Interactions Between Chemotaxis-Like Signal Transduction Pathways in Azospirillum brasilense

Tess Branon


To better understand the molecular mechanisms of signal transduction in microorganisms, interactions between chemotaxis-like signal transduction pathways were studied in the soil bacterium Azospirillium brasilense in the Alexandre lab of the University of Tennessee, Knoxville Department of Biochemistry and Cell and Molecular Biology. The bacterium studied is a motile, diazotrophic alphaproteobacterium whose genome encodes for four putative operons for chemotactic signal transduction. The Alexandre lab had studied the first chemotactic operon in A. brasilense, Che1, and found that the primary function of the Che1 operon was not the control of motility bias; rather, further experimentation and observation suggested that the Che1 operon contributed to chemotaxis but had primary effects on the regulation of cell length at division and on cell clumping behavior. Because chemotaxis is not the apparent primary function of the Che1 pathway, it was hypothesized that another chemotactic operon controls motility bias in A. brasilense. Comparative genomics and bioinformatics analyses suggested that of the other three operons, the fourth operon, Che4, was the most likely to contribute to chemotaxis behavior. In preliminary experiments, it was observed that Che1 and Che4 had opposing effects on chemotactic behavior, suggesting that Che1 and Che4 may indeed work together to modulate the motility bias. To further determine if the two sets of chemotactic proteins from the Che1 and Che4 pathways are closely associated in signaling complexes and thus physically interact, fluorescent tagging of individual chemotaxis proteins was used to observe their respective localization within the cell and to determine whether the localization of the proteins of the Che1 pathway and the proteins of the Che4 pathway rely on each others’ presence. Localization patterns of the YFP fused chemotaxis proteins supported the hypothesis of crosstalk between the Che1 and Che4


Chemotaxis, Signal Transduction, Crosstalk

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