Ectothiorhodospira Shaposhnikovii Research Articles

Arsenite as an Electron Donor for Anoxygenic Photosynthesis: Description of Three Strains of Ectothiorhodospira from Mono Lake, California and Big Soda Lake, Nevada.

Three novel strains of photosynthetic bacteria from the family Ectothiorhodospiraceae were isolated from soda lakes of the Great Basin Desert, USA by employing arsenite (As(III)) as the sole electron donor in the enrichment/isolation process. Strain PHS-1 was previously isolated from a hot spring in Mono Lake, while strain MLW-1 was obtained from Mono Lake sediment, and strain BSL-9 was isolated from Big Soda Lake. Strains PHS-1, MLW-1, and BSL-9 were all capable of As(III)-dependent growth via anoxygenic photosynthesis and contained homologs of arxA, but displayed different phenotypes. Comparisons were made with three related species: Ectothiorhodospira shaposhnikovii DSM 2111, Ectothiorhodospira shaposhnikovii DSM 243T, and Halorhodospira halophila DSM 244. All three type cultures oxidized arsenite to arsenate but did not grow with As(III) as the sole electron donor. DNA–DNA hybridization indicated that strain PHS-1 belongs to the same species as Ect. shaposhnikovii DSM 2111 (81.1% sequence similarity), distinct from Ect. shaposhnikovii DSM 243T (58.1% sequence similarity). These results suggest that the capacity for light-driven As(III) oxidation is a common phenomenon among purple photosynthetic bacteria in soda lakes. However, the use of As(III) as a sole electron donor to sustain growth via anoxygenic photosynthesis is confined to novel isolates that were screened for by this selective cultivation criterion.

Beneficial effects of Ectothiorhodospira shaposhnikovii WF on larval cultivation of Litopenaeus vannamei.

To develop high quality probiotics for shrimp larviculture, the effects of a photosynthetic purple sulphur bacterium WF identified as Ectothiorhodospira shaposhnikovii on survival and development of Litopenaeus vannamei larvae were evaluated in vivo. The larvae exhibited a better survival rate after administration of strain WF compared to the probiotic Rhodopseudomonas palustris. To investigate the effect of dose and dosing frequency, strain WF was added to larvae, stages nauplius 6 to zoea 3, at three different doses and dosing frequencies. Larval treatment with strain WF twice at 10(6) cfu/ml exhibited significantly higher survival compared to the other doses and dosing frequencies as well as the control. The effect on water quality was assessed by applying strain WF to larvae, stages nauplius 6 to postlarvae 1, under conditions of zero water exchange and one-third water exchange. The larvae exhibited higher survival and faster growth when treated under conditions of zero water exchange. No significant difference was detected in the levels of three water quality parameters and in vibrio counts between these two conditions. Therefore, E. shaposhnikovii WF acts both as a bioremediation agent and nutrient source and can benefit shrimp larvae if given at an appropriate dose and dosing frequency. Strain WF, a moderate halophile, shows great promise as a water additive in improving water quality and providing nutrition for shrimp larviculture.

Ectothiorhodospira magna sp. nov., a new large alkaliphilic purple sulfur bacterium

Two strains of purple sulfur bacteria of the family Ectothiorhodospiraceae were isolated from moderately saline steppe lakes (with pH above 9.0) of the Transbaikal region (strain B7-7) and Mongolia (strain M10). The cells of the novel strains were spiral-shaped, 2.0–3.2 × 9.6–20.0 μm, motile due to a polar tuft of flagella. Photosynthetic pigments were represented by bacteriochlorophyll a and carotenoids of the spirilloxanthin series. Photosynthetic membranes were represented by long strands of lamellae distributed throughout the whole cell; unlike most Ectothiorhodospiraceae species, the membranes were not packed into regular stacks. Bacteria were capable of weak growth on sulfide and slow grow on hydrogen under photoautotrophic conditions. The best growth was noted on sulfide in the presence of acetate and bicarbonate. Thiosulfate did not stimulate phototrophic growth, even in the presence of organic substrates. The new isolates were alkaliphiles growing at a pH optimum of 9–10. Growth was possible within a salinity range of 0–80 g/l NaCl, with an optimum at 5–15 g/l NaCl. The morphology, the structure of the photosynthetic apparatus (strands of lamellae), and the physiology of the new strains were similar to those of Thiorhodospira sibirica. However, analysis of the 16S rRNA gene sequences demonstrated that the studied isolates were closely related to the type strain Ectothiorhodospira shaposhnikovii (99% similarity) of the family Ectothiorhodospiraceae, whereas the level of similarity between the new strains and Thiorhodospira sibirica was only 94–95%. According to the results of DNA-DNA hybridization, the DNA-DNA homology level between the tested strains was almost 100%; the similarity between the new isolates and the type strain Ectothiorhodospira shaposhnikovii was only 58%. The isolates differed from other representatives of the genus Ectothiorhodospira in the structure of the gene encoding the key enzyme of autotrophic CO2 fixation, ribulose-1,5-bisphosphate carboxylase (RuBisCo), which was similar to the RuBisCo genes of members of another family of sulfur bacteria, Chromatiaceae. The new isolates of purple bacteria were described as a new species of the genus Ectothiorhodospira, Ect. magna sp. nov. with the type strain B7-7T (= VKM B-2537 = DSM 22250).

