To obtain a sustainable mutant of the medicinal mushroom Cordyceps militaris with a higher cordycepin production, high-energy ion beam irradiation was applied in the present study. Upon successful irradiation by a proton beam, 30 classes of 8-azaadenine and 28 classes of 8-azaaguanine resistant mutants were obtained of which 7 classes (A63-7, A63-8, A81-2, A81-6, G63-8, G81-3, G82-4) were selected as initially promising mutants using their antibacterial ability as an index of cordycepin production. Among these mutants, G81-3 had the highest cordycepin production of 6.84 g/l using optimized conditions compared to that of the control of 2.45 g/l (2.79 times higher). In addition, to explore the influences of different additives on the cordycepin production using the above mutant in a surface liquid culture, adenosine and glycine were used as additives. In the culture medium under the previously optimized conditions for the said mutant, 2, 4, 6, 8 and 10 g/l adenosine were separately added. These results revealed the highest cordycepin production of 8.57 g/l when using 6 g/l adenosine was 28.10% higher than that of the control (6.69 g/l). This is a highest report of cordycepin production until now. Similarly, the results of other concentrations also superseded the control. The time course of glucose showed that the glucose consumption for the 4 g/l adenosine was the fastest, while that of 10g/l was the slowest with the longest culture time among all the treatments. For the same purpose,
glycine was used with yeast extract in weight percent ratios (yeast extract/glycine) of 40/60, 50/50, 60/40, 70/30, 80/20 and 90/10 under the condition that the total amount of glycine and yeast extract were fixed. Also, the glycine was separately added as 10, 20 and 30 weight percent of yeast extract in the culture medium having the same optimized conditions with a fixed yeast extract concentration. These
results showed that the 90/10 ratio had the best cordycepin production of 6.80 g/l that was 12.40% higher versus the control (6.05 g/l). The cordycepin production of the 70/30 and 80/20 weight percent
ratios were also higher than that of the control, while the others had a lower cordycepin production compared to that of the control; especially the cordycepin production with the 10, 20 and 30 weight percent yeast extracts inversely decreased in accordance with the used glycine concentration. Regarding the time course, the glucose consumption for the 40/60 weight percent ratio of yeast extract was the fastest, while that of the 30 weight percent was the slowest with the longest culture time among all the treatments. These results suggested that both the ion beam irradiation and additives had active influences on the cordycepin production and that adenosine had a much better influence than that of glycine. It was also evident that a higher concentration of both adenosine and glycine negatively affected the cordycepin production.
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