Tantipaibulvut, Sukon; (2004) The effect of surfactant on oil uptake and erythromycin production by Saccharopolyspora erythraea. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Vegetable oils have been used as carbon sources in many fermentations to improve the antibiotic titres. However, some oil still remains at the end of the process. This study investigates how oil consumption can be increased in the production of erythromycin by Saccharopolyspora erythraea CA 340 grown on rapeseed oil. Two methods have been carried out. The first was the effect of the application of either sulphuric or phosphoric acid in the pH control. The second was the inclusion of surfactant either Disponil SMO 100 (DPN) or sodium dodecyl sulphate (SDS) in the production medium. For the effect of pH-control agent, which was studied in 2-L fermenter only, the oil consumption of the culture using phosphoric acid was higher than that using sulphuric acid while the lipase activity after 96 hr was lower. In addition, the yield of erythromycin A was also lower but not the total erythromycin. The DNA content (as a measure of biomass) was also the same. Besides that the oxygen uptake rate (OUR) and the carbon dioxide evolution rate (CER) of these cultures were also similar. However, there was a sharp drop in DOT profile after it reached 55% in the culture using sulphuric acid, which was not seen in that using phosphoric acid. For the effect of surfactant, the study was carried out in both a 2-L fermenter and shake flasks (500-ml and 2-L). In the 2-L fermenter, it appeared that Disponil at the concentration of 1.58 or 3.33 g per 29.9 g oil increased the oil uptake of this organism. The residual oil profile was 2-5 g/L lower with the earlier decrease (24 hr earlier) over a period of 168 hr. On the other hand, the DNA content was slightly higher. The OUR and CER profile also reached the maximum earlier, especially that of DPN 3.33. This surfactant also increased the rate of erythromycin synthesis before 96 hr. However, the total erythromycin concentration was lower while that of erythromycin A was similar. In contrast, SDS at 0.075% delayed the oil consumption of this culture and more residual oil remained at the end of the fermentations. It also inhibited the growth (lower contents of DNA). The OUR and CER profile in this culture was also lower than the controls. Even though the volumetric total erythromycin of this culture was lower than the controls, the yield of erythromycin per unit of consumed oil was similar while that of DPN-containing cultures was lower. There was no direct effect of DPN against the enzyme lipase when it was added in the assayed mixture and tested with either 48-hr or 96-hr culture. However, when the fermentation was carried out in 500-ml or 2-L shake flasks, none of the concentrations studied (0.1% to 1.0% (w/v)) increased the oil uptake of this organism during the 144 hr fermentation. The differences between the fixed fermenter and the shake flask fermentation are probably caused by changes in mixing and aeration. The lipase production was reduced in medium containing Disponil at concentration higher than 0.5% (w/v). The effect of the anionic surfactant, sodium dodecyl sulphate (SDS), was also investigated.

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