Production of Biogenic Manganese Oxides by Anamorphic Ascomycete Fungi Isolated from Streambed Pebbles

We characterized the production of biogenic Mn oxides by four anamorphic ascomycete fungi isolated from streambed pebbles with Mn oxide coatings. Based on the 18S rRNA gene sequences, one strain was related to members of the order Xylariales and the other three were within distinct lineages of the Pleosporales. These strains oxidized Mn(II) to deposit Mn oxides when their growth approached the stationary phase. The fungal Mn oxides showed X-ray diffraction patterns typical of poorly crystalline vernadite (δ -MnO₂), and X-ray absorption near-edge structure spectroscopy confirmed that the Mn phases consisted predominantly of Mn(IV). Mn(II) oxidation in the four strains proceeded enzymatically. The Mn(II)-oxidizing proteins were inhibited by azide and o-phenanthroline, and the proteins also oxidized typical laccase substrates including 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), showing the role of laccase or a laccase-like metalloenzyme. The mineralogical traits of the biogenic Mn oxides, and the participation of laccase-like enzymes, are in accordance with our previous results obtained with one Hypocreales ascomycete. In conclusion, phylogenetically diverse ascomycetes may use this common enzymatic system to produce solid Mn phases similar to δ -MnO₂.     

Cobalt(II) Oxidation by Biogenic Mn Oxide Produced by Pseudomonas sp. Strain NGY-1

Oxidation of Co by Mn oxide has been investigated using abiotically synthesized Mn oxide. However, oxidation of Co by biogenic Mn oxide is not well known. In this study, we isolated a Mn-oxidizing bacterium (Pseudomonas sp.), designated as strain NGY-1, from stream water. Sorption experiments on Co were carried out using biogenic Mn oxide produced by strain NGY-1. Similar sorption experiments were also conducted using a synthetic analogue of δ-MnO₂. Sorption of Co on δ-MnO₂ was faster and stronger than that on biogenic Mn oxide, which was possibly due to their structural difference and/or the presence of bacterial cells in biogenic Mn oxide. X-ray absorption near-edge structure spectra clearly demonstrated that Co was oxidized from the divalent to the trivalent state on biogenic Mn and δ-MnO₂. The oxidation property of both the biogenic Mn oxide and δ-MnO₂ was stronger under circumneutral conditions than under acidic conditions. Linear combination fitting using divalent and trivalent Co reference materials suggested that ～90% of Co was oxidized at pH ～ 6, whereas ～80% was oxidized at pH ～ 3. Oxidation properties of the biogenic Mn oxide and δ-MnO₂ were similar, but Co(II) oxidation by biogenic Mn oxide was slower than that by δ-MnO₂. The difference of Co oxidation may be caused by the coexisting bacterial cells or structural differences in the Mn oxides.

Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the supplemental file.     

Ferribacterium limneticum, gen. nov., sp. nov., an Fe(III)-reducing microorganism isolated from mining-impacted freshwater lake sediments

A dissimilatory Fe(III)-reducing bacterium was isolated from mining-impacted lake sediments and designated strain CdA-1. The strain was isolated from a 4-month enrichment culture with acetate and Fe(III)-oxyhydroxide. Strain CdA-1 is a motile, obligately anaerobic rod, capable of coupling the oxidation of acetate and other organic acids to the reduction of ferric iron. Fe(III) reduction was not observed using methanol, ethanol, isopropanol, propionate, succinate, fumarate, H₂, citrate, glucose, or phenol as potential electron donors. With acetate as an electron donor, strain CdA-1 also grew by reducing nitrate or fumarate. Growth was not observed with acetate as electron donor and O₂, sulfoxyanions, nitrite, trimethylamine N-oxide, Mn(IV), As(V), or Se(VI) as potential terminal electron acceptors. Comparative 16 S rRNA gene sequence analyses show strain CdA-1 to be most closely related (93.6% sequence similarity) to Rhodocyclus tenuis. However, R. tenuis did not grow heterotrophically by Fe(III) reduction, nor did strain CdA-1 grow photrophically. We propose that strain CdA-1 represents a new genus and species, Ferribacterium limneticum. Strain CdA-1 represents the first dissimilatory Fe(III) reducer in the β subclass of Proteobacteria, as well as the first Fe(III) reducer isolated from mine wastes. Received: 14 July 1998 / Accepted: 14 December 1998     

