Effects of caffeine on growth and metabolite production of Cordyceps militaris

Abstract

This study was aimed to address the caffeine response of Cordyceps militaris, an entomopathogenic fungi, on growth, development, metabolite production, and caffeine modification. Our results demonstrated that caffeine showed a dosage effect on growth, development, and adenosine production of C. militaris. Without caffeine, the mycelial growth rate of the control was 0.42 ± 0.02 cm/day, but at concentrations of 0, 1 and 10 mM, caffeine inhibited the mycelial growth of C. militaris with reduced growth rates of 0.37 ± 0.01 and 0.27 ± 0.01 cm/day, respectively; and the number of conidia was also reduced by 23% and 77%, respectively. Caffeine also affected the fungal metabolite production by increasing the extracellular adenosine productivity 5-fold (from 4.34 ± 0.60 µg/g/day to 24.28 ± 0.65 µg/g/day), but there was no change in the cordycepin production (p < 0.05). Interestingly, this fungus could metabolize caffeine, resulting in an accumulation of its derivatives, including theophylline (55.23 ± 2.18 µg/ml), theobromine (16.95 ± 0.97 µg/ml), and paraxanthine (12.88 ± 1.22 µg/ml). The findings provided a new understanding of how caffeine affects the growth of C. militaris. The information could be useful for the production of bioactive compounds of either adenosine or caffeine derivatives.