Study of effect of molecular mobility in chromatophore membranes of the bacterium E. shaposhnikovii on processes of photoinduced electron transport using the NMR-Spin-Echo method with isotope substitution and dehydration

The effect of dehydration and (2)H2O/H2O isotope substitution on electron transport reactions and relaxation of proton-containing groups was studied in chromatophore membranes of Ectothiorhodospira shaposhnikovii. During dehydration (including isotope substitution of hydrate water) of preliminarily dehydrated isolated photosynthetic membranes there was a partial correlation between hydration intervals within which activation of electron transport from high-potential cytochrome c to photoactive bacteriochlorophyll dimer P890 of photosynthetic reaction center and variation of spin-lattice and spin-spin proton relaxation time was observed. Partial correlation between hydration intervals can be considered as evidence of correlation between mobility of non-water proton-containing groups with proton relaxation frequency approximately 10(8) sec(-1) with efficiency of electron transfer at the donor side of the chain.

Cloning and molecular organization of the polyhydroxyalkanoic acid synthase gene (phaC) of Ralstonia eutropha strain B5786

Class I polyhydroxyalkanoic acid (PHA) synthase gene (phaC) of Ralstonia eutropha strain B5786 was cloned and characterized. R. eutropha B5786 features the ability to synthesize multicomponent PHAs with short- and medium-chain-length monomers from simple carbohydrate substrate. A correlation was made between the molecular structure of PHA synthase and substrate specificity and the ability of strain-producers to accumulate PHAs of this or that structure. A strong similarity of PHA synthase of R. eutropha strain B5786 with PHA synthase of R. eutropha strain H16, which, as opposed to strain B5786, enables to incorporate medium chain length PHAs if hexanoate is used as carbon source, exhibited 99%. A correlation between the structure of PHA synthase of B5786 strain with synthases of microorganisms which synthesize short and medium chain length PHAs similarly to B5786 strain, showed an identity level from 26 to 41% (homology with synthase of Rhodospirillum rubrum makes 41%, Ectothiorhodospira shaposhnikovii makes 26%, Aeromonas punctata makes 40%, Thiococcus pfennigii makes 28%, Rhodococcus ruber makes 38%, and with PhaCl and PhaC2 synthases of Pseudomonas sp. 61-3 makes 34 and 37%, respectively). This allows for speaking about the absence of a direct connection between the molecular organization of PHA synthases and their functional abilities, namely, the ability to synthesize PHAs of a particular composition.

Fractionation of stable carbon isotopes by photoautotrophically growing anoxygenic purple and green sulfur bacteria

Fractionation of stable carbon isotopes 12C and 13C by three pure cultures of photoautotrophic purple sulfur bacteria (Ectothiorhodospira shaposhnikovii, Lamprocystis purpureus, and Thiocapsa sp.) (PSB) and the green sulfur bacterium Prosthecochloris sp. (GSB) was investigated in 13–15-day experiments. The cultivation was carried out in a luminostat (2000 lx) on mineral media with 1–1.5 g/l NaHCO3 (inoculum) with the subsequent transfer to the medium with up to 10 g/l NaHCO3. For PSB, the difference in the quantitative characteristics of the isotopic composition of suspended carbon (including bacterial cells) and mineral carbon of the medium (Δ13C = δ13Csubstrate − δ13Cbiomass) changed from 15.0 to 34.3‰. For GSB, the range of Δ13C changes was significantly less (18.3–22.7‰). These data suggested the possibility of a pool of soluble mineral carbon in PSB cells. The pool of intracellular mineral carbon was calculated; depending on the PSB species and growth stage, it varied from 0 to 68% of the total cell carbon. The α coefficients reflecting the carbon isotope fractionation by PSB and GBS and calculated from the changes of the bicarbonate carbon isotopic composition in the medium depending on its consumption were 1.029 ± 0.003 and 1.019 ± 0.001, respectively. These α values did not depend on the growth rate. CO2 fixation on ribulose-bisphosphate was shown to be the major factor determining the carbon isotope fractionation by PSB; at the stage of CO2 penetration into the cell, fractionation was insignificant. In GSB, fractionation occurred mostly at CO2 penetration into the cell, while it was insignificant at the stage of carbon dioxide fixation in the reverse TCA cycle. Analysis of the isotopic data of the photosynthesis by PSB and GSB in meromictic lakes also revealed that in PSB-dominated natural communities suspended organic matter was more enriched with light 13C (Δ13C = 23.4−24.6‰) than in the communities with more active GSB (Δ13C = 10.2−14.0‰)

