Green Photosynthetic Bacteria Research Articles

Self-aggregation of zinc bacteriochlorophyll-d analogs with an acylhydrazone moiety as the 13-keto-carbonyl alternative.

Zinc methyl 3-hydroxymethyl-pyropheophorbides-a possessing an acylhydrazinylidene group at the 131-position were prepared by chemically modifying chlorophyll-a, which were models of bacteriochlorophyll-d as one of the light-harvesting pigments in photosynthetic green bacteria. Similar to the self-aggregation of natural bacteriochlorophyll-d in the antenna systems called chlorosomes, some of the synthetic models self-aggregated in an aqueous Triton X-100 solution to give red-shifted and broadened visible absorption bands. The newly appeared oligomeric bands were ascribable to the exciton coupling of the chlorin π-systems along the molecular y-axis, leading to intense circular dichroism bands in the red-shifted Qy and Soret regions. The self-aggregation in the aqueous micelle was dependent on the steric size of the terminal substituent at the 13-acylhydrazone moiety. An increase in the length of the oligomethylene chain as the terminal moved the red-shifted Qy maxima to shorter wavelengths, and branched alkyl and benzyl substitutes afforded no more self-aggregates to leave monomeric species in the hydrophobic environment inside the micelle. These results indicated that the acyl groups on the 13-hydrazone as the alternative of the natural 13-ketone regulated the chlorosome-like self-aggregation.

Self-aggregation of synthetic zinc bacteriochlorophyll-d analogs with pinacol boronates on the B-ring

Zinc 3-hydroxymethyl-131-oxo-bacteriochlorins possessing a variety of pinacol boronates on the B-ring were prepared from chemical modification of naturally occurring chlorophyll-a. The synthetic bacteriochlorophyll-d analogs were dissolved into an aqueous Triton X-100 solution to exhibit red-shifted and broadened electronic absorption bands with reversed S-shape circular dichroism bands, compared with their monomeric bands. The behaviors indicated that most synthetic models possessing a bacteriochlorin π-system self-aggregated inside the aqueous micelles to give similar oligomers as the J-aggregates of bacteriochlorophyll-d bearing a chlorin π-skeleton in major light-harvesting antennas of green photosynthetic bacteria, chlorosomes. The methylboronate self-aggregated more largely than the phenylboroante, and the self-aggregation was suppressed by ortho-substitution on the phenyl ring: phenyl > 1-naphthyl ≫ 9-anthryl and phenyl > 2,6-dimethylphenyl. Along with an increase in the size of the substituents on the boron atom of their boronates, the formation of the chlorosome-like self-aggregates decreased substantially.

Efficient two-step excitation energy transfer in artificial light-harvesting antenna based on bacteriochlorophyll aggregates

Chlorosomes of green photosynthetic bacteria are large light-harvesting complexes enabling these organisms to survive at extremely low-light conditions. Bacteriochlorophylls found in chlorosomes self-organize and are ideal candidates for use in biomimetic light-harvesting in artificial photosynthesis and other applications for solar energy utilization. Here we report on the construction and characterization of an artificial antenna consisting of bacteriochlorophyll c co-aggregated with β-carotene, which is used to extend the light-harvesting spectral range, and bacteriochlorophyll a, which acts as a final acceptor for excitation energy. Efficient energy transfer between all three components was observed by means of fluorescence spectroscopy. The efficiency varies with the β-carotene content, which increases the average distance between the donor and acceptor in both energy transfer steps. The efficiency ranges from 89 to 37% for the transfer from β-carotene to bacteriochlorophyll c, and from 93 to 69% for the bacteriochlorophyll c to bacteriochlorophyll a step. A significant part of this study was dedicated to a development of methods for determination of energy transfer efficiency. These methods may be applied also for study of chlorosomes and other pigment complexes.

Quenching of bacteriochlorophyll a triplet state by carotenoids in the chlorosome baseplate of green bacterium Chloroflexus aurantiacus.

