Spiroplasmal viruses: group 1 characteristics.

Virus-like particles of three morphologic groups have been detected by electron microscopy in 90% of spiroplasma strains. In this study, virus-like particles of group 1 (SpV1)--unenveloped rods 230-280 nm by 10-15 nm--were found in 575 of spiroplasmas. SpV1 occurred spontaneously in large numbers in cultures of strains B (corn stunt), G1 (tulip tree flower), BC3 (honeybee), and KC3 (honeybee), respectively; the viruses were isolated and assayed as plaque-forming units, with several of the same strains used as indicators. No virus plaqued on its strain of origin, and all except one (SpV1/BC3) plaqued best on strain BC3. Host range and yields of progeny virus differed. All isolates were identical in morphology, size, and buoyant densities; contained DNA; formed turbid 1.5 to 5.0-mm plaques; produced nonlytic infections and similar one-step growth curves; were inactivated by a single antiserum; had similar kinetics of adsorption and heat inactivation; and demonstrated similar patterns of resistance and sensitivity to a variety of physical and chemical agents, as well as an inability to infect resistant host mutants. SPV1 isolates from diverse host strains apparently share many physicochemical and biological properties, but are not identical in all biological respects.