Dissimilatory reduction of Fe(III) and other electron acceptors by a Thermus isolate

A thermophilic bacterium that can use O2, NO3-, Fe(III), and S0 as terminal electron acceptors for growth was isolated from groundwater sampled at a 3.2-km depth in a South African gold mine. This organism, designated SA-01, clustered most closely with members of the genus Thermus, as determined by 16S rRNA gene (rDNA) sequence analysis. The 16S rDNA sequence of SA-01 was >98% similar to that of Thermus strain NMX2 A.1, which was previously isolated by other investigators from a thermal spring in New Mexico. Strain NMX2 A.1 was also able to reduce Fe(III) and other electron acceptors. Neither SA-01 nor NMX2 A.1 grew fermentatively, i.e., addition of an external electron acceptor was required for anaerobic growth. Thermus strain SA-01 reduced soluble Fe(III) complexed with citrate or nitrilotriacetic acid (NTA); however, it could reduce only relatively small quantities (0.5 mM) of hydrous ferric oxide except when the humic acid analog 2,6-anthraquinone disulfonate was added as an electron shuttle, in which case 10 mM Fe(III) was reduced. Fe(III)-NTA was reduced quantitatively to Fe(II); reduction of Fe(III)-NTA was coupled to the oxidation of lactate and supported growth through three consecutive transfers. Suspensions of Thermus strain SA-01 cells also reduced Mn(IV), Co(III)-EDTA, Cr(VI), and U(VI). Mn(IV)-oxide was reduced in the presence of either lactate or H2. Both strains were also able to mineralize NTA to CO2 and to couple its oxidation to Fe(III) reduction and growth. The optimum temperature for growth and Fe(III) reduction by Thermus strains SA-01 and NMX2 A.1 is approximately 65 degrees C; their optimum pH is 6.5 to 7.0. This is the first report of a Thermus sp. being able to couple the oxidation of organic compounds to the reduction of Fe, Mn, or S.     

Uptake hydrogenase activity in denitrifying Azospirillum brasilense grown anaerobically with nitrous oxide or nitrate.

zospirillum brasilense Sp7 was grown anaerobically with N2O as the terminal electron acceptor and NH4Cl as the nitrogen source. Hydrogen uptake activity (O2-dependent H3H oxidation) was expressed in the presence and absence of 5% H2; it reached its maximum in late logarithmic phase as the malate became limiting. This activity was very stable in stationary phase, even in the absence of exogenous H2, compared with microaerobically grown cultures; this supports the hypothesis that the exclusion of O2 is critical for maintaining the integrity of the H2 uptake system in this organism. Oxygen, as well as methylene blue and N2O, supported H2 uptake, indicating the presence of electron transport components leading to O2 in anaerobically grown A. brasilense. Nitrite (0.5 mM) inhibited H2 uptake. In cultures grown with NO3- as the terminal electron acceptor and NH4Cl as the nitrogen source, in the presence and absence of exogenous H2, only low H2 uptake activity was observed. Methylene blue, O2, N2O, NO3-, and NO2- were all capable of acting as the electron acceptor for H2 oxidation. Nitrite (0.5 mM) did not inhibit H2 uptake in NO3--grown cells, as it did in N2O-grown cells. A. brasilense appears to be one of the few organisms capable of expressing the H2 uptake system under denitrifying conditions in the absence of molecular H2.     

A highly purified enrichment culture couples the reductive dechlorination of tetrachloroethene to growth.

