Introduction of perfluoroalkyl chain into the esterifying moiety of bacteriochlorophyll c in the green sulfur photosynthetic bacterium Chlorobaculum tepidum by pigment biosynthesis.

The green sulfur photosynthetic bacterium Chlorobaculum (Cba.) tepidum was grown in liquid cultures containing perfluoro-1-decanol, 1H,1H,2H,2H-heptadecafluoro-1-decanol [CF3(CF2)7(CH2)2OH] or 1H,1H-nonadecafluoro-1-decanol [CF3(CF2)8CH2OH], to introduce rigid and fluorophilic chains into the esterifying moiety of light-harvesting bacteriochlorophyll (BChl) c. Exogenous 1H,1H,2H,2H-heptadecafluoro-1-decanol was successfully attached to the 17(2)-carboxy group of bacteriochlorophyllide (BChlide) c in vivo: the relative ratio of the unnatural BChl c esterified with this perfluoroalcohol over the total BChl c was 10.3%. Heat treatment of the liquid medium containing 1H,1H,2H,2H-heptadecafluoro-1-decanol with ß-cyclodextrin before inoculation increased the relative ratio of the BChl c derivative esterified with this alcohol in the total BChl c in Cba. tepidum. In a while, 1H,1H-nonadecafluoro-1-decanol was not attached to BChlide c in Cba. tepidum, which was grown by its supplementation. These results suggest that the rigidity close to the hydroxy group of the esterifying alcohol is not suitable for the recognition by the BChl c synthase called BchK in Cba. tepidum. The unnatural BChl c esterified with 1H,1H,2H,2H-heptadecafluoro-1-decanol participated in BChl c self-aggregates in chlorosomes.

Formation of a Subunit Form of the Core Light-Harvesting Complex from Sulfur Purple Bacteria Ectothiorhodospira haloalkaliphila with Different Carotenoid Composition.

B820 subunits from a purple sulfur bacterium Ectothiorhodospira. haloalkaliphila strain ATCC 51935T were obtained by treatment of Carotenoid free LH I-RC complexes of this bacterium with P--octylglu- copyranoside (ß-OG). The same complexes with 100% carotenoid content were unable to dissociate to B820 subunits, but disintegrated to monomeric bacteriochlorophyll (BChl) regardless of their carotenoid compo- sition. The degree of dissociation of the LH 1-RC complexes with an intermediate content of carotenoids (the' B820 formation) was directly dependent on the quantity of carotenoids in the samples. The resulting B820 subunits did not contain carotenoids. B820 subunits easily aggregated to form a complex with an absorption . peak at 880 nm at decreased ß-OG concentration. Analysis of the spectra of the LH I-RC complexes isolated from the cells with different'levels of carotenogenesis inhibition led to the conclusion of the heterogeneity of the samples with a predominance in them of (a) the fraction with 100% of carotenoids and (b) the fraction of carotenoid free complexes.

Photophysical properties of the excited states of bacteriochlorophyll f in solvents and in chlorosomes.

Bacteriochlorophyll f (BChl f) is a photosynthetic pigment predicted nearly 40 years ago as a fourth potential member of the Chlorobium chlorophyll family (BChl c, d, and e). However, this pigment still has not been found in a naturally occurring organism. BChl c, d, and e are utilized by anoxygenic green photosynthetic bacteria for assembly of chlorosomes--large light-harvesting complexes that allow those organisms to survive in habitats with extremely low light intensities. Recently, using genetic methods on two different strains of Chlorobaculum limnaeum that naturally produce BChl e, two research groups produced mutants that synthesize BChl f and assemble it into chlorosomes. In this study, we present detailed investigations on spectral and dynamic characteristics of singlet excited and triplet states of BChl f with the application of ultrafast time-resolved absorption and fluorescence spectroscopies. The studies were performed on isolated BChl f in various solvents, at different temperatures, and on BChl f-containing chlorosomes in order to uncover any unusual or unfavorable properties that stand behind the lack of appearance of this pigment in natural environments.

A seventh bacterial chlorophyll driving a large light-harvesting antenna.

The discovery of new chlorophyllous pigments would provide greater understanding of the mechanisms and evolution of photosynthesis. Bacteriochlorophyll f has never been observed in nature, although this name was proposed ~40 years ago based on structurally related compounds. We constructed a bacteriochlorophyll f-accumulating mutant of the green sulfur bacterium Chlorobaculum limnaeum, which originally produced bacteriochlorophyll e, by knocking out the bchU gene encoding C-20 methyltransferase based on natural transformation. This novel pigment self-aggregates in an in vivo light-harvesting antenna, the chlorosome, and exhibits a Q(y) peak of 705 nm, more blue-shifted than any other chlorosome reported so far; the peak overlaps the maximum (~700 nm) of the solar photon flux spectrum. Bacteriochlorophyll f chlorosomes can transfer light energy from core aggregated pigments to another bacteriochlorophyll in the chlorosomal envelope across an energy gap of ~100 nm, and is thus a promising material for development of new bioenergy applications.

