A novel application for Neurospora crassa: Progress from batch culture to a membrane bioreactor for the bioremediation of phenols

Abstract

The capacity of a Neurospora crassa fungal system to produce oxidative enzymes, and their application in the biodegradation of phenolic compounds, was demonstrated in static and shaken non-immobilized batch cultures, and by capillary membrane-immobilized biofilms. Extracellular laccase activity was produced at 10–12 U/mL (800 U/g wet mass) in static flask cultures, and 1.5 U/mL (130 U/g wet mass) in shaken batch cultures, respectively, over 8–15 days. Polyphenol oxidase was shown to be produced as an intracellular enzyme, at levels of 374 U/g wet mass. The production of laccase in a capillary membrane bioreactor was sustained at a level of 10 U/mL of permeate (1080 U/g wet biomass), typically over 30–40 days. Two phenolic substrates, phenol and p-cresol, both common components of industrial effluent streams, were chosen as model pollutants for bioremediation studies using the N.crassa enzyme system. In flask cultures, 18 mg p-cresol and 23 mg phenol respectively were removed from 5 mM solutions/g wet biomass, over a 6 day period. Over the same time period, immobilized cultures were found to convert 10 mg p-cresol or 8 mg phenol/g biomass. The immobilized biomass in a continuous reactor was found to have the capacity to sustain this removal efficiency continuously for a 4-month period, whereas the batch liquid culture systems remained active for approximately 8–15 days, after which cultures were no longer viable. This is the first demonstration of the use of immobilized N.crassa biofilms and their continuous application for bioremediation of phenols.