Experiments performed in batch fermentation under phosphate-limited growth conditions showed that the citric acid yield was inversely related to the excess nitrogen concentration in the medium. Results from chernostat culture confirmed a negative relationship between the citric acid yield and both the specific growth rate and the nitrogen consumption rate. This is evidence for nitrogen catabolite repression. A fed-batch fermentation performed under dual phosphatelnitrogen limitation produced results very similar to those from a culture limited by nitrogen alone. There is no advantage in maintaining an excess of phosphate during citric acid production and the process will therefore be more economic when operated under dual limitation conditions.
Bacteria and/or bovine faecal matter were introduced into cultures of pathogenic freeliving amoebae with Baquacil. They created a biochemical oxygen demand and/or an increased Baquacil demand. Baquacil was shown to be amoebicidal under all but 1 of the conditions tested which simulated those likely to be encountered in swimming pools. Axenically and monoxenically cultured amoebae were used, and the latter exerted the greater Baquacil demand.
Studies in conventional batch culture confirmed that the maximum citric acid production rate occurred prior to exhaustion of the growth-limiting nutrient, i.e., when the growth rate was nonzero. The effects of dilution rate and the culture dissolved oxygen tension (DOT) were studied in chemostat culture. Maximum citric acid yield and production rate were observed at low dilution rate (0.017 h(-1)) and high DOT value (90% of saturation). These findings were applied to a nitrogen-limited fed batch culture, and allowed a productivity increase of 100% when compared with conventional batch culture.
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