High efficient cyclic electron flow and functional supercomplexes in Chlamydomonas cells.

A very high rate for cyclic electron flow (CEF) around PSI (~180 s1 or 210 s in minimum medium or in the presence of a carbon source respectively) is measured in the presence of methyl viologen (MV) in intact cells of Chlamydomonas reinhardtii under anaerobic conditions. The observation of an efficient CEF in the presence of methyl viologen is in agreement with the previous results reports of Asada et al. in broken chloroplasts (Plant Cell Physiol.

Light on the cell cycle of the non-photosynthetic bacterium Ramlibacter tataouinensis.

Ramlibacter tataouinensis TTB310, a non-photosynthetic betaproteobacterium isolated from a semi-arid region of southern Tunisia, forms both rods and cysts. Cysts are resistant to desiccation and divide when water and nutrients are available. Rods are motile and capable of dissemination.

Tribute in memory of Jacques Breton (1942-2018).

Jacques Breton spent his 39 years of professional life at Saclay, a center of the French Atomic Energy Commission. He studied photosynthesis with various advanced biophysical tools, often developed by himself and his numerous coworkers, obtaining a large number of new information on the structure and the functioning of antenna and of reaction centers of plants and bacteria: excitation migration in the antenna, orientation of molecules, rate of primary reactions, binding of pigments and electron transfer cofactors. Although it is much too short to illustrate his impressive work, we hope that this contribution will help maintaining the souvenir of Jacques Breton as an active and enthusiastic person, full of qualities, devoted to research and to his family as well.

Synthesis of Carotenoids of Industrial Interest in the Photosynthetic Bacterium Rhodopseudomonas palustris : Bioengineering and Growth Conditions.

Rhodopseudomonas palustris is a purple photosynthetic bacterium that accumulates in the inner membrane the photosynthetic pigment spirilloxanthin, formed from lycopene. Here, we describe the procedures used to successfully engineer Rps. palustris strains to reroute the production of lycopene toward the synthesis of ß-carotene or canthaxanthin.

Connectivity of the intracytoplasmic membrane of Rhodobacter sphaeroides: a functional approach.

The photosynthetic apparatus in the bacterium Rhodobacter sphaeroides is mostly present in intracytoplasmic membrane invaginations. It has long been debated whether these invaginations remain in topological continuity with the cytoplasmic membrane, or form isolated chromatophore vesicles. This issue is revisited here by functional approaches.

Exchange and complementation of genes coding for photosynthetic reaction center core subunits among purple bacteria.

A mutant of the phototrophic species belonging to the β-proteobacteria, Rubrivivax gelatinosus, lacking the photosynthetic growth ability was constructed by the removal of genes coding for the L, M, and cytochrome subunits of the photosynthetic reaction center complex. The L, M, and cytochrome genes derived from five other species of proteobacteria, Acidiphilium rubrum, Allochromatium vinosum, Blastochloris viridis, Pheospirillum molischianum, and Roseateles depolymerans, and the L and M subunits from two other species, Rhodobacter sphaeroides and Rhodopseudomonas palustris, respectively, have been introduced into this mutant. Introduction of the genes from three of these seven species, Rte.

Modulation of the redox state of quinones by light in Rhodobacter sphaeroides under anaerobic conditions.

Illumination of intact cells of Rhodobacter sphaeroides under anaerobic conditions has a dual effect on the redox state of the quinone pool. A large oxidation of the quinone pool is observed during the first seconds following the illumination. This oxidation is suppressed by the addition of an uncoupler in agreement with a light-induced reverse electron transfer at the level of the complex I, present both in the non-invaginated part of the membrane and in the chromatophores.

Isolation and light-stimulated expression of canthaxanthin and spirilloxanthin biosynthesis genes from the photosynthetic bacterium Bradyrhizobium sp. strain ORS278.

Some aerobic photosynthetic bacteria produce a cocktail of carotenoids, some of them being of a high economic value. A good example is the photosynthetic Bradyrhizobium sp. strain ORS278, which synthesizes, in addition to the photosynthetic carotenoid spirilloxanthin, large amounts of canthaxanthin.

Photo-induced electron transfer in intact cells of Rubrivivax gelatinosus mutants deleted in the RC-bound tetraheme cytochrome: insight into evolution of photosynthetic electron transport.