Cooperative interaction of high-potential hemes in the cytochrome subunit of the photosynthetic reaction center of bacterium Ectothiorhodospira shaposhnikovii

Cooperative interaction of the high-potential hemes (C(h)) in the cytochrome subunit of the photosynthesizing bacterium Ectothiorhodospira shaposhnikovii was studied by comparing redox titration curves of the hemes under the conditions of pulse photoactivation inducing single turnover of electron-transport chain and steady-state photoactivation, as well as by analysis of the kinetics of laser-induced oxidation of cytochromes by reaction center (RC). A mathematical model of the processes of electron transfer in cytochrome-containing RC was considered. Theoretical analysis revealed that the reduction of one heme C(h) facilitated the reduction of the other heme, which was equivalent to a 60 mV positive shift of the midpoint potential. In addition, reduction of the second heme C(h) caused a three- to four-fold acceleration of the electron transfer from the cytochrome subunit to RC.

Poly(hydroxyalkanoic acid) Biosynthesis in Ectothiorhodospirashaposhnikovii: Characterization and Reactivity of a Type III PHA Synthase.

Ectothiorhodospira shaposhnikovii is able to accumulate polyhydroxybutyrate (PHB) photoautotrophically during nitrogen-limited growth. The activity of polyhydroxyalkanoate (PHA) synthase in the cells correlates with PHB accumulation. PHA synthase samples collected during the light period do not show a lag phase during in vitro polymerization. Synthase samples collected in the dark period displays a significant lag phase during in vitro polymerization. The lag phase can be eliminated by reacting the PHA synthase with the monomer, 3-hydroxybutyryl-CoA (3HBCoA). The PHA synthase genes (phaC and phaE) were cloned by screening a genomic library for PHA accumulation in E. coli cells. The PHA synthase expressed in the recombinant E. coli cells was purified to homogeneity. Both sequence analysis and biochemical studies indicated that this PHA synthase consists of two subunits, PhaE and PhaC and, therefore, belongs to the type III PHA synthases. Two major complexes were identified in preparations of purified PHA synthase. The large complex appears to be composed of 12 PhaC subunits and 12 PhaE subunits (dodecamer), whereas the small complex appears to be composed of 6 PhaC and 6 PhaE subunits (hexamer). In dilute aqueous solution, the synthase is predominantly composed of hexamer and has low activity accompanied with a significant lag period at the initial stage of reaction. The percentage of dodecameric complex increases with increasing salt concentration. The dodecameric complex has a greatly increased specific activity for the polymerization of 3HBCoA and a negligible lag period. The results from in vitro polymerizations of 3HBCoA suggest that the PHA synthase from E. shaposhnikovii may catalyze a living polymerization and demonstrate that two PhaC and two PhaE subunits comprise a single catalytic site in the synthase complex.

Effect of isotope substitution and controlled dehydration on the photoinduced electron transport reactions of quinone acceptors and multiheme cytochrome C in bacterial photosynthetic reaction center.

