rainstorms and moisture variations through field surveys and microcosm experiments. During periods of rainstorms, the influx of dissolved organic matter (DOM) from soil overlying the cave into cave sediments significantly enhanced the correlation between core bacteria and environmental factors, particularly fluorescence spectral indices. The resource utilization of core bacteria was diminished, while the functional diversity of core fungi remained relatively unaltered. We also performed simulated experiments with restricted external DOM inputs, in which DOM content was observed to decrease and microbial diversity increase in response to artificially increased moisture content (MC). The niche breadth of core bacteria decreased and became more closely associated with DOM as the MC increased, while the niche breadth of core fungi remained predominantly unchanged. Compared to fungi, cave bacteria exhibited higher sensitivity towards variations in DOM. The core microbiome can efficiently utilize the available organic matter and participate in nitrogen- and sulfur-related metabolic processes. The study systematically revealed distinct microbial responses to rainstorm events, thereby providing valuable insights for future investigations into energy utilization within deep biospheres., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Peatlands are important sources of the greenhouse gas methane emissions equipoised by methanogens and methanotrophs. However, knowledge about how microbial functional groups associated with methane production and oxidation respond to water table fluctuations has been limited to date. Here, methane-related microbial communities and the potentials of methane production and oxidation were determined along sectioned peat layers in a subalpine peatland across four Sphagnum -dominated sites with different water table levels. Methane fluxes were also monitored at these sites. The results showed that mcrA gene copies for methanogens were the highest in the 10- to 15-cm peat layer, which was also characterized by the maximum potential methane production (24.53 ± 1.83 nmol/g/h). Copy numbers of the pmoA gene for type Ia and Ib methanotrophs were enriched in the 0-5 cm peat layer with the highest potential methane oxidation (43.09 ± 3.44 nmol/g/h). For the type II methanotrophs, the pmoA gene copies were higher in the 10- to 15-cm peat layer. Hydrogenotrophic methanogens and type II methanotrophs dominated the methane functional groups. Deterministic process contributed more to methanogenic and methanotrophic community assemblages in comparison with stochastic process. The level of water table significantly shaped methanogenic and methanotrophic community structures and regulated methane fluxes. Compared with vascular plants, Sphagnum mosses significantly reduced the methane emissions in peatlands. Collectively, these findings enhance a comprehensive understanding of the effect of the water table level on methane functional groups, with consequential implications for reducing methane emissions within peatland ecosystems.IMPORTANCEThe water table level is recognized as a critical factor in regulating methane emissions, which are largely dependent on the balance of methanogens and methanotrophs. Previous studies on peat methane emissions have been mostly focused on spatial-temporal variations and the relationship with meteorological conditions. However, the role of the water table level in methane emissions remains unknown. In this work, four representative microhabitats along a water table gradient in a Sphagnum -dominated peatland were sampled to gain an insight into methane functional communities and methane emissions as affected by the water table level. The changes in methane-related microbial community structure and assembly were used to characterize the response to the water table level. This study improves the understanding of the changes in methane-related microbial communities and methane emissions with water table levels in peatlands.

