Pigments, light penetration, and photosynthetic activity in the multi-layered microbial mats of Great Sippewissett Salt Marsh, Massachusetts

The multi-layered microbial mats in the sand flats of Great Sippewissett Salt Marsh were found to have five distinct layers of phototrophic organisms. The top 1–3 mm contained oxygenic phototrophs. The lower 3–4 mm contained anoxygenic phototrophic bacteria. The uppermost gold layer contained diatoms and cyanobacteria, and chlorophyll a was the major chlorophyll. The next layer down was green and was composed of primarily filamentous cyanobacteria containing chlorophyll a. This was followed by a bright pink layer of bacteriochlorophyll b-containing purple sulfur bacteria. The lowest layer was a thin dull green layer of green sulfur bacteria containing bacteriochlorophyll c. The distribution of the chlorophylls with depth revealed that two-thirds of the total chlorophyll in the mat was composed of bacteriochlorophylls present in the anoxygenic phototrophys. The cyanobacterial layers and both purple sulfur bacterial layers had photoautotrophic activity. Light was attenuated in the uppermost layers so that less than 5% of the total radiation at the surface penetrated to the layers of anoxygenic phototrophys.     

Structure of a bacteriochlorophyll a-protein from the green photosynthetic bacterium Prosthecochloris aestuarii.

The three-dimensional structure of a water-soluble bacteriochlorophyll a-containing protein from the green photosynthetic bacterium Prosthecochloris aestuarii has been determined by X-ray crystallography from a 2.8 Å resolution electron density map based on four isomorphous derivatives. Details of the crystallographic procedures used to obtain the map are presented.The bacteriochlorophyll a-protein is shown to consist of three identical subunits, tightly packed around a 3-fold symmetry axis. Each subunit consists of a core of seven bacteriochlorophyll a molecules enclosed within a “bag” of protein. The polypeptide chain forms an extensive 15-strand β-sheet, which is almost planar in its central region, and twisted at its extremities, and wraps around the chlorophyll core to form an efficient amphipathic layer between the chlorophylls and the aqueous environment. There are extensive contacts between the phytyl chains of the seven bacteriochlorophylls within each subunit. These hydrocarbon chains constitute an inner hydrophobic core of the molecule which may be important in forming the complex. There are also extensive contacts between the protein and both the bacteriochlorophyll head groups and tails, but relatively few contacts between the respective head groups. The seven magnesiums all appear to be five co-ordinated. In five cases the presumed ligand is a histidine side-chain, in one case a polypeptide carbonyl oxygen, and in the other case a water molecule.At low temperature, both the absorption and circular dichroism spectra of the bacteriochlorophyll a-protein show splitting which can be interpreted in general terms as due to exciton interactions between the seven chromophores, but calculations of the expected splitting based on the bacteriochlorophyll co-ordinates determined crystallographically are in poor agreement with the observed spectra. Furthermore, the observed red shift of the Q_y absorption band of bacteriochlorophyll a, from about 770 nm in organic solvents to 809 nm in the bacteriochlorophyll a-protein, is not explained by the exciton calculations. It seems likely that the red shift is due to perturbations of the spectra of the individual bacteriochlorophylls by the protein environment, but, pending the determination of the amino acid sequence, it is not possible at this time to define in detail all the proteinchlorophyll interactions. It is suggested that the bacteriochlorophyll a-protein serves as a good model for the organization of chlorophyll in vivo, and that the types of interaction seen here between chlorophyll and protein are likely to be found in other chlorophyll proteins.     