Biogeochemical Properties of Bacteriogenic Iron Oxides

Bacteriogenic iron oxides (BIOS) are composite materials that consist of intact and partly degraded remains of bacterial cells intermixed with variable amounts of poorly ordered hydrous ferric oxide (HFO) minerals. They form in response to chemical or bacterial oxidation of Fe²⁺, which gives rise to Fe³⁺. Once formed, Fe³⁺ tends to undergo hydrolysis to precipitate in association with bacterial cells. In acidic systems where the chemical oxidation of Fe²⁺ is slow, bacteria are capable of accelerating the reaction by several orders of magnitude. At circumneutral pH, the chemical oxidation of Fe²⁺ is fast. This requires Fe²⁺ oxidizing bacteria to exploit steep redox gradients where low pO₂ slows the abiotic reaction enough to allow the bacteria to compete kinetically. Because of their reactive surface properties, BIOS behave as potent sorbents of dissolved metal ions. Strong enrichments of Al, Cu, Cr, Mn, Sr, and Zn in the solid versus aqueous phase (log 10 K_d values range from 1.9 to 4.2) are common; however, the metal sorption properties of BIOS are not additive owing to surface chemical interactions between the constituent HFO and bacteria. These interactions have been investigated using acid-base tritrations, which show that the concentration of high pK_a sites is reduced in BIOS compared to HFO. At the same time, hydroxylamine insoluble material (i.e., residual bacterial fraction) is enriched in low pK_a sites relative to both BIOS and HFO. These differences indicate that low pK_a or acidic sites associated with bacteria in BIOS interact specifically with high pK_a or basic sites on intermixed HFO.     

Desulfuromonas palmitatis sp. nov., a marine dissimilatory Fe(III) reducer that can oxidize long-chain fatty acids

Studies on the microorganisms living in hydrocarbon-contaminated sediments in San Diego Bay, California led to the isolation of a novel Fe(III)-reducing microorganism. This organism, designated strain SDBY1, was an obligately anaerobic, non-motile, non-flagellated, gram-negative rod. Strain SDBY1 conserves energy to support growth from the oxidation of acetate, lactate, succinate, fumarate, laurate, palmitate, or stearate. H₂ was also oxidized with the reduction of Fe(III), but growth with H₂ as the sole electron donor was not observed. In addition to various forms of soluble and insoluble Fe(III), strain SDBY1 also coupled growth to the reduction of fumarate, Mn(IV), or S⁰. Air-oxidizedminus dithionite-reduced difference spectra exhibited peaks at 552.8, 523.6, and 422.8 nm, indicative ofc-type cytochrome(s). Strain SDBY1 shares physiological characteristics with organisms in the generaGeobacter, Pelobacter, andDesulfuromonas. Detailed analysis of the 16S rRNA sequence indicated that strain SDBY1 should be placed in the genusDesulfuromonas. The new species nameDesulfuromonas palmitatis is proposed.D. palmitatis is only the second marine organism found (afterD. acetoxidans) to oxidize multicarbon organic compounds completely to carbon dioxide with Fe(III) as an electron acceptor and provides the first pure culture model for the oxidation of long-chain fatty acids coupled to Fe(III) reduction.     

