Absence Of Electron Acceptors Research Articles

Supplementation with Amino Acid Sources Facilitates Fermentative Growth of Shewanella oneidensis MR-1 in Defined Media.

Shewanella oneidensis MR-1 is a facultative anaerobe that grows by respiration using a variety of electron acceptors. This organism serves as a model to study how bacteria thrive in redox-stratified environments. A glucose-utilizing engineered derivative of MR-1 has been reported to be unable to grow in glucose minimal medium (GMM) in the absence of electron acceptors, despite this strain having a complete set of genes for reconstructing glucose to lactate fermentative pathways. To gain insights into why MR-1 is incapable of fermentative growth, this study examined a hypothesis that this strain is programmed to repress the expression of some carbon metabolic genes in the absence of electron acceptors. Comparative transcriptomic analyses of the MR-1 derivative were conducted in the presence and absence of fumarate as an electron acceptor, and these found that the expression of many genes involved in carbon metabolism required for cell growth, including several tricarboxylic acid (TCA) cycle genes, was significantly downregulated in the absence of fumarate. This finding suggests a possibility that MR-1 is unable to grow fermentatively on glucose in minimal media owing to the shortage of nutrients essential for cell growth, such as amino acids. This idea was demonstrated in subsequent experiments that showed that the MR-1 derivative fermentatively grows in GMM containing tryptone or a defined mixture of amino acids. We suggest that gene regulatory circuits in MR-1 are tuned to minimize energy consumption under electron acceptor-depleted conditions, and that this results in defective fermentative growth in minimal media. IMPORTANCE It is an enigma why S. oneidensis MR-1 is incapable of fermentative growth despite having complete sets of genes for reconstructing fermentative pathways. Understanding the molecular mechanisms behind this defect will facilitate the development of novel fermentation technologies for the production of value-added chemicals from biomass feedstocks, such as electro-fermentation. The information provided in this study will also improve our understanding of the ecological strategies of bacteria living in redox-stratified environments.

Fundidesulfovibrio magnetotacticus sp. nov., a sulphate-reducing magnetotactic bacterium, isolated from sediments and freshwater of a pond.

A sulphate-reducing magnetotactic bacterium, designated strain FSS-1T, was isolated from sediments and freshwater of Suwa Pond located in Hidaka, Saitama, Japan. Strain FSS-1T was a motile, Gram-negative and curved rod-shaped bacterium that synthesizes bullet-shaped magnetite (Fe3O4) nanoparticles in each cell. Strain FSS-1T was able to grow in the range of pH 6.5-8.0 (optimum, pH 7.0), 22-34 °C (optimum, 28 °C) and with 0-8.0 g l-1 NaCl (optimum, 0-2.0 g l-1 NaCl). Strain FSS-1T grew well in the presence of 50 µM ferric quinate as an iron source. The major fatty acids were anteiso-C15 : 0, iso-C15 : 0 and anteiso-C17 : 0. The major menaquinone was MK-7 (H2). Strain FSS-1T contained desulfoviridin, cytochrome c 3 and catalase, but did not contain oxidase. Strain FSS-1T used fumarate, lactate, pyruvate, malate, formate/acetate, succinate, tartrate, ethanol, 1-propanol, peptone, soytone and yeast extract as electron donors, while the strain used sulphate, thiosulphate and fumarate as electron acceptors. Fumarate was fermented in the absence of electron acceptors. Analysis of the 16S rRNA gene sequence showed that strain FSS-1T is a member of the genus Fundidesulfovibrio. The gene sequence showed 96.7, 95.0, 92.0, 91.2 and 91.4% similarities to the most closely related members of the genera Fundidesulfovibrio putealis B7-43T, Fundidesulfovibrio butyratiphilus BSYT, Desulfolutivibrio sulfoxidireducens DSM 107105T, Desulfolutivibrio sulfodismutans ThAc01T and Solidesulfovibrio magneticus RS-1T, respectively. The DNA G+C content of strain FSS-1T was 67.5 mol%. The average nucleotide identity value between strain FSS-1T and F. putealis B7-43T was 80.7 %. Therefore, strain FSS-1T represents a novel species within the genus Fundidesulfovibrio, for which the name Fundidesulfovibrio magnetotacticus sp. nov. is proposed (=JCM 32405T=DSM 110007T).

