グリーンアジアのための国際資源人材育成戦略

[PY-06] Effect of culture pH on enzyme release by Phanerocheate chrysosporium for pretreatment of refractory carbonaceous gold ores

^○トワム コナドゥ コージョ¹, 笹木圭子¹, オセオアサレ クワドウォ² (1.九州大学大学院　工学研究院, 2.ペンシルバニア州立大学)

Keywords:Gold、Enzyme、Carbonaceous

Phanerocheate chrysosporium is one of the well investigated white rod fungi because of its ability to degrade complex aromatic hydrocarbons. It accomplishes the degradation of these substances through the secretion of oxidative enzymes such as lignin peroxidase (LiP), manganese peroxidase (MnP) and laccase. Thus improving the enzyme production is essential and while this has been shown to be affected by several factors, one of the least studied the stress induced by culture pH on the fungus. This study aimed to determine the effect of the culture pH on enzyme secretion and also decrease the growth period necessary for optimum production. Our findings illustrated that the culture medium pH affected P. chrysosporium in two ways; 1) pH 2.0-3.0, there was a high enzyme release but underdeveloped fungal growth and 2) pH 4.0-5.0 which had lower enzyme release and enhanced fungal growth. Furthermore, the strongly acidic medium at pH 2.0-3.0 began producing both MnP and LiP immediately while the weakly acidic medium at pH 4.0-5.0 showed a 4-5 day-lag period before LiP was detected. It indicated that increasing the acidity of the culture medium may have caused the inactivation of the cell wall proteins necessary for fungal growth and thus triggering the release of a substantive amount of oxidative enzymes as a survival mechanism. Finally, at pH 2.0 where fungal growth was severely stunted, the carbon and nitrogen sources had a limited effect on enzyme production. This led to the realization that the stress response of the fungus was induced by the pH and trace metals in culture medium. These findings will hopefully contribute to improving the yield of the relevant enzymes secreted by P. chrysosporium and also its applicability for industrial operations especially in the pretreatment of refractory carbonaceous gold ores.（企画講演で発表）