异化铁还原细菌Clostridium sp.LQ25分离及其产氢与铁还原特性

[背景] 一些异化铁还原细菌兼具铁还原和发酵产氢能力,可作为发酵型异化铁还原细菌还原机制研究的对象。[目的] 筛选出一株发酵型异化铁还原细菌。在异化铁还原细菌培养体系中,设置不同电子供体并分析电子供体。[方法] 通过三层平板法从海洋沉积物中筛选纯菌株,基于16S rRNA基因序列进行菌株鉴定。通过测定细菌培养液Fe （II）浓度及发酵产氢量分析菌株异化铁还原和产氢性质。[结果] 菌株LQ25与Clostridium butyricum的16S rRNA基因序列相似性达到100%,结合电镜形态观察,菌株命名为Clostridium sp.LQ25。在氢氧化铁为电子受体培养条件下,菌株生长较对照组（未添加氢氧化铁）显著提高。菌株LQ25能够利用丙酮酸钠、葡萄糖和乳酸钠进行生长。丙酮酸钠为电子供体时,菌株LQ25细胞生长和异化铁还原效率最高,菌体蛋白质含量是（78.88±3.40） mg/L,累积产生Fe （II）浓度为（8.27±0.23） mg/L。以葡萄糖为电子供体时,菌株LQ25发酵产氢量最高,达（475.2±14.4） mL/L,相比对照组（未添加氢氧化铁）产氢量提高87.7%。[结论] 筛选到一株具有异化铁还原和发酵产氢能力的菌株Clostridium sp.LQ25,为探究发酵型异化铁还原细菌胞外电子传递机制提供了新的实验材料。     

利用光合细菌进行微生物修复：一种降低辛硫磷在养殖水中积累的低成本方法

【背景】中国是农业生产大国,渔林农牧占比庞大。有机农药无论在畜牧业还是水产养殖业都有广泛的应用。有机磷农药(Organophosphorus Pesticide,OP)是应用最广泛的有机农药,具有低毒和不易残留的优点。OP在水体中大量积累可通过生物富集作用间接影响人体健康,由此产生的生殖毒性不容忽视。光合细菌作为环境友好型水体有益菌,部分菌种具有降解有机农药的功能。【目的】自上海海洋大学明湖中分离纯化得到一株光合细菌(编号SPZ)。探究其对辛硫磷的耐受程度及降解效果,为养殖水体中有机磷农药的生物降解提供目的菌株。【方法】利用16S rRNA基因序列分析方法对目标菌株进行种属鉴定;利用紫外分光光度法测定分离菌株SPZ和标准菌株ST在不同接种量下的OD660并测定实验周期内光合细菌在不同浓度辛硫磷中OD660的变化趋势,以示辛硫磷对光合细菌的毒性作用;利用高效液相色谱法(High Performance Liquid Chromatography,HPLC)测定菌株对水体辛硫磷的降解能力;通过HPLC测定加热致死菌与活菌对水体辛硫磷的降解能力,确定菌株对辛硫磷的降解方式。【结果】16S r...     

Geovibrio ferrireducens,a phylogenetically distinct dissimilatory Fe(III)-reducing bacterium

A new, phylogenetically distinct, dissimilatory, Fe(III)-reducing bacterium was isolated from surface sediment of a hydrocarbon-contaminated ditch. The isolate, designated strain PAL-1, was an obligately anaerobic, non-fermentative, motile, gram-negative vibrio. PAL-1 grew in a defined medium with acetate as electron donor and ferric pyrophosphate, ferric oxyhydroxide, ferric citrate, Co(III)-EDTA, or elemental sulfur as sole electron acceptor. PAL-1 also used proline, hydrogen, lactate, propionate, succinate, fumarate, pyruvate, or yeast extract as electron donors for Fe(III) reduction. It is the first bacterium known to couple the oxidation of an amino acid to Fe(III) reduction. PAl-1 did not reduce oxygen, Mn(IV), U(VI), Cr(VI), nitrate, sulfate, sulfite, or thiosulfate with acetate as the electron donor. Cell suspensions of PAL-1 exhibited dithionite-reduced minus air-oxidized difference spectra that were characteristic of c-type cytochromes. Analysis of the 16S rRNA gene sequence of PAL-1 showed that the strain is not related to any of the described metal-reducing bacteria in the Proteobacteria and, together with Flexistipes sinusarabici, forms a separate line of descent within the Bacteria. Phenotypically and phylogenetically, strain PAl-1 differs from all other described bacteria, and represents the type strain of a new genus and species, Geovibrio ferrireducens. Received: 26 September 1995 / Accepted: 28 February 1996     