A new bacteriochlorophyll from brown-colored chlorobiaceae

A new bacteriochlorophyll has been isolated by thin layer chromatography from all strains of the brown-colored Chlorobiaceae Chlorobium phaeobacteroides and Chlorobium phaeovibrioides. The new bacteriochlorophyll e —like the bacteriochlorophylls c and d—represents the major amount of bacteriochlorophyll in the cells in addition to small amounts of bacteriochlorophyll a. Bacteriochlorophyll e can be differentiated from the bacteriochlorophylls c and d by its absorption maxima in aceton and its different R _f -value in the thin layer chromatogram. The structure of the new bacteriochlorophyll e has been elucidated on the basis of mass spectra, ¹H- and ¹³C-NMR-spectra, the UV/VIS-spectrum as well as IR-, ORD-, and CD-spectra. The new bacteriochlorophyll has the same relationship to bacteriochlorophyll c as chlorophyll b from green plants to chlorophyll a; therefore, bacteriochlorophyll e represents the first formyl-substituted chlorophyll from bacteria. Similar to the bacteriochlorophylls c and d, the new bacteriochlorophyll e consists of a mixture of at least three homologues which differ from each other by different substituents on the pyrrol rings II and III.Abbreviations Used DSM Deutsche Sammlung von Mikroorganismen, Göttingen - Bchl. bacteriochlorophyll - Bph. bacteriopheophytin - P phytol - Gg geranylgeraniol - F farnesol - C Chlorobium This work was made possible by the technology program of the Bundesministerium für Forschung und Technologie.     

Das Vorkommen von Phytol und Geranylgeraniol in den Bacteriochlorophyllen roter und grüner Schwefelbakterien

The bacteriochlorophylls a of 38 strains belonging to 15 different species of the purple sulfur bacteria (Chromatiaceae) were studied with respect to the nature of the esterifying alcohol. The classical bacteriochlorophyll a_P containing phytol is the main bacteriochlorophyll in all strains. The new bacteriochlorophyll a_Gg occurs as a minor component in addition to bacteriochlorophyll a_P only in five species.The esterifying alcohol of the bacteriochlorophyll a of the reaction centers of all seven type strains of the Chlorobiaceae was shown to be phytol.The compounds withR _f -values between the bacteriophaeophytins a_P and a_Gg found by thin-layer-chromatography were shown to be artifacts of the preparation technique.All strains of the bacteriochlorophyll b-containing purple bacteria have phytol as the major esterifying alcohol; in addition, small amounts of bacteriochlorophyll b are esterified with another alcohol which is most probably all-trans-geranylgeraniol.

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Abkürzungen DSM Deutsche Sammlung von Mikroorganismen - Bchl. Bacteriochlorophyll Herrn Prof. Dr. Dr. e. h. Hans Brockmann zum 70. Geburtstag gewidmet.     

Preparation of chlorophyll a, chlorophyll b and bacteriochlorophyll a by means of column chromatography with diethylaminoethylcellulose

Chlorophyll a, chlorophyll b and bacteriochlorophyll a were prepared by means of column chromatography with Sephadex LH-20 and diethylaminoethylcellulose. This method provides purified preparations of chlorophylls in about 3 h.To prepare chlorophyll a, blue-green or red algae were used as the starting material. Chlorophyll a was extracted with 90% aqueous acetone from cells of blue-green algae, Anabaena variabilis, Anacystis nidulans and Tolypothrix tenuis, and with 90% aqueous methanol from thalli of a red alga, Porphyra yezoensis. Chlorophyll a was collected as precipitates by adding dioxane and water to the extract according to the method of Iriyama et al. [6]. The crude chlorophyll a preparation was applied to a Sephadex LH-20 column with chloroform as the eluent and then to a DEAE-cellulose column with a chloroform/methanol mixture (49 : 1, v/v) as the eluent. Analysis with thin layer chromatography revealed that the chlorophyll a preparation contained no detectable contaminants.Bacteriochlorophyll a was prepared in a similar manner from purple photosynthetic bacteria, Rhodopseudomonas spheroides and Chromatium vinosum.In order to prepare chlorophyll b, chloroplasts of spinach leaves were used as the starting material. A mixture of chlorophylls a and b was obtained in the same way as described for the preparation of chlorophyll a from the blue-green algae. To separate chlorophyll b from chlorophyll a, the mixture was applied to a diethylaminoethylcellulose column which was developed with a hexane/2-propanol mixture (5 : 2, v/v).     

