Biodegradation of phenol by Isochrysis galbana screened from eight species of marine microalgae: growth kinetic models, enzyme analysis and biodegradation pathway

Abstract

Isochrysis galbana MACC/H59 was screened from eight strains of marine microalgae to investigate its capability for phenol biodegradation. Batch incubation experiments were performed for 25 to 200 mg L−1 initial phenol concentrations. Five growth inhibitory kinetic models were used to fit the experimental data. The specific activities of phenol hydroxylase and catechol dioxygenase in I. galbana are measured. The results showed that phenol, at concentrations of less than 100 mg L−1, could be completely degraded in 4 days. The growth kinetics of I. galbana under different phenol concentrations were best fitted with a Yano model among five kinetics models tested. The values of substrate inhibition constant (117.59 mg L−1), limiting substrate concentration (183.90 mg L−1) and optimal substrate concentration (81.46 mg L−1) for phenol biodegradation of I. galbana were also obtained with the Yano model. The phenol biodegradation in I. galbana was mainly catalysed by intracellular enzymes. The ortho-pathway is significantly predominant over the meta-pathway in phenol metabolism in I. galbana. High concentrations of phenol significantly inhibited the activity of phenol hydroxylase, but had no obvious effect on catechol dioxygenase. Isochrysis galbana may be a suitable marine microalgal species for use in environmental restoration operations after accidental spills of phenol at sea.