High potential of thermotolerant Candida tropicalis no. 10 for high concentration of phenol biodegradation

Abstract

A thermotolerant Candida tropicalis strain No. 10 was isolated from a chemical contaminated soil sample. The strain was capable of degrading 100 mg/L phenol completely from 20-42°C, a wider temperature range than those previously reported in yeasts. It could also completely degrade phenol at an initial concentration up to 1,000 mg/L in a minimum mineral salt medium. The optimum temperature and initial pH were 35°C and 8, respectively. Phenol degradation was inhibited when oxygen in the medium was gradually decreased. Most tested sugars such as fructose, galactose, glucose, maltose, mannose, sorbitol and sucrose of 10 mM concentration, inhibited phenol degradation completely, whereas most organic acids; citric, lactic and succinic acids of 10 mM concentration, showed no effect. At the level above 0.31 mM glucose, phenol removal decreased in an opposite direction of glucose. Metal ions such as Co2+, Cu2+ and Ni2+ showed strong inhibition to phenol degradation whereas Zn2+ showed slightly inhibition. The strain metabolized phenol via catechol ortho-clevage pathway and the catechol 1,2-dioxygenase specific activity was comparable to other Candida spp.