Figure 5.

Growth rate and cellular morphology of cells conditionally expressing cdnL. (A) Growth curves for MR1466 and MR1467 under permissive (left) or restrictive (right) conditions. Cells were grown in the light at 33°C, 300 rpm, and aliquots of ∼10⁶ cells were innoculated into 10 ml CTT in separate flasks. One was grown in the light (permissive conditions) and one in the dark with 0.75 µM B₁₂ (restrictive conditions) at 33°C, 300 rpm; the abscissa indicates time (in hours) after the shift in growth conditions. (B) Cellular morphology of cell samples from cultures grown as in A, examined at an OD₅₅₀ ∼0.8 after DAPI-staining by DIC and fluorescence microscopy. Note the unusually elongated cells indicative of aberrant cell division on shifting to restrictive conditions for the strain conditionally expressing cdnL and the extended span of the pole regions lacking DAPI-stained foci (scale marker: 5 μm).