Process with yeasts from hydrocarbons
In addition to A. niger, several yeasts, among which
Candida catenula, Candida guilliermondii, Yarrowia lipolytica
and Candida tropicalis, have been described that form large
amounts of citric acid from n-alkanes or –even though with
lower yield– from glucose (39). When this process was
successfully used before the world oil crisis of 1973/1974, the
culture medium usually consisted of C9-C23 n-akanes in a
concentration of 100 g/l, and the best results were obtained
with Y. lipolytica in batch (duration of 5-6 days) or fed-batch
submerged systems at pH 5.0-6.5 and 1.0-1.5 vvm aeration
(60). The yield is higher than with carbohydrates (1.30-1.45
grams of acid per gram of paraffin) (14), but there are
difficulties associated with low water solubility of alkanes and
the presence of up to 50% of isocitric acid among the products,
which has to be separated during recovery (59). Therefore,
mutants with very low aconitase activity were selected using
monofluoroacetate resistance as a selection criterion (39).