A bacteriochlorophyll a antenna complex from purple bacteria absorbing at 963 nm

A recently isolated species of the photosynthetic purple sulfur bacteria, provisionally called strain 970, was investigated with respect to its antenna function by means of various spectroscopic techniques, including fluorescence and pump-probe absorption difference spectroscopy. The bacterium contains bacteriochlorophyll a and an as yet unidentified carotenoid, perhaps 3,4,3',4'-tetrahydrospirilloxanthin. It has a single antenna complex of the LH1 type, with a Q(y) absorption band situated at the unusually long wavelength of 963 nm at room temperature and 990 nm at 6 K. In contrast to many other species, the reaction center showed two well-separated absorption bands of bacteriopheophytin at 6 K, located at 747 and 762 nm. The primary electron donor showed a bleaching band centered at 925 nm upon photooxidation. Thus, the energy gap between LH1 and the primary electron donor is quite large in this strain: 425 cm(-1). Nevertheless, trapping occurred with a time constant of 65 +/- 5 ps, similar to the rates observed in other purple bacteria. As in other species, no back-transfer from the reaction center to the antenna was observed. Our results show that strain 970 is a unique subject for the study of antenna and reaction center function and organization.     

Effect of high pressure on the photochemical reaction center from Rhodobacter sphaeroides R26.1

High-pressure studies on the photochemical reaction center from the photosynthetic bacterium Rhodobacter sphaeroides, strain R26.1, shows that, up to 0.6 GPa, this carotenoid-less membrane protein does not loose its three-dimensional structure at room temperature. However, as evidenced by Fourier-transform preresonance Raman and electronic absorption spectra, between the atmospheric pressure and 0.2 GPa, the structure of the bacterial reaction center experiences a number of local reorganizations in the binding site of the primary electron donor. Above that value, the apparent compressibility of this membrane protein is inhomogeneous, being most noticeable in proximity to the bacteriopheophytin molecules. In this elevated pressure range, no more structural reorganization of the primary electron donor binding site can be observed. However, its electronic structure becomes dramatically perturbed, and the oscillator strength of its Q(y) electronic transition drops by nearly one order of magnitude. This effect is likely due to very small, pressure-induced changes in its dimeric structure.     

Carotenoid triplet state formation in Rhodobacter sphaeroides R-26 reaction centers exchanged with modified bacteriochlorophyll pigments and reconstituted with spheroidene

Triplet state electron paramagnetic resonance (EPR) experiments have been carried out at X-band on Rb. sphaeroides R-26 reaction centers that have been reconstituted with the carotenoid, spheroidene, and exchanged with 13²-OH-Zn-bacteriochlorophyll a and [3-vinyl]-13²-OH-bacteriochlorophyll a at the monomeric, accessory bacteriochlorophyll sites B_A,B or with pheophytin a at the bacteriopheophytin sites H_A,B. The primary donor and carotenoid triplet state EPR signals in the temperature range 95–150 K are compared and contrasted with those from native Rb. sphaeroides wild type and Rb. sphaeroides R-26 reaction centers reconstituted with spheroidene. The temperature dependencies of the EPR signals are strikingly different for the various samples. The data prove that triplet energy transfer from the primary donor to the carotenoid is mediated by the monomeric, BChl_B molecule. Furthermore, the data show that triplet energy transfer from the primary donor to the carotenoid is an activated process, the efficiency of which correlates with the estimated triplet state energies of the modified pigments.Abbreviations BChl bacteriochlorophyll - BPhe bacteriopheophytin - Chl chlorophyll - EPR electron paramagnetic resonance - LDAO lauryl-dimethylamine-N-oxide - Phe pheophytin     

Transient optical spectroscopy of single crystals of the reaction center from Rhodobacter sphaeroides wild-type 2.4.1

The photoactivity of the crystallized reaction centers from Rhodobacter sphaeroides wild-type strain 2.4.1 has been examined by light-induced absorption spectral changes associated with charge separation and triplet state formation in the reaction center. Upon excitation of a crystal at ambient redox potential, the primary donor 865 nm band bleaches reversibly. The kinetics of its recovery were found to be biphasic with rate constants 11.5 +/- 1.3 s-1 and 0.9 +/- 0.4 s-1 which correspond to lifetimes of 87.0 +/- 9.0 ms and 1.0 +/- 0.7 s, respectively. The ratio of the fast-to-slow component preexponential terms was 3.5 +/- 1.1 suggesting that the majority (78.9 +/- 13.0%) of the reaction centers in the crystals lack the secondary quinone, QB. The addition of sodium ascorbate to the crystals attenuates the 865 nm absorption change, and gives rise to strong carotenoid triplet-triplet absorption changes at 547 nm. These data indicate that the reaction center-bound carotenoid in the crystals is capable of accepting triplet energy from the primary donor triplet.     

