Li Zhuang

Manganese dioxide as an alternative cathodic catalyst to platinum in microbial fuel cells.

In this paper, three manganese dioxide materials, alpha-MnO(2), beta-MnO(2), gamma-MnO(2) were tested as alternative cathodic catalysts to platinum (Pt) in air-cathode microbial fuel cells (MFCs). Prepared via hydrothermal method, the manganese dioxides were characterized by X-ray powder diffraction patterns (XRD), the Brunauer-Emmett-Teller (BET) method and their average oxidation states (AOS) were determined by the potential voltammetric titration method. The electro-catalytic activity of MnO(2) in neutral pH solution was determined by linear sweep voltammetry (LSV) and the results showed that all manganese dioxides can catalyze oxygen reduction reaction (ORR) in neutral medium with different catalytic activities. beta-MnO(2) appeared to hold the highest catalytic activity due to its highest BET surface area and AOS. Beta-MnO(2) was further used as cathode catalyst in both cube and tube air-cathode MFCs, in which using Klebsiella pneumoniae (K. pneumoniae) biofilm as biocatalyst and utilizing glucose as a substrate in the anode chamber. It was found that tube MFC produced higher output power, with the maximum volumetric power density of 3773+/-347 mW/m(3), than cube MFC. This study suggests that using beta-MnO(2) instead of Pt could potentially improve the feasibility of scaling up MFC designs for real applications by lowering production cost.

Membrane-less cloth cathode assembly (CCA) for scalable microbial fuel cells

One of the main challenges for scaling up microbial fuel cell (MFC) technologies is developing low-cost cathode architectures that can generate high power output. This study developed a simple method to convert non-conductive material (canvas cloth) into an electrically conductive and catalytically active cloth cathode assembly (CCA) in one step. The membrane-less CCA was simply constructed by coating the cloth with conductive paint (nickel-based or graphite-based) and non-precious metal catalyst (MnO(2)). Under the fed-batch mode, the tubular air-chamber MFCs equipped with Ni-CCA and graphite-CCA generated the maximum power densities of 86.03 and 24.67 mW m(-2) (normalized to the projected cathode surface area), or 9.87 and 2.83 W m(-3) (normalized to the reactor liquid volume), respectively. The higher power output of Ni-CCA-MFC was associated with the lower volume resistivity of Ni-CCA (1.35 x 10(-2)Omega cm) than that of graphite-CCA (225 x 10(-2)Omega cm). At an external resistance of 100 Omega, Ni-CCA-MFC and graphite-CCA-MFC removed approximately 95% COD in brewery wastewater within 13 and 18d, and achieved coulombic efficiencies of 30.2% and 19.5%, respectively. The accumulated net water loss through the cloth by electro-osmotic drag exhibited a linear correlation (R(2)=0.999) with produced coulombs. With a comparable power production, such CCAs only cost less than 5% of the previously reported membrane cathode assembly. The new cathode configuration here is a mechanically durable, economical system for MFC scalability.

Thauera humireducens sp. nov., a humus-reducing bacterium isolated from a microbial fuel cell.

A Gram-negative, rod-shaped, non-spore-forming bacterium, designated SgZ-1(T), was isolated from the anode biofilm of a microbial fuel cell. The strain had the ability to grow under anaerobic condition via the oxidation of various organic compounds coupled to the reduction of anthraquione-2,6-disulfonate (AQDS) to anthrahydroquinone-2,6-disulfonate (AHQDS). Growth occurred in TSB in the presence of 0-5.5u200a% (w/v) NaCl (optimum 0-1u200a%), at 10-45 °C (optimum 25-37 °C) and at pH 6.0-10.0 (optimum 8.0-8.5). Based on 16S rRNA gene sequence similarity, strain SgZ-1(T) belonged to the genus Thauera. The highest level of 16S rRNA gene sequences similarity (96.7u200a%) was found to be with Thauera aminoaromatica S2(T) and Thauera selenatis AX(T), and lower values were obtained when compared with other recognized Thauera species. Chemotaxonomic analysis revealed that strain SgZ-1(T) contained Q-8 as the predominant quinone, and putrescine and 2-hydroxyputrescine as the major polyamines. The major cellular fatty acids (>5u200a%) were C16u200a:u200a1ω6c and/or C16u200a:u200a1ω7c (44.6u200a%), C16u200a:u200a0 (18.8u200a%), and C18u200a:u200a1ω6c and/or C18u200a:u200a1ω7c (12.7u200a%). Based on its phenotypic and phylogenetic properties, chemotaxonomic analysis and the results of physiological and biochemical tests, strain SgZ-1(T) (u200a=u200aKACC 16524(T)u200a=u200aCCTCC M 2011497(T)) was designated the type strain of a novel species of the genus Thauera, for which the name Thauera humireducens sp. nov. was proposed.

