Studies on production of gentamicin from Micromonosporas purpurea using crude vegetable oils
Crude vegetable oils and natural nitrogen sources were investigated to evaluate their potential as energy sources for the efficient production of gentamicin from Micromonosporas purpurea. Of the various crude vegetable oils, soybean oil was found to be the most suitable carbon source for efficient gentamicin production. An initial concentration of 40 g/l gave the highest gentamicin concentration and lipase activity, at 0.75 g/l and 298.1 U/ml, respectively. However, with more than 60 g/l oil, both of these values deceased. When 0.4 g/l of linoleic acid was added to the culture broth, the maximum gentamicin concentration was 0.82 g/l, which was about 3.0-fold higher than that obtained without the addition of linoleic acid. Soybean meal and corn steep liquor (CSL) appeared to be the most important nitrogen sources for the production of gentamicin. Especially, with a mixture of 15 g/l soybean meal and 15 g/l CSL, the gentamicin production was higher than with the use of a sole nitrogen source. The oil consumption increased with increasing agitation rate of the jar fermentor. However, the maximum gentamicin concentration of 1.45 g/l was achieved after 5 days in the culture agitated at 400 rpm.Using these basic results, fed-batch cultures were performed for 8 days in a jar fermentor. When soybean oil was used, the extracellular protease activity was 920.5 U/ml, which was 3.6-fold higher than that of the glucose medium. The maximum gentamicin concentration was 3.5 g/l, which was about 4.9-fold higher than that of the glucose medium. The product yield of the consumed soybean oil was about 12.8-fold higher than that of the glucose medium.
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