Coexistence of a sulphate-reducing Desulfovibrio species and the dehalorespiring Desulfitobacterium frappieri TCE1 in defined chemostat cultures grown with various combinations of sulfate and tetrachloroethene

A two-member co-culture consisting of the dehalorespiring Desulfitobacterium frappieri TCE1 and the sulphate-reducing Desulfovibrio sp. strain SULF1 was obtained via anaerobic enrichment from soil contaminated with tetrachloroethene (PCE). In this co-culture, PCE dechlorination to cis -dichloroethene was due to the activity of the dehalorespiring bacterium only. Chemostat experiments with lactate as the primary electron donor for both strains along with varying sulphate and PCE concentrations showed that the sulphate-reducing strain outnumbered the dehalogenating strain at relatively high ratios of sulphate/PCE. Stable co-cultures with both organisms present at similar cell densities were observed when both electron acceptors were supplied in the reservoir medium in nearly equimolar amounts. In the presence of low sulphate/PCE ratios, the Desulfitobacterium sp. became the numerically dominant strain within the chemostat co-culture. Surprisingly, in the absence of sulphate, strain SULF1 did not disappear completely from the co-culture despite the fact that there was no electron acceptor provided with the medium to be used by this sulphate reducer. Therefore, we propose a syntrophic association between the sulphate-reducing and the dehalorespiring bacteria via interspecies hydrogen transfer. The sulphate reducer was able to sustain growth in the chemostat co-culture by fermenting lactate and using the dehalogenating bacterium as a 'biological electron acceptor'. This is the first report describing growth of a sulphate-reducing bacterium in a defined two-member continuous culture by syntrophically coupling the electron and hydrogen transfer to a dehalorespiring bacterium.     

Kinetic study of PF and CarT states in the LM subunit purified from the wild-type Rhodobacter sphaeroides reaction centers

The kinetics of absorbance changes related to the charge-separated state, P^F, and to the formation and decay of the carotenoid triplet state (Car^T) were studied in the LM reaction center subunit isolated from a wild-type strain of the purple bacterium Rhodobacter sphaeroides (strain Y). The P^F lifetime is lengthened (20±1.5 ns) in the LM complex as compared to the intact reaction centers (11±1 ns). The yield of the carotenoid triplet formation is higher (0.28±0.01) in the LM complex than in native reaction centers. We interpret our results in terms of perturbations of a first-order reaction connecting the singlet and the triplet state of the radical-pair state. Our results, together with those of a recent work (Agalidis, I., Nuijs, A.M. and Reiss-Husson, F. (1987) Biochim. Biophys. Acta (in press)) are consistent with a high I to Q_A electron transfer rate in this LM subunit, which is metal-depleted.The LM complex is considerably more sensitive than the reaction centers to photooxidative damage in the presence of oxygen. This is not readily accounted for simply by the higher carotenoid triplet yield, and may suggest a greater accessibility of the internal structures in the absence of the H-subunit.The lifetime of the carotenoid triplet decay (6.4±0.3 s) in the LM subunit is unchanged compared to the native reaction centers.Abbreviations BChl bacteriochlorophyll - Bph bacteriopheophytin - Car carotenoid - Chl chlorophyll - cyt cytochrome - L, M and H subunits light, medium and heavy subunits of the reaction center complex - P^R triplet electronic state of the primary electron donor - P; Q_A the first stable electron acceptor, a bound quinone - RC reaction center - LDAO lauryldimethylamine N-oxide - SDS sodium dodecyl sulfate - UQ ubiquinone This paper is published in our new format. All future authors are requested to follow our new instructions (see Photosynthesis Research 10:519–526, 1986)—Editor.     

