Low concentrations of polycyclic aromatic hydrocarbons promote the growth of Microcystis aeruginosa.

There is an increasing need to describe the growth characteristics of cyanobacteria exposed to polycyclic aromatic hydrocarbons (PAHs) because the presence of PAHs in lakes is known to affect the growth of this kind of microorganisms. In this work, the effects of low concentrations of PAHs on Microcystis aeruginosa (M. aeruginosa) were investigated. M. aeruginosa were cultivated in the medium with a mixture of PAHs (0.486 mg L(-1) naphthalene, 0.049 mg L(-1) phenanthrene, and 0.0015 mg L(-1) pyrene) and different concentrations of nitrogen and phosphorus. During 31 d of incubation, profiles of cell number and chlorophyll-a content were determined. The results indicated that when the concentration of an individual PAH was below its no observed effect concentration (NOEC), the exposure of M. aeruginosa to a mixture of PAHs markedly promoted cell density after 7d of culture. Low concentrations of nutrients in the medium improved the growth of M. aeruginosa in the presence of PAHs. When concentrations of both phosphorus and nitrogen were 50% lower than those of the control, the specific growth rate of M. aeruginosa increased by 100% when exposed to PAHs, and the generation time decreased from 10.5 to 5.3d. The chlorophyll-a content in medium also increased from 2.23 to 3.18 μg mL(-1), which was attributed to an increase in cell numbers.