Replication of Helicoverpa zea Nuclear Polyhedrosis Virus in Homologous Cell Lines Grown in Serum-Free Media

Abstract

A parental cell line, BCIRL-HZ-AM1 (HZAM1) derived from Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) pupae and one of its clones BCIRL-HZAM1-B3 (HZ1B3), were grown as attached cells in two commercial insect serum-free media, EX-CELL 400 and SF-900, and one modified vertebrate serum-free medium, MCM1. A serum-containing medium, TC199MK, in which the cell lines were normally propagated, was used as control. Cell doubling times for HZAM1 in EX-CELL 400, SF-900, and TC199-MK, were 27, 28, and 30 hr, respectively; in contrast, there was negligible growth in MCM1. The shortest cell doubling time for HZ1B3 in serum-free medium was 25 hr, as observed in EX-CELL 400. Other cell doubling times were: 35 hr in TC199-MK, 38 hr in MCM1, and 45 hr in SF-900. Total extracellular virus production of H. zea nuclear polyhedrosis virus (HzSNPV)-infected HZAM1 cells was similar in all media (3.0-6.3 × 105 PFU/ml). Extracellular virus titers for HZ1B3 in EX-CELL 400 and SF-900 were similar (3-4 × 105 PFU/ml) but less than those produced in HZAM1. For HZ1B3, the lowest extracellular virus titer was recorded in MCM1 (0.8 × 105 PFU/ ml) and the highest in TC199-MK (12 × 105 PFU/ml). Production of HzSNPV occlusion bodies (OB) by HZAM1 cells differed slightly between the media (2.9-6.2 × 107 OB/ml). For HZ1B3 cells, OB production was similar in TC199-MK, EX-CELL 400, and SF-900 (3.6-6.0 × 107 OB/ml), but considerably lower in MCM1 (1.0 × 107 OB/ml). Occlusion bodies from both infected cell lines grown in serum-free media and in TC199-MK were equally infectious for H. zea larvae.