The nutrient requirements of insects are generally like those in vertebrates. There are some remarkable exceptions that need to be implemented when designing insect cell culture media.
Insects have no capacity for steroidogenesis and need a source for the formation of cell membrane components and the steroid hormone ecdysone (Law and Wells, 1989).
The levels of amino acids in insect blood is very high. Therefore, media for insect cell culture contains a high amount of amino acids (Grace 1962, Weiss et al. 1981).
Free organic acids levels such as citrate, succinate, oxalate, and malate are unusually high in insect blood. They range from 0.1 – 30 mmoles per insect.
Fluids are more acidic and normally range from 6.2 – 6.9 in Insect Tissue. The optimal range for most insect cell culture media is between 6.2 – 6.5 compared to 7.1 0 7.6 in most mammalian cell culture. The SF-3 Baculo Express Cell Medium is optimised to keep this range under various culture conditions (e.g. open air, open capped). There is no CO2 required to keep a constant range and the insect cell culture media are buffered with sodium phosphate. There is no pH indicator added to insect cell culture media so the colour of the media is yellow due to the supplementation of protein hydrolysates. In SF-3 Baculo Express Media, the hydrolysates are added as ultra filtrates with an 8 kDa cut off to facilitate downstream purification processes.
The osmotic pressure varies significantly from vertebrate blood, being more than twice as high. The insect cell culture media has therefore osmolality of 340 – 390 mOsmol/kg compared to 290 – 330 mOsmol/kg for vertebrate cultures.
Excess metabolism of glutamine and glucose in mammalian cell culture can result in an excess production of ammonium and lactate respectively and the accumulation of metabolic by products are often inhibitory. In insect cells, the detoxification of metabolites follows a different pathway than in mammalian cells. Insect cells have higher levels of glutamine and glucose to support cell density growth.
There has been extensive development and further investigation on the nutritional needs of insect cells. This has been based off the exceptional performance of SF-1 which is a newly improved ‘ready to use’ insect medium. It has been successful in many different academic and industrial labs, showing the following improvements:
Grace’s Insect Medium has always been popular to use in insect cell culture. It is formulated to resemble the chemical composition of hemolymph from Bombyx mori. The insect culture medium has been supplemented with FCS, yeast extract, lactalbumin hydrolysate and BSA in varying combinations and amounts. The medium is used to culture dipteran and lepidopteran cell lines.
The Mitsuhashi and Maramorosh Basal Insect Medium is suited for mosquito cell culture and must be supplemented with FCS prior to using it.
Schneider’s Drosophila Medium was originally developed for the culture of Drosophila cells but can also be used for the culture of other dipteran cell lines.