Insights on the (Auto)Photocatalysis of Ferritin.

Traditionally, ferritin has been considered a photocatalyst capable of photo-oxidizing organic molecules and transferring electrons to external electron acceptors when irradiated by UV-visible light. We have designed new approaches to resolve the uncertainties regarding its photocatalytical mechanism. Experiments with an Fe(II) chelator, an electrochromic indicator, and recombinant ferritin proteins indicate that the excited electrons at the conduction band of the ferritin core do not cross the protein shell. Instead, irradiation causes the electrons to reduce the ferrihydrite core to produce Fe(II) ions. These Fe(II) ions exit the protein shell to reduce electron acceptors. In the absence of electron acceptors or chelators, Fe(II) re-enters ferritin.

Assessment of the Carbon Monoxide Metabolism of the Hyperthermophilic Sulfate-Reducing Archaeon Archaeoglobus fulgidus VC-16 by Comparative Transcriptome Analyses.

The hyperthermophilic, sulfate-reducing archaeon, Archaeoglobus fulgidus, utilizes CO as an energy source and it is resistant to the toxic effects of high CO concentrations. Herein, transcription profiles were obtained from A. fulgidus during growth with CO and sulfate or thiosulfate, or without an electron acceptor. This provided a basis for a model of the CO metabolism of A. fulgidus. The model suggests proton translocation by “Mitchell-type” loops facilitated by Fqo catalyzing a Fdred:menaquinone oxidoreductase reaction, as the major mode of energy conservation, rather than formate or H2 cycling during respiratory growth. The bifunctional CODH (cdhAB-2) is predicted to play an ubiquitous role in the metabolism of CO, and a novel nitrate reductase-associated respiratory complex was induced specifically in the presence of sulfate. A potential role of this complex in relation to Fdred and APS reduction is discussed. Multiple membrane-bound heterodisulfide reductase (DsrMK) could promote both energy-conserving and non-energy-conserving menaquinol oxidation. Finally, the FqoF subunit may catalyze a Fdred:F420 oxidoreductase reaction. In the absence of electron acceptor, downregulation of F420H2 dependent steps of the acetyl-CoA pathway is linked to transient formate generation. Overall, carboxidotrophic growth seems as an intrinsic capacity of A. fulgidus with little need for novel resistance or respiratory complexes.

Dissolved Organic Carbon in Groundwater Overlain by Irrigated Sugarcane.

Elevated dissolved organic carbon (DOC) has been detected in groundwater beneath irrigated sugarcane on the Burdekin coastal plain of tropical northeast Australia. The maximum value of 82 mg/L is to our knowledge the highest DOC reported for groundwater beneath irrigated cropping systems. More than half of the groundwater sampled in January 2004 (n = 46) exhibited DOC concentrations greater than 30 mg/L. DOC was progressively lower in October 2004 and January 2005, with a total decrease greater than 90% indicating varying load(s) to the aquifer. It was hypothesized that the elevated DOC found in this groundwater system is sourced at or near the soil surface and supplied to the aquifer via vertical recharge following above average rainfall. Possible sources of DOC include organic-rich sugar mill by-products applied as fertilizer and/or sugarcane sap released during harvest. CFC-12 vertical flow rates supported the hypothesis that elevated DOC (>40 mg/L) in the groundwater results from recharge events in which annual precipitation exceeds 1500 mm/year (average = 960 mm/year). Occurrence of elevated DOC concentrations, absence of electron acceptors (O2 and NO3 (-) ) and both Fe(2+) and Mn(2+) greater than 1 mg/L in shallow groundwater suggest that the DOC compounds are chemically labile. The consequence of high concentrations of labile DOC may be positive (e.g., denitrification) or negative (e.g., enhanced metal mobility and biofouling), and highlights the need to account for a wider range of water quality parameters when considering the impacts of land use on the ecology of receiving waters and/or suitability of groundwater for irrigated agriculture.

