The 17-propionate esterifying variants of bacteriochlorophyll-a and bacteriopheophytin-a in purple photosynthetic bacteria

Efficient Green Light Acclimation of the Green Algae Picochlorum sp. Triggering Geranylgeranylated Chlorophylls

In analogy to higher plants, eukaryotic microalgae are thought to be incapable of utilizing green light for growth, due to the “green gap” in the absorbance profiles of their photosynthetic pigments. This study demonstrates, that the marine chlorophyte Picochlorum sp. is able to grow efficiently under green light emitting diode (LED) illumination. Picochlorum sp. growth and pigment profiles under blue, red, green and white LED illumination (light intensity: 50–200 μmol m⁻² s⁻¹) in bottom-lightened shake flask cultures were evaluated. Green light-treated cultures showed a prolonged initial growth lag phase of one to 2 days, which was subsequently compensated to obtain comparable biomass yields to red and white light controls (approx. 0.8 g_DW L⁻¹). Interestingly, growth and final biomass yields of the green light-treated sample were higher than under blue light with equivalent illumination energies. Further, pigment analysis indicated, that during green light illumination, Picochlorum sp. formed unknown pigments (X1-X4). Pigment concentrations increased with illumination intensity and were most abundant during the exponential growth phase. Mass spectrometry and nuclear magnetic resonance data indicated, that pigments X1-X2 and X3-X4 are derivatives of chlorophyll b and a, which harbor C=C bonds in the phytol side chain similar to geranylgeranylated chlorophylls. Thus, for the first time, the natural accumulation of large pools (approx. 12 mg g_DW⁻¹) of chlorophyll intermediates with incomplete hydrogenation of their phytyl chains is demonstrated for algae under monochromatic green light (Peak λ 510 nm, full width at half maximum 91 nm). The ability to utilize green light offers competitive advantages for enhancing biomass production, particularly under conditions of dense cultures, long light pathways and high light intensity. Green light acclimation for an eukaryotic microalgae in conjunction with the formation of new aberrant geranylgeranylated chlorophylls and high efficiency of growth rates are novel for eukaryotic microalgae. Illumination with green light could enhance productivity in industrial processes and trigger the formation of new metabolites–thus, underlying mechanisms require further investigation.

Cryo-EM structure of the photosynthetic RC-LH1-PufX supercomplex at 2.8-Å resolution

The reaction center (RC)-light-harvesting complex 1 (LH1) supercomplex plays a pivotal role in bacterial photosynthesis. Many RC-LH1 complexes integrate an additional protein PufX that is key for bacterial growth and photosynthetic competence. Here, we present a cryo-electron microscopy structure of the RC-LH1-PufX supercomplex from Rhodobacter veldkampii at 2.8-Å resolution. The RC-LH1-PufX monomer contains an LH ring of 15 αβ-polypeptides with a 30-Å gap formed by PufX. PufX acts as a molecular "cross brace" to reinforce the RC-LH1 structure. The unusual PufX-mediated large opening in the LH1 ring and defined arrangement of proteins and cofactors provide the molecular basis for the assembly of a robust RC-LH1-PufX supercomplex and efficient quinone transport and electron transfer. These architectural features represent the natural strategies for anoxygenic photosynthesis and environmental adaptation.

A Review of Bacteriochlorophyllides: Chemical Structures and Applications

Generally, bacteriochlorophyllides were responsible for the photosynthesis in bacteria. Seven types of bacteriochlorophyllides have been disclosed. Bacteriochlorophyllides a/b/g could be synthesized from divinyl chlorophyllide a. The other bacteriochlorophyllides c/d/e/f could be synthesized from chlorophyllide a. The chemical structure and synthetic route of bacteriochlorophyllides were summarized in this review. Furthermore, the potential applications of bacteriochlorophyllides in photosensitizers, immunosensors, influence on bacteriochlorophyll aggregation, dye-sensitized solar cell, heme synthesis and for light energy harvesting simulation were discussed.

Absorption and Fluorescence Spectral Database of Chlorophylls and Analogues

Absorption spectra and fluorescence spectra are essential for use across the photosciences, yet such spectra along with the all-important values for molar absorption coefficient (ε) and fluorescence quantum yield (Φ_f ) often are found with great difficulty. Here, a literature survey concerning the vital class of chlorophyll compounds has led to identification of spectra for 150 members. Spectra in print form have been digitized (with baseline corrections) and assembled into a database along with literature references, solvent identity and values for ε and Φ_f (where available). The database encompasses photosynthetic tetrapyrroles wherein the chromophore is a porphyrin (e.g. chlorophyll c₁ , protochlorophyll a), chlorin (e.g. chlorophyll a, bacteriochlorophyll c) or bacteriochlorin (e.g. bacteriochlorophyll a). Altogether, the database contains 305 absorption spectra (from 19 porphyrins, 109 chlorins and 22 bacteriochlorins) and 72 fluorescence spectra (from 10 porphyrins, 30 chlorins and 4 bacteriochlorins). The spectral database should facilitate comparisons and quantitative calculations. All spectra are available in print form in the Supporting Information. The entire database in digital form is available with the PhotochemCAD program for free downloading and further use at http://www.photochemcad.com.

