Effect of growth conditions on the production of manganese peroxidase by three strains of Bjerkandera adusta

We were looking for a strain of Bjerkandera adusta that produces high titres of manganese peroxidase under optimal conditions for large-scale enzyme purification. We have chosen two strains from the University of Alberta Microfungus Collection and Herbarium, UAMH 7308 and 8258, and compared the effects of growth conditions and medium composition on enzyme production with the well-characterized strain BOS55 (ATCC 90940). Of four types of cereal bran examined, rice bran at 3% (w/v) in 60 mM phosphate buffer pH 6 supported the highest levels of enzyme production. Using 100 mL medium in 500-mL Erlenmeyer flasks, maximum enzyme levels in the culture supernatant occurred after about 10 days of growth; 5.5 U·mL–1 for UAMH 7308, 4.4 U·mL–1 for UAMH 8258, and 1.7 U·mL–1 for BOS55, where units are expressed as micromoles of Mn-malonate formed per minute. Growth as submerged cultures in 10-L stirred tank reactors produced 3.5 U·mL–1 of manganese peroxidase (MnP) by UAMH 8258 and 2.5 U·mL–1 of MnP by 7308, while enzyme production by BOS55 was not successful in stirred tank reactors but could be scaled up in 2-L shake flasks containing 400 mL rice bran or glucose – malt – yeast extract (GMY) – Mn-glycolate medium to produce MnP levels of 1.7 U·mL–1. These results show that the two strains of B. adusta, UAMH 7308 and 8258, can produce between two and three times the manganese peroxidase level of B. adusta BOS55, that they are good candidates for scale up of enzyme production, and that the rice bran medium supports higher levels of enzyme production than most previously described media.Key words: growth conditions, cereal bran, manganese peroxidase, Bjerkandera adusta, white rot fungi.