Sulfobacillus sibiricus sp. nov., a new moderately thermophilic bacterium

In the course of pilot industrial testing of a biohydrometallurgical technology for processing goldarsenic concentrate obtained from the Nezhdaninskoe ore deposit (East Siberia, Sakha, Yakutiya), a new gram-positive rod-shaped spore-forming moderately thermophilic bacterium (designated as strain N1) oxidizing Fe2+, S0, and sulfide minerals in the presence of yeast extract (0.02%) was isolated from a dense pulp. Physiologically, strain N1 differs from previously described species of the genus Sulfobacillus in having a somewhat higher optimal growth temperature (55 degrees C). Unlike the type strain of S. thermosulfidooxidans, strain N1 could grow on medium with 1 mM thiosulfate or sodium tetrathionate as a source of energy only within several passages and failed to grow, in the absence of an inorganic energy source, on media with sucrose, fructose, glucose, reduced glutathione, alanine, cysteine, sorbitol, sodium acetate, or pyruvate. The G + C content of the DNA of strain N1 was 48.2 mol %. The strain showed 42% homology after DNA-DNA hybridization with the type strain of S. thermosulfidooxidans and 10% homology with the type strain of S. acidophilus. The isolate differed from previously studied strains of S. thermosulfidooxidans in the structure of its chromosomal DNA (determined by the method of pulsed-field gel electrophoresis) which remained stable as growth conditions were changed. According to the results of the 16S rRNA gene analysis, the new strain forms a single cluster with the bacteria of the species Sulfobacillus thermosulfidooxidans (sequence similarity of 97.9-98.6%). Based on these genetic and physiological features, strain N1 is described as a new species Sulfobacillus sibiricus sp. nov.     

Genotypic and phenotypic polymorphism of environmental strains of the moderately thermophilic bacterium Sulfobacillus sibiricus

Five cultures of moderately thermophilic spore-forming acidophilic chemolithotrophic bacteria were isolated from the zones of spontaneous heating of pyrrhotine-containing pyrite-arsenopyrite gold-arsenic sulfide ores in an operating open pit (strains B1, B2, B3, OFO, and SSO). Analysis of the chromosomal DNA structure revealed differences between these cultures at the strain level (apart from B3 and SSO, which had identical restriction profiles). All the strains had a similar G + C DNA molar content (47.4-48.3%). The level of DNA reassociation was 85 to 95%. The similarity between the DNA of the type strain Sulfobacillus sibiricus N1 isolated from arsenopyrite ore concentrate and that of these strains (83-93%) indicates that they belong to the same species. The strains had similar values of pH and temperature optimal for growth on ferrous iron (1.6-2.0 and 45-55 degrees C, respectively). They were mixotrophs; Fe(II), S0, and sulfide minerals along with organic compounds were used as energy sources and electron donors. However, the kinetic parameters of growth and substrate oxidation varied from strain to strain. Genetic variety of the strains from diverse ecosystems and environments is possibly the result of the different rates of microevolution processes.     

Involvement of cytochrome a in iron oxidation of a moderately thermophilic iron-oxidizing bacterium, strain TI-1.

The iron-oxidizing activity of a moderately thermophilic iron-oxidizing bacterium, strain TI-1, was located in the plasma membrane. When the strain was grown in Fe2+ (60 mM)-salts medium containing yeast extract (0.03%), the plasma membrane had iron-oxidizing activity of 0.129 mumol O2 uptake/mg/min. Iron oxidase was solubilized from the plasma membrane with 1.0% n-octyl-beta-D-glucopyranoside (OGL) containing 25% (v/v) glycerol (pH 3.0) and purified 37-fold by a SP Sepharose FF column chromatography. Iron oxidase solubilized from the plasma membrane was stable at pH 3.0, but quite unstable in the buffer with the pH above 6.0 or below 1.0. The optimum pH and temperature for iron oxidation were 3.0 and 55 degrees C, respectively. Solubilized enzyme from the membrane showed absorption peaks characteristic of cytochromes a and b. Cyanide and azide, inhibitors of cytochrome c oxidase, completely inhibited iron-oxidizing activity at 100 microM, but antimycin A, 2-n-heptyl-4-hydroxyquinoline-N-oxide (HOQNO) and myxothiazol, inhibitors of electron transport systems involved with cytochrome b, did not inhibit enzyme activity at 10 microM. The absorption spectrum of the most active enzyme fraction from SP Sepharose FF column chromatography (4.76 mumol O2 uptake/mg/min) compared with lower active fractions from the chromatography (0.009 and 2.10 mumol O2 uptake/mg/min) showed a large alpha-peak of cytochrome a at 602 nm and a smaller alpha-peak of cytochrome b at 560 nm. The absorption spectrum of pyridine ferrohemochrome prepared from the most highly purified enzyme showed an alpha-peak characteristic of heme a at 587 nm, but not the alpha-peak characteristic of heme c at 550 nm. The cytochrome a, but not cytochrome b, in the most highly purified enzyme fraction was reduced by the addition of ferrous iron at pH 3.0, indicating that electrons from Fe2+ were transported to cytochrome a, but not cytochrome b. These results strongly suggest that cytochrome a, but not cytochromes b and c, is involved in iron oxidation of strain TI-1.     