Azospirillum humicireducens sp. nov., a nitrogen-fixing bacterium isolated from a microbial fuel cell.

A Gram-negative, facultative anaerobic, motile, spiral, straight-to-slightly curved rod-shaped and nitrogen-fixing strain, designated SgZ-5(T), was isolated from a microbial fuel cell (MFC) and was characterized by means of a polyphasic approach. Growth occurred with 0-1 % (w/v) NaCl (optimum 1 %) and at pH 5.5-8.5 (optimum pH 7.2) and at 25-37 °C (optimum 30 °C) in nutrient broth (NB). The strain had the ability to grow under anaerobic conditions via the oxidation of various organic compounds coupled to the reduction of anthraquione-2,6-disulfonate (AQDS). Chemotaxonomic characteristics (main ubiquinone Q-10, major fatty acid C18 : 1ω7c/C18 : 1ω6c and DNA G+C content 67.7 mol%) were similar to those of members of the genus Azospirillum. According to the results of phylogenetic analyses, strain SgZ-5(T) belonged to the genus Azospirillum within the family Rhodospirillaceae of the class Alphaproteobacteria, and was related most closely to the type strains of Azospirillum lipoferum, Azospirillum thiophilum and Azospirillum oryzae (98.0, 97.6 and 97.1 % 16S rRNA gene sequence similarity, respectively). DNA-DNA pairing studies showed that the unidentified organism displayed reassociation values of 36.7 ± 3.7, 24.1 ± 2.2 and 22.3 ± 2.4 % to the type strains of A. lipoferum, A. thiophilum and A. oryzae, respectively. Similarities between nifH gene sequences of strain SgZ-5(T) and members of the genus Azospirillum ranged from 94.0 to 97.0 %. A combination of phenotypic, chemotaxonomic, phylogenetic and genotypic data clearly indicated that strain SgZ-5(T) represents a novel species, for which the name Azospirillum humicireducens sp. nov. is proposed. The type strain is SgZ-5(T) ( = CCTCC AB 2012021(T) = KACC 16605(T)).

Secondary Mineralization of Ferrihydrite Affects Microbial Methanogenesis in Geobacter-Methanosarcina Cocultures