Photosynthetic unit size and electron-transport chain in a photoreaction center-depleted mutant of Rhodospirillum rubrum

The aim of this work was to explain the relatively fast growth of a mutant of Rhodospirillum rubrum (F24.1) which contains 7–8% of an apparently normal photoreaction center. We explored the double hypothesis that the size of its photosynthetic unit is larger than that of the wild type and that its electron-transport chain is organized in a network rather than in isolated loops. The first feature would allow faster growth under less than saturating light intensities and the second would allow faster maximal electron fluxes than would be predicted from the photoreaction center content. With respect to the first possibility, measurements of absorbance changes at 793 nm induced by short flashes of increasing intensity indicate that the photosynthetic unit of strain F24.1 is 5.6-fold larger than that of strain S1. The second possibility was verified by measuring relative electron fluxes at the photoreaction center in the two strains. This was established in the steady state from the amount of primary donor oxidized by a continuous light beam of increasing intensity. This electron flux was found to be about 70% as high in strain F24.1 as in strain S1. A more detailed study of the electron-transport chain indicated that cytochrome c₂ is by far the main secondary electron donor in strain F24.1. No evidence could be obtained for the existence of another secondary donor in that strain. The mole ratio of cytochrome c₂ to photoreaction center is about 6 in strain F24.1 as conpared to about 0.5 in strain S1. In strain 24.1, the pool of secondary donor appears to be collectively involved in the reduction of the oxidized primary donor. The replacement time at the photoreaction center of a first equivalent of oxidized cytochrome c₂ by a second equivalent of reduced cytochrome c₂ is less than or equal to 0.2 ms. The effect of the photoreaction center content on the size of the photosynthetic unit is discussed in terms of the different models proposed for the organisation of the photosynthetic unit. We propose that the electron-transport chain is organized in a network, perhaps by virtue of the lateral mobility of some of the electron carriers such as ubiquinone and cytochrome c₂.     

Sclerotial biomass and carotenoid yield of Penicillium sp. PT95 under oxidative growth conditions and in the presence of antioxidant ascorbic acid

AIMS: To determine the effect of oxidative stress and exogenous ascorbic acid on sclerotial biomass and carotenoid yield of Penicillium sp. PT95. METHODS: In this experiment, high oxidative stress was applied by the inclusion of FeSO(4) in the growth medium and exposure to light. Low oxidative stress was applied by omitting iron from the growth medium and by incubation in the dark. Supplementation of exogenous ascorbic acid (as antioxidant) to the basal medium caused a concentration-dependent delay of sclerotial differentiation (up to 48 h), decrease of sclerotial biomass (up to 40%) and reduction of carotenoid yield (up to 91%). On the contrary, the exogenous ascorbic acid also caused a concentration-dependent decrease of lipid peroxidation in colonies of this fungus. CONCLUSIONS: Under high oxidative stress growth condition, the sclerotial biomass and carotenoid yield of PT95 strain in each plate culture reached 305 mg and 32.94 microg, which were 1.23 and 3.71 times higher, respectively, than those at low oxidative stress growth condition. These data prompted us to consider that in order to attain higher sclerotial biomass and pigment yield, the strain PT95 should be grown under high oxidative stress and in the absence of antioxidants. SIGNIFICANCE AND IMPACT OF THE STUDY: These results suggest that strain PT95 may be used for solid-state fermentation of carotenoid production under high oxidative stress growth conditions.     

Triplet state EPR of reaction centers from the HisL173→LeuL173 mutant of Rhodobacter sphaeroides which contains a heterodimer primary donor

Electron paramagnetic resonance (EPR) spectroscopy has been used to examine the triplet states in reaction centers of Rhodobacter sphaeroides which have undergone a genetic modification affecting the primary donor. Reaction centers containing the His^L173Leu^L173 substitution in the amino acid sequence have a primary donor which consists of a BChl-BPh heterodimer. The triplets formed in this heterodimer reaction center were compared with those formed in the wild-type reaction center which contains the BChl-BChl homodimer. Both reaction centers transfer triplet energy to the carotenoid under illumination at liquid nitrogen temperatures (90 K). However, the intensity of the carotenoid triplet signal is significantly decreased in the Leu^L173 mutant compared with the wild-type reaction center. At 12 K, in wild-type reaction centers only the primary donor triplet is observed. The Leu^L173 mutant exhibits a signal similar to that observed by Bylina et al. (1990) in His^M200Leu^M200 mutant reaction centers from Rb. capsulatus. The values of the zero-field splitting parameters of this triplet are discussed within the context of various models for the primary donor triplet state. No alteration in the ability of the carotenoid to quench the primary donor triplet state results from mutations at these sites.Abbreviations BChl bacteriochlorophyll - BPh bacteriopheophytin - EPR electron paramagnetic resonance - LDAO lauryl-dimethylamine N-oxide     