A new iron oxidase from a moderately thermophilic iron oxidizing bacterium strain TI-1.

Iron oxidase was purified from plasma membranes of a moderately thermophilic iron oxidizing bacterium strain TI-1 in an electrophoretically homogeneous state. Spectrum analyses of purified enzyme showed the existence of cytochrome a, but not cytochrome b and c types. Iron oxidase was composed of five subunits with apparent molecular masses of 46 kDa (alpha), 28 kDa (beta), 24 kDa (gamma), 20 kDa (delta), and 17 kDa (epsilon). As the molecular mass of a native enzyme was estimated to be 263 kDa in the presence of 0.1% n-dodecyl-beta-D-maltopyranoside (DM), a native iron oxidase purified from strain TI-1 seems to be a homodimeric enzyme (alpha beta gamma delta epsilon)(2). Optimum pH and temperature for iron oxidation were pH 3.0 and 45 degrees C, respectively. The K(m) of iron oxidase for Fe(2+) was 1.06 mM and V(max) for O(2) uptake was 13.8 micromol x mg(-1) x min(-1). The activity was strongly inhibited by cyanide and azide. Purified enzyme from strain TI-1 is a new iron oxidase in which electrons of Fe(2+) were transferred to haem a and then to the molecular oxygen.     

Ferrous iron mediated oxidation of arachidonic acid: studies employing nitroblue tetrazolium (NBT)

The oxidation of arachidonic acid by ferrous sulfate provides a useful model to study the role of iron in lipid oxidation reactions. We have employed nitroblue tetrazolium (NBT) in the present investigation to evaluate the mechanism of this reaction. In the presence of arachidonic acid, Fe⁺⁺, and O₂, the yellow dye NBT was rapidly reduced to the blue form, NBTH₂. The molar ratio of arachidonic acid to Fe⁺⁺ in this rapid reaction was 1:1, showing an interaction of one fatty acid molecule per iron molecule. Approximately one molecule of NBT was reduced per four molecules of arachidonic acid and Fe⁺⁺. Reduction of NBT was accompanied by oxidation of Fe⁺⁺ to Fe⁺⁺⁺, suggesting the transfer of four electrons from the Fe⁺⁺ to NBT to reduce the dye. Arachidonic acid was found to be unchanged when extracted at the end of the reaction, indicating formation of a complex that could dissociate leaving intact arachidonic acid. Evidence for the presence of such a complex which slowly dissociates during the reaction was obtained after longer incubations with small amounts of arachidonic acid. NBT reduction was not inhibited by agents which hydrolyze superoxide, by catalase or by agents which trap hydroxy radicals. We, therefore, propose a model in which NBT traps a radical generated on the arachidonic acid molecule. The proposed model suggests mechanisms for other fatty acid oxidation reactions such as prostaglandin and hydroperoxy fatty acid synthesis.     

Reduction of chromate, selenite, tellurite, and iron(III) by the moderately thermophilic bacterium Bacillus thermoamylovorans SKC1

A moderately thermophilic, facultatively anaerobic bacterium capable of reducing Cr(VI) (strain SKC1) was isolated from municipal sewage. Based on the analysis of the 16S rRNA gene nucleotide sequence and DNA-DNA hybridization data, strain SKC1 was identified as a representative of the species Bacillus thermoamylovorans. B. thermoamylovorans SKC1 is capable of reducing chromate with L-arabinose as an electron donor with an optimum at 50 degrees C and neutral pH. The culture is able to reduce Cr(VI) at its initial concentration in the medium of up to 150 mg/l. In addition to chromate, strain SKC1 is capable of reducing selenite and tellurite, as well as soluble forms of Fe(III). It was shown that Cr(VI), Te(IV), and Se(IV) exert a bacteriostatic effect on strain SKC1, and the reduction of these anions performs the detoxification function. This is the first communication on the reduction of chromate, selenite, tellurite, and soluble Fe(III) species by a culture of thermophilic bacilli.     