Isotope substitution of H2O by 2H2O causes an increase in the rate of dark recombination between photooxidized bacteriochlorophyll (P+) and reduced primary quinone acceptor in Rhodobacter sphaeroides reaction centers (RC) at room temperature. The isotopic effect declines upon decreasing the temperature. Dehydration of RC complexes of Ectothiorhodospira shaposhnikovii chromatophores containing multiheme cytochrome c causes a decrease in the efficiency of transfer of a photomobilized electron between the primary and secondary quinone acceptors and from cytochrome to P+. In the case of H2O medium these effects are observed at a lower hydration than in 2H2O-containing medium. In the E. shaposhnikovii chromatophores subjected to dehydration in H2O, the rate of electron transfer from the nearest high-potential cytochrome heme to P+ is virtually independent of hydration within the P/P0 range from 0.1 to 0.5. In samples hydrated in 2H2O this rate is approximately 1.5 times lower than in H2O. However, the isotopic effect of this reaction disappears upon dehydration. The intramolecular electron transfer between two high-potential hemes of cytochrome c in samples with 2H2O is inhibited within this range of P/P0, whereas in RC samples with H2O there is a trend toward gradual inhibition of the interheme electron transfer with dehydration. The experimental results are discussed in terms of the effects of isotope substitution and dehydration on relaxation processes and charge state of RC on implementation of the reactive states of RC providing electron transfer control.

The porins from the halophilic species Ectothiorhodospira shaposhnikovii and Ectothiorhodospira vacuolata.

Major outer membrane proteins with porin activity were isolated from cell envelopes of the halophilic strains Ectothiorhodospira shaposhnikovii N1 and Ectothiorhodospira vacuolata beta1. The porins were obtained as oligomers. They dissociated into monomers by heat or EDTA treatment. The molecular masses of the monomers were determined by mass spectrometry to be 39,285 and 37,160 Da for E. shaposhnikovii N1 and E. vacuolata beta1, respectively. Both were shown by analytical ultracentrifugation to be trimers of about 112, 000 Da. Circular dichroism spectra indicated predominantly beta-sheet structure. The 18 N-terminal amino acid sequences of the two porins were identical except for the amino acids in positions 12 and 14. No sequence similarity with the primary structure of known porins was found. In reconstitution experiments with lipid bilayers, the porins of E. shaposhnikovii N1 and E. vacuolata beta1 formed channels with a single-channel conductance of 1.5 and 0.7 nS, respectively, in 1 M KCl. The single-channel conductance saturated with increasing salt concentration, indicating a putative binding-site for anions in the channel since both porins exhibited anion-selectivity. For the porin of E. vacuolata beta1, but not for that of E. shaposhnikovii N1, an influence of detergent concentration on the single-channel conductance was observed.

The phylogenetic relationship among Ectothiorhodospiraceae: a reevaluation of their taxonomy on the basis of 16S rDNA analyses.

Sequences of the 16S rRNA gene were determined from all type strains of the recognized Ectothiorhodospira species and from a number of additional strains. For the first time, these data resolve the phylogenetic relationships of the Ectothiorhodospiraceae in detail, confirm the established species, and improve the classification of strains of uncertain affiliation. Two major groups that are recognized as separate genera were clearly established. The extremely halophilic species were removed from the genus Ectothiorhodospira and reassigned to the new genus Halorhodospira gen. nov., to recognize that the most halophilic eubacteria are species of this genus. These species are Halorhodospira halophila comb. nov., Halorhodospira halochloris comb. nov., and Halorhodospira abdelmalekii comb. nov. Among the slightly halophilic Ectothiorhodospira species, the classification of strains belonging to Ectothiorhodospira mobilis and Ectothiorhodospira shaposhnikovii was improved. Several strains that were tentatively identified as Ectothiorhodospira mobilis form a separate cluster on the basis of their 16S rDNA sequences and are recognized as two new species: Ectothiorhodospira haloalkaliphila sp. nov., which includes the most alkaliphilic strains originating from strongly alkaline soda lakes, and Ectothiorhodospira marina, describing isolates from the marine environment.

Removal of H2S by the purple sulphur bacterium Ectothiorhodospira shaposhnikovii

When Ectothiorhodospira shaposhnikovii VKM B-1525 was used for desuphurization of biogas in the laboratory and in a pilot plant, there was complete oxidation of H2S, the main product being elemental sulphur. The advatage of this culture over green bacteria is discussed.