Karst caves are usually considered as natural laboratories to study pristine microbiomes in subsurface biosphere. However, effects of the increasingly detected nitrate in underground karst ecosystem due to the acid rain impact on microbiota and their functions in subsurface karst caves have remained largely unknown. In this study, samples of weathered rocks and sediments were collected from the Chang Cave, Hubei province and subjected to high-throughput sequencing of 16S rRNA genes. The results showed that nitrate significantly impacted bacterial compositions, interactions, and functions in different habitats. Bacterial communities clustered according to their habitats with distinguished indicator groups identified for each individual habitat. Nitrate shaped the overall bacterial communities across two habitats with a contribution of 27.2%, whereas the pH and TOC, respectively, structured bacterial communities in weathered rocks and sediments. Alpha and beta diversities of bacterial communities increased with nitrate concentration in both habitats, with nitrate directly affecting alpha diversity in sediments, but indirectly on weathered rocks by lowering pH. Nitrate impacted more on bacterial communities in weathered rocks at the genus level than in sediments because more genera significantly correlated with nitrate concentration in weathered rocks. Diverse keystone taxa involved in nitrogen cycling were identified in the co-occurrence networks such as nitrate reducers, ammonium-oxidizers, and N 2 -fixers. Tax4Fun2 analysis further confirmed the dominance of genes involved in nitrogen cycling. Genes of methane metabolism and carbon fixation were also dominant. The dominance of dissimilatory and assimilatory nitrate reduction in nitrogen cycling substantiated nitrate impact on bacterial functions. Our results for the first time revealed the impact of nitrate on subsurface karst ecosystem in terms of bacterial compositions, interactions, and functions, providing an important reference for further deciphering the disturbance of human activities on the subsurface biosphere., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The handling editor YS declared a shared affiliation with the authors XLiu, HW, WW, XC, YW, QL, LL, LM, and XLu at the time of review., (Copyright © 2023 Liu, Wang, Wang, Cheng, Wang, Li, Li, Ma, Lu and Tuovinen.)

Karst caves are a natural oligotrophic subsurface biosphere widely distributed in southern China. Despite the progress in bacterial and fungal diversity, the knowledge about interactions between bacteria, fungi, and minerals is still limited in caves. Hence, for the first time, we investigated the interaction between bacteria and fungi living on weathered rocks in the Heshang Cave via high-throughput sequencing of 16S rRNA and ITS1 genes, and co-occurrence analysis. The mineral compositions of weathered rocks were analyzed by X-ray diffraction. Bacterial communities were dominated by Actinobacteria (33.68%), followed by Alphaproteobacteria (8.78%), and Planctomycetia (8.73%). In contrast, fungal communities were dominated by Sordariomycetes (21.08%) and Dothideomycetes (14.06%). Mineral substrata, particularly phosphorus-bearing minerals, significantly impacted bacterial (hydroxyapatite) and fungal (fluorapatite) communities as indicated by the redundancy analysis. In comparison with fungi, the development of bacterial communities was more controlled by the environmental selection indicated by the overwhelming contribution of deterministic processes. Co-occurrence network analysis showed that all nodes were positively linked, indicating ubiquitous cooperation within bacterial groups and fungal groups, as well as between bacteria and fungi under oligotrophic conditions in the subsurface biosphere. In total, 19 bacterial ASVs and 34 fungal OTUs were identified as keystone taxa, suggesting the fundamental role of fungi in maintaining the microbial ecosystem on weathered rocks. Ascomycota was most dominant in keystone taxa, accounting for 26.42%, followed by Actinobacteria in bacteria (24.53%). Collectively, our results confirmed the highly diverse bacterial and fungal communities on weathered rocks, and their close cooperation to sustain the subsurface ecosystem. Phosphorus-bearing minerals were of significance in shaping epipetreous bacterial and fungal communities. These observations provide new knowledge about microbial interactions between bacteria, fungi, and minerals in the subterranean biosphere., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Wang, Cheng, Wang, Zhou, Liu and Tuovinen.)

Bacterial communities in antimony (Sb) polluted soils have been well addressed, whereas the important players fungal communities are far less studied to date. Here, we report different responses of bacterial and fungal communities to Sb contamination and the ecological processes controlling their community assembly. Soil samples in the Xikuangshan mining area were collected and subjected to high through-put sequencing of 16S rRNA and ITS1 to investigate bacterial and fungal communities, respectively, along an Sb gradient. Sb speciation in the soil samples and other physicochemical parameters were analyzed as well. Bacterial communities were dominated by Deltaproteobacteria in the soil with highest Sb concentration, whereas Chloroflexi were dominant in the soil with lowest Sb concentration. Fungal communities in high-Sb soils were predominated by unclassified Fungi, whilst Leotiomycetes were dominant in low-Sb soil samples. Multivariate analysis indicated that Sb, pH and soil texture were the main drivers to strongly impact microbial communities. We further identified Sb-resistant microbial groups via correlation analysis. In total, 18 bacterial amplicon sequence variants (ASVs) were found to potentially involve in biogeochemical cycles such as Sb oxidation, sulfur oxidation or nitrate reduction, whereas 12 fungal ASVs were singled out for potential heavy metal resistance and plant growth promotion. Community assembly analysis revealed that variable selection contributed 100% to bacterial community assembly under acidic or high Sb concentration conditions, whereas homogeneous selection dominated fungal community assembly with a contribution over 78.9%. The community assembly of Sb-resistant microorganisms was mainly controlled by stochastic process. The results offer new insights into microbial ecology in Sb-contaminated soils, especially on the different responses of microbial communities under identical environmental stress and the different ecological processes underlining bacterial and fungal community assembly., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

