Concentration-dependent stimulatory and inhibitory effects of β-cyclocitral, longifolene, and β-ionone on Microcystis aeruginosa.

Cyanobacterial volatile organic compounds (VOCs) are well-known allelochemicals that inhibit competitors, but their specific roles within the emitting populations remain poorly understood. To uncover the effects of cyanobacterial VOCs on themselves, we investigated the cell growth, photosynthetic characteristics and gene expression in Microcystis aeruginosa in exposure to three main cyanobacterial VOCs (β-cyclocitral, longifolene, and β-ionone) under environment-relevant concentration (0.03-0.12 mM). M. aeruginosa growth was inhibited by 0.12 mM longifolene and 0.09 and 0.12 mM β-ionone, but promoted by other treatments (except of 0.12 mM β-cyclocitral), with the promotion gradually enhancing with lowering the concentration. In the growth-inhibition treatments, a remarkable burst was found in the reactive oxygen species, which might cause oxidative damage to the cells. The treatments with 0.12 mM longifolene and 0.09 and 0.12 mM β-ionone lowered the chlorophyll content and photosynthetic abilities, which might be caused by the down-regulation of associated genes. However, other treatments showed opposing effects. In addition, the treatment with 0.03 mM β-ionone elevated expression of the genes involved in growth as well as the related biological processes and cellular component formation, which might also contribute to the cell growth. However, 0.12 mM β-ionone showed opposing impacts. It can be speculated that cyanobacterial VOCs have dual effects on themselves, which depend on the concentration.