Optical and structural properties of chlorosomes of the photosynthetic green sulfur bacterium Chlorobium limicola

Isolated chlorosomes of the photosynthetic green sulfur bacterium Chorobium limicola upon cooling to 4 K showed, in addition to the near-infrared absorption band at 753 nm due to bacteriochlorophyll c, a weak band near 800 nm that could be attributed to bacteriochlorophyll a. The emission spectrum showed bands of bacteriochlorophyll c and a at 788 and 828 nm, respectively. The fluorescence excitation spectrum indicated a high efficiency of energy transfer from bacteriochlorophyll c to bacteriochlorophyll a. When all bacteriochlorophyll c absorption had been lost upon storage, no appreciable change in the optical properties of the bacteriochlorophyll a contained in these ‘depleted chlorosomes’ was observed. The fluorescence and absorption spectra of the chlorosomal bacteriochlorophyll a were clearly different from those of the soluble bacteriochlorophyll a protein present in these bacteria. The results provide strong evidence that bacteriochlorophyll a, although present in a small amount, is an integral constituent of the chlorosome. It presumably functions in the transfer of energy from the chlorosome to the photosynthetic membrane; its spectral properties and the orientation of its near-infrared optical transitions as determined by linear dichroism are such as to favor this energy transfer.     

Spatiotemporal distribution of bacteriochlorophylls in the meromictic Lake Suigetsu, Japan

The spatiotemporal distribution of chlorophyll pigments (chloropigments) in the water column of a meromictic lake, Lake Suigetsu (Fukui, Japan), was investigated. Water samples were collected from the central basin of Lake Suigetsu bimonthly between May 2008 and March 2010 at appropriate depths, including the oxic surface, oxic–anoxic interface, and anoxic bottom layers. Chlorophyll a, related to cyanobacteria and eukaryotic phytoplankton, was detected throughout the water column during the years of the study, whereas bacteriochlorophyll e, related to brown-colored green sulfur bacteria, was detected in the anoxic layers below the chemocline at a maximum concentration of 825 μg L^?1. The concentration of bacteriochlorophyll e was generally maximal at or just below the chemocline of the lake. The cellular content of bacteriochlorophyll e was estimated to be low in the upper part of the chemocline and tended to increase with increasing water depth. Bacteriochlorophyll a, which was presumably related to purple sulfur bacteria, was only detected at the chemocline during summer and autumn at concentrations of 5.4–16.3 μg L^?1. Our analysis of the chloropigment distribution for the two years of the study suggested that brown-colored green sulfur bacteria are the predominant phototroph in the anoxic layers of Lake Suigetsu, and that these play a significant role in the carbon and sulfur cycling of the lake, especially from spring to summer.     

Peroxidase-catalysed oxidation of chlorophyll by hydrogen peroxide

Chlorophyll is effectively bleached by H₂O₂ in the presence of certain phenols and peroxidase (EC 1.11.1.7) extracted from acetone powders of orange flavedo (Citrus sinensis). Optimal conditions for chlorophyll: hydrogen peroxide oxidoreductase include: pH, 5.9; [H₂O₂] 222 μM; ionic strength 0.11. A phenol is required and resorcinol is the most effective. Catechol and hydroquinone are inhibitory. Chlorophyll a, chlorophyllide a, and chlorophyll b all have similar V_max but K_m for chlorophyll a is about one-third that of chlorophyll b, while the K_m for chlorophyllide a is about one-half that of chlorophyll a. Pheophytin a was much less reactive than chlorophyll a, and Mg²⁺ included in the reaction system did not affect rates of pheophytin destruction.     

Tidal and diel fluctuations in the temporal concentrations of chlorophyll a and pheophytin at a station monitoring a high-marsh creek

The temporal distribution of chlorophyll a and pheophytin at a transect monitoring the flow at a high-marsh creek was investigated. The observed fluctuations in chlorophyll a concentration consisted of complex, superimposed, tidal and diel rhythms; pheophytin variability, on the other hand, was controlled by the tides. Transport measurements and correlation analyses supported the hypothesis that tidal forces have a major influence on the temporal fluctuation of chlorophyll a and phaeophytin concentrations in high-marsh creeks. The data indicate that it is important to consider tidal flux when designing programs to study seasonal effects, primary productivity, and phytoplankton species composition.     

A phototrophic gliding filamentous bacterium of hot springs,Chloroflexus aurantiacus,gen. and sp. nov.

