Phenanthrene and pyrene disturbed the growth of Microcystis aeruginosa as co-cultured with Chlorella pyrenoidosa.

Significant levels of polycyclic aromatic hydrocarbons (PAHs) were detected in lakes. The competition between algae would be disturbed by PAHs resulted in variations of algal growth. For controlling the cyanobacterial blooms, it is important to understand this disturbed competition between Microcystis aeruginosa and other algae. A 6-day cultivation experiment was designed to investigate the responses of M. aeruginosa to PAHs in presence of green algae. A popular green alga Chlorella pyrenoidosa was used as a representative of green algae, and phenanthrene and pyrene were selected as representatives of PAHs. The results showed that M. aeruginosa outcompeted C. pyrenoidosa under PAH contamination, and PAHs and M. aeruginosa significantly inhibited the survival of C. pyrenoidosa. PAHs disturbed the growth of algae by influencing photosynthetic pigments and phycobiliproteins, and the different alteration of Fv/Fm ratios implied that shifted algal community composition would be induced by PAHs. The Fv/Fm of the two algal mixture and individual C. pyrenoidosa was significantly negatively correlated with phenanthrene levels. However, there were no significant correlations between the Fv/Fm of M. aeruginosa and the exposure levels of phenanthrene or pyrene. Remarkably, the Fv/Fm significantly increased in M. aeruginosa at 0.15 mg L-1 pyrene, suggesting that PSII resistance to pyrene was enhanced in M. aeruginosa. Our results pointed out an increasing frequency and intensity of cyanobacterial blooms could be induced by PAHs in contaminated waters.

PAHs would alter cyanobacterial blooms by affecting the microcystin production and physiological characteristics of Microcystis aeruginosa.

The wide presence of polycyclic aromatic hydrocarbons (PAHs) in lakes necessitates a better understanding of cyanobacteria metabolites under the contamination of PAHs. The M. aeruginosa strain PCC7806 was selected to investigate the effects of naphthalene and pyrene on the physiological and biochemical reactions of cyanobacteria, including antioxidant defense system (superoxide dismutase, catalase), intracellular microcystin (MC) content, phycobiliprotein (phycocyanin, allophycocyanin) contents, and specific growth rate. Naphthalene and pyrene altered the growth of the M. aeruginosa strain, reduced the contents of phycocyanin and allophycocyanin, and stimulated the activities of antioxidant enzymes without lipid peroxidation. Remarkably, the intracellular MC content was significantly increased by 68.1% upon exposure of M. aeruginosa to 0.45 mg L-1 naphthalene, and increased by 51.5% and 77.9% upon exposure of M. aeruginosa to 0.45 mg L-1 pyrene and 1.35 mg L-1 pyrene, respectively (P＜0.05). Moreover, significant correlations were observed between these physiological reactions, referring that a series of physiological and biochemical reactions in M. aeruginosa worked together against the PAH contamination. Considering that MCs are the most studied cyanobacterial toxins, our results clarified that the promoting MC production by PAH contamination cannot be neglected when making related risk assessments of eutrophic waters.