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1.
Microbial mats which lack cyanobacteria occur at 50° to 65° C in the sulfide-containing Mammoth Springs of Yellowstone National Park. The principal organisms within these mats are filamentous bacteria which resemble Chloroflexus aurantiacus. The incorporation of [14C]-HCO 3 - into mat material depended upon both light and sulfide, and was not inhibited when complete natural light was replaced with far-red and infra-red radiation. [14C]-acetate was incorporated in a light-dependent reaction which was stimulated by, but did not require, sulfide. In situ experiments with microelectrodes demonstrated net sulfide uptake by the mat in the light, and net sulfide production by the mat in the dark, suggesting the operation of a sulfur cycle.Filamentous phototrophic bacteria isolated from the mat were incapable of sustained growth in the presence of O2.Simultaneous exposure of cultures to light and O2 caused degradation of bacteriochlorophyll c. The stimulation of light-dependent [14C]-HCO 3 - -uptake by sulfide was more pronounced in these isolates than in strains of Chloroflexus aurantiacus.  相似文献   
2.
In this paper we attempt a functional and spectral characterization of the membrane-bound cytochromes involved in respiratory electron transport by membranes from cells of Chloroflexus aurantiacus grown in the dark under oxygen saturated conditions. We conclude that the NADH-dependent respiration is carried out by a branched respiratory chain leading to two oxidases which differ in sensitivity to CN- and CO. The two routes also show a different sensitivity to the ubiquinone analogue, HQNO, the pathway through the cytochrome c oxidase being fully blocked by 5 M HQNO, whereas the alternative one is insensitive to this inhibitor. The cytochrome c oxidase containing branch is composed by at least two c-type haems with E m 7.0 of +130 and +270 mV ( bands at 550/553 nm and 549 nm, respectively), plus a b-type cytochrome with E m 7.0 of +50 mV ( band at 561 nm). From this, and previous work, we conclude that respiratory and photosynthetic electron transport components are assembled together and function on a single undifferentiated plasma membrane.Abbreviations HQNO heptylhydroxy-quinoline-N-oxide - UHDBT undecyl-hydroxydioxobenthiazole - Q/b-c ubiquinol/cytochrome c oxidoreductase complex - BChl bacteriochlorophyll  相似文献   
3.
The transfer of excitation energy in intact cells of the thermophilic green photosynthetic bacterium Chloroflexus aurantiacus was studied both at low temperature and under more physiological conditions. Analysis of excitation spectra measured at 4K indicates that the minor fraction of bacteriochlorophyll a present in the chlorosome functions as an intermediate in energy transfer between the main light-harvesting pigment BChl c and the membrane-bound B808-866 antenna complex. This supports the hypothesis that BChl a is associated with the base plate which connects the chlorosome with the membrane. The overall efficiency for energy transfer from the chlorosome to the membrane is only 15% at 4K. High efficiencies of close to 100% are observed above 40°C near the temperature where the cultures are grown. Cooling to 20°C resulted in a sudden drop of the transfer efficiency which appeared to originate in the chlorosome. This decrease may be related to a lipid phase transition. Further cooling mainly affected the efficiency of transfer between the chlorosome and the membrane. This effect can only partially be explained by a decreased Förster overlap between the chlorosomal BChl a and BChl a 808 associated with the membrane-bound antenna system. The temperature dependence of the fluorescence yield of BChl a 866 also appeared to be affected by lipid phase transitions, suggesting that this fluorescence can be used as a native probe of the physical state of the membrane.  相似文献   
4.
Spectrally pure reaction center preparations from Chloroflexus aurantiacus have been obtained in a stable form; however, the product contained several contaminating polypeptides. The reaction center pigment molecules (probably three bacteriochlorophyll a and three bacteriopheophytin a molecules) are associated with two polypeptides (Mr = 30000 and 28000) in a reaction center complex of Mr = 52000. No carotenoid is present in the complex. These data together with previous spectral data suggest that the Chloroflexus reaction center represents a more primitive evolutionary form of the purple bacterial reaction center, and that it has little if any relationship to the green bacterial component. A reaction center preparation from Rhodopseudomonas sphaeroides R26 was fully denatured at 50°C while the Chloroflexus reaction center required higher temperatures (70–75°C) for complete denaturation. Thus, an intrinsic membrane protein of a photosynthetic thermophile has been demonstrated to have greater thermal stability than the equivalent component of a mesophile.  相似文献   
5.
