The effect of process variables on lipid utilisation in the fermentation of Streptomyces clavuligerus
Many industrial fermentations use complex medium containing both carbohydrate and oils as their carbon sources. Oil supplements have been shown to increase the antibiotic titre and are a cheaper alternative carbon source, in terms of carbon per unit volume, when compared to carbohydrates. Oil supplements are also preferred on an energy supply basis and have natural antifoam properties. The major disadvantage to the use of oils in process media is the level of oil remaining at the end of the fermentation. Research has been undertaken to examine the effects of process variables on lipid utilisation and residual oil levels in 5 litre batch fermentations of Streptomyces clavuligerus. The project illustrates the way in which both the chemical environment, media composition and method of pH control, and the physical environment, such as agitation rate and particle size, may influence growth, lipase activity, lipid utilisation and secondary metabolite production. Changes in carbon source influenced growth and productivity. Addition of rapeseed oil increased final product titres by approximately 900%. The type and concentration of the nitrogen source was found to influence maximum lipase activity and initial oil utilisation rates. Media composition and pH control experiments had little effect on residual oil levels. A gas chromatography method was developed in order to analyse the changes in the composition of oil during fermentation. Derivatisation of the fatty acids by methylation was successful and revealed that the composition of residual oil was similar to that of the initial rapeseed oil added. There was no indicated specificity in the utilisation of any individual fatty acids of rapeseed oil. Increasing tip speed in the fermentation process from 1 .88m s^[-1] to 2.83 m s^[-1] increased maximum biomass levels, decreased lipase activity and did not affect clavulanic acid production. A tip speed of 3.77m s^[-1] was detrimental to growth, increasing hyphal fragmentation, and decreased lipase activity. Increasing constant tip speed did not reduce residual oil levels. Antibiotic titres were relatively unaffected by changes in tip speed. Addition of a surfactant to the complex medium, in order to facilitate oil droplet breakage and hence increase oil utilisation, was investigated. Addition of the surfactant decreased residual oil levels with an observed increase in final clavulanic acid titres. This research has shown the effect of some chemical and physical parameters on lipid utilisation and clavulanic acid production in the 5 litre batch fermentation of S. clavuligerus. Lipid utilisation could not be enhanced by increasing lipase activity or varying media composition and agitation rates. Addition of surfactant to the process media significantly reduced residual oil levels. This approach may have potential as a generic method of reducing residual oil levels and enhancing secondary metabolite titres in industrial processes using lipid based medium.