A research team jointly involving the IRD, the CEA and the CNRS has very recently found phytochromes in a strain of nitrogen-fixing bacterium, Bradyrhizobium (1), symbiont on certain tropical leguminous plants (the Aeschynomene). Techniques of molecular biology, biophysics and biochemistry revealed that the newly-discovered phytochrome has an essential role as regulator of the bacterium’s photosystem synthesis. An identical function was shown in the photosynthetic bacterium Rhodopseudomonas palustris, phylogenetically very close to Bradyrhizobium (2).
The researchers experimented by subjecting Bradyrhizobium cells to different wavelengths of light, from the red to the infrared. It appeared that the bacterial photosynthetic apparatus was synthesized in its complete form only when the phytochrome was in its active (far-red-light absorbing) configuration (3). In addition, they used genetic engineering techniques to make bacterial strains in which the gene coding for the phytochrome was suppressed. These strains showed practically no photosynthetic activity whatever the culture conditions. These experiments therefore demonstrated that the photosystem of Bradyrhizobium is totally under the control of the bacteriophytochrome. This is the first time that any definite role has been determined for phytochromes in bacteria.
Another positive result was the determination of the main action mechanisms of the phytochrome in these bacteria. The gene adjacent to that of the phytochrome encodes a protein (called transcriptional factor “ PpsR ”) already known to repress the expression of some photosynthetic genes (4). The team demonstrated that when in its active form under infrared light, the phytochrome interacts with this protein and stops its repressive action. The genes which encode the bacteria’s photosynthetic apparatus can then express themselves. In this way, the light signal transduction the phytochrome ensures in the bacterial cells would occur by direct interaction with PpsR, meaning a direct protein-protein interaction mechanism and not the induction of a biochemical reaction (phosphorelay) cascade, which has been the theory up to now. The researchers used these observations to devise a model for gene expression control by light. A patent has been filed for this model which could be useful as a new research tool in molecular biology (5).
The crucial question here is why these bacteria of the Bradyrhizobium genus should be equipped with phytochromes whereas other photosynthetic bacteria (Rhodobacter, Rubrivivax or Rhodospirillum) analysed by the IRD, the CEA and the CNRS have none. The hypothesis the researchers advance is that the phytochrome’s photosynthesis control system could represent a function-based ecological adaptation that allows interaction between the bacterium and the leguminous plant on which the bacterium is developing. The Bradyrhizobium bacterium can implant itself along stems under a layer of chlorophyllous cells which let through only infrared wavelengths Thus, the phytochrome enables the bacterium to install its photosynthetic apparatus. That will then supply part of its energy requirement for maintaining its symbiosis with the leguminous plant and fixing the nitrogen essential for the plant’s growth.
Marie-Lise Sabrie | alphagalileo
Solving the efficiency of Gram-negative bacteria
22.03.2019 | Harvard University
Bacteria bide their time when antibiotics attack
22.03.2019 | Rice University
DESY and MPSD scientists create high-order harmonics from solids with controlled polarization states, taking advantage of both crystal symmetry and attosecond electronic dynamics. The newly demonstrated technique might find intriguing applications in petahertz electronics and for spectroscopic studies of novel quantum materials.
The nonlinear process of high-order harmonic generation (HHG) in gases is one of the cornerstones of attosecond science (an attosecond is a billionth of a...
Nano- and microtechnology are promising candidates not only for medical applications such as drug delivery but also for the creation of little robots or flexible integrated sensors. Scientists from the Max Planck Institute for Polymer Research (MPI-P) have created magnetic microparticles, with a newly developed method, that could pave the way for building micro-motors or guiding drugs in the human body to a target, like a tumor. The preparation of such structures as well as their remote-control can be regulated using magnetic fields and therefore can find application in an array of domains.
The magnetic properties of a material control how this material responds to the presence of a magnetic field. Iron oxide is the main component of rust but also...
Due to the special arrangement of its molecules, a new coating made of corn starch is able to repair small scratches by itself through heat: The cross-linking via ring-shaped molecules makes the material mobile, so that it compensates for the scratches and these disappear again.
Superficial micro-scratches on the car body or on other high-gloss surfaces are harmless, but annoying. Especially in the luxury segment such surfaces are...
The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in Arizona released its first image of the surface magnetic field of another star. In a paper in the European journal Astronomy & Astrophysics, the PEPSI team presents a Zeeman- Doppler-Image of the surface of the magnetically active star II Pegasi.
A special technique allows astronomers to resolve the surfaces of faraway stars. Those are otherwise only seen as point sources, even in the largest telescopes...
Researchers at Chalmers University of Technology and the University of Gothenburg, Sweden, have proposed a way to create a completely new source of radiation. Ultra-intense light pulses consist of the motion of a single wave and can be described as a tsunami of light. The strong wave can be used to study interactions between matter and light in a unique way. Their research is now published in the scientific journal Physical Review Letters.
"This source of radiation lets us look at reality through a new angle - it is like twisting a mirror and discovering something completely different," says...
11.03.2019 | Event News
01.03.2019 | Event News
28.02.2019 | Event News
22.03.2019 | Life Sciences
22.03.2019 | Life Sciences
22.03.2019 | Information Technology