Oxidation of Dissolved Elemental Mercury by Thiol Compounds under Anoxic Conditions

Mercuric ion, Hg(2+), forms strong complexes with thiolate compounds that commonly dominate Hg(II) speciation in natural freshwater. However, reactions between dissolved aqueous elemental mercury (Hg(0)aq) and organic ligands in general, and thiol compounds in particular, are not well studied although these reactions likely affect Hg speciation and cycling in the environment. In this study, we compared the reaction rates between Hg(0)aq and a number of selected organic ligands with varying molecular structures and sulfur (S) oxidation states in dark, anoxic conditions to assess the role of these ligands in Hg(0)aq oxidation. Significant Hg(0)aq oxidation was observed with all thiols but not with ligands containing no S. Compounds with oxidized S (e.g., disulfide) exhibited little or no reactivity toward Hg(0)aq either at pH 7. The rate and extent of Hg(0)aq oxidation varied greatly depending on the chemical and structural properties of thiols, thiol/Hg ratios, and the presence or absence of electron acceptors. Smaller aliphatic thiols and higher thiol/Hg ratios resulted in higher Hg(0)aq oxidation rates than larger aromatic thiols at lower thiol/Hg ratios. The addition of electron acceptors (e.g., humic acid) also led to substantially increased Hg(0)aq oxidation. Our results suggest that thiol-induced oxidation of Hg(0)aq is important under anoxic conditions and can affect Hg redox transformation and bioavailability for microbial methylation.

CoFe2O4/TiO2 nanocatalysts for the photocatalytic degradation of Reactive Red 120 in aqueous solutions in the presence and absence of electron acceptors

Magnetic CoFe2O4 and CoFe2O4/TiO2 nanocatalysts were prepared by a co-precipitation method in which CoFe2O4 induced the formation of thermodynamically more stable rutile phase of TiO2. The structural and elemental analyses confirmed the formation of CoFe2O4 and CoFe2O4/TiO2 nanocatalysts and the specific atomic ratios of Ti, Co, Fe, and O in these catalysts. The presence of Co2+ and Fe3+ cations in its oxide forms on the surface of TiO2 led to visible light absorption in the wavelength range 550–650nm. The band gap calculated by Tauc approach showed ∼3.2, 1.1 and 2.8eV for TiO2, CoFe2O4 and CoFe2O4/TiO2 nanocatalysts, respectively. The photocatalytic degradation of Reactive Red 120 (RR120) was studied by varying its concentration and the amount of nanocatalyst in order to attain a maximum degradation. The role of electron acceptors in the photocatalytic degradation of RR120 was studied in the presence of the magnetic nanocatalysts.

Methanogenic biodegradation of two-ringed polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAH) are widespread in methane-rich subsurface environments, such as oil reservoirs and fuel-contaminated aquifers; however, little is known about the biodegradation of these compounds under methanogenic conditions. To assess the metabolism of PAH in the absence of electron acceptors, a crude oil-degrading methanogenic enrichment culture was tested for the ability to biodegrade naphthalene, 1-methylnaphthalene (1-MN), 2-methylnaphthalene (2-MN), and 2, 6-dimethylnaphthalene (2, 6-diMN). When methane was measured as an indicator of metabolism, nearly 400 μmol of methane was produced in the 2-MN- and 2, 6-diMN-amended cultures relative to substrate-unamended controls, which is close to the amount of methane stoichiometrically predicted based on the amount of substrate added (51-56 μmol). In contrast, no substantial methane was produced in the naphthalene- and 1-MN-amended enrichments. In time course experiments, metabolite analysis of enrichments containing 2-MN and 2, 6-diMN revealed the formation of 2-naphthoic acid and 6-methyl-2-naphthoic acid, respectively. Microbial community analysis by 454 pyrosequencing revealed that these PAH-utilizing enrichments were dominated by archaeal members most closely affiliated with Methanosaeta and Methanoculleus species and bacterial members most closely related to the Clostridiaceae, suggesting that these organisms play an important role in the methanogenic metabolism of the substituted naphthalenes in these cultures.

