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Denitrification plays a significant role in both wastewater treatment and nitrogen cycle. But high amount of nitrate and accumulation of nitrite inhibit these processes. In view of this, a denitrifying phototrophic bacterium was isolated, characterized based on 16s rRNA analysis and its ability to remove toxic nitrogenous compounds investigated. Different initial concentrations were used to determine the effect of concentration on nitrogen removal and the biokinetic coefficients using Michaelis–Menten rate expression. The bacterium can remove 71% of nitrate at the initial concentration of 85 mg l −1 under photoheterotrophic growth condition without nitrite or ammonium accumulation. It can also remove 62% of ammonium at initial concentrations of 52 mg l −1 under anoxic growth condition without nitrate or nitrite accumulation. The results also showed that increase in concentrations led to decrease for both NO 3 − and NH 4 –N removal. Analysis and amplification of the possible genes that are involved in denitrification revealed the possession of napA and nirK genes. This strain can therefore serve as good candidate in wastewater treatment plants that are faced with the problem of nitrite accumulation and high amount of nitrogenous compounds that inhibit cell growth during biological nitrogen removal. [ABSTRACT FROM AUTHOR]

Carotenoidless light-harvesting complexes (DPA-complexes) LH1-RC and LH2 were isolated from the purple sulfur bacterium Ectothiorhodospira haloalkaliphila in which carotenoid biosynthesis was suppressed with diphenylamine (DPA). Carotenoids of the spirilloxanthine series, which were isolated from the same bacterium, were incorporated into the DPA-complexes in vitro with an efficiency of 95-100%. The comparison of characteristics of the complexes with the incorporated carotenoids and the control complexes showed that the LH2 complexes with the incorporated carotenoids restored their absorption spectra, circular dichroism signals, and energy transfer from carotenoids to bacteriochlorophyll, which indicates that carotenoids were correctly incorporated into the structure of this complex. [ABSTRACT FROM AUTHOR]

Photosystem formation in anaerobic anoxygenic phototrophic bacteria (APB) is repressed by oxygen but is de-repressed when oxygen tension decreases. Under semiaerobic conditions, the synthesis of photopigments and pigment protein complexes in Rhodobacter ( Rba.) sphaeroides are repressed by light. AppA, a blue-light receptor, mediates this regulation. In the present study, it was showed that the synthesis of bacteriochlorophyll, carotenoid, and pigment protein complexes in Rba. azotoformans 134K20 was significantly repressed by oxygen. Oxygen exposure also led to a conversion of spheroidene to spheroidenone. In semiaerobically growing cells, light irradiation resulted in a decrease in the formation of photosystem, and blue light was found to be the most effective light source. Blue light reduced the contents of bacteriochlorophyll and carotenoid slightly, but had negligible effects on light harvesting complex (LH) 1 content, whereas the content of LH2 was significantly decreased indicating that blue light selectively repressed the synthesis of LH2 in semiaerobically growing 134K20. It was concluded that, similar to Rba. sphaeroides, a blue light receptor presented in strain 134K20 played important roles in its light-dependent repression. A possible mechanism involved in controlling the differential inhibitory of blue light on the synthesis of photosystem was discussed. [ABSTRACT FROM AUTHOR]

The heliobacteria are a family ofstrictly anaerobic, Gram-positive,photoheterotrophs in the Firmicutes. They make use of a homodimerictype I reaction center (RC) that contains ∼20 antenna bacteriochlorophyll(BChl) gmolecules, a special pair of BChl g′ molecules (P800), two 81-OH-Chl aFmolecules (A0),a [4Fe–4S] iron–sulfur cluster (FX), anda carotenoid (4,4′-diaponeurosporene). It is known that inthe presence of light and oxygen BChl gis convertedto a species with an absorption spectrum identical to that of Chl a. Here, we show that main product of the conversion is81-OH-Chl aF. Smaller amountsof two other oxidized Chl aFspecies arealso produced. In the presence of light and oxygen, the kinetics ofthe conversion are monophasic and temperature dependent, with an activationenergy of 66 ± 2 kJ mol–1. In the presenceof oxygen in the dark, the conversion occurs in two temperature-dependentkinetic phases: a slow phase followed by a fast phase with an activationenergy of 53 ± 1 kJ mol–1. The loss of BChl g′ occurs at the same rate as the loss of Bchl g; hence, the special pair converts at the same rate asthe antenna Chl’s. However, the loss of P800photooxidiationand flavodoxin reduction is not linear with the loss of BChl g. In anaerobic RCs, the charge recombination between P800+and FX–at 80K is monophasic with a lifetime of 4.2 ms, but after exposure to oxygen,an additional phase with a lifetime of 0.3 ms is observed. TransientEPR data show that the line width of P800+increasesas BChl gis converted to Chl aFand the rate of electron transfer from A0to FX, as estimated from the net polarization generated by singlet–tripletmixing during the lifetime of P800+A0–, is unchanged. The transient EPR data also showthat conversion of the BChl gresults in increasedformation of triplet states of both BChl gand Chl aF. The nonlinear loss of P800photooxidiationand flavodoxin reduction, the biphasic backreaction kinetics, andthe increased EPR line width of P800+are allconsistent with a model in which the BChl g′/BChl g′ and BChl g′/Chl aF′ special pairs are functional but theChl aF′/Chl aF′ special pair is not. [ABSTRACT FROM AUTHOR]