The role of iron in prostaglandin synthesis: Ferrous iron mediated oxidation of arachidonic acid

Arachidonic acid (AA) is the essential substrate for production of platelet endoperoxides and thromboxanes. Iron or heme is an essential cofactor for the peroxidase, lipoxygenase and cyclo-oxygenase enzymes involved in formation of these products. The present study has examined the direct interactions between iron and arachidonic acid. Iron caused the oxidation of AA into more polar products which could be detected by UV absorbtion at 232 nM or the thiobarbituric acid (TBA) reaction. High pressure liquid chromatography, chem-ionization and electron-impact mass spectrometry and nuclear magnetic resonance spectroscopy suggest that the major product was a hydroperoxide of AA. Ferrous iron (Fe⁺⁺) and oxygen were absolute requirements. Fe⁺⁺ was converted to the ferric iron (Fe⁺⁺⁺) state during oxidation of AA, but Fe⁺⁺⁺ could not substitute for Fe⁺⁺. No other enzymes, cofactors or ions were involved. Conversion of AA to a hydroperoxide by Fe⁺⁺ was inhibited by the antioxidant, 2, (3)-Tert-butyl-4-hydroxyanisole, the radical scavenger, nitroblue tetrazolium, and iron chelating agents, including EDTA, imidazole and dihydroxybenzoic acid. The reaction was not affected by superoxide dismutase, catalase or aspirin. These findings and preliminary studies of the Fe⁺⁺ induced oxidation product of AA as a substrate for prostaglandin synthesis and inhibitor of prostacyclin production indicate the critical role of Fe⁺⁺ in AA activation.     

Growth of moderately thermophilic iron-oxidizing bacterium strain TI-1 in synthetic medium

The moderately thermophilic iron-oxidizing bacterium strain TI-1, which lacks enzyme systems involved in CO₂ fixation, grows at 45°C in Fe²⁺ medium supplemented with yeast extract to give a maximum cell growth of 1.0 × 10⁸ cells per ml, but does not grow in Fe²⁺ medium without yeast extract. To elucidate the physiology of the strain, a synthetic medium was developed. It was found that the best synthetic medium was Fe²⁺-6AA, containing Fe²⁺, salts, and the following six l-amino acids: alanine, aspartic acid, glutamic acid, arginine, serine, and histidine. In this medium, strain TI-1 showed a maximum cell growth of 10 × 10⁸ cells/ml. The six amino acids in the Fe²⁺-6AA medium were used not only as a carbon source but also as a source of nitrogen. Inorganic nitrogen sources, such as ammonium ion, hydrazine, hydroxylamine, nitrite, and nitrate, were not used as a sole source of nitrogen, but rather strongly inhibited the utilization of the six amino acids at 1 mM. In the Fe²⁺ (10 mM)-6AA medium supplemented with 21 mM Fe³⁺, reduction of Fe³⁺ to Fe²⁺ that was dependent on the added amino acids was observed, suggesting another role of the amino acids in the growth of strain TI-1. Washed, intact cells of strain TI-1 had the activity to reduce Fe³⁺ to Fe²⁺.     

Genome sequence of the moderately thermophilic halophile Flexistipes sinusarabici strain (MAS10)

Flexistipes sinusarabici Fiala et al. 2000 is the type species of the genus Flexistipes in the family Deferribacteraceae. The species is of interest because of its isolated phylogenetic location in a genomically under-characterized region of the tree of life, and because of its origin from a multiply extreme environment; the Atlantis Deep brines of the Red Sea, where it had to struggle with high temperatures, high salinity, and a high concentrations of heavy metals. This is the fourth completed genome sequence to be published of a type strain of the family Deferribacteraceae. The 2,526,590 bp long genome with its 2,346 protein-coding and 53 RNA genes is a part of the Genomic Encyclopedia of Bacteria and Archaea project.     

