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Lefevre C.T.,University of Nevada, Las Vegas | Lefevre C.T.,Laboratoire Of Bioenergetique Cellulaire | Viloria N.,University of Nevada, Las Vegas | Schmidt M.L.,University of Nevada, Las Vegas | And 4 more authors.
ISME Journal | Year: 2012

Two novel magnetotactic bacteria (MTB) were isolated from sediment and water collected from the Badwater Basin, Death Valley National Park and southeastern shore of the Salton Sea, respectively, and were designated as strains BW-2 and SS-5, respectively. Both organisms are rod-shaped, biomineralize magnetite, and are motile by means of flagella. The strains grow chemolithoautotrophically oxidizing thiosulfate and sulfide microaerobically as electron donors, with thiosulfate oxidized stoichiometrically to sulfate. They appear to utilize the Calvin-Benson-Bassham cycle for autotrophy based on ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) activity and the presence of partial sequences of RubisCO genes. Strains BW-2 and SS-5 biomineralize chains of octahedral magnetite crystals, although the crystals of SS-5 are elongated. Based on 16S rRNA gene sequences, both strains are phylogenetically affiliated with the Gammaproteobacteria class. Strain SS-5 belongs to the order Chromatiales; the cultured bacterium with the highest 16S rRNA gene sequence identity to SS-5 is Thiohalocapsa marina (93.0%). Strain BW-2 clearly belongs to the Thiotrichales; interestingly, the organism with the highest 16S rRNA gene sequence identity to this strain is Thiohalospira alkaliphila (90.2%), which belongs to the Chromatiales. Each strain represents a new genus. This is the first report of magnetite-producing MTB phylogenetically associated with the Gammaproteobacteria. This finding is important in that it significantly expands the phylogenetic diversity of the MTB. Physiology of these strains is similar to other MTB and continues to demonstrate their potential in nitrogen, iron, carbon and sulfur cycling in natural environments. © 2012 International Society for Microbial Ecology All rights reserved. Source


Nilsson H.,Umea University | Cournac L.,Laboratoire Of Bioenergetique Et Biotechnologie Des Bacteries Et Microalgues | Cournac L.,CIRAD - Agricultural Research for Development | Rappaport F.,University Pierre and Marie Curie | And 2 more authors.
Biochimica et Biophysica Acta - Bioenergetics | Year: 2016

Photosynthetic water oxidation to molecular oxygen is carried out by photosystem II (PSII) over a reaction cycle involving four photochemical steps that drive the oxygen-evolving complex through five redox states Si (i=0,⋯, 4). For understanding the catalytic strategy of biological water oxidation it is important to elucidate the energetic landscape of PSII and in particular that of the final S4→S0 transition. In this short-lived chemical step the four oxidizing equivalents accumulated in the preceding photochemical events are used up to form molecular oxygen, two protons are released and at least one substrate water molecule binds to the Mn4CaO5 cluster. In this study we probed the probability to form S4 from S0 and O2 by incubating YD-less PSII in the S0 state for 2-3 days in the presence of 18. Source


Vermeglio A.,Laboratoire Of Bioenergetique Cellulaire | Vermeglio A.,French National Center for Scientific Research | Vermeglio A.,Aix - Marseille University | Nagashima S.,Tokyo Metroplitan University | And 5 more authors.
Biochimica et Biophysica Acta - Bioenergetics | Year: 2012

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 bc1 complex is the High Potential Iron-sulfur Protein. In the double mutant lacking both the reaction center-bound cytochrome and the High Potential Iron-sulfur Protein, this connection is achieved by the high potential cytochrome c8. Under anaerobic conditions, the halftime of re-reduction of the photo-oxidized primary donor by these electron donors is 3 to 4 times faster than the back reaction between P+ and the reduced primary quinone acceptor. This explains the photosynthetic growth of these two mutants. The results are discussed in terms of evolution of the type II RCs and their secondary electron donors. © 2012 Elsevier B.V. © 2012 Elsevier B.V. All rights reserved. Source


de Rivoyre M.,Laboratoire Of Bioenergetique Cellulaire | Ginet N.,Laboratoire Of Bioenergetique Cellulaire | Bouyer P.,Laboratoire Of Bioenergetique Cellulaire | Lavergne J.,Laboratoire Of Bioenergetique Cellulaire
Biochimica et Biophysica Acta - Bioenergetics | Year: 2010

Photosynthetic membranes accommodate densely packed light-harvesting complexes which absorb light and convey excitation to the reaction center (RC). The relationship between the fluorescence yield (φ) and the fraction (x) of closed RCs is informative about the probability for an excitation reaching a closed RC to be redirected to another RC. In this work, we have examined in this respect membranes from various bacteria and searched for a correlation with the arrangement of the light-harvesting complexes as known from atomic force or electron microscopies. A first part of the paper is devoted to a theoretical study analyzing the φ(x) relationship in various models: monomeric or dimeric RC-LH1 core complexes, with or without the peripheral LH2 complexes. We show that the simple "homogeneous" kinetic treatment used here agrees well with more detailed master equation calculations. We also discuss the agreement between information derived from the present technique and from singlet annihilation experiments. The experimental results show that the enhancement of the cross section of open RCs due to excitation transfer from closed units varies from 1.5 to 3 depending on species. The ratio of the core to core transfer rate (including the indirect pathway via LH2) to the rate of trapping in open units is in the range of 0.5 to 4. It is about 1 in Rhodobacter sphaeroides and does not increase significantly in mutants lacking LH2-despite the more numerous contacts between the dimeric core complexes expected in this case. The connectivity in this bacterium is due in good part to the fast transfer between the two partners of the dimeric (RC-LH1-PufX)2 complex. The connectivity is however increased in the carotenoidless and LH2-less strain R26, which we ascribe to an anomalous LH1. A relatively high connectivity was found in Rhodospirillum photometricum, although not as high as predicted in the calculations of Fassioli et al. (2010). This illustrates a more general discrepancy between the measured efficiency of core to core excitation transfer and theoretical estimates. We argue that the limited core to core connectivity found in purple bacteria may reflect a trade-off between light-harvesting efficiency and the hindrance to quinone diffusion that would result from too tightly packed LH complexes. © 2010 Elsevier B.V. Source

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