Characterization of an Iridescent Virus Isolated from the Velvetbean Caterpillar, Anticarsia gemmatalis

Abstract An insect iridescent virus has heen isolated from diseased velvetbean caterpillars, Anticarsia gemmatalis , found in Argentina. The cytopathology is similar to that reported for other iridescent viruses with infected larvae exhibiting blue-purple opalescence. Icosahedral particles ( n = 119) purified by sucrose gradient rate zonal centrifugation had dimensions of 145 ± 7 nm (point-to-point) and 136 ± 12 nm (side-to-side). The sedimentation coefficient was 2250 ± 10 S 20,w when the virus was suspended in phosphate buffer. Characterization of proteins by SDS-polyacrylamide gel electrophoresis revealed 24 polypeptides with a single major species of 53.6 kDa. Purified viral DNA had a density of 1.6902 g cm -3 in equilibrium ultracentrifugation, corresponding to a guanine:cytosine content of 32.2%. Analysis of digests of this DNA with two restriction enzymes revealed an average molecular size of 181.8 ± 5.6 kbp. A 499-bp fragment was amplified from the genome of this isolate using the polymerase chain reaction and then sequenced; data suggest this virus is very closely related to IV 1, originally isolated from Tipula paludosa . These properties indicate this virus is an isolate of the genus Iridovirus.