Nitrate-dependent iron(II) oxidation in paddy soil

Iron(III) profiles of flooded paddy soil incubated in the greenhouse indicated oxidation of iron(II) in the upper 6 mm soil layer. Measurement of oxygen with a Clark-type microelectrode showed that oxygen was only responsible for the oxidation of iron(II) in the upper 3 mm. In the soil beneath, nitrate could be used as electron acceptor instead of oxygen for the oxidation of the iron(II). Nitrate was still available 3 mm below the soil surface, and denitrifying activity was indicated by higher concentrations of nitrite between 3 and 6 mm soil depth. Nitrate was generated by nitrification from ammonium. Ammonium concentrations increased beneath 6 mm soil depth, indicating ammonium release and diffusion from deeper soil layers. High concentrations of ammonium were also found at the surface, probably resulting from N2 fixation by cyanobacteria. Experimental adjustment of the nitrate concentration in the flooding water to 200 microM stimulated nitrate-dependent iron(II) oxidation, which was indicated by significantly lower iron(II) concentrations in soil layers in which nitrate-dependent iron(II) oxidation was proposed. Soil incubated in the dark showed high iron(III) concentrations only in the layer where oxygen was still available. In this soil, the nitrogen pool was depleted because of the lack of N2 fixation by cyanobacteria. In contrast, soil incubated in the dark with 500 microM nitrate in the flooding water showed significantly higher iron(II) and significantly lower iron(II) concentrations in the anoxic soil layers, indicating nitrate-dependent iron(II) oxidation. Anoxic incubations of soil with nitrate in the flooding water also showed high concentrations of iron(II) and low concentrations of iron(II) in the upper 3 mm. As oxygen was excluded in anoxic incubations, the high iron(III) concentrations are a sign of the activity of nitrate-dependent iron(II) oxidizers. The presence of these bacteria in non-amended soil was also indicated by the most probable number (MPN) counts of nitrate-dependent iron(II) oxidizers in the layer of 3-4 mm soil depth, which revealed 1.6 x 10(6) bacteria g(-1) dry weight.     

Genome sequence of the moderately thermophilic, amino-acid-degrading and sulfur-reducing bacterium Thermovirga lienii type strain (Cas60314(T))

Thermovirga lienii Dahle and Birkeland 2006 is a member of the genus Thermovirga in the genomically moderately well characterized phylum 'Synergistetes'. Members of this relatively recently proposed phylum 'Synergistetes' are of interest because of their isolated phylogenetic position and their diverse habitats, e.g. from humans to oil wells. The genome of T. lienii Cas60314(T) is the fifth genome sequence (third completed) from this phylum to be published. Here we describe the features of this organism, together with the complete genome sequence and annotation. The 1,999,646 bp long genome (including one plasmid) with its 1,914 protein-coding and 59 RNA genes is a part of the Genomic Encyclopedia of Bacteria and Archaea project.     

Genome sequence of the moderately thermophilic sulfur-reducing bacterium Thermanaerovibrio velox type strain (Z-9701T) and emended description of the genus Thermanaerovibrio

Thermanaerovibrio velox Zavarzina et al. 2000 is a member of the Synergistaceae, a family in the phylum Synergistetes that is already well-characterized at the genome level. Members of this phylum were described as Gram-negative staining anaerobic bacteria with a rod/vibrioid cell shape and possessing an atypical outer cell envelope. They inhabit a large variety of anaerobic environments including soil, oil wells, wastewater treatment plants and animal gastrointestinal tracts. They are also found to be linked to sites of human diseases such as cysts, abscesses, and areas of periodontal disease. The moderately thermophilic and organotrophic T. velox shares most of its morphologic and physiologic features with the closely related species, T. acidaminovorans. In addition to Su883^T, the type strain of T. acidaminovorans, stain Z-9701^T is the second type strain in the genus Thermanaerovibrio to have its genome sequence published. Here we describe the features of this organism, together with the non-contiguous genome sequence and annotation. The 1,880,838 bp long chromosome (non-contiguous finished sequence) with its 1,751 protein-coding and 59 RNA genes is a part of the Genomic Encyclopedia of Bacteria and Archaea project.     

Hydrogenogenic CO conversion in a moderately thermophilic (55 degrees C) sulfate-fed gas lift reactor: competition for CO-derived H(2)

Thermophilic (55 degrees C) sulfate reduction in a gas lift reactor fed with CO gas as the sole electron donor was investigated. The reactor was inoculated with mesophilic granular sludge with a high activity of CO conversion to hydrogen and carbon dioxide at 55 degrees C. Strong competition for H(2) was observed between methanogens and sulfate reducers, while the homoacetogens present consumed only small amounts of H(2). The methanogens appeared to be more sensitive to pH and temperature shocks imposed to the reactor, but could not be completely eliminated. The fast growth rates of the methanogens (generation time of 4.5 h) enabled them to recover fast from shocks, and they rapidly consumed more than 90% of the CO-derived H(2). Nevertheless, steep increases in sulfide production in periods with low methane production suggests that once methanogenesis is eliminated, sulfate reduction with CO-rich gas as electron donor has great potential for thermophilic biodesulfurization.     

