[Show abstract][Hide abstract] ABSTRACT: We provide here insights on the life and work of Berger C. Mayne (1920-2011). We remember and honor Berger, whose study of photosynthesis began with the most basic processes of intersystem electron transport and oxygen evolution, continued with application of fluorescence techniques to the study of photophosphorylation and the unique features of photosystems in specialized cells, and concluded with collaborative study of photosynthesis in certain nitrogen fixing symbioses. Berger loved the outdoors and was dedicated to preserving the environment and to social justice, and was a wonderful friend.
Photosynthesis Research 05/2012; 112(2):81-9. DOI:10.1007/s11120-012-9742-9 · 3.50 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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). In this study, we show that BphP3(B BTAi1) acts as a bona fide bacteriophytochrome and controls, according to light conditions, the expression of the pucBA operon found in its vicinity. This light regulatory pathway is very similar to the one previously described for chromo-BphP4(Rp) in Rhodopseudomonas palustris and conducts the synthesis of a peripheral LH complex. This LH complex presents a single absorption band at low temperature, centered at 803 nm. Fluorescence emission analysis of intact cells indicates that this peripheral LH complex does not act as an efficient light antenna. One putative function of this LH complex could be to evacuate excess light energy in order to protect Bradyrhizobium strain BTAi1, an aerobic anoxygenic photosynthetic bacterium, against photooxidative damage during photosynthesis.
Journal of bacteriology 08/2008; 190(17):5824-31. DOI:10.1128/JB.00524-08 · 2.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Rhizobia having photosynthetic systems form nitrogen-fixing nodules on the stem and/or root of some species of the legumes Aeschynomene and Lotononis. This review is focused on the recent knowledge about the physiology, genetics and role of the photosystem in these bacteria. Photosynthetic electron transport seems to involve reaction centers, soluble cytochrome c2 and cytochrome bc1. Anaerobically, the electron transport system becomes over-reduced. The photosynthesis genes have been partially characterized; their organization is classical but their regulation is unusual as it is activated by far-red light via a bacteriophytochrome. This original mechanism of regulation seems well adapted to promote photosynthesis during stem symbiosis. Photosynthesis plays a major role in the efficiency of stem nodulation. It is also observed that infrared light stimulates nitrogen fixation in nodules containing photosynthetic bacteroids, suggesting that photosynthesis may additionally provides energy for nitrogen fixation, allowing for more efficient plant growth. Other aspects of these bacteria are discussed, in particular their taxonomic position and nodulation ability, the role of carotenoids and the potential for application of photosynthetic rhizobia in rice culture.
Photosynthesis Research 02/2004; 82(2):115-30. DOI:10.1007/s11120-004-1768-1 · 3.50 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Green Revolution has allowed food production in many developing countries to keep pace with population growth. But the use of chemical fertilizers as a source of fixed nitrogen is expensive and creates environmental problems. The United States Agency for International Development sponsored a collaboration between U. S. and Indian scientists to develop sources ofbiologically-fixed nitrogen fertilizers. This effort led to the discovery that photosynthetic rhizobia are found in nitrogen-fixing nodules located on the stems of Aeschynomene, a legume used as a green manure in rice fields. Such rhizobia now have been isolated from Aeschynomene nodules and soils throughout the world. Photosynthetic rhizobia which nodulate a different genus, Lotononis, have been discovered recently.
The rhizobium has the photosynthetic properties of aerobic anoxygenic phototrophs. It will grow, produce the photosynthetic system and perform photosynthetic electron transport only under aerobic conditions. It can fix nitrogen in ex planta culture and grow in the absence of any other source of fixed nitrogen. Phylogenetic studies based on 16S rRNA sequences and numerical taxonomy suggest that all of the Aeschynomene isolates are closely related to each other and form a cluster with Bradyrhizobium and Rhodopseudomonas palustris in the alpha-2 subdivision of the class Proteobacteria.
Formation of the photosynthetic system is triggered by visible and far-red light, and is suppressed by visible light. The photosynthetic system of the stem nodule endophytes probably provides energy for nitrogen fixation, diminishing competition between carbon and nitrogen fixation and allowing for more efficient plant growth.
[Show abstract][Hide abstract] ABSTRACT: Bacteriochlorophyll-containing rhizobia, which form nitrogen-fixing nodules on the stems and roots of the legume Aeschynomene, grow photosynthetically only in the presence of oxygen or auxiliary electron acceptors. We show that, in whole cells of the Rhizobium strain BTAi 1, a single-turnover excitation flash photooxidized c-type cytochrome under aerobic but not anaerobic conditions. Light-induced fluorescence yield changes show that under anaerobic conditions, the primary acceptor quinone, Q(A), is predominantly in the reduced state and so unable to accept electrons. Thus, as is the case for the aerobic photosynthetic bacterium Roseobacter denitrificans, over-reduction of Q(A) likely prohibits photosynthesis under anaerobic conditions.