A range of fungi have been investigated for their ability to hydrolyse glycocholic acid to yield cholic acid. Using thin-layer chromatography the majority of fungi tested have been shown to possess this ability. In the case of Cocbliobolus intermedius IMI 52980 the product of hydrolysis has been isolated and characterised as cholic acid. The same organism has been demonstrated to grow using glycocholic acid as the sole source of carbon and nitrogen.
The chemical hydrolysis of the carbon-nitrogen bond in bile acid conjugates occurs only under drastic alkaline conditions. Also, it has been reported that this bond can withstand cleavage by many proteolytic enzymes (Nair et al., 1967). However, many workers have demonstrated that hydrolysis to yield the free bile acid and amino acid can be effected by intestinal bacteria, and this subject has been recently reviewed by both Hayakawa (1973) and Midtvedt (1974). In most cases, however, the hydrolysis occurs only under anaerobic conditions and the work of Yesair and Himmelfarb (1970) appears to be an isolated report of hydrolysis being performed by aerobically growing bacterial cultures. Furthermore, there are no reports with regard to the ability of fungi to hydrolyse bile acid conjugates. Thus, the purpose of the present work was to investigate whether fungi are capable of performing this hydrolysis.
Materials and Methods
Organisms. All fungi were maintained on slopes of Potato Dextrose Agar (Oxoid, Ltd.) and subcultured every 4 weeks.
Cbemicals. Glycocholic acid was prepared by the method of Norman (1955). Authentic cholic acid, obtained from New Zealand Pharmaceuticals Ltd. (Palmerston North, New Zealand) was recrystallised from methanol and dried at 120oc in vacuo for 4 h.
Cultivation. Screening experiments were performed using a medium containing sucrose (20g/l), bacteriological peptone (Sg/1), MgSO 4 (0.25 g/l), K2HPO 4 (0.25 g/l), and trace