The activity of an enzyme encoded by the CT1610 gene in the green sulfur photosynthetic bacterium Chlorobaculum tepidum, which was annotated as bacteriochlorophyll (BChl) a synthase, BchG (denoted as tepBchG), was examined in vitro using the lysates of Escherichia coli containing the heterologously expressed enzyme. BChl a possessing a geranylgeranyl group at the 17-propionate residue (BChl aGG) was produced from bacteriochlorophyllide (BChlide) a and geranylgeranyl pyrophosphate in the presence of tepBchG. Surprisingly, tepBchG catalyzed the formation of BChl a bearing a farnesyl group (BChl ap) as in the enzymatic production of BChl aGG, indicating loose recognition of isoprenoid pyrophosphates in tepBchG. In contrast to such loose recognition of isoprenoid substrates, BChlide c and chlorophyllide a gave no esterifying product upon being incubated with geranylgeranyl or farnesyl pyrophosphate in the presence of tepBchG. These results confirm that tepBchG undoubtedly acts as the BChl a synthase in Cba. tepidum. The enzymatic activity of tepBchG was higher than that of BchG of Rhodobacter sphaeroides at 45 °C, although the former activity was lower than the latter below 35 °C. [ABSTRACT FROM AUTHOR]

Bacteriochlorophyll a biosynthesis requires formation of a 3-hydroxyethyl group on pyrrole ring A that gets subsequently converted into a 3-acetyl group by 3-vinyl bacteriochlorophyllide a hydratase (BchF) followed by 3-hydroxyethyl bacteriochlorophyllide a dehydrogenase (BchC). Heterologous overproduction of Chlorobaculum tepidum BchF revealed an integral transmembrane protein that was efficiently isolated by detergent solubilization. Recombinant C. tepidum BchC was purified as a soluble protein-NAD+ complex. Substrate recognition of BchC was investigated using six artificial substrate molecules. Modification of the isocyclic E ring, omission of the central magnesium ion, zinc as an alternative metal ion, and a non-reduced B ring system were tolerated by BchC. According to this broadened in vitro activity, the chlorin 3-hydroxyethyl chlorophyllide a was newly identified as a natural substrate of BchC in a reconstituted pathway consisting of dark-operative protochlorophyllide oxidoreductase, BchF, and BchC. The established reaction sequence would allow for an additional new branching point for the synthesis of bacteriochlorophyll a. Biochemical and site-directed mutagenesis analyses revealed, in contrast to theoretical predictions, a zinc-independent BchC catalysis that requires NAD+ as a cofactor. Based on these results, we are designating a new medium-chain dehydrogenase/reductase family (MDR057 BchC) as theoretically proposed from a recent bioinformatics analysis. [ABSTRACT FROM AUTHOR]

The fifth ring (E-ring) of chlorophyll (Chl) a is produced by Mg-protoporphyrin IX monomethyl ester (MPE) cyclase. There are two evolutionarily unrelated MPE cyclases: oxygen-independent (BchE) and oxygen-dependent (ChlA/AcsF) MPE cyclases. Although ChlA is the sole MPE cyclase in Synechocystis PCC 6803, it is yet unclear whether BchE exists in cyanobacteria. A BLAST search suggests that only few cyanobacteria possess bchE . Here, we report that two bchE candidate genes from Cyanothece strains PCC 7425 and PCC 7822 restore the photosynthetic growth and bacteriochlorophyll production in a bchE -lacking mutant of Rhodobacter capsulatus . We termed these cyanobacterial bchE orthologs “ chlE .” [ABSTRACT FROM AUTHOR]

