Baculovirus infection cycle

The bioreactor operation mode is normally defined at the outset of process configuration. Insect cells have been cultured in almost all known cultivation modes batch [10], repeated-batch [70], perfusion [71-74], fed-batch [75, 76], semi-continuous [77,78] and continuous [79]. In spite of this multitude of different strategies, the batch or, eventually, fed-batch mode is normally preferred due to the lytic infection cycle of the baculovirus. 

The establishment of insect cell line cultures allowed a detailed study of the infection cycle of many baculoviruses. These cell lines are easily cultured in vitro and their maintenance is relatively simple. The majority of the cell lines can be cultivated using a temperature of 25-30°C. However, the best temperature for the growth and infection of Sf9 cells is around 27-28°C (King and Possee, 1992). 

Baculovirus expression is the most frequently used method for expression in insect cells and employs Autographa californica nuclear polyhedrosis virus (AcNPV), a double stranded (ds) DNA virus that infects arthropods. The baculovirus expression system utilizes features of the viral life cycle to introduce recombinant DNA coding the gene of interest into insect cells (Miller, 1988 O Reilly et al, 1992). 

Both ECV and PDV are infectious for susceptible cultured lepidopteran cells. However, the ECV is much more highly infectious when compart on a physical particle infectious particle ratio. For natural routes of infection in the insect, the viral occlusion and the PDV is far more highly infectious than ECVQJL). The occluded baculoviruses, therefore, have a biphasic life cycle the PDV and viral occlusion are the most efficient viral forms for natural infection of the insect, and the ECV form is the most efficient for secondary infection of tissues in the insect and cells in culture. The polyhedrin gene is not essential for cell culture infection. 

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