INACTIVATION OF MECA PREVENTS RECOVERY FROM THE COMPETENT STATE AND INTERFERES WITH CELL-DIVISION AND THE PARTITIONING OF NUCLEOIDS IN BACILLUS-SUBTILIS

The development of genetic competence in Bacillus subtilis requires th e synthesis of ComK, a transcription factor, which is normally produce d as a culture enters the stationary phase. This synthesis is known to be regulated in part by the protein MecA. Loss-of-function mutations in mecA result in overexpression of ComK and its appearance early duri ng exponential growth. We show here that mecA inactivation also causes a loss of colony-forming ability, especially during stationary phase. This loss is accompanied by the appearance of cells in which normal n ucleoid separation has failed to occur. Renografin gradient fractionat ion of mecA cultures grown to competence reveals that nearly 100% of t he cells band at the low buoyant density characteristic of competent c ells, and that this low density is competence-related. The loss of via bility, the low buoyant density and the nucleoid separation defect, ar e all comK-dependent. The loss of viability can be reversed by even th e transient introduction of mecA(+). It is proposed that these effects of ComK overexpression are related to the DNA replication arrest norm ally exhibited by the competent cell fraction and that MecA is needed to reverse this arrest and to permit escape from the competent state. The shift of nearly 100% of the cells to light buoyant density in a me cA mutant culture strongly suggests that the MecA protein is a regulat or of the cell-type-specific expression of competence.