REGULATION OF DIRECTED MOTILITY IN MYXOCOCCUS-XANTHUS

Myxococcus xanthus is a Gram-negative bacterium that exhibits a comple x life cycle, During vegetative growth, cells move as large swarms. Ho wever, when starved, cells aggregate into fruiting bodies and sporulat e. Both vegetative swarming and developmental aggregation require glid ing motility, which involves the slow movement of cells on a solid sur face in the absence of flagella, The frequency of cell reversals contr ols the direction of movement and is regulated by the frz genes, which encode the 'frizzy' signal-transduction proteins, These proteins cont ain domains which bear striking similarities to the major chemotaxis p roteins of the enteric bacteria: CheA, CheY, CheW, CheR, CheB and Tar. However, significant differences exist between the Myxococcus Frz pro teins and the enteric Che/MCP proteins. For example, the Frz system co ntains three CheY-like response-regulator domains: one is present on F rzE, which also contains a CheA-like domain, and two are present on Fr zZ, which is a novel protein required for attractant, but not for repe llent, responses. The identification of multiple CheY homologues in th is system indicates a more complex regulatory pathway than that found in the enteric bacteria. While responses to repellent stimuli appear t o follow the enteric paradigm, responses to attractants during vegetat ive swarming and development are more complex and may involve self-gen erated autoattractants. The Frz signal-transduction system regulates d irected motility in M. xanthus and is essential for controlling both f ruiting-body development and vegetative swarming.