Production of β‐Cyclocitral and Its Precursor β‐Carotene in Microcystis aeruginosa: Variation at Population and Single‐Cell Levels

Abstract

Bloom‐forming cyanobacteria produce and release odorous compounds and pose threats to the biodiversity of aquatic ecosystem and to the drinking water supply. In this study, the concentrations of β‐cyclocitral in different bacterial growth phases were investigated using GC–MS to determine the growth stage of Microcystis aeruginosa at high risk for β‐cyclocitral production. Moreover, the synchronicity of the production of β‐cyclocitral and its precursor β‐carotene at both population and single‐cell levels was assessed. The results indicated that β‐cyclocitral was the main odorous compound produced by M. aeruginosa cells. The intracellular concentration of β‐cyclocitral (Cβ-cc) as well as its cellular quota (Qβ‐cc) increased synchronously in the log phase, along with the increase of cell density. However, they reached the maximum values of 415 μg/L and 10.7 fg/cell in the late stationary phase and early stationary phase, respectively. The early stage of the stationary phase is more important for β‐cyclocitral monitoring, and the sharp increase in Qβ‐cc is valuable for anticipating the subsequent increase in Cβ‐cc. The molar concentrations of β‐cyclocitral and β‐carotene showed a linear relationship, with an R2 value of 0.92, suggesting that the production of β‐ cyclocitral was linearly dependent on that of β‐carotene, especially during the log phase. However, the increase in Qβ‐cc was slower than that in β‐carotene during the stationary phase, suggesting that β‐cyclocitral production turned to be carotene oxygenase‐limited when the growth rate decreased. These results demonstrate that variations of β‐cyclocitral production on a single‐cell level during different bacterial growth phases should be given serious consideration when monitoring and controlling the production of odorous compounds by M. aeruginosa blooms.