Effect of phosphate on bacterioferritin-catalysed iron(II) oxidation

The iron(III) mineral cores of bacterioferritins (BFRs), as isolated, contain a significant component of phosphate, with an iron-to-phosphate ratio approaching 1:1 in some cases. In order to better understand the in vivo core-formation process, the effect of phosphate on in vitro core formation in Escherichia coli BFR was investigated. Iron cores reconstituted in the presence of phosphate were found to have iron-to-phosphate ratios similar to those of native cores, and possessed electron paramagnetic resonance properties characteristic of the phosphate-rich core. Phosphate did not affect the stoichiometry of the initial iron(II) oxidation reaction that takes place at the intrasubunit dinuclear iron-binding sites (phase 2 of core formation), but did increase the rate of oxidation. Phosphate had a more significant effect on subsequent core formation (the phase 3 reaction), increasing the rate up to five-fold at pH 6.5 and 25 °C. The dependence of the phase 3 rate on phosphate was complex, being greatest at low phosphate and gradually decreasing until the point of saturation at ~2 mM phosphate (for iron(II) concentrations <200 M). Phosphate caused a significant decrease in the absorption properties of both phase 2 and phase 3 products, and the phosphate dependence of the latter mirrored the observed rate dependence, suggesting that distinct iron(III)-phosphate species are formed at different phosphate concentrations. The effect of phosphate on absorption properties enabled the observation of previously undetected events in the phase 2 to phase 3 transition period.Abbreviations BFR Bacterioferritin - EcBFR Escherichia coli BFR - PaBFR Pseudomonas aeruginosa BFR - AvBFR Azotobacter vinelandii BFR - ITPG Isopropyl -d-thiogalactopyranoside - MES 2-(N-morpholino)-ethanesulfonic acid     

Reduction of chromate,selenite, tellurite,and iron (III) by the moderately thermophilic bacterium <Emphasis Type="Italic">Bacillus thermoamylovorans</Emphasis> SKC1

A moderately thermophilic, facultatively anaerobic bacterium capable of reducing Cr(VI) (strain SKC1) was isolated from municipal sewage. Based on the analysis of the 16S rRNA gene nucleotide sequence and DNA-DNA hybridization data, strain SKC1 was identified as a representative of the species Bacillus thermoamylovorans. B. thermoamylovorans SKC1 is capable of reducing chromate with L-arabinose as an electron donor with an optimum at 50°C and neutral pH. The culture is able to reduce Cr(VI) at its initial concentration in the medium of up to 150 mg/l. In addition to chromate, strain SKC1 is capable of reducing selenite and tellurite, as well as soluble forms of Fe(III). It was shown that Cr(VI), Te(IV), and Se(IV) exert a bacteriostatic effect on strain SKC1, and the reduction of these anions performs the detoxification function. This is the first communication on the reduction of chromate, selenite, tellurite, and soluble Fe(III) species by a culture of thermophilic bacilli.     

Interaction between iron(II) and hydroxamic acids: oxidation of iron(II) to iron(III) by desferrioxamine B under anaerobic conditions

Interaction between iron(II) and acetohydroxamic acid (Aha), alpha-alaninehydroxamic acid (alpha-Alaha), beta-alaninehydroxamic acid (beta-Alaha), hexanedioic acid bis(3-hydroxycarbamoyl-methyl)amide (Dha) or desferrioxamine B (DFB) under anaerobic conditions was studied by pH-metric and UV-Visible spectrophotometric methods. The stability constants of complexes formed with Aha, alpha-Alaha, beta-Alaha and Dha were calculated and turned out to be much lower than those of the corresponding iron(II) complexes. Stability constants of the iron(II)-hydroxamate complexes are compared with those of other divalent 3d-block metal ions and the Irving-Williams series of stabilities was found to be observed. Above pH 4, in the reactions between iron(II) and desferrioxamine B, the oxidation of the metal ion to iron(III) by the ligand was found. The overall reaction that resulted in the formation of the tris-hydroxamato complex [Fe(HDFB)]+ and monoamide derivative of DFB at pH 6 is: 2Fe2+ + 3H4DFB+ = 2[Fe(HDFB)]+ + H3DFB-monoamide+ + H2O + 4H+. Based on these results, the conclusion is that desferrioxamine B can uptake iron in iron(III) form under anaerobic conditions.     