According to the literature, pyrite (FeS 2 ) oxidation has been previously determined to involve thiosulfate as the first aqueous intermediate sulfur product, which is further oxidized to sulfate. In the present study, pyrite oxidation by Acidithiobacillus ferrooxidans was studied using electrochemical and metabolic approaches in an effort to extend existing knowledge on the oxidation mechanism. Due to the small surface area, the reaction rate of a compact pyrite electrode in the form of polycrystalline pyrite aggregate in A. ferrooxidans suspension was very slow at a spontaneously formed high redox potential. The slow rate made it possible to investigate the oxidation process in detail over a term of 100 days. Using electrochemical parameters from polarization curves and levels of released iron, the number of exchanged electrons per pyrite molecule was estimated. The values close to 14 and 2 electrons were determined for the oxidation with and without bacteria, respectively. These results indicated that sulfate was the dominant first aqueous sulfur species formed in the presence of bacteria and elemental sulfur was predominantly formed without bacteria. The stoichiometric calculations are consistent with high iron-oxidizing activities of bacteria that continually keep the released iron in the ferric form, resulting in a high redox potential. The sulfur entity of pyrite was oxidized to sulfate by Fe 3+ without intermediate thiosulfate under these conditions. Cell attachment on the corroded pyrite electrode surface was documented although pyrite surface corrosion by Fe 3+ was evident without bacterial participation. Attached cells may be important in initiating the oxidation of the pyrite surface to release iron from the mineral. During the active phase of oxidation of a pyrite concentrate sample, the ATP levels in attached and planktonic bacteria were consistent with previously established ATP content of iron-oxidizing cells. No significant upregulation of three essential genes involved in energy metabolism of sulfur compounds was observed in the planktonic cells, which represented the dominant biomass in the pyrite culture. The study demonstrated the formation of sulfate as the first dissolved sulfur species with iron-oxidizing bacteria under high redox potential conditions. Minor aqueous sulfur intermediates may be formed but as a result of side reactions.

Microbial fuel cells (MFCs) have potential to treat industrial wastewater containing organic compounds and simultaneously generate power. Organic compounds include textile dyes with various chromophore groups, which can be decolorized reductively by microorganisms under anaerobic conditions. In the present study, we examined the decolorization of Reactive Black 5 (RB5) azo dye and Reactive Blue 4 (RBL4) anthraquinone dye under open circuit potential in MFCs with graphite plate and graphite felt electrodes and a microbial consortium originally derived from bovine rumen fluid. RB5 dye was more than 90% decolorized in 120, 165, and 225 min at 50, 100, and 200 mg L -1 concentrations, respectively. RBL4 dye at 50 and 100 mg L -1 took 225 and 300 min to decolorize, while 200 mg L -1 RBL4 dye was not decolorized at all. Under closed circuit conditions, decolorization increased with decrease in external load, whereas current generation increased with external resistance. The results demonstrate that the reductive cleavage of the chromophore was more rapid with RB5 than with RBL4.