Excitation energy transfer and trapping dynamics in the core complex of the filamentous photosynthetic bacterium Roseiflexus castenholzii.

The light-harvesting core complex of the thermophilic filamentous anoxygenic phototrophic bacterium Roseiflexus castenholzii is intrinsic to the cytoplasmic membrane and intimately bound to the reaction center (RC). Using ultrafast transient absorption and time-resolved fluorescence spectroscopy with selective excitation, energy transfer, and trapping dynamics in the core complex have been investigated at room temperature in both open and closed RCs. Results presented in this report revealed that the excited energy transfer from the BChl 800 to the BChl 880 band of the antenna takes about 2 ps independent of the trapping by the RC. The time constants for excitation quenching in the core antenna BChl 880 by open and closed RCs were found to be 60 and 210 ps, respectively. Assuming that the light harvesting complex is generally similar to LH1 of purple bacteria, the possible structural and functional aspects of this unique antenna complex are discussed. The results show that the core complex of Roseiflexus castenholzii contains characteristics of both purple bacteria and Chloroflexus aurantiacus.

Self-assembly and energy transfer in artificial light-harvesting complexes of bacteriochlorophyll c with astaxanthin.

Chlorosomes, the light-harvesting antennae of green photosynthetic bacteria, are based on large aggregates of bacteriochlorophyll molecules. Aggregates with similar properties to those in chlorosomes can also be prepared in vitro. Several agents were shown to induce aggregation of bacteriochlorophyll c in aqueous environments, including certain lipids, carotenes, and quinones. A key distinguishing feature of bacteriochlorophyll c aggregates, both in vitro and in chlorosomes, is a large (>60 nm) red shift of their Q(y) absorption band compared with that of the monomers. In this study, we investigate the self-assembly of bacteriochlorophyll c with the xanthophyll astaxanthin, which leads to the formation of a new type of complexes. Our results indicate that, due to its specific structure, astaxanthin molecules competes with bacteriochlorophylls for the bonds involved in the aggregation, thus preventing the formation of any significant red shift compared with pure bacteriochlorophyll c in aqueous buffer. A strong interaction between both the types of pigments in the developed assemblies, is manifested by a rather efficient (~40%) excitation energy transfer from astaxanthin to bacteriochlorophyll c, as revealed by fluorescence excitation spectroscopy. Results of transient absorption spectroscopy show that the energy transfer is very fast (<500 fs) and proceeds through the S(2) state of astaxanthin.

A red-shifted chlorophyll.

Chlorophylls are essential for light-harvesting and energy transduction in photosynthesis. Four chemically distinct varieties have been known for the past 60 years. Here we report isolation of a fifth, which we designate chlorophyll f. Its in vitro absorption (706 nanometers) and fluorescence (722 nanometers) maxima are red-shifted compared to all other chlorophylls from oxygenic phototrophs. On the basis of the optical, mass, and nuclear magnetic resonance spectra, we propose that chlorophyll f is [2-formyl]-chlorophyll a (C55H70O6N4Mg). This finding suggests that oxygenic photosynthesis can be extended further into the infrared region and may open associated bioenergy applications.

Kinetic analysis of demetalation of bacteriochlorophyll c and e homologs purified from green sulfur photosynthetic bacteria.

Substituent-dependent demetalation kinetics of natural bacteriochlorophyll (BChl) c and e homologs purified from two green sulfur photosynthetic bacteria was first studied. Separated BChl e homologs, which possessed a formyl group at the 7-position of their chlorin macrocycles, exhibited a significantly slow removal of central magnesium to free-base bacteriopheophytins in acidic aqueous acetone compared with the corresponding BChl c homologs, which possessed a methyl group at the 7-position. Additional methyl groups at the 8(2)-position of both BChl c and e molecules had little effect on the demetalation kinetics.

Comparison between chlorosomes containing bacteriochlorophyll-c and chlorosomes containing bacteriochlorophyll-d isolated from two substrains of green sulfur photosynthetic bacterium Chlorobium vibrioforme NCIB 8327.

