Studies on the Morphogenesis of Nocardioform Organisms Related to the 'rhodochrous' Taxon in Synchronous Cultures

Abstract

In nocardioform organisms related to the ‘rhodochrous’ taxon (Nocardia restricta, Nocardia or Jensenia canicruria), morphogenesis was affected by nutritional conditions, especially the nature of the carbon source. With glucose, growth was slow and the bacteria divided at each doubling of the cell mass. With succinate or acetate, growth was much more rapid during the exponential phase and cells grew as long rods. Later, when growth slowed down, septa, which were clearly visible in thin sections examined by electron microscopy, gradually appeared and divided the organism into smaller cells. During the stationary phase of growth, cells recovered their original spherical shape. Synchronous growth of these bacteria was achieved in liquid synthetic medium by inoculating fresh medium with spherical cells taken from an advanced stationary phase culture. The synchrony was shown by the periodicity of DNA replication and protein synthesis. The fragmentation of the rods was studied during incorporation of labelled diamino-pimelic acid into cell walls. Septa did not form simultaneously but in distinct phases. The regular periodicity of their formation suggested that this process is coordinated in time and is related to the organism's growth rate. The data are interpreted using Cooper and Helm-stetter's model for cell division in prokaryotes.