Growth and division of Spiroplasma citri: elongation of elementary helices.

The smallest viable cell of Spiroplasma citri is a two-turn helix (elementary helix). This elementary helix grows into longer parental cells, which then divide by constriction. The helical morphology is conserved during this process. The growth pattern of S. citri membranes has been investigated by different methods of membrane labeling. When labeling is done with specific antibodies, a diffuse growth of the membrane is observed. On the contrary, pulse-labeling of the membrane with tritiated amino acids reveals a polar growth of the organism. Finally, labeling of oxydo reduction sites with potassium tellurite also indicates a polarity in the organism. These results are discussed, and a scheme for spiroplasma growth is proposed.