Characterization of the effects of nitrogen and carbon sources on protein production of suspension cultures of soybean (Glycine max L. Merrill)

Abstract

A shear resistant photosynthetic suspension culture of Glycine max has been used to study the effects of inorganic nitrogen and carbon on cell mass, protein and chlorophyll production, and the kinetics of nitrogen and carbon uptake. Different nitrate:ammonium ratios in the media were studied by varying concentrations of inorganic nitrogen salts in a full factorial experiment. The results showed that 38.6 mM nitrate and 10.3 mM ammonium provided the highest cell growth and protein and chlorophyll contents. At higher ammonium concentrations, regardless of nitrate concentration, cell mass, protein and chlorophyll contents decreased. Sucrose proved to be the best sugar source for growing this soybean suspension culture. Different concentrations of sucrose and carbon dioxide were also studied in a full factorial experiment. The results showed that a combination of 1% sucrose and 2% carbon dioxide (in air) provided the highest cell growth and protein and chlorophyll production. However, the chlorophyll content declined when the sugar concentration increased to 5% with all concentrations of carbon dioxide. The cultures had an absolute requirement for sugar to some extent regardless of carbon dioxide concentration. Protein patterns and amino acid compositions of suspension cultures were compared with those from different parts of the soybean plant, seedlings and commercially isolated soy protein which is used in the food industry. It was found that the electrophoretic pattern of the cultured cell protein was similar to that of the leaf cells. The cultured cell protein contained most of the bands which appeared in the commercially isolated soy protein as well as several other bands. The levels of essential amino acids in the cultured cell protein, in general, were higher than those in the commercially isolated soy protein. The soybean suspension cultures grew well in a bioreactor and produced a high cell mass and protein content in a short time. This showed the feasibility of scaling up for rapid production of high cell mass and protein.