The quantum requirement for H2 production by anoxygenic phototrophic bacteria

Cultures from three groups of phototrophic bacteria (green sulphur bacteria, purple non-sulphur bacteria and purple sulphur bacteria) were investigated in respect of the quantum requirement for H2 production (QH2). Rates of H2 formation were determined by means of a Clark-type H2 electrode with dense suspensions of whole cells and malate, acetate or sulphide as electron donor. At low light intensities (0–3 W·m−2 of monochromatic light) the minimum quantum requirement was 8.6 quanta per H2 with Chlorobium vibrioforme, 7.5 with Rhodospirillum rubrum, and 23.2 with Ectothiorhodospira shaposhnikovii. The physiological efficiency, defined as the measured QH2 compared to the theoretical value calculated from the energy requirement of the physiological processes involved, was 94%, 88%, or 28%, respectively. With increasing light intensities the quantum requirement also increased. Various hydrogenase inhibitors either inhibited both H2 uptake and production (Cu2+, NO), or affected neither of these activities (CO, C2H2, N2O, ethylenedinitrilotetraacetate). An uptake hydrogenase-deficient Hup−-mutant of R. rubrum had higher rates of net H2 production but a similar quantum requirement. The energetic efficiency of H2 production by various biological and artificial systems is discussed.

Abundance, subunit composition, redox properties, and catalytic activity of the cytochrome bc1 complex from alkaliphilic and halophilic, photosynthetic members of the family Ectothiorhodospiraceae.

Ubiquinol-cytochrome c oxidoreductase (cytochrome bc1) complexes were demonstrated to be present in the membranes of the alkaliphilic and halophilic purple sulfur bacteria Ectothiorhodospira halophila, Ectothiorhodospira mobilis, and Ectothiorhodospira shaposhnikovii by protoheme extraction, immunoblotting, and electron paramagnetic resonance spectroscopy. The gy values of the Rieske [2Fe-2S] clusters observed in membranes of E. mobilis and E. halophila were 1.895 and 1.910, respectively. In E. mobilis membranes, the cytochrome bc1 complex was present in a stoichiometry of approximately 0.2 per reaction center. This complex was isolated and characterized. It contained four prosthetic groups: low-potential cytochrome b (cytochrome bL; Em = -142 mV), high-potential cytochrome b (cytochrome bH; Em = 116 mV), cytochrome c1 (Em = 341 mV), and a Rieske iron-sulfur cluster. The absorbance spectrum of cytochrome bL displayed an asymmetric alpha-band with a maximum at 564 nm and a shoulder at 559 nm. The alpha bands of cytochrome bH and cytochrome c1 peaked at 559.5 and 553 nm, respectively. These prosthetic groups were associated with three different polypeptides: cytochrome b, cytochrome c1, and the Rieske iron-sulfur protein, with apparent molecular masses of 43, 30, and 21 kDa, respectively. No evidence for the presence of a fourth subunit was obtained. Maximal ubiquinol-cytochrome c oxidoreductase activity of the purified complex was observed at pH 8; the turnover rate was 57 mol of cytochrome c reduced.(mol of cytochrome c1)-1.s-1. The complex showed a strikingly low sensitivity towards typical inhibitors of cytochrome bc1 complexes.

Chemical composition of the lipopolysaccharides of Ectothiorhodospira shaposhnikovii, Ectothiorhodospira mobilis, and Ectothiorhodospira halophila

Lipopolysaccharides were isolated from the moderate halophilic Ectothiorhodospira shaposhnikovii slight to and Ectothiorhodospira mobilis and from the extremely halophilic Ectothiorhodospira halophila by the hot phenol-water and purified by the phenol-chloroform-petroleum ether methods. The isolated lipopolysaccharides of all three species contained 3-deoxy-d-manno-octulosonic acid and d-glycero-d-mannoheptose indicating the existence of a core. They contained additionally glucose and uronic acids (E. shaposhnikovii and E. mobilis) or glucose, uronic acids and threonine (E. halophila). Sodium deoxycholate gel-electrophoresis of the three lipopolysaccharides, each showing only one major band, indicated R-type character of the lipopolysaccharides of the three Ectothiorhodospira species. The lipid A fractions of the lipopolysaccharides from E. shaposhnikovii and E. mobilis represented phosphorylated “mixed” lipid A types with both 2,3-diamino-2,3-dideoxy-d-glucose and d-glucosamine. The lipid A from E. halophila contained also phosphate and 2,3-diamino-2,3-dideoxy-d-glucose but only traces of d-glucosamine, which would indicated lipid ADAG. The fatty acid spectra were characterized by amide-bound 3-OH-10:0 and 3-OH-12:0 (E. shaposhnikovii), 3-OH-10:0 (E. mobilis), or 3-OH-10:0,3-OH-14:0, and 3-oxo-14-0 (E. halophila). The predominant ester-bound fatty acids were 14:0 and 16:0 (E. shaposhnikovii and E. mobilis), or 12:0 and 14:1 (E. halophila).