To capture weak light fluxes, green photosynthetic bacteria have unique structures - chlorosomes, consisting of 104-5 molecules of bacteriochlorophyll (BChl) c, d, e. Chlorosomes are attached to the cytoplasmic membrane through the baseplate, a paracrystalline protein structure containing BChl a and carotenoids (Car). The most important function of Car is the quenching of triplet states of BChl, which prevents the formation of singlet oxygen and thereby provides photoprotection. In our work, we studied the dynamics of the triplet states of BChl a and Car in the baseplate of Chloroflexus aurantiacus chlorosomes using picosecond differential spectroscopy. BChl a of the baseplate was excited into the Qy band at 810 nm, and the corresponding absorption changes were recorded in the range of 420-880 nm. It was found that the formation of the Car triplet state occurs in ∼1.3 ns, which is ∼3 times faster than the formation of this state in the peripheral antenna of C. aurantiacus according to literature data. The Car triplet state was recorded by the characteristic absorption band T1 → Tn at ∼550 nm. Simultaneously with the appearance of absorption T1 → Tn, there was a bleaching of the singlet absorption of Car in the region of 400-500 nm. Theoretical modeling made it possible to estimate the characteristic time of formation of the triplet state of BChl a as ∼0.5 ns. It is shown that the experimental data are well described by the sequential scheme of formation and quenching of the BChl a triplet state: BChl a* → BChl aT → CarT. Thus, carotenoids from green bacteria effectively protect the baseplate from possible damage by singlet oxygen.

Low-frequency vibrations of bacteriochlorophyll oligomers in chlorosomes of photosynthetic green bacteria

In green photosynthetic bacteria, light absorption occurs in bacteriochlorophyll (BChl) c/d/e oligomers, which are located in chlorosomes - unique structures created by nature to collect the energy of very weak light fluxes. Using coherent femtosecond spectroscopy at cryogenic temperature, we detected and studied low-frequency vibrational motions of BChl c oligomers in the chlorosomes of the green bacteria Chloroflexus (Cfx.) aurantiacus. The objects of the study were chlorosomes isolated from bacterial cultures grown under different light intensity. It was found that the Fourier spectrum of low-frequency coherent oscillations in the Qy band of BChl c oligomers depends on the light intensity used for the growth of bacteria. It turned out that the number of low-frequency vibrational modes of chlorosomes increases as the illumination under which they were cultivated decreases. Also, the frequency range within which these modes are observed expands, and the frequencies of most modes change. Theoretical modeling of the obtained data and analysis of the literature led to the conclusion that the structural basis of Cfx. aurantiacus chlorosomes are short linear chains of BChl c combined into more complex structures. An increase in the length of these chains in chlorosomes grown under weaker light leads to the observed changes in the spectrum of vibrations of BChl c oligomers. This increase is an effective mechanism for the adaptation of bacteria to changing external conditions.

Low-Frequency Oscillations of Bacteriochlorophyll Oligomers in Chlorosomes of Photosynthetic Green Bacteria.

In green photosynthetic bacteria, light is absorbed by bacteriochlorophyll (BChl) c/d/e oligomers, which are located in chlorosomes - unique structures created by Nature to collect the energy of very weak light fluxes. Using coherent femtosecond spectroscopy at cryogenic temperature, we detected and studied low-frequency vibrational motions of BChl c oligomers in chlorosomes of the green bacteria Chloroflexus (Cfx.) aurantiacus. The objects of the study were chlorosomes isolated from the bacterial cultures grown under different light intensity. It was found that the Fourier spectrum of low-frequency coherent oscillations in the Qy band of BChl c oligomers depends on the light intensity used for the growth of bacteria. It turned out that the number of low-frequency vibrational modes of chlorosomes increases as illumination under which they were cultivated decreases. Also, the frequency range within which these modes are observed expands, and frequencies of the most modes change. Theoretical modeling of the obtained data and analysis of the literature led to conclusion that the structural basis of Cfx. aurantiacus chlorosomes are short linear chains of BChl c combined into more complex structures. Increase in the length of these chains in chlorosomes grown under weaker light leads to the observed changes in the spectrum of vibrations of BChl c oligomers. This increase is an effective mechanism for bacteria adaptation to changing external conditions.

