Heterotrophic production of ascorbic acid by microalgae

An aerobic fermentation process has been developed for the production of L-ascorbic acid (vitamin C). After an extensive screening program for microorganisms capable of synthesizing L-ascorbic acid, a unicellular green microalga, Chlorella pyrenoidosa , was selected. This microalga has a number of characteristics which recommend it as an industrial organism: it can double every 3.5 hours when growing aerobically in the dark on a glucose-minimal salts medium; its small size and tough cell wall make it very insensitive to shear, allowing very high impeller velocities; it can be grown to cell densities of 100 g/L dry weight; it is readily mutable by classical mutagenesis techniques; and it has efficient growth kinetics with respect to yield of cell mass on glucose and oxygen. Fermentation process development and classical strain improvement have resulted in a greater than 60-fold increase in intracellular ascorbic acid concentration compared to the parent strain C. pyrenoidosa UTEX 1663. The process is compatible with existing industrial fermentation technology and equipment, and is described in U.S. Patent 5,001,059. Patents have been submitted for a process in which the ascorbic acid accumulates extracellularly.