Effects of zinc on stationary-phase phenotype and macromolecular synthesis accompanying outgrowth of Candida albicans

Abstract

When cultures of Candida albicans which had entered stationary phase due to the depletion of zinc (zinc-limiting conditions) were compared with cultures which had entered stationary phase due to the depletion of another growth-limiting component (zinc-excess conditions), at least two cellular characteristics were found to differ: (i) zinc-limited cells appeared more homogeneous and larger on the average than zinc-excess cells, and (ii) zinc-limited cells evaginated on the average of 40 min later than zinc-excess cells. In the present study, it is demonstrated that the distribution of volumes for a stationary-phase culture of zinc-excess cells is skewed towards very small volumes, but even the smallest cells contain nuclei; in contrast, the volumes of zinc-limited cells are evenly distributed around a much larger mean value; the evagination kinetics of zinc-excess cells released into fresh medium are far less synchronous than are those of zinc-limited cells, and the smaller cells in the population take much longer to evaginate than do the larger cells; the onset of net RNA accumulation and achievement of a maximum rate of [3H]uridine incorporation occur significantly earlier in zinc-excess cells than in zinc-limited cells released into fresh medium; and the onset of net protein accumulation and [3H]leucine incorporation occur significantly earlier in zinc-excess cells than in zinc-limited cells released into fresh medium. These results indicate that although zinc-excess cells are extremely heterogeneous in volume, they may still be homogeneously blocked in the nuclear division cycle, and that the later average evagination time of released zinc-limited cells may be due to a delay in the onset of protein synthesis, which in turn may be due to the time necessary to reaccumulate zinc to levels sufficient for the reinitiation of RNA synthesis.