A microscopically pure enrichment culture of a gram-negative anaerobic bacterium, in the present article referred to as PER-K23, was isolated from an anaerobic packed-bed column in which tetrachloroethene (PCE) was reductively transformed to ethane via trichloroethene (TCE), cis-1,2-dichloroethene (cis-1,2-DCE), chloroethene, and ethene. PER-K23 catalyzes the dechlorination of PCE via TCE to cis-1,2-DCE and couples this reductive dechlorination to growth. H2 and formate were the only electron donors that supported growth with PCE or TCE as an electron acceptor. The culture did not grow in the absence of PCE or TCE. Neither O2, NO3-, NO2-, SO4(2-), SO3(2-), S2O3(2-), S, nor CO2 could replace PCE or TCE as an electron acceptor with H2 as an electron donor. Also, organic electron acceptors such as acetoin, acetol, dimethyl sulfoxide, fumarate, and trimethylamine N-oxide and chlorinated ethanes, DCEs, and chloroethene were not utilized. PER-K23 was not able to grow fermentatively on any of the organic compounds tested. Transferring the culture to a rich medium revealed that a contaminant was still present. Dechlorination was optimal between pH 6.8 and 7.6 and a temperature of 25 to 35 degrees C. H2 consumption was paralleled by chloride production, PCE degradation, cis-1,2-DCE formation, and growth of PER-K23. Electron balances showed that all electrons derived from H2 or formate consumption were recovered in dechlorination products and biomass. Exponential growth could be achieved only in gently shaken cultures.(ABSTRACT TRUNCATED AT 250 WORDS)     

Response of Halomonas campisalis to saline stress: changes in growth kinetics, compatible solute production and membrane phospholipid fatty acid composition

The haloalkaliphile Halomonas campisalis, isolated near Soap Lake, Washington, was grown under both aerobic and denitrifying conditions from 0 to 260 g L(-1) NaCl, with optimal growth occurring at 20 and 30 g L(-1) NaCl, respectively. Halomonas campisalis was observed to produce high concentrations of compatible solutes, most notably ectoine (up to 500 mM within the cytoplasm), but hydroxyectoine and glycine betaine were also detected. The types and amounts of compatible solutes produced depended on salinity and specific growth rate, as well as on the terminal electron acceptor available (O(2) or NO(3) (-)). A decrease in ectoine production was observed with NO(3) (-) as compared with O(2) as the terminal electron acceptor. In addition, changes in the phospholipid fatty acid composition were measured with changing salinity. An increase in trans fatty acids was observed in the absence of salinity, and may be a response to membrane instability. Cyclic fatty acids were also observed to increase, both in the absence of salinity, and at very high salinities, indicating cell stress at these conditions.     

Ferrovibrio denitrificans gen. nov., sp. nov., a novel neutrophilic facultative anaerobic Fe(II)-oxidizing bacterium

A neutrophilic Fe(II)-oxidizing bacterium was isolated from the redox zone of a low-salinity spring in Krasnodar krai (Russia), at the FeS-Fe(OH)(3) interface deposited at the sediment surface. The cells of strain Sp-1 were short, thin motile vibrioids with one polar flagellum dividing by binary fission. The optimal values and ranges for pH and temperature were pH 6.2 (5.5-8) and 35?°C (5-45?°C), respectively. The organism was a facultative anaerobe. Strain Sp-1 was capable of organotrophic, lithoheterotrophic and mixotrophic growth with Fe(II) as an electron donor. The denitrification chain was 'disrupted'. Oxidation of Fe(II) was coupled to reduction of NO3 - to NO2 - or of N(2) O to N(2) , as well as under microaerobic conditions, with O(2) as an electron acceptor. The DNA G+C content was 64.2?mol%. According to the results of phylogenetic analysis, the strain was 10.6-12% remote from the closest relatives, members of the genera Sneathiella, Inquilinus, Oceanibaculum and Phaeospirillum within the Alphaproteobacteria. Based on its morphological, physiological and taxonomic characteristics, together with the results of phylogenetic analysis, strain Sp-1 is described as a member of a new genus Ferrovibrio gen. nov., with the type species Ferrovibrio denitrificans sp. nov. and the type strain Sp-1(T) (=?LMG 25817(T) =?VKM B-2673(T) ).     