Rhodospirillum rubrum has the potential for biomass resource recycling combined with sewage purification. However, low biomass production and yield restricts the potential for sewage purification. This research investigated the improvement of biomass production, yield and organics reduction by Mg2+ in R. rubrum wastewater treatment. Results showed that with optimal dosage (120 mg/L), biomass production reached 4,000 mg/L, which was 1.5 times of that of the control group. Biomass yield was improved by 43.3%. Chemical oxygen demand (COD) removal reached over 90%. Hydraulic retention time was shortened by 25%. Mechanism analysis indicated that Mg2+ enhanced the isocitrate dehydrogenase and Ca2+/Mg2+-ATPase activities, bacteriochlorophyll content on respiration and photophosphorylation. These effects then enhanced ATP production, which led to more biomass accumulation and COD removal. With 120 mg/L Mg2+ dosage, the isocitrate dehydrogenase and Ca2+/Mg2+-ATPase activities, bacteriochlorophyll content, ATP production were improved, respectively, by 33.3%, 50%, 67%, 41.3% compared to those of the control group. [ABSTRACT FROM AUTHOR]

'Bacterial consortium' sensu lato applies to mutualism or syntrophy-based systems consisting of unrelated bacteria. Consortia of cyanobacteria have been preferentially studied on A nabaena epibioses; non-photosynthetic satellites of other filamentous or unicellular cyanobacteria were also considered although structure-functional data are few. At the same time, information about consortia of cyanobacteria which have light-harvesting antennae distinct from standard phycobilisome was missing. In this study, we characterized first, via a polyphasic approach, the cultivable consortium of P rochlorothrix hollandica CCAP 1490/1 (filamentous cyanobacterium which contains chlorophylls a, b/carotenoid/protein complex in the absence of phycobilisome) and non-photosynthetic heterotrophic bacteria. The strains of most abundant satellites were isolated and identified. Consortium metagenome reconstructed via 454-pyro and Illumina sequencing was shown to include, except for P . hollandica, several phylotypes of P roteobacteria and Bacteroidetes. The ratio of consortium members was essentially stable irrespective of culture age, and restored after artificially imposed imbalance. The consortium had a complex spatial arrangement as demonstrated by FISH and SEM images of the association, epibiosis, and biofilm type. Preliminary data of metagenome annotation agreed with the hypothesis that satellite bacteria contribute to P . hollandica protection from reactive oxygen species ( ROS). [ABSTRACT FROM AUTHOR]

We report the synthesis and characterization of a new sulfur-containing derivative of bacteriochlorophyll a. The latter was isolated from biomass of the nonsulfur purple bacterium Rhodobacter capsulatus strain B10. The developed photosensitizer is N-aminobacteriopurpurinimide with an exocyclic amino group acylated with a lipoic acid moiety, which is a biogenic substance that acts as a cofactor of the pyruvate dehydrogenase and α-ketoglutarate dehydrogenase complexes in the body. The disulfide moiety of lipoic acid confers the compound aurophilicity, thus allowing its conjugation with gold nanoparticles (NP-Au) via S-Au bonds. The shape and the size of the resulting nanoconjugate with immobilized photosensitizer (PS-Au) were assessed by dynamic light scattering and transmission electron microscopy. The conjugated nanoparticles are spherical with hydrodynamic diameter of 100-110 nm. The PS-Au conjugate absorbs light at 824 nm and emits strong fluorescence at 830 nm, which allowed in vivo study of its dynamic biodistribution in rats bearing sarcoma M-1. Compared to the free photosensitizer, PS loaded on the gold nanoparticles (PS-Au) showed extended circulation time in the blood and enhanced tumor uptake due to nonspecific passive targeting when the drug accumulates in tumor sites through the leaky tumor neovasculature and does not return to the circulation. [ABSTRACT FROM AUTHOR]