Chloroflexus aurantiacus, gen. and sp. n., is a filamentous phototrophic bacterium of hot springs. On an agar surface, holotype strain J-10-fl glides at 0.01–0.04 μm/sec. The filaments are 0.6–0.7 μm in width and indeterminate in length. Pigments include bacteriochlorophyll c and bacteriochlorophyll a (identified by spectrophotometry) in addition to β and γ-carotene and glycosides of the latter. Chlorobium vesicles are present. Photoheterotrophic growth occurs under anaerobic conditions. Aerobic chemoheterotrophic growth also occurs in darkness or light. Bacteriochlorophyll syntheses cease under aerobic conditions but some types of carotenoids continue to be made. The filament coloration is orange under all except anaerobic conditions in low light intensity where it is dull green. The pH optimum is near 8, the temperature optimum between 52° and 60°C. The DNA base composition for strain J-10-fl is 54.9 ± 1.0 moles % guanine + cytosine. Chloroflexus is unique in that there have been no previous reports of filamentous or gliding phototrophic bacteria. The combinations of bacteriochlorophylls a and c and the presence of chlorobium vesicles in a photoheterotroph and in an organism capable of aerobic growth are also unique. This metabolically versatile organism extends the taxonomic and phylogenetic limits of the “green line” of phototrophic bacteria.     

Quest for minor but key chlorophyll molecules in photosynthetic reaction centers – unusual pigment composition in the reaction centers of the chlorophyll d-dominated cyanobacterium Acaryochloris marina

A short overview, based on our own findings, is given of the minor pigments that function as key components in photosynthesis. Recently, we found the presence of chlorophyll a, chlorophyll d′ and pheophytin a as minor pigments in the chlorophyll d-dominated cyanobacterium Acaryochloris marina. This revised version was published online in June 2006 with corrections to the Cover Date.     

A solvent partitioning procedure for the separation of chlorophylls from their degradation products and carotenoid pigments

A simple liquid/liquid partitioning procedure was developed which employed aqueous acetonitrile and hexane, for the isolation of chlorophyll and pheophytin. This procedure separated these pigments from other interfering pigmented compounds. The efficacy of this solvent separation method was evaluated using commercially available chlorophylla, b, pheophytina, b, carotenoids, and algal pigment extracts. The recovery efficiencies of this solvent partitioning process for chlorophyll a and pheophytina have been shown to be 95–98% and 93–96%, respectively, furthermore, the chlorophylla fraction was practically free of any contaminating pigments. It appears that a more accurate assessment of chlorophylla and pheophytina can be accomplished employing liquid/liquid partitioning than with the present standard method.     

Competitive Inhibitions of the Chlorophyll Synthase of Synechocystis sp. Strain PCC 6803 by Bacteriochlorophyllide a and the Bacteriochlorophyll Synthase of Rhodobacter sphaeroides by Chlorophyllide a