ABSTRACT The transformation of ferrihydrite to stable iron oxides over time has important consequences for biogeochemical cycling of many metals and nutrients. The response of methanogenic activity to the presence of iron oxides depends on the type of iron mineral, but the effects of changes in iron mineralogy on methanogenesis have not been characterized. To address these issues, we constructed methanogenic cocultures of Geobacter and Methanosarcina strains with different ferrihydrite mineralization pathways. In this system, secondary mineralization products from ferrihydrite are regulated by the presence or absence of phosphate. In cultures producing magnetite as the secondary mineralization product, the rates of methanogenesis from acetate and ethanol increased by 30.2% and 135.3%, respectively, compared with a control lacking ferrihydrite. Biogenic magnetite was proposed to promote direct interspecies electron transfer between Geobacter and Methanosarcina in a manner similar to that of c-type cytochrome and thus facilitate methanogenesis. Vivianite biomineralization from ferrihydrite in the presence of phosphate did not significantly influence the methanogenesis processes. The correlation between magnetite occurrence and facilitated methanogenesis was supported by increased rates of methane production from acetate and ethanol with magnetite supplementation in the defined cocultures. Our data provide a new perspective on the important role of iron biomineralization in biogeochemical cycling of carbon in diverse anaerobic environments. IMPORTANCE It has been found that microbial methanogenesis is affected by the presence of iron minerals, and their influences on methanogenesis are associated with the mineralogical properties of the iron minerals. However, how changes in iron mineralogy affect microbial methanogenesis has not been characterized. To address this issue, we constructed methanogenic cocultures of Geobacter and Methanosarcina strains with different ferrihydrite mineralization pathways. The experimental results led to two contributions, i.e., (i) the transformation of iron minerals might exert an important influence on methanogenesis under anaerobic conditions and (ii) both biogenic and chemical magnetite can accelerate syntrophic ethanol oxidization between Geobacter metallireducens and Methanosarcina barkeri. This study sheds new light on the important role of iron biomineralization in the biogeochemical cycling of carbon in diverse anaerobic environments, particularly in iron-rich natural and agricultural wetland soils.

Fontibacter ferrireducens sp. nov., an Fe(III)-reducing bacterium isolated from a microbial fuel cell.

A novel, dissimilatory Fe(III)-reducing bacterium, designated strain SgZ-2(T), which could couple glucose oxidation to iron reduction for energy conservation, was isolated from a microbial fuel cell. The isolate was Gram-staining-negative, catalase-positive, oxidase-negative and facultatively anaerobic. The strain was able to grow on tryptic soy agar at 15-37 °C and in the presence of 0-5u200a% (w/v) NaCl. The predominant cellular fatty acids (>5u200a%) were iso-C15u200a:u200a0, iso-C17u200a:u200a0 3-OH and iso-C17u200a:u200a1ω9c; the major respiratory quinone was MK-7; the major polar lipids were phosphatidylethanolamine, an unidentified aminolipid and three other unidentified lipids; and the DNA G+C content was 55.3 mol%. Phylogenetic analyses based on 16S rRNA sequences showed that the novel strain was most closely related to Fontibacter flavus CC-GZM-130(T) (99.9u200a% sequence similarity), and was a member of the family Cyclobacteriaceae. The levels of DNA-DNA relatedness observed between strain SgZ-2(T) and F. flavus CCM 7650(T) (<41u200a%) indicated that the two strains represented two distinct species. Based on phylogenetic analyses and phenotypic characteristics, strain SgZ-2(T) represents a novel species of the genus Fontibacter, for which the name Fontibacter ferrireducens sp. nov. is proposed. The type strain is SgZ-2(T) (u200a=u200aCCTCC M 2011498(T) u200a=u200aKACC 16525(T)).

Oceanobacillus luteolus sp. nov., isolated from soil.

Two Gram-stain-positive, rod-shaped and endospore-forming bacteria, designated WM-1T and WM-4, were isolated from a paddy soil and a forest soil, respectively, in South China. Comparative 16S rRNA gene sequence analyses showed that both strains were members of the genus Oceanobacillus and most closely related to Oceanobacillus chironomi LMG 23627T with pairwise sequence similarity of 96.0%. The isolates contained menaquinone-7 (MK-7) as the respiratory quinone and anteiso-C15:0, anteiso-C17:0 and iso-C15:0 as the major fatty acids (>10%). Polar lipids consisted of a predominance of diphosphatidylglycerol and moderate to minor amounts of phosphatidylglycerol and phosphatidylinositol. The cell-wall peptidoglycan contained meso-diaminopimelic acid. The DNA G+C content was 38.6-39.2 mol%. The 16S rRNA gene sequence of strain WM-1T displayed 99.7u200a% similarity to that of strain WM-4, and DNA-DNA hybridization between the two strains showed a relatedness value of 91u200a%. Based on the results of this polyphasic study, strains WM-1T and WM-4 represent a novel species in the genus Oceanobacillus, for which the name Oceanobacillus luteolus sp. nov. is proposed. The type strain is WM-1T (=KCTC 33119T=CGMCC 1.12406T).