Transformations of selenate and selenite by Stenotrophomonas maltophilia isolated from a seleniferous agricultural drainage pond sediment

A Gram-negative bacterium, identified as Stenotrophomonas maltophilia by fatty acid analysis and 16S rRNA sequencing, was isolated from a seleniferous agricultural evaporation pond sediment collected in the Tulare Lake Drainage District, California. In cultures exposed to the atmosphere, the organism reduces selenate (SeO4(2-)) and selenite (SeO3(2-)) to red amorphous elemental selenium (Se degrees ) only upon reaching stationary phase, when O2 levels are less than 0.1 mg l(-1). In 48 h, S. maltophilia removed 81.2% and 99.8% of added SeO4(2-) and SeO3(2-) (initial concentration of 0.5 mM), respectively, from solution. Anaerobic growth experiments revealed that the organism was incapable of using SeO4(2-), SeO3(2-), SO4(2-) or NO3- as a terminal electron acceptor. Transmission electron microscopy of cultures spiked with either Se oxyanion were found to contain spherical extracellular deposits. Analysis of the deposits by energy-dispersive X-ray spectroscopy revealed that they consist of Se. Furthermore, S. maltophilia was active in producing volatile alkylselenides when in the presence of SeO4(2-) and SeO3(2-). The volatile products were positively identified as dimethyl selenide (DMSe), dimethyl selenenyl sulphide (DMSeS) and dimethyl diselenide (DMDSe) by gas chromatography-mass spectrometry. Our findings suggest that this bacterium may contribute to the biogeochemical cycling of Se in seleniferous evaporation pond sediments and waters. This organism may also be potentially useful in a bioremediation scheme designed to treat seleniferous agricultural wastewater.     

Fe(III) reduction activity and cytochrome content of Shewanella putrefaciens grown on ten compounds as sole terminal electron acceptor

Shewanella putrefaciens was grown on a series of ten alternate compounds as sole terminal electron acceptor. Each cell type was analyzed for Fe(III) reduction activity, absorbance maxima in reduced-minus-oxidized difference spectra and heme-containing protein content. High-rate Fe(III) reduction activity, pronounced difference maxima at 521 and 551 nm and a predominant 29.3 kDa heme-containing protein expressed by cells grown on Fe(III), Mn(IV), U(VI), SO3(2-) and S2O3(2-), but not by cells grown on O2, NO3, NO2-, TMAO or fumarate. These results suggest that microbial Fe(III) reduction activity is enhanced by anaerobic growth on metals and sulfur compounds, yet is limited under all other terminal electron-accepting conditions.     

Growth and respiration ofBradyrhizobium japonicum USDA 143 with nitrous oxide as the terminal electron acceptor

Bradyrhizobium japonicum USDA 143 grew chemoorganotrophically under anoxic conditions with exogenous N₂O as the sole terminal electron acceptor. Cell growth and dissimilatory N₂O reduction were significantly inhibited by C₂H₂ when either N₂O or N₂O plus NO ₃ ^– served as terminal electron acceptor(s). Reduction of N₂O accounted for 20% of the energy for cell growth in cultures supplied with NO ₃ ^– as the terminal electron acceptor. Nitrous oxide was produced stoichiometrically in cultures containing NO ₃ ^– and C₂H₂, but cell growth was proportionately reduced when compared with cultures supplied with an equal amount of NO ₃ ^– . Exogenous N₂O delayed the reduction of NO ₃ ^– in cultures supplied with both electron acceptors. Direct amperometric monitoring of N₂O respiration showed a specific activity of 0.082±0.004 moles N₂O/min/mg cell protein, and azide inhibited cell respiration.     

Blood oxygen transport in common map turtles during simulated hibernation

We assessed the effects of cold and submergence on blood oxygen transport in common map turtles (Graptemys geographica). Winter animals were acclimated for 6-7 wk to one of three conditions at 3 degrees C: air breathing (AB-3 degrees C), normoxic submergence (NS-3 degrees C), and hypoxic (PO2=49 Torr) submergence (HS-3 degrees C). NS-3 degrees C turtles exhibited a respiratory alkalosis (pH 8.07; PCO2=7.9 Torr; [lactate]=2.2 mM) relative to AB-3 degrees C animals (pH 7.89; PCO2=13.4 Torr; [lactate]=1.1 mM). HS-3 degrees C animals experienced a profound metabolic acidosis (pH 7.30; PCO2=7.9 Torr; [lactate]=81 mM). NS-3 degrees C turtles exhibited an increased blood O2 capacity; however, isoelectric focusing revealed no seasonal changes in the isohemoglobin (isoHb) profile. Blood O2 affinity was significantly increased by cold acclimation; half-saturation pressures (P50's) for air-breathing turtles at 3 degrees and 22 degrees C were 6.5 and 18.8 Torr, respectively. P50's for winter animals submerged in normoxic and hypoxic water were 5.2 and 6.5 Torr, respectively. CO2 Bohr slopes (Delta logP50/Delta pH) were -0.15, -0.16, and -0.07 for AB-3 degrees C, NS-3 degrees C, and HS-3 degrees C turtles, respectively; the corresponding value for AB-22 degrees C was -0.37. The O2 equilibrium curve (O2EC) shape was similar for AB-3 degrees C and NS-3 degrees C turtles; Hill plot n coefficients ranged from 1.8 to 2.0. The O2EC shape for HS-3 degrees C turtles was anomalous, exhibiting high O2 affinity below P50 and a right-shifted segment above half-saturation. We suggest that increases in Hb-O2 affinity and O2 capacity enhance extrapulmonary O2 uptake by turtles overwintering in normoxic water. The anomalous O2EC shape and reduced CO2 Bohr effect of HS-3 degrees C turtles may also promote some aerobic metabolism in hypoxic water.     

