Osborne, Matthew David; (2001) Oil utilisation in oxytetracycline fermentation by Streptomyces rimosus. Doctoral thesis (Ph.D), UCL (University College London).

Preview

Text Oil_utilisation_in_oxytetracyc.pdf Download (18MB) | Preview

Abstract

Many commercial bioprocesses use complex media, containing lipid oil as either their sole carbon source or with a carbohydrate supplement. Compared to carbohydrates, oils have been shown to stimulate antibiotic productivity and provide a more cost effective means of supplying carbon, when assessed on a carbon per unit volume basis. Oil also has technical advantages, such as facilitating more concentrated feed addition (gram atoms of carbon per unit volume) and antifoam properties. The major disadvantage of oils, however is the sometimes inordinate residual concentration at the end of the process, which can interfere with efficient down-stream processing. In this project, research has been undertaken to examine factors affecting lipid utilisation and final residual oil concentration in 5 and 7 L fed batch fermentation of two industrial, mutant strains of Streptomyces rimosus. One strain, M38182, had been subjected to significantly more cycles of mutation and selection than the other (M4018) and was the current production strain when the project was initiated. This project provided an opportunity to study the influence of physical bioreactor conditions on secondary metabolite production and lipid assimilation of highly mutated commercial strains. On initially comparing the two strains, in addition to much greater OTC titres in M38182 than M4018 processes it was apparent that the final residual oil concentration differed considerably. The M38182 strain had an unmetabolised residual oil concentration of 18 gL-1, over double that of the M4018 strain. M38182 also attained a considerably higher broth viscosity than M4018. However, in experiments conducted to investigate the effect of broth viscosity on oil utilisation it was found that the final residual oil concentration was independent of viscosity. Staining of the oil fed to the process was used in order to visualise oil within the broth. Image analysis indicated oil mainly existed as discrete droplets and that freshly fed and residual oil showed little interaction. The droplets were also considerably smaller (5 to 30 μm) than the terminal eddy size (400 to 600 μm) in the broth. This suggested that the oil droplets behaved as rigid spheres, and that their diameter was not determined by the turbulent flow field alone. Droplet size was predicted reasonably well when a correlation based on the phase properties of the liquids was used (mean value of approximately 60 μm), indicating that interfacial tension was important in determining droplet size. Feeding of the oil in the form of a microemulsion decreased the oil droplet diameter to 300 nm. This increased oil utilisation, which in turn decreased residual oil concentrations in processes of both strains. This indicated that a reduction in oil droplet size facilitated oil utilisation. The fmal residual oil in the M38182 strain was however still considerably higher than that in the M4018 strain. It is suggested that this could have been due to differences in cell surface properties or lipase specificity of the M38182 strain. The results presented here improve our understanding of the factors involved in oil utilisation and indicate potential strategies for improving residual oil utilisation, and therefore decreasing the level of residual oil remaining unmetabolised. This should decrease the costs of secondary metabolite production by improving downstream processing and reducing raw material requirement.

Download activity - last month

Export as XMLJSONCSV

Download activity - last 12 months

Export as CSVXMLJSON

Downloads by country - last 12 months

Export as CSVJSONXML

Archive Staff Only

View Item