Self-aggregation behavior of dimeric chlorophyll-a derivatives linked with ethynylene and m-phenylene moieties.

Chlorophyll(Chl)-a derivatives inserting an ethynylene-m-phenylene group between a zinc chlorin ring and a hydroxymethyl group, in which various substituents were introduced on the benzene spacer, were prepared as model compounds for the light-harvesting antennae (chlorosomes) of photosynthetic green bacteria. These compounds were synthesized from a C3-ethynylated Chl-a derivative via sequential Sonogashira cross-coupling reaction, and the effects of the substituents on the phenylene linker on their self-aggregation behaviors were investigated by electronic absorption, circular dichroism, and infrared absorption spectroscopic measurements. These studies exhibited that some compounds gave the disordered self-assemblies including several species; however, the zinc complex of the dimeric Chl-a derivative primarily allowed a single J-aggregate species in an aqueous Triton X-100 micellar solution. Additional control experiments revealed that its self-assembly was constructed through the hydrogen and coordination bonding involving the hydroxymethyl group on benzene ring, keto-carbonyl group at C13-position, and central zinc atom, and this is consistent with a conventional chlorosomal manner.

ADAPTATION OF GREEN PHOTOSYNTHETIC BACTERIA TO DIFFERENT ILLUMINATION INTENSITY ACCORDING TO SPECTROSCOPY DATA ON CHLOROSOMES

The absorption and circular dichroism spectra of chlorosomes isolated from green photosynthetic bacteria Chloroflexus aurantiacus grown under di erent illumination were studied. It was found that as the intensity of the growth light decreases, the spectra shift to the red side and become narrower and larger in amplitude. Theoretical modeling of the data obtained was performed using the theory of excitons. The conclusion was formulated that the number of bacteriochlorophyll c molecules in linear chains, which form the basis of the elementary blocks of chlorosomes, become greater as the intensity of light at which bacteria are grown decreases. It was suggested that this phenomenon increases the e ciency of capturing weak light uxes and thereby increases the chances of bacterial survival in conditions of sunlight de ciency.

Structural basis of a bi-functional malonyl-CoA reductase (MCR) from the photosynthetic green non-sulfur bacterium Roseiflexus castenholzii.

Malonyl-CoA reductase (MCR) is a NADPH-dependent bi-functional enzyme that performs alcohol dehydrogenase and aldehyde dehydrogenase (CoA-acylating) activities in the N- and C-terminal fragments, respectively. It catalyzes the two-step reduction of malonyl-CoA to 3-hydroxypropionate (3-HP), a key reaction in the autotrophic CO2 fixation cycles of Chloroflexaceae green non-sulfur bacteria and the archaea Crenarchaeota. However, the structural basis underlying substrate selection, coordination, and the subsequent catalytic reactions of full-length MCR is largely unknown. For the first time, we here determined the structure of full-length MCR from the photosynthetic green non-sulfur bacterium Roseiflexus castenholzii (RfxMCR) at 3.35 Å resolution. Furthermore, we determined the crystal structures of the N- and C-terminal fragments bound with reaction intermediates NADP+ and malonate semialdehyde (MSA) at 2.0 Å and 2.3 Å, respectively, and elucidated the catalytic mechanisms using a combination of molecular dynamics simulations and enzymatic analyses. Full-length RfxMCR was a homodimer of two cross-interlocked subunits, each containing four tandemly arranged short-chain dehydrogenase/reductase (SDR) domains. Only the catalytic domains SDR1 and SDR3 incorporated additional secondary structures that changed with NADP+-MSA binding. The substrate, malonyl-CoA, was immobilized in the substrate-binding pocket of SDR3 through coordination with Arg1164 and Arg799 of SDR4 and the extra domain, respectively. Malonyl-CoA was successively reduced through protonation by the Tyr743-Arg746 pair in SDR3 and the catalytic triad (Thr165-Tyr178-Lys182) in SDR1 after nucleophilic attack from NADPH hydrides. IMPORTANCE The bi-functional MCR catalyzes NADPH-dependent reduction of malonyl-CoA to 3-HP, an important metabolic intermediate and platform chemical, from biomass. The individual MCR-N and MCR-C fragments, which contain the alcohol dehydrogenase and aldehyde dehydrogenase (CoA-acylating) activities, respectively, have previously been structurally investigated and reconstructed into a malonyl-CoA pathway for the biosynthetic production of 3-HP. However, no structural information for full-length MCR has been available to illustrate the catalytic mechanism of this enzyme, which greatly limits our capacity to increase the 3-HP yield of recombinant strains. Here, we report the cryo-electron microscopy structure of full-length MCR for the first time and elucidate the mechanisms underlying substrate selection, coordination, and catalysis in the bi-functional MCR. These findings provide a structural and mechanistic basis for enzyme engineering and biosynthetic applications of the 3-HP carbon fixation pathways.

