Developmental expression of dnaA is required for sporulation and timing of fruiting body formation in Myxococcus xanthus.

Inhibition of DNA replication within the first 6 h of development results in a block in the developmental programme in the social soil bacterium Myxococcus xanthus. We have interpreted these data to imply that M. xanthus requires a new round of DNA replication early in the developmental programme. To further understand the role of DNA replication during development in M. xanthus we focused on the regulation of dnaA which encodes the initiator protein of DNA replication. In this work, we demonstrate that immediately upon nutrient deprivation dnaA (MXAN1001) transcript levels decrease to 10-15% of vegetative levels and then transiently increase between 4 and 6 h post initiation. This expression is dependent on several early developmental regulators, including relA (MXAN3204), sigD (MXAN2957) and sdeK (MXAN1014). It is also dependent upon an 85 bp region located just upstream to the dnaA promoter. Our data suggest that while developmental dnaA expression is not essential for development, its expression allows for the proper timing and maximum efficiency of the sporulation process. In addition, we speculate that developmental control of dnaA expression may provide a mechanism for predetermination of cell fate during the differentiation process.