Chlorosomes containing bacteriochlorophyll(BChl)-c and those containing BChl-d were isolated from two substrains of Chlorobium vibrioforme f. sp. thiosulfatophilum NCIB 8327, respectively. The two types of chlorosomes were investigated from the following aspect, what kinds of effects the molecular structure of chlorosomal BChls had on structural and spectroscopic properties of in vivo self-aggregates in chlorosomes without alteration of the other components such as chlorosomal proteins and lipids; both chlorosomes were expected to have the same components except for light-harvesting BChls. In their visible absorption spectra, the differences of Soret and Q(y) peak positions between BChl-c containing and BChl-d containing chlorosomes were similar to the differences between monomeric BChl-c and d. An inverse S-shaped CD signal in the Q(y) region of BChl-d containing chlorosomes was 1.4 times larger than that of BChl-c containing chlorosomes, when the Q(y) absorbance of the two chlorosomes was almost the same. This implies that the excitonic interaction of BChl-d is larger than that of BChl-c in natural chlorosomes. Resonance Raman spectroscopy showed that BChl self-assemblies in both chlorosomes were essentially formed by the same local structural interaction among 3(1)-hydroxy group, 13-keto group, and central magnesium. BChl-d self-aggregates in chlorosomes were more tolerant of 1-hexanol than in vivo BChl-c aggregates, suggesting that the molecular structure of BChl-d provided more stable self-assemblies than BChl-c in natural chlorosomes.

Distribution of chloropigments in suspended particulate matter and benthic microbial mat of a meromictic lake, Lake Kaiike, Japan.

We investigated the distribution of chloropigments in a small meromictic lake, Lake Kaiike, south-west Japan. In the water-column, concentrations of Chl a related to cyanobacteria, BChl a related to purple sulphur bacteria, and three types of BChl e homologues (BChls e1, e2 and e3) related to brown-coloured green sulphur bacteria, were maximal at the redox boundary. Below the redox boundary, absolute concentrations of Chl a and BChl a gradually decreased with depth, whereas BChls e remained rather constant. Suspended particulate matter (SPM) at the deeper region of the anoxic water-column was enriched in highly alkylated BChl e homologues compared with SPM at the redox boundary. The shift in the relative content of highly alkylated BChl e homologues beneath the boundary was associated with community related adaptation of brown-coloured green sulphur bacteria to changes in light quality/quantity, resulting from the optical absorption and reflectance of SPMs in the overlying water-column. Benthic microbial mats were characterized by high abundances of BChls e, in which highly alkylated homologues were substantially abundant. This suggests that the BChls e in the microbial mat may be derived from the low-light adapted brown-coloured green sulphur bacteria forming the bacterial mat.

Isolation and characterization of the B798 light-harvesting baseplate from the chlorosomes of Chloroflexus aurantiacus.

The B798 light-harvesting baseplate of the chlorosome antenna complex of the thermophilic, filamentous anoxygenic phototrophic bacterium Chloroflexus aurantiacus has been isolated and characterized. Isolation was performed by using a hexanol-detergent treatment of freeze-thawed chlorosomes. The isolated baseplate consists of Bchl a, beta-carotene, and the 5.7 kDa CsmA protein with a ratio of 1.0 CsmA protein/1.6 Bchl a/4.2 beta-carotenes. The baseplate has characteristic absorbance at 798 nm as well as carotenoid absorbance maxima at 519, 489, and 462 nm. The energy transfer efficiency from the carotenoids to the Bchl a is 30% as measured by steady-state and ultrafast time-resolved fluorescence and absorption spectroscopies. Energy equilibration within the Bchl a absorbing regions exhibits ultrafast kinetics. Circular dichroism spectroscopy shows no evidence for excitonically coupled Bchl a pools within the 798 nm region.

Novel carotenoid glucoside esters from alkaliphilic heliobacteria.

Pigments of three species of alkaliphilic heliobacteria of the genus Heliorestis, H. daurensis, H. baculata and an undescribed species Heliorestis strain HH, were identified using spectroscopic methods. In these species, bacteriochlorophyll g esterified with farnesol was present, as for other heliobacteria. The carotenoids consisted of 4,4'-diaponeurosporene, also found in other heliobacteria, plus the novel pigments OH-diaponeurosporene glucoside esters (C16:0 and C16:1). In addition, trace amounts of biosynthetic intermediates, OH-diaponeurosporene and OH-diaponeurosporene glucoside, were found. Trace amounts of a carotenoid with 20 carbon atoms, 8,8'-diapo-zeta-carotene, were also found in these species as well as in the non-alkaliphilic heliobacteria. The non-alkaliphilic species Heliophilum fasciatum also contained trace amounts of the two OH-diaponeurosporene glucoside esters. The results are used to predict the pathway of carotenoid biosynthesis in heliobacteria.