Predicted Structure of the BciC Enzyme Catalyzing the Removal of the C132-Methoxycarbonyl Group for Biosynthesis of Chlorosomal Chlorophylls: A Mechanism for Dual Catalytic Functions of Hydrolysis and Decarboxylation inside Its Active Site.

Green photosynthetic bacteria, one of the phototrophs, have the largest and most efficient light-harvesting antenna systems, called chlorosomes. The core part of chlorosomes consists of unique bacteriochlorophyll c/d/e molecules. In the biosynthetic pathway of these molecules, a BciC enzyme catalyzes the removal of the C132-methoxycarbonyl group of chlorophyllide a. Two sequential reactions have been proposed for the BciC enzymatic demethoxycarbonylation: the BciC enzyme would catalyze the hydrolysis of the C132-methoxycarbonyl group, and the resulting carboxylic acid would be rapidly decarboxylated to generate pyrochlorophyllide a. In this study, we computationally predicted the three-dimensional structure of the BciC protein. Its active site was proposed based on structural analysis using docking simulation. In vitro enzymatic reaction assays of mutated BciC supported the prediction. The BciC enzymatic hydrolysis would be an aspartic/glutamic acid hydrolase, which involves the amino residues E85 and D180. Furthermore, Y58 and H126 might depend on stabilization and/or recognition with the substrate. Most importantly, H137 would protonate 13-C═O or deprotonate C132-COOH in the hydrolyzed product to promote decarboxylation. In conclusion, the BciC enzyme has the dual functions of hydrolysis and decarboxylation.

Self-aggregation of 32-substituted bacteriochlorophyll-d analogs in aqueous micelle

As naturally occurring bacteriochlorophyll-[Formula: see text] models, zinc methyl (31R)-bacteriopheophorbides-[Formula: see text] possessing ethyl, vinyl, and ethynyl groups at the 32-position were prepared by chemically modifying chlorophyll-[Formula: see text]. The synthetic molecules self-aggregated in an aqueous Triton X-100 micelle solution similarly as in the major light-harvesting antenna of photosynthetic green bacteria to give supramolecularly ordered large oligomers with red-shifted and broadened visible absorption bands, compared with the monomeric bands. The sequential hydrogenation of the 32-ethynyl to ethyl group via the vinyl group gradually suppressed the chlorosomal self-aggregation ability. The successive elongation of the 31-alkyl chain from a methyl to propyl group via an ethyl group also diminished the [Formula: see text]-aggregation ability. These decreases in the self-aggregation were ascribable to the steric enhancement of the 32-substituents near the 31-hydroxy group requisite for the [Formula: see text]-aggregation.

