Peacock, Lynn Miranda; (1997) Lipid metabolism in Streptomyces lividans TK24. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Oils and lipids are used as carbon sources and media supplements in a number of industrial antibiotic fermentations. This is both for economic reasons and because higher cell biomass and improved antibiotic titres often occur. This research aims to elucidate fatty acid metabolism in antibiotic-producing Streptomyces, using Streptomyces lividans as a model. S. lividans was grown on defined media with lipids as sole carbon sources or as co-substrates with other, simpler, carbohydrate compounds. Free fatty acids were toxic in many cases but triacylglycerols (TAG) aided growth if provided in conjunction with glucose or dextrin. TAG produced lower growth rates than cells grown solely with glucose. TAG and other fatty acid-containing substrates promoted actinorhodin production, an antibiotic-related pigment. S. lividans repressed fatty acid synthesis in the presence of TAG and incorporated externally provided fatty acids into cellular lipids. Lipids also affected cell morphology. The addition of TAG to defined media in a 20 L fermentation caused a decrease in size of the filamentous aggregates usually formed. The enzymes involved in lipid metabolism were also studied. Lipase production was investigated in shake flask and 20 L fermentations; activity reached a peak in the rapid growth phase, followed by a decline in stationary phase. This pattern of activity was mirrored by that of the β-oxidation enzymes, which are responsible for internal fatty acid metabolism. Expression of the β-oxidation enzymes only occurred in the presence of fatty acid-containing compounds, and was repressed in cells that were also supplied with glucose. The activities of the individual enzymes of the β-oxidation pathway have also been determined, and the assays used modified to maximise the activity seen in the S. lividans cell-free extract. The enzymes were subject to a small-scale protein purification, where a probable multienzyme complex containing enoyl-CoA hydratase, 3-hydroxyacyl- CoA dehydrogenase and 3-ketoacyl-CoA thiolase activities was identified. Activity of an acyl-CoA dehydrogenase was also isolated in the process. Fatty acid β-oxidation in cell- free systems of S. lividans has now been greatly clarified.

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