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 Programming cells with computer-like logic
27.07.2017 | Wyss Institute for Biologically Inspired Engineering at Harvard

nachricht Identified the component that allows a lethal bacteria to spread resistance to antibiotics
27.07.2017 | Institute for Research in Biomedicine (IRB Barcelona)

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Physicists Design Ultrafocused Pulses

Physicists working with researcher Oriol Romero-Isart devised a new simple scheme to theoretically generate arbitrarily short and focused electromagnetic fields. This new tool could be used for precise sensing and in microscopy.

Microwaves, heat radiation, light and X-radiation are examples for electromagnetic waves. Many applications require to focus the electromagnetic fields to...

Im Focus: Carbon Nanotubes Turn Electrical Current into Light-emitting Quasi-particles

Strong light-matter coupling in these semiconducting tubes may hold the key to electrically pumped lasers

Light-matter quasi-particles can be generated electrically in semiconducting carbon nanotubes. Material scientists and physicists from Heidelberg University...

Im Focus: Flexible proximity sensor creates smart surfaces

Fraunhofer IPA has developed a proximity sensor made from silicone and carbon nanotubes (CNT) which detects objects and determines their position. The materials and printing process used mean that the sensor is extremely flexible, economical and can be used for large surfaces. Industry and research partners can use and further develop this innovation straight away.

At first glance, the proximity sensor appears to be nothing special: a thin, elastic layer of silicone onto which black square surfaces are printed, but these...

Im Focus: 3-D scanning with water

3-D shape acquisition using water displacement as the shape sensor for the reconstruction of complex objects

A global team of computer scientists and engineers have developed an innovative technique that more completely reconstructs challenging 3D objects. An ancient...

Im Focus: Manipulating Electron Spins Without Loss of Information

Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.

For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

Closing the Sustainability Circle: Protection of Food with Biobased Materials

21.07.2017 | Event News

»We are bringing Additive Manufacturing to SMEs«

19.07.2017 | Event News

 
Latest News

Programming cells with computer-like logic

27.07.2017 | Life Sciences

Identified the component that allows a lethal bacteria to spread resistance to antibiotics

27.07.2017 | Life Sciences

Malaria Already Endemic in the Mediterranean by the Roman Period

27.07.2017 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>