A bioinspired sequential energy transfer system constructed via supramolecular copolymerization

Sequential energy transfer is ubiquitous in natural light harvesting systems to make full use of solar energy. Although various artificial systems have been developed with the biomimetic sequential energy transfer character, most of them exhibit the overall energy transfer efficiency lower than 70% due to the disordered organization of donor/acceptor chromophores. Herein a sequential energy transfer system is constructed via supramolecular copolymerization of σ-platinated (hetero)acenes, by taking inspiration from the natural light harvesting of green photosynthetic bacteria. The absorption and emission transitions of the three designed σ-platinated (hetero)acenes range from visible to NIR region through structural variation. Structural similarity of these monomers faciliates supramolecular copolymerization in apolar media via the nucleation-elongation mechanism. The resulting supramolecular copolymers display long diffusion length of excitation energy (> 200 donor units) and high exciton migration rates (~1014 L mol−1 s−1), leading to an overall sequential energy transfer efficiency of 87.4% for the ternary copolymers. The superior properties originate from the dense packing of σ-platinated (hetero)acene monomers in supramolecular copolymers, mimicking the aggregation mode of bacteriochlorophyll pigments in green photosynthetic bacteria. Overall, directional supramolecular copolymerization of donor/acceptor chromophores with high energy transfer efficiency would provide new avenues toward artificial photosynthesis applications.

Self-Assembly of a Zinc Bacteriochlorophyll-d Analog with a Lipophilic Tertiary Amide Group in the 17-Substituent

Abstract Self-assembled aggregates of bacteriochlorophyll(BChl)-c/d/e pigments play key roles in major light-harvesting antenna systems of photosynthetic green bacteria. Herein, we report the self-assembly of a lipophilic zinc BChl-d model with an N,N-didodecylamide in the 17-substituent. The present model formed two types of J-aggregates, which formed under kinetic and thermodynamic controls.

Substituted Methylenation at the 132 -Position of a Chlorophyll-a Derivative via Mixed Aldol Condensation, Optical Properties of the Synthetic Bacteriochlorophyll-d Analogs, and Self-aggregation of Their Zinc Complexes.

Chlorophyll-a derivatives possessing a substituted methylene group at the 132 -position were prepared by the mixed aldol condensation of methyl 3-hydroxymethyl-pyropheophorbide-a with aldehydes bearing a methyl, p-nitro/cyanophenyl, or pentafluorophenyl group. Their electronic absorption spectra were dependent on the substituents at the methylene terminal. The Soret bands were broadened by increasing the group electronegativity of the substituents, which was ascribable to the charge transfer from the core chlorin to the peripheral substituent in a molecule. Although their Qy absorption and fluorescence emission bands resembled each other, the emission intensities decreased with an increase in the electronegativity because of intramolecular electron transfer quenching. Some of their zinc complexes self-aggregated in a less polar organic solvent to give red-shifted and broadened absorption bands with intense circular dichroism couplets, which were similar to those of bacteriochlorophyll-c/d aggregates in natural chlorosomes as the main light-harvesting antennas of green photosynthetic bacteria and their models. The J-aggregation was suppressed with an enhancement in the size of the 132 -substituents.

Superradiance of bacteriochlorophyll c aggregates in chlorosomes of green photosynthetic bacteria

Chlorosomes are the main light-harvesting complexes of green photosynthetic bacteria that are adapted to a phototrophic life at low-light conditions. They contain a large number of bacteriochlorophyll c, d, or e molecules organized in self-assembling aggregates. Tight packing of the pigments results in strong excitonic interactions between the monomers, which leads to a redshift of the absorption spectra and excitation delocalization. Due to the large amount of disorder present in chlorosomes, the extent of delocalization is limited and further decreases in time after excitation. In this work we address the question whether the excitonic interactions between the bacteriochlorophyll c molecules are strong enough to maintain some extent of delocalization even after exciton relaxation. That would manifest itself by collective spontaneous emission, so-called superradiance. We show that despite a very low fluorescence quantum yield and short excited state lifetime, both caused by the aggregation, chlorosomes indeed exhibit superradiance. The emission occurs from states delocalized over at least two molecules. In other words, the dipole strength of the emissive states is larger than for a bacteriochlorophyll c monomer. This represents an important functional mechanism increasing the probability of excitation energy transfer that is vital at low-light conditions. Similar behaviour was observed also in one type of artificial aggregates, and this may be beneficial for their potential use in artificial photosynthesis.