Dermal carotenoid measurements via pressure mediated reflection spectroscopy

We describe a reflection‐based method for the quantitative detection of carotenoid antioxidants in living human skin. The skin tissue site of interest is illuminated with broad‐band white light spanning the spectral range from 350–850 nm and the spectral composition of the diffusively reflected light is analyzed in real time. Topical pressure is applied to temporarily squeeze blood out of the illuminated tissue volume. In this way the influence of oxy‐hemoglobin on the reflection spectra is effectively reduced. After a short optical clearing time the carotenoid absorption becomes easily discernable in a 460–500 nm spectral window and its optical density can be calculated with high accuracy. Our empirical methodology provides a non‐invasive rapid determination of skin carotenoid levels, can be used to monitor skin carotenoid concentration changes over time in response to carotenoid containing natural or supplemental diets, and is easily adaptable for applications in clinical and field settings. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dual role of the plastid terminal oxidase in tomato

The plastid terminal oxidase (PTOX) is a plastoquinol oxidase whose absence in tomato (Solanum lycopersicum) results in the ghost (gh) phenotype characterized by variegated leaves (with green and bleached sectors) and by carotenoid-deficient ripe fruit. We show that PTOX deficiency leads to photobleaching in cotyledons exposed to high light primarily as a consequence of reduced ability to synthesize carotenoids in the gh mutant, which is consistent with the known role of PTOX as a phytoene desaturase cofactor. In contrast, when entirely green adult leaves from gh were produced and submitted to photobleaching high light conditions, no evidence for a deficiency in carotenoid biosynthesis was obtained. Rather, consistent evidence indicates that the absence of PTOX renders the tomato leaf photosynthetic apparatus more sensitive to light via a disturbance of the plastoquinone redox status. Although gh fruit are normally bleached (most likely as a consequence of a deficiency in carotenoid biosynthesis at an early developmental stage), green adult fruit could be obtained and submitted to photobleaching high light conditions. Again, our data suggest a role of PTOX in the regulation of photosynthetic electron transport in adult green fruit, rather than a role principally devoted to carotenoid biosynthesis. In contrast, ripening fruit are primarily dependent on PTOX and on plastid integrity for carotenoid desaturation. In summary, our data show a dual role for PTOX. Its activity is necessary for efficient carotenoid desaturation in some organs at some developmental stages, but not all, suggesting the existence of a PTOX-independent pathway for plastoquinol reoxidation in association with phytoene desaturase. As a second role, PTOX is implicated in a chlororespiratory mechanism in green tissues.     

Effect of oxidative stress and exogenous beta-carotene on sclerotial differentiation and carotenoid yield of Penicillium sp. PT95

AIMS: To determine the effect of oxidative stress and exogenous beta-carotene on sclerotial differentiation and carotenoid yield of Penicillium sp. PT95. METHODS AND RESULTS: In this experiment, high oxidative stress was applied by inclusion of FeCl(3) (10 micromol l(-1)) in the growth medium and by light exposure. Low oxidative stress was applied by omitting iron from the growth medium and by incubation in the dark. Supplementation of exogenous beta-carotene (as antioxidant) to the basal medium caused a concentration-dependent delay of sclerotial differentiation (up to 72 h), decrease of sclerotial biomass (up to 43%) and reduction of carotenoid yield (up to 92%). On the contrary, the exogenous beta-carotene also caused a concentration-dependent decrease of lipid peroxidation in colonies of this fungus. CONCLUSIONS: Under high oxidative stress growth condition, the sclerotial biomass and carotenoid yield of PT95 strain in each plate culture reached 141 mg and 30.03 microg, which were 1.53 and 3.51 times higher respectively, than that at low oxidative stress growth condition. SIGNIFICANCE AND IMPACT OF THE STUDY: These data prompted us to consider that in order to attain higher sclerotial biomass and pigment yield, the strain PT95 should be grown under high oxidative stress and in the absence of antioxidants.     