The membrane-bound photooxidizable cytochrome c-554 from Chloroflexus aurantiacus has been purified. The purified protein runs as a single heme staining band on SDS-PAGE with an apparent molecular mass of 43 000 daltons. An extinction coefficient of 28 ± 1 mM–1 cm–1 per heme at 554 nm was found for the dithionite-reduced protein. The potentiometric titration of the hemes takes place over an extended range, showing clearly that the protein does not contain a single heme in a well-defined site. The titration can be fit to a Nernst curve with midpoint potentials at 0, +120, +220 and +300 mV vs the standard hydrogen electrode. Pyridine hemochrome analysis combined with a Lowry protein assay and the SDS-PAGE molecular weight indicates that there are a minimum of three, and probably four hemes per peptide. Amino acid analysis shows 5 histidine residues and 29% hydrophobic residues in the protein. This cytochrome appears to be functionally similar to the bound cytochrome from Rhodopseudomonas viridis. Both cytochrome c-554 from C. aurantiacus and the four-heme cytochrome c-558-553 from R. viridis appear to act as direct electron donors to the special bacteriochlorophyll pair of the photosynthetic reaction center. They have a similar content of hydrophobic amino acids, but differ in isoelectric point, thermodynamic characteristics, spectral properties, and in their ability to be photooxidized at low temperature.Abbreviations LDAO lauryl dimethyl amine-N-oxide - SDS-PAGE sodium dodecyl sulfate polyacrylamide gel electrophoresis - mV millivolt - Em.8 midpoint potential at pH 8.0 - ODV optical density x volume in ml  相似文献   
6.
Whole cells and isolated chlorosomes (antenna complex) of the green photosynthetic bacterium Chloroflexus aurantiacus have been studied by absorption spectroscopy (77 K and room temperature), fluorescence spectroscopy, circular dichroism, linear dichroism and electron spin resonance spectroscopy. The chlorosome absorption spectrum has maxima at 450 (contributed by carotenoids and bacteriochlorophyll (BChl) a Soret), 742 (BChl c) and 792 nm (BChl a) with intensity ratios of 20:25. The fluorescence emission spectrum has peaks at 748 and 802 nm when excitation is into either the 742 or 450 nm absorption bands, respectively. Whole cells have fluorescence peaks identical to those in chlorosomes with the addition of a major peak observed at 867 nm. The CD spectrum of isolated chlorosomes has an asymmetric-derivative-shaped CD centered at 739 nm suggestive of exciton interaction at least on the level of dimers. Linear dichroism of oriented chlorosomes shows preferential absorption at 742 nm of light polarized parallel to the long axis of the chlorosome. This implies that the transition dipoles are also oriented more or less parallel to the long axis of the chlorosome. Treatment with ferricyanide results in the appearance of a 2.3 G wide ESR spectrum at g 2.002. Whole cells grown under different light conditions exhibit different fluorescence behavior when absorption is normalized at 742 nm. Cells grown under low light conditions have higher fluorescence intensity at 748 nm and lower intensity at 802 nm than cells grown under high light conditions. These results indicate that the BChl c in chlorosomes is highly organized, and transfers energy from BChl c (742 nm) to a connector of baseplate BChl B792 (BChl a) presumably located in the chlorosome baseplate adjacent to the cytoplasmic membrane.  相似文献   
7.
