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Current Trends in Biotechnology and Pharmacy Vol. 5 (3) 1282-1297 July 2011, ISSN 0973-8916 (Print), 2230-7303 (Online) 1289 The performance of a microbial culture can be strongly influenced by the type of the inoculum as shown in Fig. 2. Thus, the age and size of the inoculum should be optimized to improve the performance of the fermentation process. Our results showed that maximum inhibition zone, corresponding to maximum anticandidal activity, was observed at inoculum age 48-72 hrs, while both the biomass yield remained unaffected. On the other hand, the cell growth increased by increasing the inoculum size, increase in anticandidal activity was not observed on using more than 2 ml inoculum/50 ml production medium. The anticandidal activity production (Fig.3A) seems to be no way correlated to the biomass yield. Starch showed maximum inhibition zone, whereas maximum growth was produced by maltose. Minimum inhibition zone was produced by fructose while minimum biomass was recorded by sucrose. These findings were in agreement with the fact that secondary metabolite production in actinomycetes is often stimulated by slowly assimilated complex carbohydrates or oils in the production media, while it decreased when more rapidly utilized monosaccharide such as glucose were present (30). A possible explanation of this phenomenon Fig. 2. The growth and anticandidal activity as affected by N.luteus inoculum Fig. 3. Role of carbon nutrition on the growth and anticandidal activities of N.luteus A. Effect of carbon source B. Effect of starch concentration El-Refai et al
Current Trends in Biotechnology and Pharmacy Vol. 5 (3) 1282-1297 July 2011, ISSN 0973-8916 (Print), 2230-7303 (Online) 1290 is that glucose or other simple carbon sources cause catabolite repression in which the production of an enzyme of secondary metabolite biosynthesis is inhibited. The growth profile and antibacterial biosynthesis by the tested organism was not only affected by the nature of the used carbon source, but also with its level. Results (Fig. 3B) showed that the activity increased with increasing the starch concentration till it reached a maximum of 30 mm at 10 gm/l after which it remained constant while the dry weight values kept increasing with increasing starch concentrations. Antibiotic production from alkaliphilic actinomycetes isolate A2D, identified as S. tanashiensis strain A2D, was higher in medium having glucose (1 %) as carbon source while highest biomass resulted on using 1.5 %(w/v) glucose concentration (31). However, maximum growth and antibiotic production by Streptomyces sp. 201, were obtained in medium supplemented with mannitol as a sole carbon source followed by sucrose and glycerol (32). Our results showed that organic nitrogen sources such as peptone, corn steep liquor and specially yeast extract were highly favorable for anticandidal activity although this doesn’t necessarily correlate to the growth of Nocardioides luteus, as shown in Fig. 4A. On the other hand, the tested inorganic nitrogen sources resulted in a decreased anticandidal production that also doesn’t correlate with growth. Maximum inhibition zone was observed on using yeast extract. Therefore, it was chosen as a sole nitrogen source instead of casein and KNO 3 in the proceeding work. The activity increased with increasing the nitrogen source concentration till it reached a maximum at the concentration 3.76 gm/l, then constant through the concentration 4 gm/l. Thereafter, it began to decrease. The dry weight increased gradually as well by increasing the yeast extract concentrations until reaching 4 gm/l, after which it started to decrease, Fig. 4B. The superiority of the organic nitrogen sources has been reported by many investigators (30-33). Fig. 4. Role of nitrogen nutrition on the growth and anticandidal activity of N.luteus A. Effect of nitrogen source B. Effect of nitrogen concentration Studies on the production of actinomycin by Nocardioides luteus
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(December 7-9, 2011) Venue: Karunya
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