Cavanagh, Mary Elizabeth; (2001) The utilisation of oil during streptomycete fermentations. Masters thesis (M.Phil), UCL (University College London).

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Abstract

Many industrial antibiotic fermentations use mixed substrates such as complex sugars and oils as sources of carbon. Oils are included because they may result in higher antibiotic titres and can be cheaper than the alternative refined sugar carbon sources. This study examines the effects of oil substrate utilisation in an antibiotic producing Streptomyces clavuligerus fermentation and illustrates the factors which influence the efficient utilisation of these oil substrates. Batch fermentations at 51 scale show both the utilisation of oil in the presence of other carbon sources and that the oil is degraded by the action of lipase. The use of a complex medium containing both oil and sugar appears to stimulate the rate of growth of the organism and also results in an increase in antibiotic titre. The lipase produced appears to be cell-associated and its expression is dependent on medium composition as well as the environmental conditions. For example, variation in the carbon and nitrogen sources leads to changes in the time of lipase expression and the amount of lipase produced whilst maximum activity is exhibited at 30°C and pH 7.2. The level of lipase activity was affected by the dissolved oxygen concentration and the agitation rate and was inactivated during the later stages of the fermentation. It was proposed that this was due to either the effect of shear or denaturation of the enzyme by the gas/liquid interface. At the end of the fermentation a residual amount of oil was found to be present. The composition of the residual oil was found to be similar to the oil added at the start of the fermentation. The study showed that metabolism of the oil ceased due to both the physical limitation of oil mass transfer in the fermenter environment as well as lipase inactivation. Increasing the agitation rate had a negligible effect with respect to oil utilisation as did increasing the dissolved oxygen concentration.

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