Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

The Role Of Phytochromes In Bacteria Revealed

13.05.2002


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.



The study of phytochromes in photosynthetic bacteria could in the long term bring a better understanding of the operational mechanisms of these light sensors in plants. Rhodopseudomonas palustris, the other bacterium studied by the IRD, the CEA and the CNRS, is a particularly suitable model for analysing phytochrome function in general. The entire genome of this bacterium has recently been sequenced and shown to contain six different copies of phytochromes, which is exceptional.


(1) In other words, they use light as an energy source both for their own growth and to enable the symbiosis with the leguminous plants to operate and fix the nitrogen these plants need for their development.
(2) R. palustris is known to microbiologists as one of the most versatile bacteria, capable of adapting its metabolism to highly varied environmental conditions.
(3) Most bacterial phytochromes so far identified are active under infrared light, unlike plant phytochromes which sensitive to red light.
(4) This protein, termed PpsR, has been isolated from several other micro-organisms. It recognizes a particular region of DNA upstream of the gene it controls. The protein fixes on this region, thus preventing the passage of RNA polymerase and blocking transcription.
(5) See the press release issued jointly by CEA/CNRS/IRD.

Marie-Lise Sabrie | alphagalileo
Further information:
http://www.ird.fr

More articles from Life Sciences:

nachricht Making fuel out of thick air
08.12.2017 | DOE/Argonne National Laboratory

nachricht ‘Spying’ on the hidden geometry of complex networks through machine intelligence
08.12.2017 | Technische Universität Dresden

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Scientists channel graphene to understand filtration and ion transport into cells

Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.

To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...

Im Focus: Towards data storage at the single molecule level

The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.

Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...

Im Focus: Successful Mechanical Testing of Nanowires

With innovative experiments, researchers at the Helmholtz-Zentrums Geesthacht and the Technical University Hamburg unravel why tiny metallic structures are extremely strong

Light-weight and simultaneously strong – porous metallic nanomaterials promise interesting applications as, for instance, for future aeroplanes with enhanced...

Im Focus: Virtual Reality for Bacteria

An interdisciplinary group of researchers interfaced individual bacteria with a computer to build a hybrid bio-digital circuit - Study published in Nature Communications

Scientists at the Institute of Science and Technology Austria (IST Austria) have managed to control the behavior of individual bacteria by connecting them to a...

Im Focus: A space-time sensor for light-matter interactions

Physicists in the Laboratory for Attosecond Physics (run jointly by LMU Munich and the Max Planck Institute for Quantum Optics) have developed an attosecond electron microscope that allows them to visualize the dispersion of light in time and space, and observe the motions of electrons in atoms.

The most basic of all physical interactions in nature is that between light and matter. This interaction takes place in attosecond times (i.e. billionths of a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

AKL’18: The opportunities and challenges of digitalization in the laser industry

07.12.2017 | Event News

 
Latest News

PhoxTroT: Optical Interconnect Technologies Revolutionized Data Centers and HPC Systems

11.12.2017 | Information Technology

Large-scale battery storage system in field trial

11.12.2017 | Power and Electrical Engineering

See, understand and experience the work of the future

11.12.2017 | Event News

VideoLinks
B2B-VideoLinks
More VideoLinks >>>