Giant cell formation in Acholeplasma laidlawii, strain JA1.

Striking alterations, which looked like blebs, were observed in colonies of Acholeplasma laidlawii, strain JA 1. "Craters" were seen on the surface of these colonies by scanning electron microscopy. In addition, giant cells of acholeplasma, up to 14 microns in diameter, i.e. approximately 20 times the size of a normal A. laidlawii cell, were visible in the colonies. The large forms were surrounded by a unit membrane. After infection with group 1 and group 2 mycoplasma-viruses, the proportion of altered colonies and the number of large cells within these colonies increased. A strain of A. laidlawii, which was not susceptible to infection with the three known acholeplasma-viruses did not exhibit comparable morphological changes. The development of the giant cells can be explained either by cell fusion or by a lag of cell division behind genome replication. Blebs and "craters" may result from the destruction of mycoplasma organisms within the complex structure of the colony. There is also suggestive evidence that strain JA 1 carries a virus in some cryptic form.