| Bacteria respond to subtle changes in the environment through the use of motility and chemotaxis. Recent studies of the regulation of chemotaxis pathways have shown significant differences from the paradigm pathway of enteric bacteria. This thesis focuses on the regulation of the Frz chemotaxis pathway of Myxococcus xanthus. The frz genes are similar to the enteric chemotaxis genes and are required for the formation of developmental fruiting bodies and for multicellular behaviors. In this thesis, I present evidence for two novel regulatory mechanisms of the Frz pathway. The first mechanism concerns the regulation by selective methylation of multiple sites of the receptor, FrzCD. To gain insight into the regulation of methylation of FrzCD, each of the seven potential methylation sites of FrzCD were mutated by site-directed mutagenesis. In this thesis, I show that methylation of FrzCD is site selective, each of the mutations lead to different phenotypic effects. The mutations had different effects on development versus vegetative conditions, indicating different adaptational mechanisms are used for different physiological states. The positioning of the methylation sites of FrzCD suggests a mechanism of activation. The second novel mechanism concerns the regulation of the Frz signal transduction pathway by a second CheW-like protein, FrzB. The CheW protein is thought to bridge the interaction of chemoreceptors to the kinase. Interestingly, the Frz pathway contains two cheW-like proteins, frzA and frzB common for the other chemotaxis pathways of M. xanthus. To determine the roles of FrzA and FrzB, I studied their interactions with the other components in the Frz pathway. FrzA associated with the receptor and the kinase, whereas FrzB only associated with the receptor. Thus it appears that FrzA functions as a true CheW homologue whereas FrzB has a novel regulatory role. Affinity measurements of the interactions suggest several possible models by which FrzB regulates the pathway. These novel regulatory mechanisms illustrate the adaptation of chemotaxis pathways to meet the challenges of signal perception in multicellular bacterial communities. |