异化铁还原细菌LQ25还原重金属Cr (VI)的特性研究

[背景] 异化铁还原细菌能够在还原Fe （III）的同时将毒性较大的Cr （VI）还原成毒性较小的Cr （III）,解决铬污染的问题。[目的] 基于丁酸梭菌（Clostridium butyricum） LQ25异化铁还原过程制备生物磁铁矿,开展异化铁还原细菌还原Cr （VI）的特性研究。[方法] 构建以氢氧化铁为电子受体和葡萄糖为电子供体的异化铁培养体系。菌株LQ25培养结束时制备生物磁铁矿。设置不同初始Cr （VI）浓度（5、10、15、25和30 mg/L）,分别测定菌株LQ25对Cr （VI）还原效率以及生物磁铁矿对Cr （VI）的还原效率。[结果] 菌株LQ25在设置的Cr （VI）浓度范围内都能良好生长。当Cr （VI）浓度为15 mg/L时,在异化铁培养条件下,菌株LQ25对Cr （VI）的还原率为63.45%±5.13%,生物磁铁矿对Cr （VI）的还原率为87.73%±9.12%,相比菌株还原Cr （VI）的效率提高38%。pH变化能影响生物磁铁矿对Cr （VI）的还原率,当pH 2.0时,生物磁铁矿对Cr （VI）的还原率最高,几乎达到100%。电子显微镜观察发现生物磁铁矿表面有许多孔隙,X-射线衍射图谱显示生物磁铁矿中Fe （II）的存在形式是Fe （OH）₂。[结论] 基于异化铁还原细菌制备生物磁铁矿可用于还原Cr （VI）,这是一种有效去除Cr （VI）的途径。     

Diversity of Culturable Bacteria,from the Anaerobic Zone of the Meromictic Lake Pavin,Able to Perform Dissimilatory-Iron Reduction in Different in Vitro Conditions

A culture-dependent study was performed with the aim of assessing the carbon, electron and Fe(III) sources used for the dissimilatory Fe(III) reduction pathway and the diversity of culturable Fe(III)-reducers in the anoxic zone of the meromictic Lake Pavin. This metabolic pathway was investigated in enrichment cultures inoculated with water samples collected at 70 m depth in the anoxic zone of Lake Pavin. Combinations of different media, organic acids, and incubation gas phases were performed. The potential for Fe(III) reduction in the different growth conditions was assessed by measuring the accumulation of Fe(II) overtime. Bacterial community structure was determined in each growth conditions by Temporal Temperature gradient Gel Electrophoresis (TTGE) profiles of 16S rDNA genes and bands of interest in positive enrichments were sequenced. Comparisons of bacterial community structure between growth conditions revealed that the electron donor, the basal media as well as the Fe(III) source yielded to the selection of different bacterial populations, suggesting that Fe(III) reducers occupy different ecological niches in the anoxic zone of Lake Pavin. Facultative Fe(III) reducers, such as fermentative (e.g., Pseudomonas, Clostridium) and sulphate-reducing (e.g., Desulfovibrio sp.) bacteria, were retrieved in enrichments but well-known obligatory Fe(III) reducers (e.g., Geobacter) were not detected. A greater Fe(III) reduction was noted under H₂:CO₂ gas phase, suggesting that H₂ is used as an electron donor for Fe(III) reduction. Acetate was not used as a precursor for this terminal electron-accepting process, and a high Fe(III) reduction was observed with fumarate provided as the electron donor and carbon sources suggesting that this metabolite may be energetically more beneficial for Fe(III)-reducers.     

Anaerobic Oxidation of [1,2-14C]Dichloroethene under Mn(IV)-Reducing Conditions

Anaerobic oxidation of [1,2-¹⁴C]dichloroethene to ¹⁴CO₂ under Mn(IV)-reducing conditions was demonstrated. The results indicate that oxidative degradation of partially chlorinated solvents like dichloroethene can be significant even under anoxic conditions and demonstrate the potential importance of Mn(IV) reduction for remediation of chlorinated groundwater contaminants.     

