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Chapter 27 : The frz Signal Transduction System Controls Multicellular Behavior in Myxococcus xanthus
Myxococcus xanthus is an unusual gram-negative bacterium in that it exhibits a variety of social behaviors and has a complex life cycle. This chapter focuses on the frz signal transduction system, which is a two-component signal transduction system involved in the social behavior of M. xanthus. The authors investigated the isolation of mutants defective in development, and were particularly interested in one group of these mutants, called frizzy or frz, which sporulated normally but formed tangled, frizzy filaments under fruiting conditions instead of the normal fruiting bodies. Based on recombinational and complementation analyses, the frz genes were grouped into at least five complementation groups: frzA, frzB, frzC, frzE, and frzF. The homologies did not prove that the frz genes were chemotaxis genes, because the conserved protein motifs could have evolved new functions. To show spatial chemotactic movement in M. xanthus, it was necessary to set up agar plates, which maintain steep and stable chemical gradients. The authors set up these gradients using petri plates that contain multiple compartments, and found that most frz mutants were no longer able to respond to the spatial or temporal chemical gradients and did not exhibit any chemotactic movements. Western immunoblot and primer extension analysis showed that FrzZ is indeed expressed in vivo during both vegetative growth and development. Genetic, biochemical, behavioral, and molecular biology studies all indicate that the frz genes are the chemotaxis genes of M. xanthus.