The photosynthetic growth of Synechocystis sp. strain PCC 6803 is hampered by exogenously added bacteriochlorophyllide a (Bchlide a) in a dose-dependent manner. The growth inhibition caused by Bchlide a, however, is relieved by an increased level of exogenously added chlorophyllide a (Chlide a). The results are explained by the competitive inhibition of chlorophyll synthase by Bchlide a, with inhibition constants (K_Is) of 0.3 mM and 1.14 mM in the presence of sufficient geranylgeranyl pyrophosphate (GGPP) and phytyl pyrophosphate (PPP), respectively. Surprisingly, the bacteriochlorophyll synthase of Rhodobacter sphaeroides is inhibited competitively by Chlide a, with K_Is of 0.54 mM and 0.77 mM in the presence of sufficient GGPP and PPP, respectively. Consistently, exogenously added Chlide a inhibits the metabolic conversion of exogenously added Bchlide a to bacteriochlorophyll a by an R. sphaeroides bchFNB-bchZ mutant that neither synthesizes nor metabolizes Chlide a. The metabolic inhibition by Chlide a, however, is relieved by the elevated level of Bchlide a. Thus, the chlorophyll synthase of Synechocystis sp. PCC 6803 and the bacteriochlorophyll synthase of R. sphaeroides, both of which perform ping-pong-type reactions, are inhibited by Bchlide a and Chlide a, respectively. Although neither inhibitor is catalyzed by the target enzyme, inhibitions in the competitive mode suggest a structural similarity between their active sites.The biosynthetic pathways for bacteriochlorophyll a (Bchl a) and chlorophyll a (Chl a) share the metabolic steps from protoporphyrin IX to chlorophyllide a (Chlide a) (Fig. ​(Fig.1).1). The C₂₀ moiety from geranylgeranyl pyrophosphate (GGPP) can be directly esterified to ring D of Chlide a by chlorophyll synthase (ChlG) to yield geranylgeranylated Chl a (Chl a_gg), which is subsequently reduced (at positions 6, 10, and 14 of GG) by chlorophyll reductase (ChlP) to yield phytylated Chl a (Chl a_p, but it is usually abbreviated as Chl a) (2, 7). The chlorophyll synthase of Avena sativa has a broad substrate specificity for C₂₀, and it may accept either GGPP or phytyl pyrophosphate (PPP) as the first substrate in its ping-pong-type reaction (27). Either a geranylgeranylated or phytylated enzyme esterifies the second substrate Chlide a, yielding Chl a_gg or Chl a, respectively (5, 24). Chlorophyll reductase reduces either the GG moiety of Chl a_gg or free GGPP, yielding Chl a or free PPP, respectively (25).Open in a separate windowFIG. 1.Chl a and Bchl a biosynthetic pathways (6, 7). The chemical structures of Chlide a and Bchlide a are shown. bchF codes for 3-vinyl bacteriochlorophyllide hydratase; bchXYZ for three subunits comprising COR; bchC for 3-hydroxyethyl bacteriochlorophyllide dehydrogenase; chlG and bchG for chlorophyll synthase and bacteriochlorophyll synthase, respectively; and chlP and bchP for chlorophyll reductase and bacteriochlorophyll reductase, respectively.Chlide a may be further metabolized to bacteriochlorophyllide a (Bchlide a) (Fig. ​(Fig.1).1). Chlide a reductase (COR) reduces ring B of Chlide a to form 3-vinyl bacteriochlorophyllide a, whose C-3-vinyl group on ring A is then converted into an acetyl group through the activities of hydratase (BchF) and dehydrogenase (BchC) to form Bchlide a (6). The hydratase reaction may alternatively precede that of COR (Fig. ​(Fig.1).1). Once Bchlide a is formed, its ring D is esterified with the C₂₀ geranylgeranyl moiety by bacteriochlorophyll synthase (BchG), yielding geranylgeranylated Bchl a (Bchl a_gg) (3). The C₂₀ moiety is subsequently reduced by bacteriochlorophyll reductase (BchP), yielding the phytylated Bchl a (Bchl a_p, but it is usually abbreviated as Bchl a) (1).The biosynthesis of Chl a has been regarded as a metabolism that evolved after Bchl a (33). ChlG and ChlP have been thought to emerge through the gene duplication of BchG and BchP, respectively. Recently, we found that the COR reaction, which is specific to Bchl a biosynthesis, generates superoxide at low levels of oxygen (16), and we further proposed that the degeneration of the superoxide-generating COR step may be associated with the emergence of cyanobacterium-based Chl a biosynthesis (15).The predicted sequence of ChlG of Synechocystis sp. strain PCC 6803 bears 35% identity with that of Rhodobacter sphaeroides BchG. Nonetheless, chlorophyll synthase and bacteriochlorophyll synthase exhibit a high degree of substrate specificity to distinguish their own Mg-tetrapyrrole substrates from that of the other enzyme (23, 28). We further examined whether chlorophyll synthase and bacteriochlorophyll synthase are affected by Bchlide a and Chlide a, respectively, which are structurally similar to each other. In this work, we found that the chlorophyll synthase of Synechocystis sp. PCC 6803 is competitively inhibited by Bchlide a. We further found that the bacteriochlorophyll synthase of R. sphaeroides is competitively inhibited by Chlide a. Thus, the active site of chlorophyll synthase is recognized by Bchlide a, while that of bacteriochlorophyll synthase is recognized by Chlide a. The results suggest a structural similarity between the active sites of the two enzymes.     