Arsenite Oxidation Using Biogenic Manganese Oxides Produced by a Deep-Sea Manganese-Oxidizing Bacterium,Marinobacter sp. MnI7-9

Marinobacter sp. MnI7-9, a deep-sea manganese [Mn(II)]-oxidizing bacterium isolated from the Indian Ocean, showed a high resistance to Mn(II) and other metals or metalloids and high Mn(II) oxidation/removal abilities. This strain was able to grow well when the Mn(II) concentration reached up to 10 mM, and at that concentration, 76.4% of the added Mn(II) was oxidized and 23.4% of the Mn(II) was adsorbed by the generated biogenic Mn oxides (total 99.9% Mn removal). Scanning electron microscope observation and X-ray diffraction analysis showed that the biogenic Mn oxides were in stick shapes, adhered to the cell surface, and contained two typical crystal structures of γ-MnOOH and δ-MnO₂. In addition, the biogenic Mn oxides generated by strain MnI7-9 showed abilities to oxidize the highly toxic As(III) to the less toxic As(V), in both co-culture and after-collection systems. In the co-culture system containing 10 mM Mn(II) and 55 μM As(III), the maximum percentage of As(III) oxidation was 83.5%. In the after-collection system using the generated biogenic Mn oxides, 90% of the As(III) was oxidized into As(V), and the concentration of As(III) decreased from 55.02 to 5.55 μM. This study demonstrates the effective bioremediation by a deep-sea Mn(II)-oxidizing bacterium for the treatment of As-containing water and increases the knowledge of deep-sea bacterial Mn(II) oxidation mechanisms. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the supplemental file.     

A Hydrogen-Oxidizing, Fe(III)-Reducing Microorganism from the Great Bay Estuary, New Hampshire

A dissimilatory Fe(III)- and Mn(IV)-reducing bacterium was isolated from bottom sediments of the Great Bay estuary, New Hampshire. The isolate was a facultatively anaerobic gram-negative rod which did not appear to fit into any previously described genus. It was temporarily designated strain BrY. BrY grew anaerobically in a defined medium with hydrogen or lactate as the electron donor and Fe(III) as the electron acceptor. BrY required citrate, fumarate, or malate as a carbon source for growth on H₂ and Fe(III). With Fe(III) as the sole electron acceptor, BrY metabolized hydrogen to a minimum threshold at least 60-fold lower than the threshold reported for pure cultures of sulfate reducers. This finding supports the hypothesis that when Fe(III) is available, Fe(III) reducers can outcompete sulfate reducers for electron donors. Lactate was incompletely oxidized to acetate and carbon dioxide with Fe(III) as the electron acceptor. Lactate oxidation was also coupled to the reduction of Mn(IV), U(VI), fumarate, thiosulfate, or trimethylamine n-oxide under anaerobic conditions. BrY provides a model for how enzymatic metal reduction by respiratory metal-reducing microorganisms has the potential to contribute to the mobilization of iron and trace metals and to the immobilization of uranium in sediments of Great Bay Estuary.     

Evidence for rapid microscale bacterial redox cycling of iron in circumneutral environments

The potential for microscale bacterial Fe redox cycling was investigated in microcosms containing ferrihydrite-coated sand and a coculture of a lithotrophic Fe(II)-oxidizing bacterium (strain TW2) and a dissimilatory Fe(III)-reducing bacterium (Shewanella alga strain BrY). The Fe(II)-oxidizing organism was isolated from freshwater wetland surface sediments which are characterized by steep gradients of dissolved O₂ and high concentrations of dissolved and solid-phase Fe(II) within mm of the sediment–water interface, and which support comparable numbers (10⁵–10⁶ mL⁻¹) of culturable Fe(II)-oxidizing and Fe(III)-reducing reducing. The coculture systems showed minimal Fe(III) oxide accumulation at the sand-water interface, despite intensive O₂ input from the atmosphere and measurable dissolved O₂ to a depth of 2 mm below the sand–water interface. In contrast, a distinct layer of oxide precipitates formed in systems containing Fe(III)-reducing bacteria alone. Examination of materials from the cocultures by fluorescence in situ hybridization indicated close physical juxtapositioning of Fe(II)-oxidizing and Fe(III)-reducing bacteria in the upper few mm of sand. Our results indicate that Fe(II)-oxidizing bacteria have the potential to enhance the coupling of Fe(II) oxidation and Fe(III) reduction at redox interfaces, thereby promoting rapid microscale cycling of Fe. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Synergistic Effects of High Nitrate Concentrations on Sediment Bioreduction