Isolation of anaerobic respiratory mutants of Shewannella putrefaciens and genetic analysis of mutants deficient in anaerobic growth on Fe3+.

A genetic approach was used to study (dissimilatory) ferric iron (Fe3+) reduction in Shewanella putrefaciens 200. Chemical mutagenesis procedures and two rapid plate assays were developed to facilitate the screening of Fe3+ reduction-deficient mutants. Sixty-two putative Fe3+ reduction-deficient mutants were identified, and each was subsequently tested for its ability to grow anaerobically on various compounds as sole terminal electron acceptors, including Fe3+, nitrate (NO3-), nitrite (NO2-), manganese oxide (Mn4+), sulfite (SO3(2-)), thiosulfate (S2O3(2-)), trimethylamine N-oxide, and fumarate. A broad spectrum of mutants deficient in anaerobic growth on one or more electron acceptors was identified. Nine of the 62 mutants (designated Fer mutants) were deficient only in anaerobic growth on Fe3+ and retained the ability to grow on all other electron acceptors. These results suggest that S. putrefaciens expresses at least one terminal Fe3+ reductase that is distinct from other terminal reductases coupled to anaerobic growth. The nine Fer mutants were conjugally mated with an S. putrefaciens genomic library harbored in Escherichia coli S17-1. Complemented S. putrefaciens transconjugants were identified by the acquired ability to grow anaerobically on Fe3+ as the sole terminal electron acceptor. All recombinant cosmids that conferred the Fer+ phenotype appeared to carry a common internal region.     

Fermentative toluene degradation in anaerobic defined syntrophic cocultures

A syntrophic coculture of a new sulfate-reducing isolate, strain TRM1, with Wolinella succinogenes degraded toluene with either fumarate or NO3- as the terminal electron acceptor. Neither strain TRM1 nor W. succinogenes could metabolise toluene under these conditions in pure culture. Syntrophic degradation was 2-3 times slower than toluene utilisation by strain TRM1 in pure culture with sulfate as electron acceptor. The culture did not produce benzoate or fatty acids like acetate or propionate in detectable amounts. An increase in biomass of the syntrophic toluene-degrading culture was shown in a growth curve with nitrate as the terminal electron acceptor. Both partner organisms were detected microscopically at the end of the growth experiment. Syntrophic degradation of toluene with W. succinogenes and fumarate as the terminal electron acceptor was also demonstrated with the iron reducer Geobacter metallireducens. The results provide the first example of a fermentative oxidation of an aromatic hydrocarbon in a defined coculture.     

