Isolation of Mycoplasmatales Virus-laidlawii 3, a New Virus Infecting Acholeplasma laidlawii

Agricultural Research Council Institute for Research on Animal Diseases Compton, Newbury, Berkshire, England Two fundamentally different viruses that infect Acholeplasma laidlawii have so far been isolated. They have been designated Mycoplasmatales virus-laidlawii 1 (MV-L1) and Mycoplasmatales virus-laidlawii 2 (MV-L2). MV-L1 is an unenveloped helical DNA virus, 16 nm in diameter and 90 nm in length (Bruce et al. 1972); while MV-L2 is a predominantly spherical enveloped virus with a mean diameter of 80 nm (range 52 to 125 nm). Its nucleic acid appears to be DNA (Gourlay et al. 1973). This report describes the isolation of another virus which infects A. laidlawii and which differs from both MV-L1 and MV-L2. Four serial tenfold dilutions of two clones of the M1305/68 strain of Acholeplasma laidlawii resistant to MV-L2 (Gourlay, 1972) were prepared in phosphate-buffered saline, pH 7.3, containing 5% foetal calf serum. Drops (0.02 ml) of each dilution were placed on glucose serum (GS) agar plates (Gourlay & Wyld, 1972) and the plates were examined after incubation at 37 °C for 48 h. Received 21 December 1972; accepted 30 January 1973.