Groundwaters at nuclear sites can be characterized by low pH and high nitrate concentrations (10–100 mM). These conditions are challenging for bioremediation, often inhibiting microbial Fe(III)-reduction which can limit radionuclide migration. Here, sediment microcosms representative of the UK Sellafield site were used to study the influence of variable pH and nitrate concentrations on microbially-mediated TEAP (terminal electron accepting processes) progression. The rate of reduction through the terminal electron accepting cascade NO^? ₃ > NO^? ₂ > Mn(IV)/Fe(III) > SO^2? ₄ at low pH (～5.5) was slower than that in bicarbonate buffered systems (pH ～ 7.0), but in the low pH systems, denitrification and associated pH buffering resulted in conditioning of the sediments for subsequent Fe(III) and sulfate-reduction. Under very high nitrate conditions (100 mM), bicarbonate buffering (pH ～ 7.0) was necessary for TEAP progression beyond denitrification and the reduction of 100 mM nitrate created alkaline conditions (pH 9.5). 16S rRNA gene analysis showed that close relatives of known nitrate reducers Bacillus niacini and Ochrobactrum grignonense dominated the microbial communities in this reduced sediment. In Fe(III)-reducing enrichment cultures from the 100 mM nitrate system, close relatives of the Fe(III)-reducing species Alkaliphilus crotonatoxidans and Serratia liquifaciens were observed. These results highlight that under certain conditions and contrary to expectations, denitrification may support bioreduction via pH conditioning for optimal metal reduction and radionuclide immobilization.     

Biodegradation of methidathion by Serratia sp. in pure cultures using an orthogonal experiment design, and its application in detoxification of the insecticide on crops

An enrichment culture method was applied to the isolation of a bacterial strain responsible for biodegradation of methidathion residues, from a methidathion-treated orchard. The strain (SPL-2) was identified as Serratia sp. according to its physiological characteristics and 16S rRNA gene phylogenetic analysis. Serratia sp. was able to grow in a poor medium consisting of mineral salts and using methidathion as the sole carbon source at a concentrations of 50–150 mg/L. The effects of multifactors on degradation of methidathion in pure cultures by Serratia sp. were investigated using an orthogonal experimental design L₉ (3⁴). On the basis of range analysis and ANOVA results, the most significant factors were temperature and inoculum size. The optimal conditions for methidathion biodegradation in pure cultures were a temperature in 30 °C, an inoculum size of 10 %, pH?=?7 and an aeration rate of 200 rpm. Two different concentrations of strain SPL-2 fermenting liquids (OD₆₀₀?=?0.2 and OD₆₀₀?=?0.4) were prepared and applied to remove methidathion residues from agricultural products, and this process can be described by a first order rate model. In contrast to controls, the DT₅₀ of methidathion was shortened by 35.7 %, 8.2 % and by 62.3 %, 57.5 % on OD₆₀₀?=?0.2 and OD₆₀₀?=?0.4 treated haricot beans and peaches, respectively. These results suggest that the isolated bacterial strain may have potential for use in bioremediation of methidathion-contaminated crops.     