Photochemical properties of Escherichia coli DNA photolyase: a flash photolysis study

Escherichia coli DNA photolyase contains a stable flavin neutral blue radical that is involved in photosensitized repair of pyrimidine dimers in DNA. We have investigated the effect of illumination on the radical using light of lambda greater than 520 nm from either a camera flash or laser. We find that both types of irradiations result in the photoreduction of the flavin radical with a quantum yield of 0.10 +/- 0.02. While photoreduction with the camera flash is minimal in the absence of an electron donor (dithiothreitol), laser flash photolysis at 532 nm reduces the flavin to the same extent in the presence or absence or an electron donor. Thus, it is concluded that the primary step in photoreduction involves an electron donor that is a constituent of the enzyme itself. Laser flash photolysis produces a transient absorption band at 420 nm that probably represents the absorption of the lowest excited doublet state (2(1)IIII*) of the radical and decays with first-order kinetics with k1 = 0.8 X 10(6) s-1. The photoreduction data combined with the results of recent studies on the activity of dithionite-reduced enzyme suggest that electron donation by excited states of E-FADH2 is the mechanism of flavin photosensitized dimer repair by E. coli DNA photolyase.     

Excited states and primary charge separation in the pigment system of the green photosynthetic bacterium Prosthecochloris aestuarii as studied by picosecond absorbance difference spectroscopy

Picosecond absorbance difference spectra at a number of delay times after a 35 ps excitation flash and kinetics of absorbance changes were measured of the membrane vesicle preparation Complex I from the photosynthetic green sulfur bacterium Prosthecochloris aestuarii. After chemical oxidation of the primary donor the excitation pulse produced singlet and triplet excited states of carotenoid and bacteriochlorophyll a. With active reaction centers present also the flash-induced primary charge separation and subsequent electron transfer were observed. The singlet excited state of the carotenoid, formed by direct excitation at 532 nm, is characterized by an absorbance band peaking at 590 nm. Its average lifetime was calculated to be about 1 ps. Excited singlet states of bacteriochlorophyll a were characterized by a bleaching of their ground state Q_y absorption bands. Singlet excited states, localized on the so-called core complex, were produced by energy transfer from excited carotenoid. Their lifetime was about 70 ps. A decay component of about 280 ps was ascribed to singlet excited bacteriochlorophyll a in the bacteriochlorophyll a protein. These singlet excitations were partly converted to the triplet state. With active reaction centers, oxidation of the primary donor, P-840, characterized by the bleaching of its Q_y and Q_x absorption bands, was observed. This oxidation was accompanied by a bleaching between 650 and 680 nm and an absorbance increase between 680 and 750 nm. These changes, presumably due to reduction of bacteriopheophytin c (Van Bochove, A.C., Swarthoff, T., Kingma, H., Hof, R.M., Van Grondelle, R., Duysens, L.N.M. and Amesz, J. (1984) Biochim. Biophys. Acta 764, 343–346), were attributed to the reduction of the primary electron acceptor. Electron transfer to a secondary acceptor occurred with a time-constant of 550 ± 50 ps. Since no absorbance changes due to reduction of this acceptor were observed in the red or infrared region, we tentatively assume that this acceptor is an iron-sulfur center.     

Orientation of Photosystem-I pigments: low temperature linear dichroism spectroscopy of a highly-enriched P700 particle isolated from spinach

The linear dichroism of Photosystem I particles containing 10 chlorophylls per P700 has been investigated at 10 K. The particles were oriented by uniaxial squeezing of polyacrylamide gels. The oxidation state of P700 was altered either by incubation of the gels with redox mediators or by low temperature illumination. The Q_Y transitions of the primary electron donor P700, of the remaining unoxidized chlorophyll in P700⁺ and of a chlorophyll molecule absorbing at 686 nm, which presumably corresponds to the primary electron acceptor A₀, are all preferentially oriented perpendicular to the gel squeezing direction. The Q_Y transition of the chlorophyll forms absorbing at 670 and 675 nm appear tilted at 40 ± 5° from this orientation axis. This orientation of the various chlorophylls is compared to that previously reported for more native Photosystem I particles.Abbreviations PSI Photosystem I - P700 primary electron donor of PSI - A₀ primary electron acceptor of PSI     

Interaction of chloroplasts with inhibitors: induction of chlorosis by diuron during prolonged illumination in vitro

