Bacterial adaption and differentiation
Motility significantly contributes to the fitness of bacteria. Generally, bacteria can move using one or more of three different types of motility machineries. These nanomachines include flagella, type IV pili (T4P) and gliding machineries. While the flagella and T4P machineries are highly conserved the machineries for gliding are not highly conserved.
Motility is essential for formation of both types of cellular patterns or biofilms in M. xanthus. M. xanthus moves by means of T4P and gliding. The rod-shaped M. xanthus cells move in the direction of their long axis and have a leading cell pole and a lagging cell pole. Occasionally, cells reverse their direction of movement and during a reversal, the old leading pole becomes the new lagging cell pole. T4P assemble at the leading cell pole and during a reversal they disassemble at the old leading pole and reassemble at the new leading cell pole. In the case of the gliding motility system, the machinery (which is often referred to as focal adhesion complexes, FAC) assembles at the leading cell pole and disassemble at the lagging cell pole in moving cells. During a reversal, the cell poles at which FAC assemble and disassemble also switches. So, in total, during a reversal, the two motility machineries switch polarity.
In vegetative cells, cells at the edge of a colony efficiently explore the neighborhood by moving away from the colony and then reversing to return to the colony. During the aggregation stage of fruiting body formation, the C-signal induces a decrease in the cellular reversal frequency and switches cell behavior from an oscillatory mode to a unidirectional mode in which cells are moving towards nascent fruiting bodies. In our motility research we focus on elucidating how the two motility machineries assemble and function as well as on the mechanisms underlying polarity switching of the two motility systems. We also aim to understand at the molecular level how the C-signal inhibits reversals.
T4P are surface structures that are found on a large number of different bacterial species and they have important function in biofilm formation, virulence and motility. T4P function depends on the assembly of a macromolecular complex consisting of 10 proteins that localize to the outer membrane, periplasm, inner membrane and cytoplasm. We have shown that eight of these proteins localize to both cell poles and remain stationary during reversals. Conversely, the PilB and PilT motor ATPases that energize extension and retraction of T4P, respectively, localize to opposite poles with PilB predominantly at the leading and PilT predominantly at the lagging pole, and these proteins switch poles during reversals. In other words, type IV pili pole-to-pole switchings involve the disassembly of the type IV pili machinery at the old leading pole and reassembly of this machinery at the new leading pole.
Currently, we are focusing on analyses to understand how T4P proteins are targeted to the poles. We are also focusing on analyses to understand the structure of FAC and how they assemble and disassemble at opposite poles.
Some of our recent publications on motility:
Jakovljevic, V., Leonardy, S., Hoppert, M. & Søgaard-Andersen, L. (2008) PilB and PilT are ATPases acting antagonistically in type IV pili function in Myxococcus xanthus. J. Bacteriol. 190, 2411-2421.
Leonardy, S., Bulyha, I. & Søgaard-Andersen, L. (2008) Reversing cells and oscillating proteins. Mol. BioSystems 4, 1009 - 1014.
Clausen, M., Jakovljevic, V., Søgaard-Andersen, L. & Maier, B. (2009) High force generation is a conserved property of type IV pilus systems. J. Bacteriol. 191, 4633-4638.
Bulyha, I., Schmidt, C., Lenz, P., Jakovljevic, V., Höne, A., Maier, B., Hoppert, M., & Søgaard-Andersen, L. (2009) Regulation of the type IV pili molecular machine by dynamic localization of two motor proteins. Mol. Microbiol. 74, 691-706.
Søgaard-Andersen, L. (2011) Directional intracellular trafficking in bacteria. Proc. Natl. Acad. Sci. USA 108, 7283-7284.
Bulyha, I., Lindow,S., Lin, L., Bolte, K., Wuichet, K., Kahnt, J., van der Does, C., Thanbichler, M. & Søgaard-Andersen, L. (2013) Two small GTPases act in concert with the bactofilin cytoskeleton to regulate dynamic bacterial cell polarity. Dev. Cell. 25, 119-131.
Friedrich, C., Bulyha, I. & Søgaard-Andersen, L. (2014) Outside-in assembly pathway of the type IV pili system in Myxococcus xanthus. J. Bacteriol. 196, 378-390.
Siewering, K., Jain, S., Friedrich, C., Webber-Birungi, M.T., Semchonok, D.A., Binzen, I., Wagner, A., Huntley, S., Kahnt, J., Klingl, A., Boekema, E.J., Søgaard-Andersen, L. & van der Does, C. (2014) Peptidoglycan-binding protein TsaP functions in surface assembly of type IV pili. Proc. Natl. Acad. Sci. USA. 111, E953-E961.
Jakobczak, B., Keilberg, D., Wuichet, K. & Søgaard-Andersen, L. (2015) Contact- and protein transfer-dependent stimulation of assembly of the gliding motility machinery in Myxococcus xanthus. PLOS Genetics 11, e1005341.