Characterization of a combined DNA initiation and cell division mutant of Bacillus subtilis.

The temperature-sensitive mutation in Bacillus subtilis 168-134ts, a conditional lethal DNA initiation mutant, was transferred to the minicell producing strain, CU 403 div IV-B1, to study he relationship of DNA synthesis to cell division. Markers in the combined mutant were verified by transduction. DNA replication kinetics, genome location by autoradiography, and clonal analysis of cell division patterns during spore outgrowths were investigated. Growth of the double mutant at the restrictive temperature results in an impressive reduction of the percentage cell length covered by DNA grain clusters (60.2% at 30 degrees C compared to 8.6% after 2 h at 45 degress C). The probability of a minicell producing division in double mutant clones is essentially the same at 30 degrees C and during the initial 2-3 h growth at 45 degrees C at which time lysis begins. Residual division at 45 degrees C is attributable to processes initiated at 30 degrees C. The CU 403 div IV-B1, 134ts, double mutant divides about 25% as frequently relative to growth as do wild type CU 403 clones when incubated at permissive temperature. This is approximately 15% greater division suppression than previously found in the CU 403 div IV-B1 mutant strain, and is presumably due to interactions of the mutant gene products both of which affect DNA.