Synthesis of macromolecules in synchronously grown Arthrobacter

The synchronous growth of Arthrobacter has not yet been studied. We have shown that synchrony of A. crystallopoietes and A. globiformis cultures can be achieved in a liquid synthetic medium by inoculating a fresh medium with cells taken from an advanced stationary phase culture. DNA content measurements and pulsed incorporations of tritiated thymidine have been used to show that DNA synthesis occurs in a stepwise manner in these synchronized cultures. The use of absorbance of cultures as a monitor of synchronized cell growth was especially useful since cells did not separate during the exponential phase. The breaks in the absorbance versus time curve indicated a slow-down in mass synthesis. Protein and RNA synthesis occurred in two waves during the time necessary for a doubling of cell mass: a first increase was observed at the beginning of the DNA replication; after a slow-down, a second sharp increase occurred after the replication of DNA. These results are discussed in relation to previous data on the existence of a differential transcription during the development of A. crystallopoietes.