Dimension control in Micrococcus flavus
The effect of nutrition on growth rate, cell size, and cell arrangement in Micrococcus flavus is described in relation to earlier studies of other bacteria. Progressive improvements in nutrition reduced the generation time from 15 to 1.7 h (at 25 °C), but septum formation occurred at about the same cell age in all growth cycles. In Gram-negative bacteria, the division site is also formed at a constant cell age, just before cell separation so that cells occur singly. In M. flavus, however, the time between septum formation and the related cell separation exceeded one generation time so that cells were either in pairs or tetrads. This arrangement of cells in groups is more typical of Gram-positive bacteria. The change in cell dimensions from hemispheres to spheres was also found to occur in M. flavus at a constant cell age, just before septum formation. With reference to three taxonomically unrelated bacteria, the arrangement of cells in groups is shown to result from the interrelation between growth rate and the timing of septum formation within the cell cycle.