Investigation on photocatalytic potential of Au–Ta2O5 semiconductor nanoparticle by degrading Methyl Orange in aqueous solution by illuminating with visible light

A semiconductor photocatalytic process has shown great potential as a low cost, environmentally friendly and sustainable treatment technology for the treatment of wastewater. Hence, a wide band gap Ta2O5 semiconductor nanoparticle was prepared by the hydrothermal method and considerable efforts have been taken to narrow the band gap, i.e., the surface modification has been done with a noble metal (Au0) by a deposition precipitation method. As synthesized, Au–Ta2O5 semiconductor was well characterized by X-ray diffraction (XRD), X-ray photo electron spectroscopy (XPS), transmission electron microscopy (TEM) and diffused reflectance UV-vis spectroscopy (DRS). The photocatalytic potential of Au–Ta2O5 semiconductor was investigated by degrading Methyl Orange in the presence and absence of electron acceptors by illuminating with visible light of intensity 80 600 ± 10 Lux.

Ag3PO4/SnO2 semiconductor nanocomposites with enhanced photocatalytic activity and stability

Ag3PO4/SnO2 semiconductor nanocomposites exhibit much higher photocatalytic activity and good stability than pure Ag3PO4 for the photodegradation of organic compounds (methyl orange) in the absence of electron acceptors under visible light.

Desulfovibrio butyratiphilus sp. nov., a Gram-negative, butyrate-oxidizing, sulfate-reducing bacterium isolated from an anaerobic municipal sewage sludge digester

Strictly anaerobic, mesophilic, sulfate-reducing bacterial strains were isolated from two anaerobic municipal sewage sludge digesters. One representative strain (BSY(T)) was characterized phenotypically and phylogenetically. Cells were Gram-negative, motile by means of a single polar flagellum, non-spore-forming, curved rods. Cells had desulfoviridin and cytochrome type c. Catalase and oxidase activities were not detected. The optimum NaCl concentration for growth was 0.5 % (w/v). The optimum temperature was 35 degrees C and the optimum pH was 7.1. Strain BSY(T) utilized butyrate, 2-methylbutyrate, valerate, pyruvate, lactate, ethanol, 1-propanol, butanol and H(2) as electron donors for sulfate reduction. This strain grew lithoautotrophically with H(2)/CO(2) under sulfate-reducing conditions. Most organic electron donors were incompletely oxidized to mainly acetate, whereas 2-methylbutyrate and valerate were oxidized to equivalent amounts of acetate and propionate. Strain BSY(T) utilized thiosulfate as an electron acceptor, and grew with pyruvate in the absence of electron acceptors. The genomic DNA G+C content of strain BSY(T) was 63.3 mol%. Menaquinone MK-6(H(2)) was the major respiratory quinone. Major cellular fatty acids were C(14 : 0), C(16 : 0), C(16 : 1) omega7 and C(18 : 1)omega7. Phylogenetic analyses based on 16S rRNA and dissimilatory sulfite-reductase beta-subunit gene sequences assigned strain BSY(T) to the genus Desulfovibrio in the family Desulfovibrionaceae within the class Deltaproteobacteria . Its closest recognized relative based on 16S rRNA gene sequences was the type strain of Desulfovibrio putealis (95.3 % similarity). On the basis of significant differences in 16S rRNA gene sequences and phenotypic characteristics, the sewage sludge strains are considered to represent a single novel species of the genus Desulfovibrio, for which the name Desulfovibrio butyratiphilus sp. nov. is proposed. The type strain is BSY(T) (=JCM 15519(T)=DSM 21556(T)).

Microbiology to Help Solve Our Energy Needs

Our society depends greatly on fossil fuels, and the environmental consequences of this are well known and include significant increases of the CO(2) concentration in the earth's atmosphere. Although microbiology has traditionally played only a minor role in fossil-fuel extraction, two novel key discoveries indicate that this may change. First, the realization that oil components can be converted to methane and CO(2) by methanogenic consortia in the absence of electron acceptors (oxygen, nitrate, sulfate) explains how much of the world's oil has been biodegraded in situ. In addition to inorganic nutrients, only water is needed for these methanogenic conversions. Hence, continued methanogenic biodegradation may have shaped the heavy-oil reservoirs that are so prevalent today. The potential to exploit these reactions, for example, by in situ gasification, is currently being actively investigated. Second, injection of nitrate in oil and gas fields can lower sulfide concentrations. High sulfide concentrations, caused by the action of sulfate-reducing bacteria (SRB), are associated with increased risk of corrosion, reservoir plugging (through precipitated sulfides), and human safety. Nitrate injection into an oil field stimulates subsurface heterotrophic nitrate-reducing bacteria (hNRB) and nitrate-reducing, sulfide-oxidizing bacteria (NR-SOB). Nitrite, formed by these NRB by partial reduction of nitrate, is a strong and specific SRB inhibitor. Nitrate injection has, therefore, promise in positively controlling the oil-field sulfur cycle. There is now more interest in and potential to apply petroleum microbiology than there has been in the past, allowing microbiologists to contribute to a sustainable energy future.