In the bacterial photosynthetic reaction center (RC), asymmetric protein environment of the bacteriochlorophyll (BChl) dimer largely determines the photophysical and photochemical properties of the primary electron donor. Previously, we noticed significant differences in properties of Rhodobacter sphaeroides RCs with identical mutations in symmetry-related positions - I(M206)H and I(L177)H. The substitution I(L177)H resulted in covalent binding of BChl P with the L-subunit, as well as in 6-coordination of BChl B, whereas in RC I(M206)H no such changes of pigment-protein interactions were found. In addition, the yield of RC I(M206)H after its isolation from membranes was significantly lower than the yield of RC I(L177)H. This study shows that replacement of amino acid residues in the M203-M206 positions near BChls P and B by symmetry-related residues from the L-subunit near BChls P and B leads to further decrease in RC amount in the membranes associated obviously with poor assembly of the complex. Introduction of a new hydrogen bond between BChl P and its protein environment by means of the F(M197)H mutation stabilized the mutant RC but did not affect its low yield. We suggest that the mutation I(M206)H and substitution of amino acid residues in M203-M205 positions could disturb glycolipid binding on the RC surface near BChl B that is important for stable assembly of the complex in the membrane. [ABSTRACT FROM AUTHOR]

Roseovarius mucosus Biebl et al. 2005 is a bacteriochlorophyll a-producing representative of the marine Roseobacter group within the alphaproteobacterial family Rhodobacteraceae, which was isolated from the dinoflagellate Alexandrium ostenfeldii. The marine Roseobacter group was found to be abundant in the ocean and plays an important role for global and biogeochemical processes. Here we describe the features of the R. mucosus strain DFL-24T together with its genome sequence and annotation generated from a culture of DSM 17069T. The 4,247,724 bp containing genome sequence encodes 4,194 protein-coding genes and 57 RNA genes. In addition to the presence of four plasmids, genome analysis revealed the presence of genes associated with host colonization, DMSP utilization, cytotoxins, and quorum sensing that could play a role in the interrelationship of R. mucosus with the dinoflagellate A. ostenfeldii and other marine organisms. Furthermore, the genome encodes genes associated with mixotrophic growth, where both reduced inorganic compounds for lithotrophic growth and a photoheterotrophic lifestyle using light as additional energy source could be used. [ABSTRACT FROM AUTHOR]

Thefate of triplet excited states in the Fenna–Matthew–Olson(FMO) pigment–protein complex is studied by means of time-resolvednanosecond spectroscopy and exciton model simulations. Experimentsreveal microsecond triplet excited-state energy transfer between thebacteriochlorophyll (BChl) pigments, but show no evidence of tripletenergy transfer to molecular oxygen, which is known to produce highlyreactive singlet oxygen and is the leading cause of photo damage inphotosynthetic proteins. The FMO complex is exceptionally photo stabledespite the fact it contains no carotenoids, which could effectivelyquench triplet excited states of (bacterio)chlorophylls and are usuallyfound within pigment–protein complexes. It is inferred thatthe triplet excitation is transferred to the lowest energy pigment,BChl 3, within the FMO complex, whose triplet state energy is shiftedby pigment–protein interactions below that of the singlet oxygenexcitation. Thus, the energy transfer to molecular oxygen is blockedand the FMO does not need carotenoids for photo protection. [ABSTRACT FROM AUTHOR]

Size exclusion chromatography was used to assess the relative size of intact and diphenylamine-treated (DPA, with suppressed carotenoid synthesis) peripheral light-harvesting complexes (LH2 complexes) of the sulfur bacterium Allochromatium minutissimum. Both LH2 complexes were nonamers and had the same elution volume V, coinciding with that for the LH2 complex of Rhodoblastus acidophilus (strain 10050). Their molecular weight was 150 kDa. Both pheophytinization of bacteriochlorophyll (BChl) at low pH and treatment with the detergent LDAO, which affects the hydrophobic interactions between the neighboring protomers, result in the fragmentation of the ring of the isolated LH2 complexes and formation of 55-kDa fragments with molecular weights corresponding to one-third of the initial value. Fragmentation caused by both pheophytinization and detergent treatment was much more rapid in DPA LH2 complexes than in the intact ones. The 55-kDa fragments formed at low pH values contained monomeric bacteriopheophytin, while the fragments of a similar molecular weight formed at pH 8.0 in the presence of the detergent contained monomeric BChl. The observed fragmentation was hypothesized to reflect the inherent C symmetry of the LH2 complexes, with the preliminarily assembled trimers used as building blocks. [ABSTRACT FROM AUTHOR]