Reproduction of Asian chipmunks (Tamias sibiricus) in captivity

Factors affecting reproduction in captive Asian chipmunks, Tamias sibiricus, were examined by means of a survey of chipmunk breeders in Great Britain. Sixteen breeders were asked about the conditions under which their chipmunks were kept and their success in breeding them. Results covered 205 female-years of pairing. Breeding was promoted by large cage size and early weaning of young, and inhibited by the presence of other rodent species nearby and by extended photoperiod. A diet of seeds and nuts, with some fresh fruits and vegetables, appeared to be adequate for breeding. Breeding occurred in 80–91& of female-years when neither extra lighting nor other rodents were present, irrespective of cage size. Weaning age affected the occurrence of second litters in a year. Second litters were born less often (0–13&) of breeding (female-years) if young of the first litter remained with the mother 8 weeks or longer. Second litters were more frequent (14–45& of breeding female-years) if first litters were removed by 6.5 weeks of age, and this frequency increased with cage size. Litter size also increased with cage size (means ranged from 3 to 7). Overall breeding success increased with cage size and decreased with the presence of other rodents. In most colonies without other rodents near, mean success rate ranged from 3.1 to 8.5 young/female-year. In colonies with other rodents present mean success rate varied from 0 to 3.3 young/female-year. It is suggested that the mechanisms that control population size in the wild also act to inhibit or promote breeding in captivity.     

Initial iron oxidation in horse spleen apoferritin. Characterization of a mixed-valence iron(II)-iron(III) complex.

In ferritin, iron is stored by oxidative deposition of the ferrous ion to form a hydrous ferric oxide mineral core. Two intermediates, formed during the initial stages of iron accumulation in apoferritin, have been observed previously in our laboratory and have been identified as a mononuclear Fe3(+)-protein complex and a mixed-valence Fe2(+)-Fe3(+)-protein complex. The physical characteristics of the mixed-valence Fe2(+)-Fe3+ complex and its relationship to the mononuclear Fe3+ complex in horse spleen apoferritin samples to which 0-240 iron atoms were added was examined by EPR spectroscopy. The results indicate that the mononuclear complex is not a precursor to the formation of the mixed-valence complex. Competitive binding studies with Cd2+, Zn2+, Tb3+, and UO2+(2) suggest that the mixed-valence complex is formed on the interior of the protein in the vicinity of the 2-fold axis of the subunit dimer. The mixed-valence complex could be generated by the partial oxidation of Fe2+ in apoferritin containing 120 Fe2+ or by the addition of up to 120 Fe2+ to ferritin already containing 18 Fe3+/protein molecule. The fact that the complex is generated during early Fe2+ oxidation suggests that it may be a key intermediate during the initial oxidative deposition of iron in the protein. The unusual EPR powder lineshape at 9.3 GHz of the mixed-valence complex was simulated with a rhombic g-tensor (gx = 1.95, gy = 1.88, gz = 1.77) and large linewidths and g-strain parameters. The presence of significant g-strain in the complex probably accounts for the failure to observe an EPR signal at 35 GHz and likely reflect considerable flexibility in the structure of the metal site. The temperature dependence of the EPR intensity in the range 8-38 K was modeled successfully by an effective spin Hamiltonian including exchange coupling (-2JS1.S2) and zero-field terms, from which an antiferromagnetic coupling of J = -4.0 +/- 0.5 cm-1 was obtained. This low value for J may reflect the presence of a mu-oxo bridge(s) in the dimer.     

Induction of 1,N(2)-etheno-2'-deoxyguanosine in DNA exposed to beta-carotene oxidation products

Epidemiological studies testing the effect of β-carotene in humans have found a relative risk for lung cancer in smokers supplemented with β-carotene. We investigated the reactions of retinal and β-apo-8′-carotenal, two β-carotene oxidation products, with 2′-deoxyguanosine to evaluate their DNA damaging potential. A known mutagenic adduct, 1,N²-etheno-2′-deoxyguanosine, was isolated and characterized on the basis of its spectroscopic features. After treatment of calf thymus DNA with β-carotene or β-carotene oxidation products, significantly increased levels of 1,N²-etheno-2′-deoxyguanosine and 8-oxo-7,8-dihydro-2′-deoxyguanosine were quantified in DNA. These lesions are believed to be important in the development of human cancers. The results reported here may contribute toward an understanding of the biological effects of β-carotene oxidation products.