Anaerobic sulfide oxidation with nitrate by a freshwater Beggiatoa enrichment culture

A lithotrophic freshwater Beggiatoa strain was enriched in O2-H2S gradient tubes to investigate its ability to oxidize sulfide with NO3- as an alternative electron acceptor. The gradient tubes contained different NO3- concentrations, and the chemotactic response of the Beggiatoa mats was observed. The effects of the Beggiatoa sp. on vertical gradients of O2, H2S, pH, and NO3- were determined with microsensors. The more NO3- that was added to the agar, the deeper the Beggiatoa filaments glided into anoxic agar layers, suggesting that the Beggiatoa sp. used NO3- to oxidize sulfide at depths below the depth that O2 penetrated. In the presence of NO3- Beggiatoa formed thick mats (>8 mm), compared to the thin mats (ca. 0.4 mm) that were formed when no NO3- was added. These thick mats spatially separated O2 and sulfide but not NO3- and sulfide, and therefore NO3- must have served as the electron acceptor for sulfide oxidation. This interpretation is consistent with a fourfold-lower O2 flux and a twofold-higher sulfide flux into the NO3- -exposed mats compared to the fluxes for controls without NO3-. Additionally, a pronounced pH maximum was observed within the Beggiatoa mat; such a pH maximum is known to occur when sulfide is oxidized to S0 with NO3- as the electron acceptor.     

Denitrification at extremely high pH values by the alkaliphilic, obligately chemolithoautotrophic, sulfur-oxidizing bacterium Thioalkalivibrio denitrificans strain ALJD

Thioalkalivibrio denitrificans is the first example of an alkaliphilic, obligately autotrophic, sulfur-oxidizing bacterium able to grow anaerobically by denitrification. It was isolated from a Kenyan soda lake with thiosulfate as electron donor and N2O as electron acceptor at pH 10. The bacterium can use nitrite and N2O, but not nitrate, as electron acceptors during anaerobic growth on reduced sulfur compounds. Nitrate is only utilized as nitrogen source. In batch culture at pH 10, rapid growth was observed on N2O as electron acceptor and thiosulfate as electron donor. Growth on nitrite was only possible after prolonged adaptation of the culture to increasing nitrite concentrations. In aerobic thiosulfate-limited chemostats, Thioalkalivibrio denitrificans strain ALJD was able to grow between pH values of 7.5 and 10.5 with an optimum at pH 9.0. Growth of the organism in continuous culture on N2O was more stable and faster than in aerobic cultures. The pH limit for growth on N2O was 10.6. In nitrite-limited chemostat culture, growth was possible on thiosulfate at pH 10. Despite the observed inhibition of N2O reduction by sulfide, the bacterium was able to grow in sulfide-limited continuous culture with N2O as electron acceptor at pH 10. The highest anaerobic growth rate with N2O in continuous culture at pH 10 was observed with polysulfide (S8(2-)) as electron donor. Polysulfide was also the best substrate for oxygen-respiring cells. Washed cells at pH 10 oxidized polysulfide to sulfate via elemental sulfur in the presence of N2O or O2. In the absence of the electron acceptors, elemental sulfur was slowly reduced which resulted in regeneration of polysulfide. Cells of strain ALJD grown under anoxic conditions contained a soluble cd1-like cytochrome and a cytochrome-aa3-like component in the membranes.     

Effects of nitrate and nitrite on dissimilatory iron reduction by Shewanella putrefaciens 200.

The inhibitory effects of nitrate (NO3-) and nitrite (NO2-) on dissimilatory iron (FE3+) reduction were examined in a series of electron acceptor competition experiments using Shewanella putrefaciens 200 as a model iron-reducing microorganism. S. putrefaciens 200 was found to express low-rate nitrate reductase, nitrite reductase, and ferrireductase activity after growth under highly aerobic conditions and greatly elevated rates of each reductase activity after growth under microaerobic conditions. The effects of NO3- and NO2- on the Fe3+ reduction activity of both aerobically and microaerobically grown cells appeared to follow a consistent pattern; in the presence of Fe3+ and either NO3- or NO2-, dissimilatory Fe3+ and nitrogen oxide reduction occurred simultaneously. Nitrogen oxide reduction was not affected by the presence of Fe3+, suggesting that S. putrefaciens 200 expressed a set of at least three physiologically distinct terminal reductases that served as electron donors to NO3-, NO2-, and Fe3+. However, Fe3+ reduction was partially inhibited by the presence of either NO3- or NO2-. An in situ ferrozine assay was used to distinguish the biological and chemical components of the observed inhibitory effects. Rate data indicated that neither NO3- nor NO2- acted as a chemical oxidant of bacterially produced Fe2+. In addition, the decrease in Fe3+ reduction activity observed in the presence of both NO3- and NO2- was identical to the decrease observed in the presence of NO2- alone. These results suggest that bacterially produced NO2- is responsible for inhibiting electron transport to Fe3+.     