There is now evidence that aerobic anoxygenic phototrophic (AAP) bacteria are widespread across aquatic systems, yet the factors that determine their abundance and activity are still not well understood, particularly in freshwaters. Here we describe the patterns in AAP abundance, cell size and pigment content across wide environmental gradients in 43 temperate and boreal lakes of Québec. AAP bacterial abundance varied from 1.51 to 5.49 x 105 cells mL-1, representing <1 to 37% of total bacterial abundance. AAP bacteria were present year-round, including the ice-cover period, but their abundance relative to total bacterial abundance was significantly lower in winter than in summer (2.6% and 7.7%, respectively). AAP bacterial cells were on average two-fold larger than the average bacterial cell size, thus AAP cells made a greater relative contribution to biomass than to abundance. Bacteriochlorophyll a (BChla) concentration varied widely across lakes, and was not related to AAP bacterial abundance, suggesting a large intrinsic variability in the cellular pigment content. Absolute and relative AAP bacterial abundance increased with dissolved organic carbon (DOC), whereas cell-specific BChla content was negatively related to chlorophyll a (Chla). As a result, both the contribution of AAP bacteria to total prokaryotic abundance, and the cell-specific BChla pigment content were positively correlated with the DOC:Chla ratio, both peaking in highly colored, low-chlorophyll lakes. Our results suggest that photoheterotrophy might represent a significant ecological advantage in highly colored, low-chlorophyll lakes, where DOC pool is chemically and structurally more complex. [ABSTRACT FROM AUTHOR]

Two alkaliphilic strains of nonsulfur purple bacteria (NPB), B7-4 and B8-2, were isolated from moderately saline alkaline steppe lakes in southeast Siberia with pH values above 9.0. The isolates were motile, polymorphous cells (from short rods to long spindly cells) 1-2.5 × 2.5-7 μm. Intracellular membranes of vesicular type were mostly located at the cell periphery. The microorganisms contained bacteriochlorophyll a and carotenoids of the spheroidene and spirilloxanthin series. The photosynthetic apparatus was represented by LH2 and LH1 light-harvesting complexes. In the presence of organic compounds, the strains grew aerobically in the dark or anaerobically in the light. Capacity for photo- and chemoautotrophic growth was not detected. The cbbL gene encoding RuBisCO was not revealed. Optimal growth of both strains occurred at 2% NaCl (range from 0.5 to 4%), pH 8.0-8.8 (range from 7.5 to 9.7), and 25-35°C. The DNA G+C content was 67.6-69.8 mol %. Pairwise comparison of the nucleotides of the 16S rRNA genes revealed that strains B7-4 and B8-2 belonged to the same species (99.9% homology) and were most closely related to the aerobic alkaliphilic bacteriochlorophyll a-containing anoxygenic phototrophic bacterium (APB) Roseibacula alcaliphilum De (95.2%) and to NPB strains Rhodobaca barguzinensis VKM B-2406 (94.2%) and Rbc. bogoriensis LBB1 (93.9%). The isolates were closely related to the NPB Rhodobacter veldkampii DSM 11550 (94.8%) and to aerobic bacteriochlorophyll a-containing bacteria Roseinatronobacter monicus ROS 35 and Roseicitreum antarcticul ZS2-28 (93.5 and 93.9%, respectively). New strains were described as a new NPB genus and species of the family Rhodobacteriaceae, Rhodobaculum claviforme gen. nov., sp. nov., with B7-4 (VKM B-2708, LMG 28126) as the type strain. [ABSTRACT FROM AUTHOR]

