Phonprapai, Chanan; (2002) Effect of rapeseed oil on the nitrogen balance of laboratory and pilot-scale fermentation of Saccharopolyspora erythraea. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The aim of this project is to identify the crucial factors in fermentation culture, which should enhance the understanding of the relationship between the organism and the engineering environment, and reduce process variability through an effective control. An investigation of feeding strategies for oil in a fermentation process, in order to bring about improvements in the flux to antibiotic production, is also included. Saccharopolyspora erythraea strain NRRL 2338 and CA 340 were used throughout this study, where strain CA 340 has performed the major part. Different ingredients for oil based and non-oil based media in baffled flask experiments were used to identify the most suitable medium for enhancing growth, enzyme activity, and antibiotic production, where the presence of trace elements was also taken into account. This study further investigated the effect of using dextrin and sucrose as the source of carbohydrate. An influence of nitrate on culture growth and the presence of ammonium ion in fermentation medium, were also studied. In addition, the 20 L pilot scale fermentation was used to investigate an effect of the scale upon an improvement in the biomass and the product formation. Three identical batch fermentation were done, for identifying growth, product and residual oil profiles. To extend growth and maintain antibiotic titres at the achievable level, residual oil utilisation rate was calculated and used as an initial feeding rate for fed- batch fermentation studies, which four different constant feeding rates (low, low-to-high, medium, and high), were applied. Furthermore, seven off-line analysis were done throughout this study. They were the measurements of biomass concentration (w/v), lipase activity, amylase activity, ammonium ion concentration, nitrate ion concentration, residual oil concentration, and antibiotic concentration. An on-line gas analysis has also been used to observe a respiratory stage of the culture. In summary, the results from the fermentation revealed that the environment, built up from rapeseed oil, dextrin and soybean flour, gave the high biomass (w/v) and product titres. The fermentation quickly consumes nitrate added either at the start of the fermentation or during the growth phase, but the overall nitrogen balance suggests that it is later released as ammonia along with any other nitrogen not required for growth, including that present in the soybean flour. Increased levels of rapeseed oil suppress the production of ammonia as do other carbon sources such as sucrose or dextrin. This suggests that the standard medium used for these fermentations is carbon limited. These conditions were further studied at the pilot scale. A switch in the rapeseed oil feed from a low to a high rate during a batch fed fermentation increases product titres and specific productivity. Furthermore, with this feeding condition the amount of rapeseed oil remained at the low level throughout the fermentation. This study confirms that the ability to identify the factors which affect the cell behaviour under a particular engineering environment are essential for the enhancement of bioprocesses.

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