Almost all the known isolates of acidophilic or acid-tolerant sulphate-reducing bacteria (SRB) belong to the spore-forming genus Desulfosporosinus in the Firmicutes. The objective of this study was to isolate acidophilic/acid-tolerant members of the genus Desulfovibrio belonging to deltaproteobacterial SRB. The sample material originated from microbial mat biomass submerged in mine water and was enriched for sulphate reducers by cultivation in anaerobic medium with lactate as an electron donor. A stirred tank bioreactor with the same medium composition was inoculated with the sulphidogenic enrichment. The bioreactor was operated with a temporal pH gradient, changing daily, from an initial pH of 7.3 to a final pH of 3.7. Among the bacteria in the bioreactor culture, Desulfovibrio was the only SRB group retrieved from the bioreactor consortium as observed by 16S rRNA-targeted denaturing gradient gel electrophoresis. Moderately acidophilic/acid-tolerant isolates belonged to Desulfovibrio aerotolerans-Desulfovibrio carbinophilus-Desulfovibrio magneticus and Desulfovibrio idahonensis-Desulfovibrio mexicanus clades within the genus Desulfovibrio. A moderately acidophilic strain, Desulfovibrio sp. VK (pH optimum 5.7) and acid-tolerant Desulfovibrio sp. ED (pH optimum 6.6) dominated in the bioreactor consortium at different time points and were isolated in pure culture.

The purpose of this study was to synthesize a series of solid solution jarosites by biological oxidation of ferrous iron at pH2.2-4.4 and ambient temperature in media containing mixtures of K(+) (0, 1, 4, 6, 12, 31 mM) and NH4(+) (6.1, 80, 160, 320 mM). The starting material was a liquid medium for Acidithiobacillus ferrooxidans comprised of 120 mM FeSO4 solution and mineral salts at pH2.2. Following inoculation with A. ferrooxidans, the cultures were incubated in shake flasks at 22°C. As bacteria oxidized ferrous iron, ferric iron hydrolyzed and precipitated as jarosite-group minerals (AFe3(SO4)2(OH)6) and/or schwertmannite (idealized formula Fe8O8(OH)6(SO4)·nH2O). The precipitates were characterized by X-ray diffraction (XRD), elemental analysis, and Munsell color. Schwertmannite was the dominant mineral product at low combinations of K(+) (≤ 4 mM) and NH4(+) (≤ 80 mM) in the media. At higher single or combined concentrations, yellowish jarosite phases were produced, and Munsell hue provided a sensitive means of detecting minor schwertmannite in the oxidation products. Although the hydrated ionic radii of K(+) and NH4(+) are similar, K(+) greatly facilitated the formation of a jarosite phase compared to NH4(+). Unit cell and cell volume calculations from refinements of the powder XRD patterns indicated that the jarosite phases produced were mostly ternary (K, NH4, H3O)-solid solutions that were also deficient in structural Fe, especially at low NH4 contents. Thus, ferric iron precipitation from the simulated bioleaching systems yielded solid solutions of jarosite with chemical compositions that were dependent on the relative concentrations of K(+) and NH4(+) in the synthesis media. No phase separations involving discrete, end-member K-jarosite or NH4-jarosite were detected in the un-aged precipitates., (Copyright © 2014 Elsevier B.V. All rights reserved.)

The purpose of this study was to characterize precipitates formed in anaerobic, H2S-producing cultures of two Tissierella isolates and Desulfosporosinus strain DB. The cultures were grown in Cu-containing media as part of a larger study of Cu resistance in anaerobic sulfidogens. The Tissierella strains produced H2S from peptone. Desulfosporosinus formed H2S from peptone or through dissimilatory sulfate reduction with lactate. Tissierella cultures precipitated iron phosphate, vivianite, but no crystalline phases or Cu sulfides were detected. Multiple Cu sulfides, including chalcopyrite and covellite, were detected in Desulfosporosinus cultures but vivianite was not formed. Ion microprobe spectra and electron microscopic examination showed major variation in the elemental composition and morphological differences depending on incubation conditions. Extended incubation time for at least 1-2 months increased the crystallinity of the precipitates. The results highlight biogeochemical differences in sulfide and phosphate precipitates between the two major groups of Firmicutes although they may share the same habitat including the human intestinal tract.