Fermentative Utilization of Glycerol by Escherichia coli and Its Implications for the Production of Fuels and Chemicals

Availability, low prices, and a high degree of reduction make glycerol an ideal feedstock to produce reduced chemicals and fuels via anaerobic fermentation. Although glycerol metabolism in Escherichia coli had been thought to be restricted to respiratory conditions, we report here the utilization of this carbon source in the absence of electron acceptors. Cells grew fermentatively on glycerol and exhibited exponential growth at a maximum specific growth rate of 0.040 +/- 0.003 h(-1). The fermentative nature of glycerol metabolism was demonstrated through studies in which cell growth and glycerol utilization were observed despite blocking several respiratory processes. The incorporation of glycerol in cellular biomass was also investigated via nuclear magnetic resonance analysis of cultures in which either 50% U-13C-labeled or 100% unlabeled glycerol was used. These studies demonstrated that about 20% of the carbon incorporated into the protein fraction of biomass originated from glycerol. The use of U-13C-labeled glycerol also allowed the unambiguous identification of ethanol and succinic, acetic, and formic acids as the products of glycerol fermentation. The synthesis of ethanol was identified as a metabolic determinant of glycerol fermentation; this pathway fulfills energy requirements by generating, in a redox-balanced manner, 1 mol of ATP per mol of glycerol converted to ethanol. A fermentation balance analysis revealed an excellent closure of both carbon (approximately 95%) and redox (approximately 96%) balances. On the other hand, cultivation conditions that prevent H2 accumulation were shown to be an environmental determinant of glycerol fermentation. The negative effect of H2 is related to its metabolic recycling, which in turn generates an unfavorable internal redox state. The implications of our findings for the production of reduced chemicals and fuels were illustrated by coproducing ethanol plus formic acid and ethanol plus hydrogen from glycerol at yields approaching their theoretical maximum.

Hydrogen Metabolism in Shewanella oneidensis MR-1

Shewanella oneidensis MR-1 is a facultative sediment microorganism which uses diverse compounds, such as oxygen and fumarate, as well as insoluble Fe(III) and Mn(IV) as electron acceptors. The electron donor spectrum is more limited and includes metabolic end products of primary fermenting bacteria, such as lactate, formate, and hydrogen. While the utilization of hydrogen as an electron donor has been described previously, we report here the formation of hydrogen from pyruvate under anaerobic, stationary-phase conditions in the absence of an external electron acceptor. Genes for the two S. oneidensis MR-1 hydrogenases, hydA, encoding a periplasmic [Fe-Fe] hydrogenase, and hyaB, encoding a periplasmic [Ni-Fe] hydrogenase, were found to be expressed only under anaerobic conditions during early exponential growth and into stationary-phase growth. Analyses of DeltahydA, DeltahyaB, and DeltahydA DeltahyaB in-frame-deletion mutants indicated that HydA functions primarily as a hydrogen-forming hydrogenase while HyaB has a bifunctional role and represents the dominant hydrogenase activity under the experimental conditions tested. Based on results from physiological and genetic experiments, we propose that hydrogen is formed from pyruvate by multiple parallel pathways, one pathway involving formate as an intermediate, pyruvate-formate lyase, and formate-hydrogen lyase, comprised of HydA hydrogenase and formate dehydrogenase, and a formate-independent pathway involving pyruvate dehydrogenase. A reverse electron transport chain is potentially involved in a formate-hydrogen lyase-independent pathway. While pyruvate does not support a fermentative mode of growth in this microorganism, pyruvate, in the absence of an electron acceptor, increased cell viability in anaerobic, stationary-phase cultures, suggesting a role in the survival of S. oneidensis MR-1 under stationary-phase conditions.

