A GENETIC LINK BETWEEN LIGHT RESPONSE AND MULTICELLULAR DEVELOPMENT IN THE BACTERIUM MYXOCOCCUS-XANTHUS

The Gram-negative bacterium Myxococcus xanthus responds to blue light by producing carotenoid pigments (Car(+) phenotype). Genes for caroten oid synthesis lie at two unlinked chromosomal sites, the carC and the carBA operon, but are integrated in a single ''light regulon'' by the action of common trans-acting regulatory elements. Three known regulat ory genes are grouped together at the (light-inducible) carQRS operon. By screening the Car phenotype of a large collection of transposon-in duced mutants, we have identified a new car locus that has been named carD (carD1 for the mutant allele). The carD gene product plays a crit ical role in the light regulon, as it is required for activation of th e carQRS and carC promoters by blue light. The carD1 mutant is impaire d in the (starvation-induced) developmental process that allows M. xan thus cells both to form multicellular fruiting bodies and to sporulate . Our results indicate that the carD gene product is also required for the expression of a particular set of development-specific genes that are normally activated through the action of intercellular signals.