This review discusses anaerobic production of methane, hydrogen, ethanol, butanol and electricity from microalgal biomass. The amenability of microalgal biomass to these bioenergy conversion processes is compared with other aquatic and terrestrial biomass sources. The highest energy yields (kJ g(-1) dry wt. microalgal biomass) reported in the literature have been 14.8 as ethanol, 14.4 as methane, 6.6 as butanol and 1.2 as hydrogen. The highest power density reported from microalgal biomass in microbial fuel cells has been 980 mW m(-2). Sequential production of different energy carriers increases attainable energy yields, but also increases investment and maintenance costs. Microalgal biomass is a promising feedstock for anaerobic energy conversion processes, especially for methanogenic digestion and ethanol fermentation. The reviewed studies have mainly been based on laboratory scale experiments and thus scale-up of anaerobic utilization of microalgal biomass for production of energy carriers is now timely and required for cost-effectiveness comparisons., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The aim of this study was to test three flat-plate photobioreactor configurations for cultivation of marine green alga Dunaliella tertiolecta under non-axenic growth conditions and to characterize and quantify the associated bacteria. The photobioreactor cultivations were conducted using tap water-based media. Static mixers intended to enhance mixing and light utilization did not generally increase algal growth at the low light intensities used. The maximum biomass concentration (measured as volatile suspended solids) and maximum specific growth rate achieved in the flat plate with no mixer were 2.9 g l⁻¹ and 1.3 day⁻¹, respectively. Based on quantitative polymerase chain reaction, bacterial growth followed the growth of D. tertiolecta. Based on 16S rDNA amplification and denaturing gradient gel electrophoresis profiling, heterotrophic bacteria in the D. tertiolecta cultures mainly originated from the non-axenic algal inocula, and tap water heterotrophs were not enriched in high chloride media (3 % salinity). Bacterial communities were relatively stable and reproducible in all flat-plate cultivations and were dominated by Gammaproteobacteria, Flavobacteria, and Alphaproteobacteria.

Background: Microalgae are a promising feedstock for biofuel and bioenergy production due to their high photosynthetic efficiencies, high growth rates and no need for external organic carbon supply. In this study, utilization of Chlorella vulgaris (a fresh water microalga) and Dunaliella tertiolecta (a marine microalga) biomass was tested as a feedstock for anaerobic H2 and CH4 production., Results: Anaerobic serum bottle assays were conducted at 37°C with enrichment cultures derived from municipal anaerobic digester sludge. Low levels of H2 were produced by anaerobic enrichment cultures, but H2 was subsequently consumed even in the presence of 2-bromoethanesulfonic acid, an inhibitor of methanogens. Without inoculation, algal biomass still produced H2 due to the activities of satellite bacteria associated with algal cultures. CH4 was produced from both types of biomass with anaerobic enrichments. Polymerase chain reaction-denaturing gradient gel electrophoresis profiling indicated the presence of H2-producing and H2-consuming bacteria in the anaerobic enrichment cultures and the presence of H2-producing bacteria among the satellite bacteria in both sources of algal biomass., Conclusions: H2 production by the satellite bacteria was comparable from D. tertiolecta (12.6 ml H2/g volatile solids (VS)) and from C. vulgaris (10.8 ml H2/g VS), whereas CH4 production was significantly higher from C. vulgaris (286 ml/g VS) than from D. tertiolecta (24 ml/g VS). The high salinity of the D. tertiolecta slurry, prohibitive to methanogens, was the probable reason for lower CH4 production.

Under certain conditions, sanitary sewer overflows (SSOs) containing raw wastewater may be discharged to public land and can contribute to environmental and public health issues. Although this problem has attracted the attention of local, state, and federal government and regulators, relatively little SSO abatement research has been published. This study used fixed-media bioreactors, a proven onsite technology in rural areas, to treat wet weather SSO wastewater and reduce its effects on the receiving water environment. The results of this 32-month laboratory study showed that fixed-media bioreactors, especially sand bioreactors, efficiently removed organic matter, solids, and nutrients during six-hour simulated SSO peak flows. Five-day biochemical oxygen demand (BODs) of the simulated SSO varied between 40 and 125 mg/L. The average effluent concentration of BOD5 was 13 mg/L in sand bioreactors at a hydraulic loading rate of 20.4 cm/h. In addition to having high hydraulic loadings, SSO events occur infrequently. This irregularity requires that treatment systems quickly start up and effectively treat wastewater after a period of no flow. This research found that an interval up to six months between two SSO peak flows did not affect the bioreactor performance. Based on this work, fixed-media bioreactors have the potential to reduce the effects of SSOs on the water environment by following proper design parameters and operation strategies. The pollution loading of approximately 18 g BODs/m2 x h is recommended for the efficient performance of sand bioreactors in the SSO treatment.