Das Vorkommen von Bacteriochlorophyll aP und aGg in Stämmen aller Arten der Rhodospirillaceae

Summary The bacteriochlorophylls a of 60 strains belonging to 13 different species of the purple nonsulfur bacteria (Rhodospirillaceae) were studied with respect to the nature of the esterifying alcohol. The new bacteriochlorophyll a_Gg containing all-trans-geranylgeraniol is the main bacteriochlorophyll in all strains of Rhodospirillum rubrum. Rhodospirillum photometricum contains the new and the classical bacteriochlorophyll a_P (phytol as esterifying alcohol) in nearly equal amounts. The strains of all other species contain the classical bacteriochlorophyll a_P.     

Isolation and properties of a pigment-protein complex associated with the reaction center of the green photosynthetic sulfur bacterium Prosthecochloris aestuarii

The membrane-bound pigment system of green sulfur bacteria consists of light-harvesting bacteriochlorophyll a-protein and a ‘core complex’ that is associated with the reaction center (Kramer, H.J.M., Kingma, H., Swarthoff, T. and Amesz, J. (1982) Biochim. Biophys. Acta 681, 359–364). The isolation and properties of the core complex from Prosthecochloris aestuarii are described. The complex has a molecular mass of 200 ± 50 kDa and contains bacteriochlorophyll a, carotenoid and pigments absorbing near 670 nm (probably bacteriopheophytin c and an unidentified pigment). Fluorescence emission spectra and sodium dodecyl sulfate polyacrylamide gel electrophoresis showed the absence of light-harvesting bacteriochlorophyll a-protein. The preparation showed no reaction center activity. Circular and linear dichroism spectra indicated that the structure of the core complex was basically not altered by the isolation procedure. Comparison with the CD spectrum of the intrinsic membrane-bound pigment-protein complex indicates that the latter contains 14 bacteriochlorophyll a molecules (two subunits) belonging to the light-harvesting protein and about 20 bacteriochlorophyll a molecules belonging to the core complex.     

Femtosecond spectroscopy of native and carotenoidless purple-bacterial LH2 clarifies functions of carotenoids

EET between the two circular bacteriochlorophyll compartments B800 and B850 in native (containing the carotenoid rhodopin) and carotenoidless LH2 isolated from the photosynthetic purple sulfur bacterium Allochromatium minutissimum was investigated by femtosecond time-resolved transient absorption spectroscopy. Both samples were excited with 120-fs laser pulses at 800 nm, and spectral evolution was followed in the 720-955 nm range at different delay times. No dependence of transient absorption in the B800 band on the presence of the carotenoid rhodopin was found. Together with the likewise virtually unchanged absorption spectra in the bacteriochlorophyll Q_y region, these observations suggest that absence of rhodopin does not significantly alter the structure of the pigment-protein complex including interactions between bacteriochlorophylls. Apparently, rhodopin does also not accelerate B800 to B850 EET in LH2, contrary to what has been suggested previously. Moreover, “carotenoid-catalyzed internal conversion” can also be excluded for the bacteriochlorophylls in LH2 of A. minutissimum. Together with previous results obtained with two-photon fluorescence excitation spectroscopy, it can also be concluded that there is neither EET from rhodopin to B800 nor (back-)EET from B800 to rhodopin.     

Bacteriochlorophyll a-protein interactions in a complex from Prosthecochloris aestuarii. A Resonance Raman study

