Chisa Yasunaga

Coinfection of Spodoptera exigua and Spodoptera frugiperda cell lines with the nuclear polyhedrosis viruses of Autographa californica and Spodoptera exigua

The Autographa californica multinucleocapsid nuclear polyhedrosis virus (AcMNPV) has a broad host range among Lepidoptera. In contrast, the Spodoptera exigua MNPV (SeMNPV) can replicate efficiently only in S. exigua larvae or S. exigua-derived cell lines. In this study, we examined the coinfection of S. exigua Se301 and Spodoptera frugiperda IPLB-SF21AEII (Sf21) cell lines with SeMNPV and AcMNPV recombinant (Ac360-501β-gal) which was constructed for expression of β-galactosidase under control of the polyhedrin promoter. Coinfection led to the restriction as the level of late gene expression, nonoccluded virus production, and DNA replication of Ac360-501β-gal in both Se301 and Sf21 cell lines. In contrast, Ac360-501β-gal supported the SeMNPV replication in Sf21 cells. Occurrence of recombinants, between Ac360-501β-gal and SeMNPV, with expanded host range was not observed in coinfected Sf21 cells. This suggests that Ac360-501β-gal supports the SeMNPV replication through trans-activation.

A New Method for Inoculation of Poor Germinator, Nosema sp. NIS M11 (Microsporida: Nosematidae), into an Insect Cell Culture

ABSTRACT. Spores of Nosema sp. NIS M11, primed with 0.1 N KOH solution, were mixed with either physiological salt solutions or IPL‐41 medium, an insect cell culture medium, for germination. In the latter medium, only a few spores germinated, while high percentages of spore germination were obtained in physiological salt solutions, particularly in Rinaldinis solution. By using the salt solutions as inoculation media, KOH‐primed NIS M11 spores were inoculated into the Spodoptera frugiperda SF21AEII cell line. The initial infection levels were consistently higher than that obtained by using IPL‐41 medium. Among the salt solutions, Rinaldinis solution, containing KCl in place of NaCl, gave the highest percentage of initial cell infection. Increased osmolarity of salt solutions did not improve the efficiency of spore germination and infection of N. sp. NIS M11.

Effects of host cell density on cell infection level in Antheraea eucalypti (Lepidoptera: Saturniidae) cell cultures persistently infected with Nosema bombycis (Microsporida: Nosematidae)

ABSTRACT. Spores of Nosema bombycis Y9101, isolated from the beet armyworm, Spodoptera exigua, were primed with an alkaline solution and inoculated into Antheraea eucalypti cell cultures. Infected cells were subcultured every five days at three cell densities (2.5 × 103, 5.0 × 103, and 1.0 × 104 cells/cm2). A difference was observed in the spread of N. bombycis Y9101 infection between low‐density and higher‐density cultures of host cells. The host cell density did not affect the productivity of secondary infective forms of the parasite. The principal factor determining the rate of microsporidian infection in vitro was the number of host cells existing within the reach of extruded short‐coiled polar tubes from spores germinated intracellularly.