A primary symptom of diuron (DCMU) phytotoxicity in plants is the destruction of chlorophyll. To study this process in vitro, chloroplasts from pea leaves (Pisum sativum L.) have been incubated in the light with DCMU for periods of up to 34 hours. The sequence of photodestruction of chlorophylls and carotenoids has been followed to try and establish the nature of the chloroplast protection mechanisms that are destroyed by DCMU. β-Carotene decays most rapidly, followed by chlorophyll a and xanthophylls which are destroyed in a constant ratio, followed finally by chlorophyll b. Bypassing the DCMU block in the electron transport system with an artificial electron donor provides complete protection against chlorophyll and carotenoid photodestruction. The same protection by this electron donor system is afforded to stroma-free lamellae from which soluble reductants have been removed so that NADPH formation, which has been proposed as an essential part of a protective xanthophyll cycle, is not possible. Both this and the simultaneous loss of chlorophyll a and xanthophylls tend to preclude the breakdown of a xanthophyll cycle from the possible protective mechanisms inhibited or destroyed by DCMU.     

Quantum yield and rate of formation of the carotenoid triplet state in photosynthetic structures

The formation of the triplet state of carotenoids (detected by an absorption peak at 515 nm) and the photo-oxidation of the primary donor of Photosystem II, P-680 (detected by an absorption increase at 820 nm) have been measured by flash absorption spectroscopy in chloroplasts in which the oxygen evolution was inhibited by treatment with Tris. The amount of each transient form has been followed versus excitation flash intensity (at 590 or 694 nm). At low excitation energy the quantum yield of triplet formation (with the Photosystem II reaction center in the state Q⁻) is about 30% that of P-680 photo-oxidation. The yield of carotenoid triplet formation is higher in the state Q⁻ than in the state Q, in nearly the same proportion as chlorophyll a fluorescence. It is concluded that, for excited chlorophyll a, the relative rates of intersystem crossing to the triplet state and of fluorescence emission are the same in vivo as in organic solvent. At high flash intensity the signal of P-680⁺ completely saturates, whereas that of carotenoid triplet continues to increase.

The rate of triplet-triplet energy transfer from chlorophyll a to carotenoids has been derived from the rise time of the absorption change at 515 nm, in chloroplasts and in several light-harvesting pigment-protein complexes. In all cases the rate is very high, around 8 · 10⁷ s⁻¹ at 294 K. It is about 2–3 times slower at 5 K. The transitory formation of chlorophyll triplet has been verified in two pigment-protein complexes, at 5 K.     

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.     

含奥氏酮嗜盐紫色硫细菌的分离鉴定及系统发育分析

[目的]为挖掘我国紫色硫细菌物种和光合蛋白基因资源.[方法]采用Pfennig紫色硫细菌无机选择性培养基和琼脂稀释法.[结果]从青岛东风盐场分离获得一株含奥氏酮、耐高浓度硫化物、嗜盐耐碱紫色硫细菌菌株283-1.该菌株能氧化硫化物产生硫粒储存在细胞内、嗜盐、细胞含有奥氏酮类胡萝卜素、细菌叶绿素a强吸收峰位于830 nm处、运动、不产生气囊,表明属于Marichromatium属.16S rDNA序列同源性比较和系统发育分析也表明这一点.但该菌株能在1%～15%NaCl、7.5 mmol/L 高浓度硫化物、45℃、5000lux、pH9.0条件下生长良好,能很好的光同化C3和C4有机酸和葡萄糖酸钠等特性,与Marichromatium属4个种有明显不同.[结论]菌株283-1是Marichromatium属一个新分离物,编号 Marichromatium sp.283-1.     

外源β-胡萝卜素、光照对青霉PT95菌株菌核分化和类胡萝卜素产率的影响

初步研究了外源β-胡萝卜素和光照对青霉PT5菌株菌核分化和类胡萝卜素产率的影响。结果表明,在培养基中加入外源β-胡萝卜素后,PT5菌株渗出液出现的时间、菌核出现的时间延迟了,但菌核成熟的时间没变。培养基中的外源β-胡萝卜素浓度越大,其渗出液、菌核出现的时间越迟。外源β-胡萝卜素亦能降低PT5菌株的脂质过氧化水平和菌核中的类胡萝卜素含量。高氧胁迫的光照培养条件有利于PT95菌株的菌核分化和色素在菌核中的积累;与低氧胁迫的黑暗培养条件相比,其菌核生物量和类胡萝卜素产率分别增加了18．7％和101％。以上实验结果表明,若想获得高的菌核生物量和类胡萝卜素产率,应该尽可能在高氧胁迫、无抗氧化剂存在的条件下培养PT5菌株。