Raman spectra of bacteriochlorophyll a (BChl) bound to the soluble protein complex from Prosthecochloris aestuarii have been obtained at low temperature, using the resonance effect on their Q_x for Soret electronic bands. These spectra show that the acetyl carbonyls of at least four of the seven molecules bound to the monomer subunit of the complex and the ketone carbonyls of at least five of them are oriented close to the mean plane of the conjugated part of the dihydrophorbin macrocycle. Up to three bacteriochlorophyll molecules may have their ketone carbonyls free from hydrogen-bonding and up to two may have their acetyl carbonyls similarly free. Several of the binding sites of the remaining conjugated carbonyls are probably the same as those binding the conjugated carbonyls of bacteriochlorophyll (and of bacteriopheophytin) in reaction centers and in antenna structures of purple bacteria and as those binding chlorophyll in the antenna of higher plants and algae. The present resonance Raman spectra confirm that the magnesium atoms of most of the seven bacteriochlorophylls are pentacoordinated. They also show that polarisation effects from their local environments induce changes in the groundstate structures of the dihydrophorbin skeletons of the complexed molecules with respect to those of isolated, monomeric bacteriochlorophyll. These changes are quasi-identical for the seven molecules. These environmental effects predominate over any structural change brought about by intermolecular bonding of the conjugated carbonyls or of the magnesium atoms. The dihydrophorbin rings of the seven molecules thus appear to be immersed in a nearly homogeneous medium of low permittivity, although specific van der Waals interactions may polarise the free carbonyls to quite different extents. The possible implications of these observations on the interpretation of the electronic spectrum of the set of complexed bacteriochlorophylls are discussed.     

Effect of Iron on Growth and Ultrastructure of Acaryochloris marina

The cyanobacterial genus Acaryochloris is the only known group of oxygenic phototrophs that contain chlorophyll d rather than chlorophyll a as the major photosynthetic pigment. Studies on this organism are still in their earliest stages, and biochemical analysis has rapidly outpaced growth optimization. We have investigated culture growth of the major strains of Acaryochloris marina (MBIC11017 and MBIC10697) by using several published and some newly developed growth media. It was determined that heavy addition of iron significantly enhanced culture longevity. These high-iron cultures showed an ultrastructure with thylakoid stacks that resemble traditional cyanobacteria (unlike previous studies). These cultures also show a novel reversal in the pigment ratios of the photosystem II signature components chlorophyll a and pheophytin a, as opposed to those in previous studies.     

Spectral and photochemical properties of borohydride-treated D1-D2-cytochrome b-559 complex of photosystem II

The D1-D2-cytochrome b-559 reaction center complex of photosystem II with an altered pigment composition was prepared from the original complex by treatment with sodium borohydride (BH⁻₄). The absorption spectra of the modified and original complexes were compared to each other and to the spectra of purified chlorophyll a and pheophytin a (Pheo a) treated with BH⁻₄ in methanolic solution. The results of these comparisons are consistent with the presence in the modified complex of an irreversibly reduced Pheo a molecule, most likely 13¹-deoxo-13¹-hydroxy-Pheo a, replacing one of the two native Pheo a molecules present in the original complex. Similar to the original preparation, the modified complex was capable of a steady-state photoaccumulation of Pheo⁻ and P680⁺. It is concluded that the pheophytin a molecule which undergoes borohydride reduction is not involved in the primary charge separation and seems to represent a previously postulated photochemically inactive Pheo a molecule. The Q_y and Q_x transitions of this molecule were determined to be located at 5°C at 679.5–680 nm and 542 nm, respectively.     

Analysis of lipophilic pigments from a phototrophic microbial mat community by high performance liquid chromatography

An assay for lipophilic pigments in phototrophic microbial mat communities using reverse phase-high performance liquid chromatography was developed which allows the separation of 15 carotenoids and chloropigments in a single 30 min program. Lipophilic pigments in a laminated mat from a commercial salina near Laguna Guerrero Negro, Baja California Sur, Mexico reflected their source organims. Myxoxanthopyll, echinenone, canthaxanthin, and zeaxanthin were derived from cyanobacteria; chlorophyll c, and fucoxanthin from diatoms; chlorophyll a from cyanobacteria and diatoms; bacteriochlorophylls a and c, bacteriophaeophytin a, and γ-carotene from Chloroflexus spp.; and β-carotene from a variety of phototrophs. Sensitivity of detection was 0.6–6.1 ng for carotenoids and 1.7–12 ng for most chloropigments. This assay represents a significant improvement improvement over previous analyses of lipophilic pigments in microbial mats and promises to have a wider application to other types of phototrophic communities.