Metal Reduction at Low pH by a Desulfosporosinus species: Implications for the Biological Treatment of Acidic Mine Drainage

We isolated an acid-tolerant sulfate-reducing bacterium, GBSRB4.2, from coal mine-derived acidic mine drainage (AMD)-derived sediments. Sequence analysis of partial 16S rRNA gene of GBSRB4.2 revealed that it was affiliated with the genus Desulfosporosinus. GBSRB4.2 reduced sulfate, Fe(III) (hydr)oxide, Mn(IV) oxide, and U(VI) in acidic solutions (pH 4.2). Sulfate, Fe(III), and Mn(IV) but not U(VI) bioreduction led to an increase in the pH of acidic solutions and concurrent hydrolysis and precipitation of dissolved Al³⁺. Reduction of Fe(III), Mn(IV), and U(VI) in sulfate-free solutions revealed that these metals are enzymatically reduced by GBSRB4.2. GBSRB4.2 reduced U(VI) in groundwater from a radionuclide-contaminated aquifer more rapidly at pH 4.4 than at pH 7.1, possibly due to the formation of poorly bioreducible Ca-U(VI)-CO₃ complexes in the pH 7.1 groundwater.     

Alkaline iron(III) reduction by a novel alkaliphilic,halotolerant, <Emphasis Type="Italic">Bacillus</Emphasis> sp. isolated from salt flat sediments of Soap Lake

A halotolerant, alkaliphilic dissimilatory Fe(III)-reducing bacterium, strain SFB, was isolated from salt flat sediments collected from Soap Lake, WA. 16S ribosomal ribonucleic acid gene sequence analysis identified strain SFB as a novel Bacillus sp. most similar to Bacillus agaradhaerens (96.7% similarity). Strain SFB, a fermentative, facultative anaerobe, fermented various hexoses including glucose and fructose. The fructose fermentation products were lactate, acetate, and formate. Under fructose-fermenting conditions in a medium amended with Fe(III), Fe(II) accumulated concomitant with a stoichiometric decrease in lactate and an increase in acetate and CO₂. Strain SFB was also capable of respiratory Fe(III) reduction with some unidentified component(s) of Luria broth as an electron donor. In addition to Fe(III), strain SFB could also utilize nitrate, fumarate, or O₂ as alternative electron acceptors. Optimum growth was observed at 30°C and pH 9. Although the optimal salinity for growth was 0%, strain SFB could grow in a medium with up to 15% NaCl by mass. These studies describe a novel alkaliphilic, halotolerant organism capable of dissimilatory Fe(III) reduction under extreme conditions and demonstrate that Bacillus species can contribute to the microbial reduction of Fe(III) in environments at elevated pH and salinity, such as soda lakes.     

Inhibition of nitrous oxide reduction in forest soil microcosms by different forms of methanobactin

Copper plays a critical role in controlling greenhouse gas emissions as it is a key component of the particulate methane monooxygenase and nitrous oxide reductase. Some methanotrophs excrete methanobactin (MB) that has an extremely high copper affinity. As a result, MB may limit the ability of other microbes to gather copper, thereby decreasing their activity as well as impacting microbial community composition. Here, we show using forest soil microcosms that multiple forms of MB; MB from Methylosinus trichosporium OB3b (MB-OB3b) and MB from Methylocystis sp. strain SB2 (MB-SB2) increased nitrous oxide (N₂O) production as well caused significant shifts in microbial community composition. Such effects, however, were mediated by the amount of copper in the soils, with low-copper soil microcosms showing the strongest response to MB. Furthermore, MB-SB2 had a stronger effect, likely due to its higher affinity for copper. The presence of either form of MB also inhibited nitrite reduction and generally increased the presence of genes encoding for the iron-containing nitrite reductase (nirS) over the copper-dependent nitrite reductase (nirK). These data indicate the methanotrophic-mediated production of MB can significantly impact multiple steps of denitrification, as well as have broad effects on microbial community composition of forest soils.     

Aerobic reduction of manganese oxide by Salmonella sp. strain MR4

A new isolate of Salmonella, strain MR4, reduced Mn(IV)O₂ at 2.3 mM under aerobic conditions by about 83% over 24 h. Direct contact of cells to MnO₂ was not necessary as the cell-free spent medium produced a similar amount of Mn(II). Pyruvate (1.6 mM) and oxalate (0.8 mM) were identified in the culture medium and presumed to have a role in Mn(II) production in this microorganism.