A giant chlorophyll-protein complex induced by iron deficiency in cyanobacteria.

Cyanobacteria are abundant throughout most of the world's water bodies and contribute significantly to global primary productivity through oxygenic photosynthesis. This reaction is catalysed by two membrane-bound protein complexes, photosystem I (PSI) and photosystem II (PSII), which both contain chlorophyll-binding subunits functioning as an internal antenna. In addition, phycobilisomes act as peripheral antenna systems, but no additional light-harvesting systems have been found under normal growth conditions. Iron deficiency, which is often the limiting factor for cyanobacterial growth in aquatic ecosystems, leads to the induction of additional proteins such as IsiA (ref. 3). Although IsiA has been implicated in chlorophyll storage, energy absorption and protection against excessive light, its precise molecular function and association to other proteins is unknown. Here we report the purification of a specific PSI-IsiA supercomplex, which is abundant under conditions of iron limitation. Electron microscopy shows that this supercomplex consists of trimeric PSI surrounded by a closed ring of 18 IsiA proteins binding around 180 chlorophyll molecules. We provide a structural characterization of an additional chlorophyll-containing, membrane-integral antenna in a cyanobacterial photosystem.

Magnesium insertion by magnesium chelatase in the biosynthesis of zinc bacteriochlorophyll a in an aerobic acidophilic bacterium Acidiphilium rubrum.

To elucidate the mechanism for formation of zinc-containing bacteriochlorophyll a in the photosynthetic bacterium Acidiphilium rubrum, we isolated homologs of magnesium chelatase subunits (bchI, -D, and -H). A. rubrum bchI and -H were encoded by single genes located on the clusters bchP-orf168-bchI-bchD-orf320-crtI and bchF-N-B-H-L as in Rhodobacter capsulatus, respectively. The deduced sequences of A. rubrum bchI, -D, and -H had overall identities of 59. 8, 40.5, and 50.7% to those from Rba. capsulatus, respectively. When these genes were introduced into bchI, bchD, and bchH mutants of Rba. capsulatus for functional complementation, all mutants were complemented with concomitant synthesis of bacteriochlorophyll a. Analyses of bacteriochlorophyll intermediates showed that A. rubrum cells accumulate magnesium protoporphyrin IX monomethyl ester without detectable accumulation of zinc protoporphyrin IX or its monomethyl ester. These results indicate that a single set of magnesium chelatase homologs in A. rubrum catalyzes the insertion of only Mg(2+) into protoporphyrin IX to yield magnesium protoporphyrin IX monomethyl ester. Consequently, it is most likely that zinc-containing bacteriochlorophyll a is formed by a substitution of Zn(2+) for Mg(2+) at a step in the bacteriochlorophyll biosynthesis after formation of magnesium protoporphyrin IX monomethyl ester.

The major carotenoid in all known species of heliobacteria is the C30 carotenoid 4,4'-diaponeurosporene, not neurosporene.

The carotenoids of five species of heliobacteria (Heliobacillus mobilis, Heliophilum fasciatum, Heliobacterium chlorum, Heliobacterium modesticaldum, and Heliobacterium gestii) were examined by spectroscopic methods, and the C30 carotene 4,4'-diaponeurosporene was found to be the dominant pigment; heliobacteria were previously thought to contain the C40 carotenoid neurosporene. In addition, trace amounts of the C30 diapocarotenes diapolycopene, diapo-zeta-carotene, diapophytofluene, and diapophytoene were also found. Up to now, diapocarotenes have been found in only three species of chemoorganotrophic bacteria, but not in phototropic organisms. Furthermore, the esterifying alcohol of bacteriochlorophyll g from all known species of heliobacteria was determined to be farnesol (C15) instead of the usual phytol (C20). Heliobacteria may be unable to produce geranylgeranyol (C20).

Rhodospira trueperi gen. nov., spec. nov., a new phototrophic Proteobacterium of the alpha group.

A new phototrophic purple bacterium was isolated from a flat, laminated microbial mat in a salt marsh near Woods Hole, Mass., USA. The spiral-shaped bacterium was highly motile and had bipolar tufts of flagella and intracytoplasmic membranes of the vesicular type. The major photosynthetic pigments were identified as the carotenoid tetrahydrospirilloxanthin and bacteriochlorophyll b. The long wavelength in vivo absorption maximum of the bacteriochlorophyll was at 986 nm. The marine bacterium showed optimal growth in the presence of 2% NaCl. It utilized a number of organic substrates as carbon and energy sources and required vitamins and sulfide as a reduced sulfur source for growth. In the presence of sulfide, elemental sulfur globules were formed outside the cells. Elemental sulfur was not further oxidized to sulfate. The new isolate had a unique lipid and fatty acid composition, and according to the 16S rRNA gene sequence, it is most similar to Rhodospirillum rubrum. It is described as a new species and assigned to a new genus with the proposed name Rhodospira trueperi.