Enhancement of photosynthetic bacteria biomass production and wastewater treatment efficiency by zero-valent iron nanoparticles

Photosynthetic bacteria (PSB) wastewater treatment is a novel technology for wastewater purification and resources recovery but is restricted by low efficiency. This paper applied zero-valent iron nanoparticles (Fe⁰ NPs) to enhance its performance. Results showed that 20 mg/L Fe⁰ NPs under light-anaerobic condition significantly increased the PSB biomass production and wastewater chemical oxygen demand removal by 122% and 164.3%, and shortened the time required for wastewater purification by 33%; these effects were far more better than the addition of Fe²⁺. The mechanism was because the addition of Fe⁰ NPs promoted the intracellular ATP content and pigments (carotenoid and bacteriochlorophyll) contents, and up-regulated dehydrogenase and succinate dehydrogenase activity; the increase rate reached 38.7%, 39.6%, 22.0%, 23.9% and 218.2%, respectively.

Unusual features in the photosynthetic machinery of Halorhodospira halochloris DSM 1059 revealed by complete genome sequencing

Halorhodospira halochloris is an anaerobic, halophilic, purple photosynthetic bacterium belonging to γ-Proteobacteria. H. halochloris is also characteristic as a thermophilic phototrophic isolate producing bacteriochlorophyll (BChl) b. Here, we report the complete genome sequence of H. halochloris DSM 1059. The genetic arrangement for this bacterium's photosynthetic apparatus is of particular interest; its genome contains two sets of puf operons encoding the reaction center and core light-harvesting 1 (LH1) complexes having almost identical nucleotide sequences (e.g., 98.8-99.9% of nucleotide identities between two sets of pufLM genes, but 100% of deduced amino acid sequence identities). This duplication of photosynthetic genes may provide a glimpse at natural selection in action. The β-polypeptides of the LH1 complex in purple bacteria usually contain two histidine residues to bind BChl a; however, those of H. halochloris were revealed to have four histidine residues, indicating unusual pigment organization in the LH1 complex of this species. Like in other BChl b-producing phototrophs, the genome of H. halochloris lacks the divinyl reductase genes bciA and bciB. The phylogeny of chlorophyllide a oxidoreductase, which catalyzes committed steps in the synthesis of BChl a and BChl b, indicates that evolution toward BChl b production is convergent. Geranylgeranyl reductase (BchP) of H. halochloris has an insertion region in its primary structure, which could be important for its unusual sequential reduction reactions.

Molecular Structures and Functions of Chlorophylls-a Esterified with Geranylgeranyl, Dihydrogeranylgeranyl, and Tetrahydrogeranylgeranyl Groups at the 17-Propionate Residue in a Diatom, Chaetoceros calcitrans

The 17-propionate ester group of chlorophyll(Chl)-a in some oxygenic phototrophs was investigated using HPLC. Chls-a esterified with partially dehydrogenated forms of a phytyl group were found in fully grown cells of a diatom, Chaetoceros calcitrans: geranylgeranyl (GG), dihydrogeranylgeranyl (DHGG), and tetrahydrogeranylgeranyl (THGG). Chls-a bearing such esterifying groups were reported to be found only in greening processes of higher plants, and thus these Chls-a have been thought to be biosynthetic precursors for phytylated Chl-a. Their molecular structures were unambiguously determined using ¹H and ¹³C NMR spectroscopy and mass spectrometry. In particular, the positions of C═C double bonds in DHGG were identified at C2═C3, C6═C7, and C14═C15, and those in THGG were determined to be at C2═C3 and C14═C15. Notably, the present DHGG was different from the previously determined DHGG of bacteriochlorophyll-a in purple bacteria (C2═C3, C10═C11, and C14═C15). Moreover, thylakoid membranes as well as fucoxanthin-chlorophyll-a/c proteins called FCPs were isolated from the diatom, and their Chl-a compositions were analyzed. Chls-a esterified with GG, DHGG, and THGG were detected by HPLC, indicating that such Chls-a were not merely biosynthetic precursors, but photosynthetically active pigments.

In Vitro Enzymatic Activities of Bacteriochlorophyll a Synthase Derived from the Green Sulfur Photosynthetic Bacterium Chlorobaculum tepidum

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 aF) 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.