Microalgal biomass has been a focus in the sustainable energy field, especially biodiesel production. The purpose of this study was to assess the feasibility of treating microalgal biomass and cellulose by anaerobic digestion for H2 production. A microbial consortium, TC60, known to degrade cellulose and other plant polymers, was enriched on a mixture of cellulose and green microalgal biomass of Dunaliella tertiolecta, a marine species, or Chlorella vulgaris, a freshwater species. After five enrichment steps at 60°C, hydrogen yields increased at least 10% under all conditions. Anaerobic digestion of D. tertiolecta and cellulose by TC60 produced 7.7 mmol H2/g volatile solids (VS) which were higher than the levels (2.9-4.2 mmol/g VS) obtained with cellulose and C. vulgaris biomass. Both microalgal slurries contained satellite prokaryotes. The C. vulgaris slurry, without TC60 inoculation, generated H2 levels on par with that of TC60 on cellulose alone. The biomass-fed anaerobic digestion resulted in large shifts in short chain fatty acid concentrations and increased ammonium levels. Growth and H2 production increased when TC60 was grown on a combination of D. tertiolecta and cellulose due to nutrients released from algal cells via lysis. The results indicated that satellite heterotrophs from C. vulgaris produced H2 but the Chlorella biomass was not substantially degraded by TC60. To date, this is the first study to examine H2 production by anaerobic digestion of microalgal biomass. The results indicate that H2 production is feasible but higher yields could be achieved by optimization of the bioprocess conditions including biomass pretreatment.

In this study, the applicability of three modelling approaches was determined in an effort to describe complex relationships between process parameters and to predict the performance of an integrated process, which consisted of a fluidized bed bioreactor for Fe(3+) regeneration and a gravity settler for precipitative iron removal. Self-organizing maps were used to visually evaluate the associations between variables prior to the comparison of two different modelling methods, the multiple regression modelling and artificial neural network (ANN) modelling, for predicting Fe(III) precipitation. With the ANN model, an excellent match between the predicted and measured data was obtained (R (2) = 0.97). The best-fitting regression model also gave a good fit (R (2) = 0.87). This study demonstrates that ANNs and regression models are robust tools for predicting iron precipitation in the integrated process and can thus be used in the management of such systems.

A sulfate-reducing bacterium, designated as strain R2, was isolated from wastewater of a ball-bearing manufacturing facility in Tomsk, Western Siberia. This isolate was resistant up to 800 mg Cu/l in the growth medium. By comparison, Cu-resistance of reference cultures of sulfate-reducing bacteria ranged from 50 to 75 mg Cu/l. Growth experiments with strain R2 showed that Cu was an essential trace element and, on one hand, enhanced growth at concentrations up to 10 mg/l but, on the other hand, the growth rate decreased and lag-period extended at copper concentrations of >50 mg/l. Phenotypic characteristics and a 1078 bp nucleotide sequence of the 16S rDNA placed strain R2 within the genus Desulfovibrio. Desulfovibrio R2 carried at least one plasmid of approximately of 23.1 kbp. A 636 bp fragment of the pcoR gene of the pco operon that encodes Cu resistance was amplified by PCR from plasmid DNA of strain R2. The pco genes are involved in Cu-resistance in some enteric and aerobic soil bacteria. Desulfovibrio R2 is a prospective strain for bioremediation purposes and for developing a homologous system for transformation of Cu-resistance in sulfate-reducing bacteria.