Acclimation of Isochrysis galbana Parke (Isochrysidaceae) for enhancing its tolerance and biodegradation to high-level phenol in seawater

Marine microalgae with high removal efficiency of phenol are needed for the remediation of polluted seawater in cases involving phenol spills. To achieve this purpose, adaptive laboratory evolution (ALE) was performed by a microalga Isochrysis galbana Parke MACC/H59, which is capable of degrading phenol at concentrations of less than 100 mg L−1 in 4 d. Two acclimation conditions were used: (i) 90 d at 100 mg L−1 phenol, and (ii) 90 d at 100 mg L−1 phenol followed by another 90 d at 200 mg L−1 phenol. By doing so, two strains (PAS-1 and PAS-2) could be obtained respectively. They grew rapidly at phenol concentrations up to 200 mg L−1 and 300 mg L−1, respectively, with a specific growth rate 2.52–3.40 times and 1.93–3.23 times that of the control (without phenol). Also, both strains had a higher removal capacity of phenol than the unacclimated alga. Phenol at an initial concentration of 200 mg L−1 was completely removed in 5 d thereby. For 300 mg L−1 phenol, a removal efficiency of 92% was achieved in 10 days by using PAS-2, with a removal rate constant of 30.01 d−1 (about twice that of PAS-1) and a half-life of 4.90 d (about half that of PAS-1), showing that a better strain may be obtained by extending the acclimation time. The enhancement of phenol biodegradation can be explained by the elevated activity of phenol hydroxylase (PH) in both strains. These results indicated that ALE could be an efficient tool used to enhance the tolerance and biodegradation of marine microalgae to phenol in seawater.