E 8 - Lotte Søgaard-Andersen

Surface- and contact-dependent motility in the soil bacterium Myxococcus xanthus


   
    

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Prof. Dr. Lotte Søgaard-Andersen

Max Planck Institute for Terrestrial Microbiology 

Karl-von-Frisch-Straße 10, 35043 Marburg

+49 - 6421 - 178201

sogaard@mpi-marburg.mpg.de

http://www.mpi-marburg.mpg.de/sogaard/

 

Research summary:

Cells of the deltaproteobacterium Myxococcus xanthus undergo major lifestyle changes in response to nutrient availability. In the presence of nutrients, the rod-shaped cells grow and divide and form colonies where cells at the edge spread outwards in a highly coordinated manner. In response to nutrient limitation, cells initiate a developmental program that culminates in the formation of multicellular fruiting bodies inside which the rod-shaped motile cells differentiate to spherical spores. Formation of spreading colonies as well as the spore-filled fruiting bodies depends on cellular motility and its regulation.

The ultimate goal of this project is to understand how M. xanthus responds to environmental changes in nutrient accessibility with changes in motility behavior and, subsequently, the formation of these two morphologically distinct biofilms. M. xanthus cells move by means of two motility systems, i.e. gliding motility and type IV pili (T4P)-dependent motility. T4P are highly dynamic structures that undergo cycles of extension, adhesion and retraction and during a retraction event a cell is pulled forward. In M. xanthus T4P-dependent motility is cell-cell contact dependent because exopolysaccharides (EPS) stimulate T4P retractions. Because T4P-dependent motility is essential for the formation of both types of biofilms, it is essential to understand how the T4P machinery function mechanistically and how T4P retractions are stimulated in a contactdependent manner by EPS.

In the previous funding period we elucidated the assembly pathway of the T4P machinery, revealed the overall architecture of this machinery using electron cryo-tomography, mapped the location of all of the components of this machinery, identified several interacting T4P machinery proteins, and proposed a detailed pseudo-atomic hypothetical model for the structure and function of this machinery. Moreover, we demonstrated that the second messenger c-di-GMP regulates T4P formation and EPS accumulation in growing cells. To understand mechanistically how T4P function is stimulated in response to cell-cell contacts, we propose two lines of investigations. First, building on our model for the T4P machinery, we aim to determine how proteins at the base of the T4P machinery interact to extend and retract pili. Secondly, we aim to elucidate the composition and structure of M. xanthus EPS and determine how c-di-GMP regulates EPS accumulation and in that way T4P function in M. xanthus.

 

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