Origin and early evolution of photosynthesis   总被引:12,自引:0,他引:12  
Photosynthesis was well-established on the earth at least 3.5 thousand million years ago, and it is widely believed that these ancient organisms had similar metabolic capabilities to modern cyanobacteria. This requires that development of two photosystems and the oxygen evolution capability occurred very early in the earth's history, and that a presumed phase of evolution involving non-oxygen evolving photosynthetic organisms took place even earlier. The evolutionary relationships of the reaction center complexes found in all the classes of currently existing organisms have been analyzed using sequence analysis and biophysical measurements. The results indicate that all reaction centers fall into two basic groups, those with pheophytin and a pair of quinones as early acceptors, and those with iron sulfur clusters as early acceptors. No simple linear branching evolutionary scheme can account for the distribution patterns of reaction centers in existing photosynthetic organisms, and lateral transfer of genetic information is considered as a likely possibility. Possible scenarios for the development of primitive reaction centers into the heterodimeric protein structures found in existing reaction centers and for the development of organisms with two linked photosystems are presented.Abbreviation Gyr gigayears  相似文献   
8.
The development of chlorosomes and their pigmentation were studied by growing Chloroflexus aurantiacus strain Ok-7o-fl first under conditions under which BChl c-synthesis is low (50°C, 2000 lux and 30°C, 1500 lux) and subsequently under conditions promoting high BChl c-synthesis (50°C, 400 lux). Electron microscopic observations on and chemical analyses of isolated cell components showed that in BChl c-depleted cells chlorosome-like structures (chlorosome bags) are attached to fragments of cytoplasmic membranes. These chlorosome bags exhibit a periodic fine structure caused by the construction of the baseplates of the chlorosomes. The baseplates are closely attached to the cytoplasmic membrane, they are rich in phospholipids and apparently contain a 790 nm-BChl a-complex. Chlorosome bags of BChl c-depleted cells always contain a limited amount of light-harvesting pigment complexes (BChlc, - and -carotene). The light-harvesting system is restored (50°C, 400 lux) by first refilling the existing chlorosome bags before cell division takes place.Abbreviations BChl Bacteriochlorophyll - LH Light-harvesting complex - RC Reaction center  相似文献   
9.
Abstract A saltern near La Baule (Bretagne, France) was remodeled in a programmable temperature and humidity controlled walk-in environmental chamber resembling the characteristics of the original saltern. The saltern showed different types of microbial mats predominantly composed of algae, oxy- and anoxyphotobacteria, and associated chemoorganotrophic bacteria, fungi and animals. Well-developed microbial mats were found up to a salinity of 10% during the three or four months in summer when salinity gradients and NaCl precipitation were established. The main phototrophic organisms were diatoms, the cyanobacteria Aphanothece, Microcoleus, Spirulina , and Oscillatoria , and Chromatiaceae. At higher salinity, Halobacterium sp., diatoms, and Dunaliella were dominant. Typical microbial mats and saltern-typical invertebrate, algal and bacterial species also developed in the saltern model, building up a stable community. The ionic composition of the brines and physicochemical parameters were similar to those determined for the original saltern. Different photosynthetic organisms, e.g. a filamentous purple bacterium and a hypersaline Chloroflexus -like organism, could be enriched within the microbial mats by changing the light regime.  相似文献   
10.
The composition, abundance and apparent molecular masses of chlorosome polypeptides from Chlorobium tepidum and Chlorobium vibrioforme 8327 were compared. The most abundant, low-molecular-mass chlorosome polypeptides of both strains had similar electrophoretic mobilities and abundances, but several of the larger proteins were different in both apparent mass and abundance. Polyclonal antisera raised against recombinant chlorosome proteins of Cb. tepidum recognized the homologous proteins in Cb. vibrioforme, and a one-to-one correspondence between the chlorosome proteins of the two species was confirmed. As previously shown [Ormerod et al. (1990) J Bacteriol 172: 1352–1360], acetylene strongly suppressed the synthesis of bacteriochlorophyll c in Cb. vibrioforme strain 8327. No correlation was found between the bacteriochlorophyll c content of cells and the cellular content of chlorosome proteins. Nine of ten chlorosome proteins were detected in acetylene-treated cultures, and the chlorosome proteins were generally present in similar amounts in control and acetylene-treated cells. These results suggest that the synthesis of chlorosome proteins and the assembly of the chlorosome envelope is constitutive. It remains possible that the synthesis of bacteriochlorophyll c and its insertion into chlorosomes might be regulated by environmental parameters such as light intensity.This revised version was published online in October 2005 with corrections to the Cover Date.  相似文献   
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