Anaerobic oxidation of 2-chloroethanol under denitrifying conditions by<Emphasis Type="Italic"> Pseudomonas stutzeri</Emphasis> strain JJ

A bacterium that uses 2-chloroethanol as sole energy and carbon source coupled to denitrification was isolated from 1,2-dichloroethane-contaminated soil. Its 16 S rDNA sequence showed 98% similarity with the type strain of Pseudomonas stutzeri (DSM 5190) and the isolate was tentatively identified as Pseudomonas stutzeri strain JJ. Strain JJ oxidized 2-chloroethanol completely to CO(2) with NO(3)(- )or O(2) as electron acceptor, with a preference for O(2) if supplied in combination. Optimum growth on 2-chloroethanol with nitrate occurred at 30 degrees C with a mu(max) of 0.14 h(-1) and a yield of 4.4 g protein per mol 2-chloroethanol metabolized. Under aerobic conditions, the mu(max) was 0.31 h(-1). NO(2)(-) also served as electron acceptor, but reduction of Fe(OH)(3), MnO(2), SO(4)(2-), fumarate or ClO(3)(-) was not observed. Another chlorinated compound used as sole energy and carbon source under aerobic and denitrifying conditions was chloroacetate. Various different bacterial strains, including some closely related Pseudomonas stutzeri strains, were tested for their ability to grow on 2-chloroethanol as sole energy and carbon source under aerobic and denitrifying conditions, respectively. Only three strains, Pseudomonas stutzeri strain LMD 76.42, Pseudomonas putida US2 and Xanthobacter autotrophicus GJ10, grew aerobically on 2-chloroethanol. This is the first report of oxidation of 2-chloroethanol under denitrifying conditions by a pure bacterial culture.     

Effects of electron donor and acceptor conditions on reductive dehalogenation of tetrachloromethane by Shewanella putrefaciens 200.

Shewanella putrefaciens 200 is a nonfermentative bacterium that is capable of dehalogenating tetrachloromethane to chloroform and other, unidentified products under anaerobic conditions. Since S. putrefaciens 200 can respire anaerobically by using a variety of terminal electron acceptors, including NO3-, NO2-, and Fe(III), it provides a unique opportunity to study the competitive effects of different electron acceptors on dehalogenation in a single organism. The results of batch studies showed that dehalogenation of CT by S. putrefaciens 200 was inhibited by O2, 10 mM NO3-, and 3 mM NO2-, but not by 15 mM Fe(III), 15 mM fumarate, or 15 mM trimethylamine oxide. Using measured O2, Fe(III), NO2-, and NO3- reduction rates, we developed a speculative model of electron transport to explain inhibition patterns on the basis of (i) the kinetics of electron transfer at branch points in the electron transport chain, and (ii) possible direct inhibition by nitrogen oxides. In additional experiments in which we used 20 mM lactate, 20 mM glucose, 20 mM glycerol, 20 mM pyruvate, or 20 mM formate as the electron donor, dehalogenation rates were independent of the electron donor used. The results of other experiments suggested that sufficient quantities of endogenous substrates were present to support transformation of tetrachloromethane even in the absence of an exogenous electron donor. Our results should be significant for evaluating (i) the bioremediation potential at sites contaminated with both halogenated organic compounds and nitrogen oxides, and (ii) the bioremediation potential of iron-reducing bacteria at contaminated locations containing significant amounts of iron-bearing minerals.     

Isolation of U(VI) reduction-deficient mutants of Shewanella putrefaciens

A U(VI) reduction-deficient mutant (Urr) screening technique was developed and combined with chemical mutagenesis procedures to identify a Urr mutant of Shewanella putrefaciens strain 200. The Urr mutant lacked the ability to grow anaerobically on U(VI) and NO(2)(-), yet retained the ability to grow anaerobically on eight other compounds as terminal electron acceptor. All 11 members of previously isolated sets of Fe(III) and Mn(IV) reduction-deficient mutants of S. putrefaciens 200 displayed Urr-positive phenotypes with the Urr screen and were capable of anaerobic growth on U(VI). This is the first reported isolation of a respiratory mutant that is unable to grow anaerobically on U(VI) as terminal electron acceptor.     

