Use of plant-derived protein hydrolysates for enhancing growth of Bombyx mori (silkworm) insect cells in suspension culture.

The successful suspension culture of the Bombyx mori (silkworm) cell lines Bm5 and BmN4 without FBS (fetal-bovine serum) was first realized in Sf-900 II SFM (serum-free medium) (Gibco BRL, Rockville, MD, U.S.A.) supplemented with a plant-derived protein hydrolysate. The addition of 0.5% HyPep 1510 (Difco Co., Detroit, MI, U.S.A.) and 10 mM glutamine to Sf-900 II SFM at 4 days of culture was found effective in increasing the cell concentration to 8.5x10(6) cells/ml. The replacement of medium with Sf-900 II SFM supplemented with 0.5% HyPep 1510 at 6 days of culture increased the cell concentration by 1.1x10(7) cells/ml. When Sf-900 II SFM was supplemented with 0.5% Hypep 1510, 16 days, which was half of the conventional adaptation time, was sufficient for the B. mori cell line to adapt to SFM and shear stress while maintaining a stable viability. The beta-galactosidase activity in Sf-900 II SFM supplemented with 0.5% Hypep 1510 was 4.9x10(3) units/ml, which was 2-fold higher than that of the FBS-supplemented medium. By SDS/PAGE, only the band corresponding to beta-galactosidase was detected in the sample from the media supplemented with plant-derived protein hydrolysates, while thick bands corresponding to proteins having lower molecular masses than beta-galactosidase were detected in samples from the FBS-supplemented media. These results suggest that plant-derived protein hydrolysates are promising FBS substitutes for enhancing the growth of B. mori cells and facilitating the purification of recombinant proteins produced by baculovirus infection.