Deletion of two of the major electron carriers, the reaction center-bound tetrahemic cytochrome and the HiPIP, involved in the light-induced cyclic electron transfer pathway of the purple photosynthetic bacterium, Rubrivivax gelatinosus, significantly impairs its anaerobic photosynthetic growth. Analysis on the light-induced absorption changes of the intact cells of the mutants shows, however, a relatively efficient photo-induced cyclic electron transfer. For the single mutant lacking the reaction center-bound cytochrome, we present evidence that the electron carrier connecting the reaction center and the cytochrome bc(1) complex is the High Potential Iron-sulfur Protein.

The photosynthetic apparatus and photoinduced electron transfer in the aerobic phototrophic bacteria Roseicyclus mahoneyensis and Porphyrobacter meromictius.

Photosynthetic electron transfer has been examined in whole cells, isolated membranes and in partially purified reaction centers (RCs) of Roseicyclus mahoneyensis, strain ML6 and Porphyrobacter meromictius, strain ML31, two species of obligate aerobic anoxygenic phototrophic bacteria. Photochemical activity in strain ML31 was observed aerobically, but the photosynthetic apparatus was not functional under anaerobic conditions. In strain ML6 low levels of photochemistry were measured anaerobically, possibly due to incomplete reduction of the primary electron acceptor (Q(A)) prior to light excitation, however, electron transfer occurred optimally under low oxygen conditions.

The cyst-dividing bacterium Ramlibacter tataouinensis TTB310 genome reveals a well-stocked toolbox for adaptation to a desert environment.

Ramlibacter tataouinensis TTB310(T) (strain TTB310), a betaproteobacterium isolated from a semi-arid region of South Tunisia (Tataouine), is characterized by the presence of both spherical and rod-shaped cells in pure culture. Cell division of strain TTB310 occurs by the binary fission of spherical "cyst-like" cells ("cyst-cyst" division). The rod-shaped cells formed at the periphery of a colony (consisting mainly of cysts) are highly motile and colonize a new environment, where they form a new colony by reversion to cyst-like cells.

The cytochrome c₈ involved in the nitrite reduction pathway acts also as electron donor to the photosynthetic reaction center in Rubrivivax gelatinosus.

The purple photosynthetic bacterium Rubrivivax gelatinosus has, at least, four periplasmic electron carriers, i.e., HiPIP, two cytochromes c₈with low- and high-midpoint potentials, and cytochrome c₄ as electron donors to the photochemical reaction center.

Characterization of bacteriophytochromes from photosynthetic bacteria: histidine kinase signaling triggered by light and redox sensing.

Bacteria detect environmental changes, thanks to two-component signal-transduction systems, composed, in general, of a sensor coupled to a histidine kinase and a DNA binding response regulator. Anoxygenic photosynthetic bacteria like Rhodopseudomonas (Rps.) palustris, possess a highly versatile metabolism and can grow via photosynthesis using light energy or via respiration through oxygen consumption.

Cytochrome c4 can be involved in the photosynthetic electron transfer system in the purple bacterium Rubrivivax gelatinosus.

Three periplasmic electron carriers, HiPIP and two cytochromes c8 with low- and high-midpoint potentials, are present in the purple photosynthetic bacterium Rubrivivax gelatinosus. Comparison of the growth rates of mutants lacking one, two, or all three electron carrier proteins showed that HiPIP is the main electron donor to the photochemical reaction center and that high-potential cytochrome c8 plays a subsidiary role in the electron donation in photosynthetically growing cells. However, the triple deletion mutant was still capable of photosynthetic growth, indicating that another electron donor could be present.

Identification of novel genes putatively involved in the photosystem synthesis of Bradyrhizobium sp. ORS 278.

In aerobic anoxygenic phototrophs, oxygen is required for both the formation of the photosynthetic apparatus and an efficient cyclic electron transfer. Mutants of Bradyrhizobium sp. ORS278 affected in photosystem synthesis were selected by a bacteriochlorophyll fluorescence-based screening.

Menaquinone as pool quinone in a purple bacterium.

Purple bacteria have thus far been considered to operate light-driven cyclic electron transfer chains containing ubiquinone (UQ) as liposoluble electron and proton carrier. We show that in the purple gamma-proteobacterium Halorhodospira halophila, menaquinone-8 (MK-8) is the dominant quinone component and that it operates in the Q(B)-site of the photosynthetic reaction center (RC). The redox potentials of the photooxidized pigment in the RC and of the Rieske center of the bc(1) complex are significantly lower (E(m) = +270 mV and +110 mV, respectively) than those determined in other purple bacteria but resemble those determined for species containing MK as pool quinone.

