Stress sensing; protein localization


Bacteria respond to a variety of individual stresses by switching on a common set of genes that makes them resistant to stresses in general. Little is known about how the different stresses are sensed. We isolated a mutant in Pseudomonas putida that lost the capacity to develop general resistance. The mutated was identified to be flhF, which encodes a G-protein. This location of this protein was traced to the flagella-bearing pole of the cell. The nature of the cascade activated by this protein in response to stresses is under investigation.

Mutation in flhF has another interesting effect: it renders the bacterium unable to place flagella at the cell pole. Instead, the flagella become randomly distributed. FlhF resembles some of the proteins of the Signal Recognition Particle pathway of membrane protein translocation, and may work in conjunction with this pathway to transport FliF (the first protein in flagellar synthesis) to a specific spot on the cell membrane. This is under investigation. As placement of proteins in specific cellular locations is critical to cell function, the results should provide insights in a phenomenon of general importance.

Pandza. S., M. Baetens, C-H. Park, T. Au, M. Keyhan, and A. Matin. 2000. The putative G-protein FLHF has a role in polar flagellar placement and general stress response induction in Pseudomonas putida. Molecular Microbiology 36: 414-42 [PDF]

Flagellar arrangement of different Pseudomonas. putida strains: A. wild type, or the flhF transposon mutant complemented with a single copy of the flhF gene; B. flhF transposon mutant; C. mutant complemented with multiple copies of the flhF gene.

Flagellar location and the location of the FlhF protein as determined by fusing the latter to the green fluorescent protein. Note that in dividing cells, flagella are located at the pole distal to the division septum, i.e., the pole where the fluorescence is seen.