Detection of 132-carboxy-chlorin produced by the in vitro BciC enzymatic hydrolysis of zinc chlorophyllide

Green photosynthetic bacteria with an efficient light-harvesting system contain special chlorophyll molecules, called bacteriochlorophylls c, d, e, in their main antennae. In the biosynthetic pathway, a BciC enzyme is proposed to catalyze the hydrolysis of the C132-methoxycarbonyl group of chlorophyllide a, but the resulting C132-carboxy group has not been detected yet because it is spontaneously removed due to the instability of the β-keto-carboxylic acid. In this study, the in vitro BciC enzymatic reactions of zinc methyl (131R/S)-hydroxy-mesochlorophyllides a were examined and a carboxylic acid possessing the C132S-OH was first observed as the hydrolyzed product of the C132-COOCH3.

Utilization of blue-green light by chlorosomes from the photosynthetic bacterium Chloroflexus aurantiacus: Ultrafast excitation energy conversion and transfer

Chlorosomes of photosynthetic green bacteria are unique molecular assemblies providing efficient light harvesting followed by multi-step transfer of excitation energy to reaction centers. In each chlorosome, 104–105 bacteriochlorophyll (BChl) c/d/e molecules are organized by self-assembly into high-ordered aggregates. We studied the early-time dynamics of the excitation energy flow and energy conversion in chlorosomes isolated from Chloroflexus (Cfx.) aurantiacus bacteria by pump-probe spectroscopy with 30-fs temporal resolution at room temperature. Both the S2 state of carotenoids (Cars) and the Soret states of BChl c were excited at ~490 nm, and absorption changes were probed at 400–900 nm. A global analysis of spectroscopy data revealed that the excitation energy transfer (EET) from Cars to BChl c aggregates occurred within ~100 fs, and the Soret → Q energy conversion in BChl c occurred faster within ~40 fs. This conclusion was confirmed by a detailed comparison of the early exciton dynamics in chlorosomes with different content of Cars. These processes are accompanied by excitonic and vibrational relaxation within 100–270 fs. The well-known EET from BChl c to the baseplate BChl a proceeded on a ps time-scale. We showed that the S1 state of Cars does not participate in EET. We discussed the possible presence (or absence) of an intermediate state that might mediates the Soret → Qy internal conversion in chlorosomal BChl c. We discussed a possible relationship between the observed exciton dynamics and the structural heterogeneity of chlorosomes.

Femtosecond excited-state dynamics in chlorosomal carotenoids of the photosynthetic bacterium Chloroflexus aurantiacus revealed by near infrared pump-probe spectroscopy.

In photosynthetic green bacteria, chlorosomes provide light harvesting with high efficiency. Chlorosomal carotenoids (Cars) participate in light harvesting together with the main pigment, bacteriochlorophyll (BChl) c/d/e. In the present work, we studied the excited-state dynamics in Cars from Chloroflexus (Cfx.) aurantiacus chlorosomes by near infrared pump-probe spectroscopy with 25 fs temporal resolution at room temperature. The S2 state of Cars was excited at a wavelength of ∼520 nm, and the absorption changes were probed at 860-1000 nm where the excited state absorption (ESA) of the Cars S2 state occurred. Global analysis of the spectroscopy data revealed an ultrafast (∼15 fs) and large (>130 nm) red shift of the S2 ESA spectrum together with the well-known S2 → S1 IC (∼190 fs) and Cars → BChl c EET (∼120 fs). The S2 lifetime was found to be ∼74 fs. Our findings are in line with earlier results on the excited-state dynamics in Cars in vitro. To explain the extremely fast S2 dynamics, we have tentatively proposed two alternative schemes. The first scheme assumed the formation of a vibrational wavepacket in the S2 state, the motion of which caused a dynamical red shift of the S2 ESA spectrum. The second scheme assumed the presence of two potential minima in the S2 state and incoherent energy transfer between them.