Reconstitution of the bacterial core light-harvesting complexes of Rhodobacter sphaeroides and Rhodospirillum rubrum with isolated alpha- and beta-polypeptides, bacteriochlorophyll alpha, and carotenoid.

Methodology has been developed to reconstitute carotenoids and bacteriochlorophyll alpha with isolated light-harvesting complex I (LHI) polypeptides of both Rhodobacter sphaeroides and Rhodospirillum rubrum. Reconstitution techniques first developed in this laboratory using the LHI polypeptides of R. rubrum, R. sphaeroides, and Rhodobacter capsulatus reproduced bacteriochlorophyll alpha spectral properties characteristic of LHI complexes lacking carotenoids. In this study, carotenoids are supplied either as organic-solvent extracts of chromatophores or as thin-layer chromatography or high performance liquid chromatography-purified species. The resulting LHI complexes exhibit carotenoid and bacteriochlorophyll a spectral properties characteristic of native LHI complexes of carotenoid-containing bacteria. Absorption and circular dichroism spectra support the attainment of a native-like carotenoid environment in the reconstituted LHI complexes. For both R. sphaeroides- and R. rubrum-reconstituted systems, fluorescence excitation spectra reveal appropriate carotenoid to bacteriochlorophyll alpha energy-transfer efficiencies based on comparisons with the in vivo systems. In the case of R. rubrum reconstitutions, carotenoids afford protection from photodynamic degradation. Thus, carotenoids reconstituted into LHI exhibit spectral and functional characteristics associated with native pigments. Heterologous reconstitutions demonstrate the applicability of the developed assay in dissecting the molecular environment of carotenoids in light-harvesting complexes.

Enrichment of bacteriochlorophyll g' in membranes of Heliobacterium chlorum by ether extraction. Unequivocal evidence for its existence in vivo.

Treatment of H. chlorum membrane preparations with diethyl ether of high degrees of water saturation raised the bacteriochlorophyll (BChl) g' mole fraction, as determined by HPLC analysis of their acetone extracts, toward a level of 40% of total BChl g or higher. Starting from pure BChl g, the BChl g' mole fraction should never exceed 24.6% which is the equilibrium value in diethyl ether. The existence (and possible functioning) of BChl g' in vivo is thus unequivocally demonstrated.

Bacteriochlorophyll c formation via the C5 pathway of 5-aminolevulinic acid synthesis in Chloroflexus aurantiacus.

Biosynthesis of 5-aminolevulinic acid (ALA) in Chloroflexus aurantiacus, a thermophilic bacterium forming bacteriochlorophyll c, is shown to proceed via the C5 pathway by demonstrating (1) the specific labeling of its chlorin ring with [1 - 13C]glutamate and (2) the enzyme activity to produce ALA from glutamate in a cell-free extract. From the phylogenetic distribution it is suggested that ALA synthetase distributed in some aerobic eubacteria could be monophyletic in origin.

Evidence for anoxygenic photosynthesis from the distribution of bacteriochlorophylls in the Black Sea.

The contribution of anoxygenic photosynthesis to carbon cycling in the Black Sea, the world's largest body of anoxic marine water, has been vigorously investigated and debated for over four decades. Penetration of light into the sulphide-containing deep water may result in a zone of anaerobic primary production by photosynthetic bacteria. We report here the results of analyses of photosynthetic pigments in samples of suspended particulate matter collected from two stations in the western basin of the Black Sea. Our data demonstrate high concentrations of a bacterio-chlorophyll at the chemocline, and thus the potential for anoxygenic photosynthesis as a component of primary production in the carbon cycle of the Black Sea. More than 95% of the pigments in the bacteriochlorophyll-maximum are accounted for by a series of aromatic carotenoids and bacteriochlorophylls-e, including a previously unreported geranyl ester of 4-i-butyl bacteriochlorophyll-e. The distribution of pigments is characteristic of the obligate phototrophs Chlorobium phaeobacteroides and C. phaeovibriodes. Total depth-integrated bacteriochlorophyll at one station exceeded total chlorophyll-a in the overlying oxygenated portion of the euphotic zone. We suggest that anoxygenic photosynthesis is a relatively recent phenomenon in the Black Sea initiated by shallowing of the chemocline over the past decade and development of an anoxic layer devoid of O2 and H2S.