Potential of the green microalga Chlorella vulgaris to fight against fluorene contamination: evaluation of antioxidant systems and identification of intermediate biodegradation compounds

Abstract

Polycyclic aromatic hydrocarbons (PAHs) have high risks for human and living organisms due to their mutagenic and carcinogenic properties. Here, the effect of different concentrations of fluorene as a persistent toxic PAH on growth parameters and antioxidant systems in the green microalga Chlorella vulgaris was investigated. Intriguingly, cell number as well as dry and fresh weight of the alga were raised at 2 ppm fluorene compared to the control sample. However, with the increasing levels of fluorene from 10 to 50 mg L−1, the growth parameters gradually decreased. Accordingly, cells of C. vulgaris were found to enhance the activity of ROS scavenging enzymes after 7 days of exposure to fluorene in a concentration-dependent manner. Exposure to 25 and 50 mg L−1 fluorene was led to a significant decrease at chlorophyll content, whereas the concentration of carotenoids was not changed. Total phenol and flavonoid contents were markedly raised in 50 mg L−1 of fluorene compared to the control. Although flow cytometry assessment showed no substantial reduction in the viability at 50 mg L−1 fluorene-treated samples for 24 h, chlorophyll fluorescence was noticeably reduced. The results of SEM analysis revealed that the 50 mg L−1 fluorene treatment clearly damaged the algal cells after 24 h. The ability of the alga for biodegradation of fluorene was assessed by GC-MS. Consequently, a number of produced intermediate compounds were identified. These findings displayed that C. vulgaris had not only notable resistance against fluorene but also noteworthy potential for its degradation.