Complete genome of Thauera humireducens SgZ-1, a potential bacterium for environmental remediation and wastewater treatment

Thauera humireducens SgZ-1(T) (KACC 16524(T)=CCTCC M2011497(T)), isolated from the anode biofilm of a microbial fuel cell, is able to grow under anaerobic conditions via the oxidation of various organic compounds coupled to the reduction of humus, Fe(III) species and nitrate. Addtionally, the strain has the ability to produce exopolysaccharide (EPS). Here, we report the complete genome sequence of T. humiruducens SgZ-1(T), which is relevant to metabolism of electron donors and acceptors for environmental remediation and wastewater treatment.

Bacillus nitroreducens sp. nov., a humus-reducing bacterium isolated from a compost.

A Gram-staining-positive, facultative anaerobic, motile and rod-shaped bacterium, designated GSS08T, was isolated from a windrow compost pile and characterized by means of a polyphasic approach. Growth occurred with 0–4xa0% (w/v) NaCl (optimum 1xa0%), at pH 6.5–9.5 (optimum pH 7.5) and at 20–45xa0°C (optimum 37xa0°C). Anaerobic growth occurred with anthraquinone-2,6-disulphonate, fumarate and NO3− as electron acceptor. The main respiratory quinone was MK-7. The predominant polar lipids were diphosphatidylglycerol and phosphatidylethanolamine. The major fatty acids (>5xa0%) were iso-C15:0 (43.1xa0%), anteiso-C15:0 (27.4xa0%) and iso-C16:0 (8.3xa0%). The DNA Gxa0+xa0C content was 39.6xa0mol%. The phylogenetic analysis based on 16S rRNA gene sequences revealed that strain GSS08T formed a phyletic lineage with the type strain of Bacillus humi DSM 16318T with a high sequence similarity of 97.5xa0%, but it displayed low sequence similarity with other valid species in the genus Bacillus (<96.0xa0%). The DNA–DNA relatedness between strains GSS08T and B. humi DSM 16318T was 50.8xa0%. The results of phenotypic, chemotaxonomic and genotypic analyses clearly indicated that strain GSS08T represents a novel species, for which the name Bacillus nitroreducens sp. nov. is proposed. The type strain is GSS08T (=KCTC 33699Txa0=xa0MCCC 1K01091T).

Bacillus dabaoshanensis sp. nov., a Cr(VI)-tolerant bacterium isolated from heavy-metal-contaminated soil

A Cr(VI)-tolerant, Gram-staining-positive, rod-shaped, endospore-forming and facultative anaerobic bacterium, designated as GSS04T, was isolated from a heavy-metal-contaminated soil. Strain GSS04T was Cr(VI)-tolerant with a minimum inhibitory concentration of 600xa0mgxa0l−1 and was capable of reducing Cr(VI) under both aerobic and anaerobic conditions. Growth occurred with presence of 0–3xa0% (w/v) NaCl (optimum 1xa0%), at pH 5.5–10.0 (optimum pH 7.0) and 15–50xa0°C (optimum 30–37xa0°C). The main respiratory quinone was MK-7 and the major fatty acids were anteiso-C15:0 and iso-C15:0. The DNA G+C content was 41.1xa0mol%. The predominant polar lipid was diphosphatidylglycerol. Based on 16S rRNA gene sequence similarity, the closest phylogenetic relative was Bacillus shackletonii DSM 18868T (97.6xa0%). The DNA–DNA hybridization between GSS04T and its closest relatives revealed low relatedness (<70xa0%). The results of phenotypic, chemotaxonomic and genotypic analyses clearly indicated that strain GSS04T represents a novel species of the genus Bacillus, for which the name Bacillus dabaoshanensis sp. nov. is proposed. The type strain is GSS04T (=CCTCC AB 2013260Txa0=xa0KCTC 33191T).