Synthesis of glycogen by Chlorobium limicola IMV K-8 while growth in wastewater

Due to the high content of organic compounds, the distillery wastewater can be a good substrate for the production of glycogen during cultivation of green photosynthetic bacteria. Green photosynthetic bacteria Chlorobium limicola IMV K-8 are producers of glycogen and show exoelectrogenic properties when grown alone or inside the co-culture with heterotrophic bacteria-exoelectrogens in wastewater of various origins. In our previous works it was found that due to the phototrophic growth of C. limicola IMV K-8 in the distillery wastewater significantly reduces the content of compounds of nitrogen, sulfur, Ca2+, Mg2+ and others. The study of the patterns of glycogen synthesis by green photosynthetic bacteria during growth in such an extreme environment as the wastewater of a distillery has prospects for the development of biotechnology for the production of this polysaccharide. The aim of the study was to investigate the glycogen content in C. limicola IMV K-8 cells under different growth conditions in the wastewater of the distillery. Bacteria were grown in the wastewater of the distillery under light (phototrophic growth) and without light exposure (heterotrophic growth). Bacterial cells grown on GSB medium under light (phototrophic growth) and without light (heterotrophic growth) exposure were used as controls. Glycogen content was determined at 7, 14, 21 and 30 days of growth by the glucose oxidase method. Glucose or glycogen in the wastewater of the distillery without the introduction of bacteria was not detected. It was found that the content of glycogen in cells of C. limicola IMV K-8 grown in the wastewater of the distillery, under light exposure increased from 3.8 % to 39.8 % of cells dry weight from the seventh to third day of growth during 30 days of cultivation and was 2 times higher the glycogen content of cells on GSB medium. It is assumed that the bacteria C. limicola IMV K-8 use available in the water sources of carbon and other compounds necessary for cell metabolism along with glycogen biosynthesis and bioremediation of wastewater. During C. limicola IMV K-8 growth in the darkness there is an assimilation of organic sources of carbon (acetate, pyruvate and probably organic compounds of wastewater), which allows cells to remain viable for 30 days without additional sources of carbon, nitrogen, etc., but significant glycogen synthesis does not occur. The glycogen formed under phototrophic conditions can be further a source of carbon or a substrate for electric current generation by exoelectrogenic bacteria.

Self-aggregation of zinc bacteriochlorophyll-d analog bearing B-ring reduced chlorin and 17-acrylate residue

Abstract As a model of bacteriochlorophyll(BChl)-d specifically found in major light-harvesting antennae (chlorosomes) of photosynthetic green bacteria, zinc methyl 7,8-dihydro-17,18,171,172-tetradehydro-bacteriopheophorbide-d was prepared from naturally occurring BChl-a through the double dehydration of the cis-17,18-diol. The synthetic B-ring reduced Zn-BChl-d analog bearing the 17-acrylate residue in tetrahydrofuran exhibited a more bathochromically shifted Soret band in the monomeric state than its counterpart with the 17-propionate residue, while the former's Qy band slightly moved to a longer wavelength and was somewhat broadened in comparison with the latter's. Compared with the monomeric bands, the acrylated pigment self-aggregated in 1% tetrahydrofuran and hexane to give more red-shifted and broadened Soret and Qy bands at blue-to-green and far-red regions, respectively, which were similar to the J-aggregates of BChl-d in chlorosomes. By contrast, the propionated pigment remained monomeric under the same conditions. These spectral differences were owing to the 17-substitution effect including the π-conjugating and electron-withdrawing 17-acrylate residue.