Catabolic repression of hydrogenase synthesis in Ectothiorhodospira shaposhnikovii

The hydrogenase activity of purple sulfur bacterium Ectothiorhodospira shaposhnikovii was minimal when grown in acetate excess. Molecular hydrogen evolved to the nitrogenase activity of cells cultivated in chemostat under ammonium limitation did not increase the hydrogenase activity. Under acetate limitation, the flow rate decline increased the hydrogenase activity of cells and simultaneously the intracellular content of cyclic adenosine-5′-monophospate. Therefore, the hydrogenase synthesis by E. shaposhnikovii is regulated by catabolic repression.

Effects of dehydration and low temperatures on the oxidation of high-potential cytochrome c by photosynthetic reaction centers in Ectothiorhodospira shaposhnikovii

Effects of temperature and dehydration on the efficiency of electron transfer from membrane-bound high-potential cytochromes c h to the reaction-center bacteriochlorophyll (P-890) in Ectothiorhodospira shaposhnikovii have been studied. A kinetic analysis of the cytochrome oxidation suggests that there are at least two conformational states of the c h-P-890 complex, of which only one allows photoinduced electron transfer from cytochrome to P-890 +. Lowering the temperature of dehydration leads to a change in the proportion of the populations in the two conformations. The observed 2-fold deceleration of cytochrome oxidation can be related only to the diminution of the amount of photoactive cytochromes per reaction center. The rate constant for the transfer of an electron from cytochrome c h to bacteriochlorophyll is 2.8 · 10 5 s −1 and is independent of temperature and dehydration (as estimated within the accuracy of the experiments). The effects produced by low temperature and dehydration are completely reversible. The thermodynamic parameters of the transition of the cytochrome from the nontransfer to electron-transfer conformation were estimated. For room temperature (+ 20°C) in chromatophore preparations, ΔG = −5.4 kJ · M −1, ΔH = 60 kJ · M −1, ΔS = 0.22 kJ · M −1 · K −1. For Triton X-100 subchromatophore preparations, the absolute values of the above parameters are significantly lower: ΔG = −2.8 kJ · M −1, ΔH = 18 kJ · M −1, and ΔS = 0.075 kJ · M −1 · K −1. To a larger extent, the above parameters are diminished for chromatophore preparations in an 80% glycerol solution: ΔG = −1.7 kJ · M −1, ΔH = 6 kJ · M −1, ΔS = 0.025 kJ · M −1 · K −1. The data suggest the hydrophobic character of the forces that maintain the P-890- c h complex in the electron-transfer conformation. The results obtained suggest that electron tunneling within the complex cannot occur until a specific conformational configuration of the complex is formed. The efficiency of cytochrome c h oxidation is determined by the temperature, the degree of dehydration and the environmental conditions, whereas the transfer of an electron itself in the electron-transfer configuration is essentially independent of temperature and hydration.

The mobility of chromatophore membranes from Ectothiorhodospira Shaposhnikovii revealed by Rayleigh scattering of M�ssbauer radiation (RSMR) experiments

Chromatophores from Ectothiorhodospira Shaposhnikovii in solvents of different viscosity were investigated by RSMR experiments in the temperature range between 112 K and room temperature. Additional RSMR-experiments were done on solvents only. The mobility of the molecules and within the molecules is the given by the Debye-Waller factor which yields the meansquare displacement, \(\overline {\left\langle {x^2 } \right\rangle }\), averaged over the atoms in the system. The mobility of the atoms of the chromatophores roughly follows the mobility of the atoms of the solvents. At low temperatures the mobility of the chromatophores remains slightly larger than the mobility of the frozen solvent. At room temperature, however, \(\overline {\left\langle {x^2 } \right\rangle }\) of the chromatophores remains significantly smaller.

The biosynthesis of carbamoyl phosphate by Ectothiorhodospira shaposhnikovii and its utilization in carbamoylation reactions

The biosynthesis of carbamoyl phosphate by Ectothiorhodospira shaposhnikovii and its utilization in carbamoylation reactions

The biosynthesis of carbamoyl phosphate byEctothiorhodospira shaposhnikoviiand its utilization in carbamoylation reactions

Carbamoyl phosphate is synthesized by the purple bacterium Ectothiorhodospira shaposhnikovii from CO2, NH3 and ATP and is used for enzymatic transfer of the carbamoyl moiety to ornithine. In addition to this reaction nonenzymatic carbamoylation of some amino derivatives occurs, especially at high concentrations of the carbamoyl acceptors and at a temperature of about 45°C. The role of such reactions is discussed.