Date of Degree
PhD (Doctor of Philosophy)
John R. Kirby
Myxococcus xanthus is a δ-proteobacterium that displays a complex, multicellular life cycle involving vegetative growth, coordinated motility, and a developmental program culminating in sporulation. M. xanthus utilizes two genetically distinct yet coordinated systems to regulate motility comprised of either Type IV pili (T4P) or focal adhesion complexes (FAC). Both motility systems are regulated, in part, by multiple chemosensory systems. During development, cells aggregate into foci and gradually lose motility to become quiescent fruiting bodies containing mature heat- and sonication-resistant myxospores. In this study, I have characterized a new chemosensory system, Che6, in M. xanthus for its role in motility and development. The Che6 chemosensory system is comprised by six homologs to known chemotaxis proteins, Mcp6, CheW6a, CheW6b, CheA6, CheR6, and CheB6 and includes two previously identified proteins, a potassium efflux channel (KefC) and a sensor kinase (SocD).
Mutations in each of the corresponding genes were found to affect motility and to disrupt development. Notably, the motility defects were well defined in a background strain with an impaired T4P system. In this background, the che6 mutants were observed to either positively or negatively affect reversal frequencies, highlighting their role in either FAC or T4P-based motility systems. Developmental defects were also identified for the che6 mutants and affected the timing of aggregation and sporulation. Interestingly, the overproduction of the CheB6 methylesterase resulted in spore formation independent of fruiting body formation. Uncoupling of sporulation and fruiting body formation for this mutant was found to be independent of a key developmental signal known as the C-signal.
Moreover, we have demonstrated for the first time the association of a potassium efflux channel (KefC) with a chemosensory system (Che6) in bacteria. In this study, we provide evidence demonstrating that KefC provides an input signal for Mcp6 which transduces a signal through CheA to the histidine kinase SocD which serves as an output to regulate both motility and development in M. xanthus.
Copyright 2011 Jodie Catherine Scott
Scott, Jodie Catherine. "Che6 chemosensory regulation of multicellularity in myxococcus xanthus." doctoral dissertation, University of Iowa, 2011.