Characterization of an iridescent virus isolated from the velvetbean caterpillar, Anticarsia gemmatalis

An insect iridescent virus has been 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 S20,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.