Reaction of caa3-type terminal cytochrome oxidase from the thermophilic bacterium PS3 with oxygen and carbon monoxide at low temperatures.

Reaction of O2 and CO with a caa3-type terminal cytochrome oxidase (EC 1.9.3.1) from the thermophilic bacterium PS3 grown with high aeration was studied at low temperatures. The CO recombination at the temperature range studied (-50 degrees C to -80 degrees C) followed first-order kinetics with an activation energy of 29.3 kJ/mol (7.0 kcal/mol). In the presence of O2 at -113 degrees C the photolysed reduced form binds O2 to form an 'oxy' intermediate similar to Compound A. At a higher temperature (-97 degrees C) another intermediate, similar to Compound B, is formed as a result of electron transfer from the enzyme to the liganded O2.     

Characterization of Desulfitobacterium chlororespirans sp. nov., which grows by coupling the oxidation of lactate to the reductive dechlorination of 3-chloro-4-hydroxybenzoate.

Strain Co23, an anaerobic spore-forming microorganism, was enriched and isolated from a compost soil on the basis of its ability to grow with 2,3-dichlorophenol (DCP) as its electron acceptor, ortho chlorines were removed from polysubstituted phenols but not from monohalophenols. Growth by chlororespiration was indicated by a growth yield of 3.24 g of cells per mol of reducing equivalents (as 2[H]) from lactate oxidation to acetate in the presence of 3-chloro-4-hydroxybenzoate but no growth in the absence of the halogenated electron acceptor. Other indicators of chlororespiration were the fraction of electrons from the electron donor used for dechlorination (0.67) and the H2 threshold concentration of < 1.0 ppm. Additional electron donors utilized for reductive dehalogenation were pyruvate, formate, butyrate, crotonate, and H2. Pyruvate supported homoacetogenic growth in the absence of an electron acceptor. Strain Co23 also used sulfite, thiosulfate, and sulfur as electron acceptors for growth, but it did not use sulfate, nitrate or fumarate. The temperature optimum for growth was 37 degrees C; however, the rates of dechlorination were optimum at 45 degrees C and activity persisted to temperatures as high as 55 degrees C. The 16S rRNA sequence was determined, and strain Co23 was found to be related to Desulfitobacterium dehalogenans JW/IU DC1 and Desulfitobacterium strain PCE1, with sequence similarities of 97.2 and 96.8%, respectively. The phylogenetic and physiological properties exhibited by strain Co23 place it into a new species designated Desulfitobacterium chlororespirans.     

Physiological study and taxonomy of Alcaligenes species: A denitrificans, A. odorans and A faecalis

We have studied 43 strains of the species Alcaligenes dentrificans, A. odorans, and A. faecalis. Twenty-five of them were isolated by enrichment culture on minimal medium containing an organic acid (L-malate, succinate, tartrate, adipate, or itaconate) and N2O as a respiratory electron acceptor. These constitute a single phenon with the A. dentrificans strain type and 9 other strains isolated from clinical specimens. However, strain 4 differs from the other 34 strains in 12 nutritional characters, in its ability to effect a meta cleavage of diphenols, and by the absence of tetrathionate reductase. The percentages of G + C are the following: strains isolated from soil, 66.4 +/- 1.1; collection strains, 67.0 +/- 1.3. The 5 strains of A. odorans differ from the 34 strains of A. denitrificans (not including strain 4) in their inability to denitrify nitrate and use D-saccharate, adipate, pimelate, suberate, beta-hydroxy-beta-methylglutarate meso-tartrate, azelate, and itaconate. Their percentage of G + C is much lower: 56.1 +/- 0.4. From the nutritional point of view the 3 strains of A. faecalis resemble A. dentrificans. However, they differ from the latter by their inability to grow anaerobically on NO3-, NO2-, N2O, and by a slightly lower percentage of G+ C: 64.3 +/- 0.0. The 43 strains synthesize poly-beta-hydroxybutyric acid. None of them is chemolithotrophic.