A novel thermophilic, microaerophilic, anoxygenic, and chlorophototrophic member of the phylum Acidobacteria, Chloracidobacterium thermophilum strain BT, was isolated from a cyanobacterial enrichment culture derived from microbial mats associated with Octopus Spring, Yellowstone National Park, Wyoming. C. thermophilum is strictly dependent on light and oxygen and grows optimally as a photoheterotroph at irradiance values between 20 and 50 μmol photons m-2 s-1. C. thermophilum is unable to synthesize branched-chain amino acids (AAs), L-lysine, and vitamin B12, which are required for growth. Although the organism lacks genes for autotrophic carbon fixation, bicarbonate is also required. Mixtures of other AAs and 2-oxoglutarate stimulate growth. As suggested from genomic sequence data, C. thermophilum requires a reduced sulfur source such as thioglycolate, cysteine, methionine, or thiosulfate. The organism can be grown in a defined medium at 51°C (Topt; range 44-58°C) in the pH range 5.5-9.5 (pHopt = ~7.0). Using the defined growth medium and optimal conditions, it was possible to isolate new C. thermophilum strains directly from samples of hot spring mats in Yellowstone National Park, Wyoming. The new isolates differ from the type strain with respect to pigment composition, morphology in liquid culture, and temperature adaptation. [ABSTRACT FROM AUTHOR]

Aerobic anoxygenic phototrophic bacteria (AAnPB) are bacteriochlorophyll a-containing photoheterotrophic organisms that rely on phototrophy and heterotrophy processes for energy acquisition. Here, we demonstrate the ubiquitous distribution of AAnPB in the Uwa Sea and their relatively larger cell size among members of the bacteria community. The contribution of AAnPB in terms of cell number to the total bacterial abundance ranged from 3.5 % to 7.9 %. The mean cell volume for AAnPB was 2.78 ± 0.72 times larger than the mean cell volume of the total bacteria. The ratio of the contribution of their biovolume to the total bacteria was estimated to be 9.7-22 %. [ABSTRACT FROM AUTHOR]

Bacteriochlorophyll a biosynthesis requires the stereo- and regiospecific two electron reduction of the C7-C8 double bond of chlorophyllide a by the nitrogenase-like multisubunit metalloenzyme, chlorophyllide a oxidoreductase (COR). ATP-dependent COR catalysis requires interaction of the protein subcomplex (BchX)2 with the catalytic (BchY/BchZ)2 protein to facilitate substrate reduction via two redox active iron-sulfur centers. The ternary COR enzyme holocomplex comprising subunits BchX, BchY, and BchZ from the purple bacterium Roseobacter denitrificans was trapped in the presence of the ATP transition state analog ADP⋅AlF4-. Electron paramagnetic resonance experiments revealed a [4Fe-4S] cluster of subcomplex (BchX)2. A second [4Fe-4S] cluster was identified on (BchY/BchZ)2. Mutagenesis experiments indicated that the latter is ligated by four cysteines, which is in contrast to the three cysteine/one aspartate ligation pattern of the closely related dark-operative protochlorophyllide a oxidoreductase (DPOR). In subsequent mutagenesis experiments a DPOR-like aspartate ligation pattern was implemented for the catalytic [4Fe-4S] cluster of COR. Artificial cluster formation for this inactive COR variant was demonstrated spectroscopically. A series of chemically modified substrate molecules with altered substituents on the individual pyrrole rings and the isocyclic ring were tested as COR substrates. The COR enzyme was still able to reduce the B ring of substrates carrying modified substituents on ring systems A, C, and E. However, substrates with a modification of the distantly located propionate side chain were not accepted. A tentative substrate binding mode was concluded in analogy to the related DPOR system. [ABSTRACT FROM AUTHOR]

Esterifying chains of chlorophyllous pigments play important roles in the formation of photosynthetic supramolecules, but their effects have not thoroughly been unraveled yet. Substitution of the esterifying chains in these pigments will be one possible strategy to elucidate this enigma. Recently, unnatural bacteriochlorophylls (BChls)cpossessing a hydroxy group at the terminus of the esterifying chains were successfully biosynthesised in the green sulfur bacteriumChlorobaculum(Cba.)tepidumgrown by supplementation of α,ω-diols. In this paper,in vitroassembling behaviours of unnatural BChlscisolated fromCba. tepidumgrown with 1,8-octanediol, 1,12-dodecanediol and 1,16-hexadecanediol were characterised in aqueous Triton X-100 micelles to investigate the effects of the terminal hydroxy group in the esterifying chains of BChlscon self-aggregates such as chlorosomes, major antenna complexes in green photosynthetic bacteria. The bacteriochlorophyll (BChl)cderivatives monoesterified with α,ω-diols formed chlorosomal self-aggregates, but their formations were much slower than those of natural BChlc. TheQyabsorption bands of the residual monomers of these BChlcderivatives were larger than those of natural BChlc. These suggest that the esterifying α,ω-diols in these unnatural BChlscsomewhat interfered with formation of chlorosome-like aggregates compared with the natural esterifying farnesol. [ABSTRACT FROM AUTHOR]

