Linear growth and lipid synthesis in the oleaginous yeastRhodotorula gracilis

Abstract

A kinetic analysis was made of batch cultures of an industrially important yeastRhodotorula gracilis, using a nitrogen-limited medium. The exponential phase of growth lasted 15 h, followed by a linear phase up to 36 h. The generation time was 2.8 h (15–36 h of fermentation) which corresponded to a μ of 0.248/h. The lipid synthesis was partially growth-associated with the linear growth phase (15–36 h) and the early stationary phase (36–60 h). The rate of linear growth was estimated as 0.267 g cell per L per h and the rate for lipid synthesis over the period of 15–60 h was 0.17 g lipid per L per h. More than 50% of the total supplied nitrogen was assimilated by the organism and the rest remained in the medium. Sugar assimilation was nearly 100% by the end of 60-h fermentation. At 0 h the intracellular protein was 3.3% and it significantly increased to 11.7% by the end of 12 h. Morphological and physiological characteristics were also found to change during different stages of growth.