How Vibrio cholerae finds its way: A key piece of the puzzle solved
Vibrio cholerae, the bacterium that causes cholera disease, is able to swim by means of a polar flagellum. Swimming is used to find new areas in which the bacterium can grow and importantly to find food, but also to escape from obnoxious substances. When in search of food, bacteria swim toward the highest concentration of food molecules in the environment by a process called chemotaxis. Since the ability to perform chemotaxis is vital for the spreading of many bacterial species in the environment and important for the ability of many human pathogens – like V. cholerae – to cause disease, it is important to learn how this process is regulated, in order to potentially stop the spread of infectious bacteria and prevent human infections. The correct placement of the apparatus responsible for chemotactic behavior within the cell – the chemotaxis array - is very important for the bacterium’s ability to perform chemotaxis. Therefore, it is important to understand the processes that are responsible for where and when chemotaxis arrays are positioned in the cell. Scientists at the Max Planck Institute in Marburg have discovered how V. cholerae positions the chemotaxis arrays to its cell poles. Their results were recently published in the journal eLife.
Proteins important for chemotactic behavior group together in large complexes called chemotaxis arrays. It was already known that V. cholerae chemotaxis arrays are placed at both the cell poles of the bacterium by a protein called ParP. This localization of arrays at both cell poles makes sure that when the bacterium divides in the middle, then each new daughter cell receives a chemotaxis array and both daughters are immediately able to search for food when cell division is finished. In the absence of ParP, the chemotaxis arrays are no longer placed correctly at the cell poles and the bacteria are compromised in their ability to do chemotaxis and search for food. Particularly, in the case of ParP, it is not known how ParP can access the very large structures of chemotaxis arrays without disrupting their formation, and at the same time attach these structures to the cell poles.
To understand how ParP is able to direct chemotaxis arrays to the cell poles in V. cholerae, Alejandra Alvarado, a doctoral researcher in the research group of Dr. Simon Ringgaard, searched for partner proteins that could help ParP place chemotaxis arrays at this site. Together with her coworkers, she discovered that ParP interacts with other chemotaxis proteins that are part of the chemotaxis arrays. Via these interactions, ParP is able to integrate into the chemotaxis arrays and stimulates the formation of new arrays. They also discovered that ParP consists of two separate parts with different functions. One part directs ParP itself to the cell pole while the other part is responsible for ParP’s integration into the arrays. The linkage of these two domains of ParP, allows ParP to couple the positioning of arrays at the cell pole to their formation at this site. In this way ParP ensures that chemotaxis arrays are only formed at the cell pole and that this region of the cell is properly developed before cell division.
Alvarado A., Kjær A., Yang W., Mann P., Briegel A., Waldor M.K., Ringgaard S. (2017) Coupling chemosensory array formation and localization. eLife, 2017;6:e31058, doi: 10.7554/eLife.31058