The Substrate Radical of Escherichia coli Oxygen-independent Coproporphyrinogen III Oxidase HemN

During porphyrin biosynthesis the oxygen-independent coproporphyrinogen III oxidase (HemN) catalyzes the oxidative decarboxylation of the propionate side chains of rings A and B of coproporphyrinogen III to form protoporphyrinogen IX. The enzyme utilizes a 5'-deoxyadenosyl radical to initiate the decarboxylation reaction, and it has been proposed that this occurs by stereo-specific abstraction of the pro-S-hydrogen atom at the beta-position of the propionate side chains leading to a substrate radical. Here we provide EPR-spectroscopic evidence for intermediacy of the latter radical by observation of an organic radical EPR signal in reduced HemN upon addition of S-adenosyl-L-methionine and the substrate coproporphyrinogen III. This signal (g(av) = 2.0029) shows a complex pattern of well resolved hyperfine splittings from at least five different hydrogen atoms. The radical was characterized using regiospecifically labeled (deuterium or 15N) coproporphyrinogen III molecules. They had been generated from a multienzyme mixture and served as efficient substrates. Reaction of HemN with coproporphyrinogen III, perdeuterated except for the methyl groups, led to the complete loss of resolved proton hyperfine splittings. Substrates in which the hydrogens at both alpha- and beta-positions, or only at the beta-positions of the propionate side chains, or those of the methylene bridges, were deuterated showed that there is coupling with hydrogens at the alpha-, beta-, and methylene bridge positions. Deuterium or 15N labeling of the pyrrole nitrogens without labeling the side chains only led to a slight sharpening of the radical signal. Together, these observations clearly identified the radical signal as substrate-derived and indicated that, upon abstraction of the pro-S-hydrogen atom at the beta-position of the propionate side chain by the 5'-deoxyadenosyl radical, a comparatively stable delocalized substrate radical intermediate is formed in the absence of electron acceptors. The observed hyperfine constants and g values show that this coproporphyrinogenyl radical is allylic and encompasses carbon atoms 3', 3, and 4.

Desulfovibrio frigidus sp. nov. and Desulfovibrio ferrireducens sp. nov., psychrotolerant bacteria isolated from Arctic fjord sediments (Svalbard) with the ability to reduce Fe(III)

Strains 18T, 61T and 77 were isolated from two permanently cold fjord sediments on the west coast of Svalbard. The three psychrotolerant strains, with temperature optima at 20-23 degrees C, were able to grow at the freezing point of sea water, -2 degrees C. The strains oxidized important fermentation products such as hydrogen, formate and lactate with sulfate as the electron acceptor. Sulfate could be replaced by sulfite, thiosulfate or elemental sulfur. Poorly crystalline and soluble Fe(III) compounds were reduced in sulfate-free medium, but no growth occurred under these conditions. In the absence of electron acceptors, fermentative growth was possible. The pH optimum for the strains was around 7.1. The DNA G+C contents were 43.3 and 42.0 mol% for strains 18T and 61T, respectively. Strains 18T, 61T and 77 were most closely related to Desulfovibrio hydrothermalis (95.0-95.7 % 16S rRNA gene sequence similarity). Strains 18T and 77, exhibiting 99.9 % sequence similarity, represent a novel species for which the name Desulfovibrio frigidus sp. nov. is proposed. The type strain is strain 18T (=DSM 17176T = JCM 12924T). Strain 61T was closely related to strains 18T and 77 (97.6 and 97.5 % 16S rRNA gene sequence similarity), but on the basis of DNA-DNA hybridization strain 61T represents a novel species for which the name Desulfovibrio ferrireducens sp. nov. is proposed. The type strain is strain 61T (=DSM 16995T = JCM 12925T).

