The focus of our research is to determine how signal transduction regulates directed motility and behavior in the bacterium Myxococcus xanthus. M. xanthus represents an excellent model system to address questions concerning cell-cell signaling and directed movement as cells form multicellular fruiting bodies. M. xanthus fruiting bodies are similar to biofilms formed by Pseudomonas and are of public health interest since biofilms render organisms multidrug resistant. Previously, we have shown that the Frz signal transduction system regulates vegetative swarming and developmental aggregation by controlling the reversal frequency of cells. Our data to date indicate that this pathway has multiple inputs and multiple outputs and, somehow, these are all coordinated. We propose the following specific aims to understand this signaling: 1 - Input signaling -We hypothesize that there are at least two major inputs to the Frz pathway: (i) one occurs through FrzF, the methyltransferase, where controlled methylation activates or inactivates the receptor, FrzCD; (ii) the second principal input to the pathway is proposed to be through FrzB, a second CheW, which may be involved in receptor clustering or alternatively in coupling FrzE to other chemosensory pathways in M. xanthus. We plan experiments to characterize these input pathways. 2 - Output signaling - The Frz system contains four CheY-like receiver domains that together control two different motility systems. We plan to study the pathway output by constructing deletions in these domains. We plan to explore the hypothesis that FrzE signals FrzSCheY to activate S-motility and FrzECheA controls A-motility. FrzS, which is required for S-motility forms a structure at the cell poles that will be characterized. 3 - Regulation - We plan to investigate the regulation of the Frz pathway with an emphasis on how signal feedback occurs. Feedback regulation involves methylation and demethylation of FrzCD, but how it functions is not known. We plan to test several hypotheses as to how this might occur.