Photosynthetic system in Blastochloris viridis revisited.

The bacterium Blastochloris viridis carries one of the simplest photosynthetic systems, which includes a single light-harvesting complex that surrounds the reaction center, membrane soluble quinones, and a soluble periplasmic protein cytochrome c(2) that shuttle between the reaction center and the bc(1) complex and act as electron carriers, as well as the ATP synthase. The close arrangement of the photosynthetic membranes in Bl. viridis, along with the extremely tight arrangement of the photosystems within these membranes, raises a fundamental question about the diffusion of the electron carriers.

Vertical distribution and characterization of aerobic phototrophic bacteria at the Juan de Fuca Ridge in the Pacific Ocean.

The vertical distribution of culturable anoxygenic phototrophic bacteria was investigated at five sites at or near the Juan de Fuca Ridge in the Pacific Ocean. Twelve similar strains of obligately aerobic phototrophic bacteria were isolated in pure culture, from depths ranging from 500 to 2,379 m below the surface. These strains appear morphologically, physiologically, biochemically, and phylogenetically similar to Citromicrobium bathyomarinum strain JF-1, a bacterium previously isolated from hydrothermal vent plume waters.

Bacteriophytochromes in anoxygenic photosynthetic bacteria.

Since the first discovery of a bacteriophytochrome in Rhodospirillum centenum, numerous bacteriophytochromes have been identified and characterized in other anoxygenic photosynthetic bacteria. This review is focused on the biochemical and biophysical properties of bacteriophytochromes with a special emphasis on their roles in the synthesis of the photosynthetic apparatus.

Control of peripheral light-harvesting complex synthesis by a bacteriophytochrome in the aerobic photosynthetic bacterium Bradyrhizobium strain BTAi1.

The recent sequence analysis of the photosynthetic and plant-symbiotic Bradyrhizobium sp. strain BTAi1 revealed the unexpected presence of a pucBA operon encoding the apoproteins of peripheral light-harvesting (LH) complexes. This pucBA operon is found close to a bacteriophytochrome gene (BphP3(B BTAi1)) and a two-component transcriptional regulator gene (TF(BTAi1) gene).

Dual role for a bacteriophytochrome in the bioenergetic control of Rhodopseudomonas palustris: enhancement of photosystem synthesis and limitation of respiration.

In the purple photosynthetic bacterium Rhodopseudomonas palustris, far-red illumination induces photosystem synthesis via the action of the bacteriophytochrome RpBphP1. This bacteriophytochrome antagonizes the repressive effect of the transcriptional regulator PpsR2 under aerobic condition. We show here that, in addition to photosystem synthesis, far-red light induces a significant growth rate limitation, compared to cells grown in the dark, linked to a decrease in the respiratory activity.

Evolution of a bacteriophytochrome from light to redox sensor.

Bacteriophytochromes are red/far-red photoreceptors that bacteria use to mediate sensory responses to their light environment. Here, we show that the photosynthetic bacterium Rhodopseudomonas palustris has two distinct types of bacteriophytochrome-related protein (RpBphP4) depending upon the strain considered. The first type binds the chromophore biliverdin and acts as a light-sensitive kinase, thus behaving as a bona fide bacteriophytochrome.

Legumes symbioses: absence of Nod genes in photosynthetic bradyrhizobia.

Leguminous plants (such as peas and soybeans) and rhizobial soil bacteria are symbiotic partners that communicate through molecular signaling pathways, resulting in the formation of nodules on legume roots and occasionally stems that house nitrogen-fixing bacteria. Nodule formation has been assumed to be exclusively initiated by the binding of bacterial, host-specific lipochito-oligosaccharidic Nod factors, encoded by the nodABC genes, to kinase-like receptors of the plant. Here we show by complete genome sequencing of two symbiotic, photosynthetic, Bradyrhizobium strains, BTAi1 and ORS278, that canonical nodABC genes and typical lipochito-oligosaccharidic Nod factors are not required for symbiosis in some legumes.

A singular bacteriophytochrome acquired by lateral gene transfer.

Bacteriophytochromes are phytochrome-like proteins that mediate photosensory responses in various bacteria according to their light environment. The genome of the photosynthetic and plant-symbiotic Bradyrhizobium sp. strain ORS278 revealed the presence of a genomic island acquired by lateral transfer harboring a bacteriophytochrome gene, BrBphP3.