Adaptation of Bacillus subtilis to oxygen limitation

Bacillus subtilis grows anaerobically by at least two different pathways, respiration using nitrate as an electron acceptor and fermentation in the absence of electron acceptors. Regulatory mechanisms have evolved allowing cells to shift to these metabolic capabilities in response to changes in oxygen availability. These include transcriptional activation of fnr upon oxygen limitation, a process requiring the ResD-ResE two-component signal transduction system that also regulates aerobic respiration. FNR then activates transcription of other anaerobically induced genes including the narGHJI operon which encodes a respiratory nitrate reductase. Genes involved in fermentative growth are controlled by an unidentified FNR-independent regulatory pathway.

Desulfovibrio putealis sp. nov., a novel sulfate-reducing bacterium isolated from a deep subsurface aquifer

A novel sulfate-reducing bacterium was isolated from a well that collected water from a deep aquifer at a depth of 430 m in the Paris Basin, France. The strain, designated B7-43T, was made up of vibrioid cells that were motile by means of a single polar flagellum. Cells contained desulfoviridin. In the presence of sulfate, the following substrates were used as energy and carbon sources: lactate, pyruvate, malate, fumarate, ethanol, butanol, acetate/H2 and glycine. Sulfite and thiosulfate were also used as electron acceptors in the presence of lactate. In the absence of electron acceptors, pyruvate, malate and fumarate were fermented. Optimal growth was obtained in 1 g NaCl l(-1) and at pH 7. On the basis of 16S rRNA gene sequence analysis, the isolate was most closely related to members of the genus Desulfovibrio (90 % similarity). It is thus proposed that strain B7-43T (=DSM 16056T=ATCC BAA-905T) represents a novel species within this genus, Desulfovibrio putealis sp. nov.

Desulfacinum subterraneum sp.nov.--a new thermophilic sulfate-reducing bacterium isolated from a high temperature oil field

A new thermophilic sulfate-reducing bacterium isolated from the high-temperature White Tiger oil field (Vietnam) is described. Cells of the bacterium are oval (0.4-0.6 by 0.6-1.8 microns), nonmotile, non-spore-forming, and gram-negative. Growth occurs at 45 to 65 degrees C (with an optimum at 60 degrees C) at NaCl concentrations of 0 to 50 g/l. In the course of sulfate reduction, the organism can utilize lactate, pyruvate, malate, fumarate, ethanol, salts of fatty acids (formate, acetate, propionate, butyrate, caproate, palmitate), yeast extract, alanine, serine, cysteine, and H2 + CO2 (autotrophically). In addition to sulfate, the bacterium can use sulfite, thiosulfate, and elemental sulfur as electron acceptors. In the absence of electron acceptors, the bacterium can ferment pyruvate and yeast extract (a yet unrecognized capacity of sulfate reducers) with the formation of acetate and H2. The G + C content of DNA is 60.8 mol %. The level of DNA-DNA hybridization of the isolate (strain 101T) and Desulfacinum infernum (strain B alpha G1T) is as low as 34%. Analysis of the nucleotide sequence of 16S rDNA places strain 101T in the phylogenetic cluster of the Desulfacinum species within the sulfate reducer subdivision of the delta subclass of Proteobacteria. All these results allowed the bacterium studied to be described as a new species, Desulfacinum subterraneum sp. nov., with strain 101 as the type strain.

Light induced redox reactions involving mammalian ferritin as photocatalyst

Under excitation by visible light the iron storage protein ferritin catalyses the reduction of cytochrome c and viologens as well as the oxidation of carboxylic acids, thiol compounds, and sulfite. The photochemically active element of ferritin is its mineral ferrihydrite semiconductor core. Band-gap excitation of these microcrystals leads to generation of electron-hole pairs that are sufficiently long-lived and reactive to engage in redox reactions with components of the medium. Photoreduction of cytochrome c and viologens occurs due to electron transfer from the conduction band of the iron oxide cluster through the protein shell surrounding the ferritin core. Laser photolysis coupled with time-resolved kinetics spectroscopy showed the electron transfer to propylviologen sulfonate to proceed in the microsecond time range. In the absence of electron acceptor at pH < 7, light excitation results in photodissolution of the iron oxide cluster with concomitant formation of Fe(II). These novel findings concerning the photocatalytic activity of ferritin with its inherent biological implications are discussed.