Most purple photosynthetic bacteria contain bacteriochlorophyll(BChl)- a (a magnesium complex) and bacteriopheophytin(BPhe)- a (its free base) as their photoactive pigments. These pigments are composed of two parts: a cyclic tetrapyrrole as the chromophore and a long hydrocarbon-chain as the propionate-type esterifying group at the 17-position. The hydrocarbon-chain is usually an isoprenoid-type C 20 phytyl (Phy) group in both the pigments. In the ester group of BChl- a , several variants such as geranylgeranyl (GG), dihydrogeranylgeranyl (DHGG) and tetrahydrogeranylgeranyl (THGG) groups were found in the final stage of BChl- a biosynthesis. On the other hand, the esterifying variants in BPhe- a have not been studied as much due to the lower levels of this pigment relative to BChl- a . The esterifying group does not affect the electronic absorption properties of such pigments in the monomeric state, but drastically alters the hydrophobicity. In this study, BChl- a and BPhe- a in the six phylogenetically distinct classes of purple bacteria were analyzed in terms of their esterifying groups in the 17-propionate residues, using high-performance liquid chromatography. Both BChls- a and BPhes- a carrying GG, DHGG and THGG in addition to the usual Phy were found for all the bacterial species studied at measurable levels. In some of the species, the ratio of BPhes- a esterified with GG, DHGG and THGG over the total BPhe- a drastically decreased in comparison with that of the corresponding BChls- a . Especially, the relative content of BPhe- a with GG largely decreased. This observation might indicate that BPhe- a as a cofactor of reaction centers was preferentially esterified with partially reduced and flexible chains (THGG and Phy) rather than less reduced and rigid ones (GG and DHGG). [ABSTRACT FROM AUTHOR]

Under photosynthetic growth, purple non–sulfur photosynthetic bacterium Rhodobacter sphaeroides can use a diverse array of substrates for the source of carbon donor. Substrates such as acetate and succinate are most commonly used to study energetic and metabolic networks, especially in the production and consummation of NADPH during the citric acid cycle (TCA cycle) and ethylmalonyl–CoA pathway, respectively. Although the utilization of both substrate, the bacterium will grow at different growth rate and this also influence the biosynthesis of photosynthetic pigments as important components for overall photosynthesis. For this study, Rhodobacter sphaeroides strain 2.4.1, GA and G1C have been grown in acetate and succinate. Here, preliminary results on the evaluation the pigment ratio at different stages of the growth is reported, especially on the growth in succinate substrate. [ABSTRACT FROM AUTHOR]

Photosynthetic purple bacteria have developed sophisticated processes to adapt their photosynthetic unit towards changes in light illumination in which the cells grow. Some purple bacteria show pronounced modification of their PSU from changing the composition and content of photosynthetic pigments, i.e. carotenoids, to replacing different composition of polypeptides that alter the Q y absorption bands of bacteriochlorophyll. Adjusting the spectrum by shifting spectral band position or tuning absorption intensity of spectral band are keys to collect light energy at specific ecological niches they inhabit. Furthermore photoprotection system will ensure the complex from damage. [ABSTRACT FROM AUTHOR]

Photosynthesis converts light energy to chemical energy to fuel life on earth. Light energy is harvested by antenna pigments and transferred to reaction centers (RCs) to drive the electron transfer (ET) reactions. Here, we present cryo-electron microscopy (cryo-EM) structures of two forms of the RC from the microaerophilic Chloracidobacterium thermophilum (CabRC): one containing 10 subunits, including two different cytochromes; and the other possessing two additional subunits, PscB and PscZ. The larger form contained 2 Zn-bacteriochlorophylls, 16 bacteriochlorophylls, 10 chlorophylls, 2 lycopenes, 2 hemes, 3 Fe 4 S 4 clusters, 12 lipids, 2 Ca 2+ ions and 6 water molecules, revealing a type I RC with an ET chain involving two hemes and a hybrid antenna containing bacteriochlorophylls and chlorophylls. Our results provide a structural basis for understanding the excitation energy and ET within the CabRC and offer evolutionary insights into the origin and adaptation of photosynthetic RCs., (© 2022. The Author(s).)