Mass production of single cell oil (SCO) by rhodororula glutinis NRRL Y-1091 on fed batch culture

Abstract

$\underline{Rhodotorula} \underline{glutinis}$ NRRL Y-1091, an oleaginous microorganism, was cultivated to produce a large amount of lipid by fed batch culture. Glucose was semicontinuously introduced with 60% solution at a rate which ensured the glucose solution of 10-25 g/l during the growth. Mineral sources were fed with the concentrated solution into culture broth and quantitatively traced. During the initial cultivation under nitrogen-excess condition, oxygen supplied with air only was limited at the concentration of 30-40g dried cell weight per liter medium. The accumulation of intracellular lipid was initiated from after oxygen limitation and, when arbitrarily stopping the supply of nitrogen source at the biomass concentration of 60-70 g/l, continuously increased at the similar rate with that under oxygen-limited condition. Finally, the microbe was cultivated to high dense culture (90-100 g/l) with air only and intracellularly accumulated a large amount of lipid (35-40%) after 120hr cultivation. Main lipid was a neutral lipid (80-85%) and the components of fatty acids in the total lipid were mainly composed of palmitic acid (C16:0) and oleic acid (C18:1). The overall growth yield, Yx/s, and the overall fat coefficient were 0.35 and 0.14, respectively. However, the instantaneous growth yield gradually decreased as the culture time passed. This was due to the fact that the energy content of biomass, $\gamma_b \sigma_b$, increased with the increase of lipids content, which are high energy substance. Some factors that would make the high density culture possible are as follows: 1. Supply of sufficient oxygen for the extention of exponential growth phase, 2. optimal feeding of nutrients, such as glucose and mineral sources, into concentrated solutions, 3. no product inhibition by fermentation byproducts, 4. low oxygen requirement in lipid accumulation phase.