الفهرس يوجد فقط 14 صفحة متاحة للعرض العام
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المستخلص
Ultraviolet-light mutagenesis had been used in the induction of cephalosporin C (CPC) production in Cephalosporium acremonium ATCC ١١٥٥٠. Selection of high antibiotic-producers among the mutants was carried out by agar diffusion method using Bacillus subtilis ATCC ٦٦٣٣, and then final selection of the highest CPC producing mutant was carried out in shake flasks in which it produced ٩٠٠ mg/L. The isolated mutant (M١٠٤) produced about ٦٤ mg/L in a fed batch process with soybean oil in NBS stirred-tank bioreactor (working volume ٤L), which was a very low concentration compared to that obtained previously in shake flasks. This low CPC level may have been due to the low dissolved oxygen level that was observed during this fermentation and could be explained by the high biomass concentration in the culture that inhibited dissolution of oxygen in the culture broth. Cephalosporin C production showed a fluctuation with an upper value of ٦٤ mg/L at ١١٧ hours. The fluctuation in CPC production may have been related to the soybean oil feeding regimen, which was tested in the following experiment. This experiment, which was carried out in shake flasks, pointed out that soybean oil presence increased the cephalosporin C production, but it should be below ١٠٪ of the medium volume either added initially or later on during the fermentation time. CPC production was repressed similarly in absence of soybean oil (٢١٩ mg/L) and in excess oil concentration (٢١١٫٣ mg/L), as excess oil concentration impair oxygen transfer to the medium interfering with CPC production. In the last experiment, the mutant M ١٠٤ produced ٢١٦٠ mg/L CPC in a batch process in NBS stirred-tank bioreactor (working volume ٤L). Soybean oil was not added in this fermentation experiment. The fermentation and sugar assimilation behavior of the strain M١٠٤ have been investigated. It has been observed that adequate aeration is critically important to supply oxygen that is necessary for antibiotic biosynthesis. The diauxic phenomenon has been observed in this fermentation process in which a mixture of an easily metabolized sugar (glucose) with another more difficult to be assimilated (sucrose) is used to build up the antibiotic-producing biomass (by glucose) and to make the fungus attain the physiological state of antibiotic production (by sucrose). The maximum CPC concentration was obtained at ٩٦ hours of fermentation time, the maximum specific productivity was ١٨٦ mg CPC/g dry weight at ١٣٦ hours, and the maximum rate of CPC production was ٣١ mg/L.hr at ٦٤ hours.