Extracellular production of L-ascorbic acid by Chlorella protothecoides, Prototheca species, and mutants of P. moriformis during aerobic culturing at low pH.
Nine strains of Chlorella protothecoides and 43 strains representing the five species of Prototheca were screened in flask culture for their ability to synthesize L-ascorbic acid (AA). Ascorbic acid was detected in all strains, ranging from 4.8 to 0.38 mg AA g x (-1) of dry cells. Organisms selected for further study grew well and maintained their AA productivity above a pH of 3.5. They can produce AA using a variety of carbon and nitrogen sources. Aerobic fermentation of selected strains resulted in extracellular accumulation of AA up to 76 mg x l(-1). By classical mutagenesis and selection methods, we created mutants of Prototheca moriformis ATCC 75669 that produced greater quantities of AA than the wild-type strain (78.4 vs 21.9 mg AA g x (-1) of cells). A process based on extracellular production could greatly reduce the cost of AA manufacture by eliminating the need for extraction of the AA from the cells.