Inhibition of the photosynthetic activity of Synedra sp. by sonication: Performance and mechanism.

The impacts of sonication on the photosynthetic activity of Synedra sp. (diatom) and its mechanism were investigated for the first time. Three photosynthetic parameters, i.e., effective quantum yield (Φ), initial slope of rapid light curves (α) and maximum relative electron transport rate (rETR) were employed to evaluate its photosynthetic activity during sonication for the first time. The results showed that 600 kHz is the optimal frequency for the inhibition of the photosynthetic activity and biomass as the ultrasonic frequencies varied from 100 to 800 kHz. When the photosynthetic activity was inhibited to be not detected by sonication, Φ, α and rETR gradually recovered from 0 to 36.4%, 35.2% and 48.3% of that in the blank group, respectively, after 12-day cultivation (no sonication). However, the biomass was still suppressed to 9.2% of that in the blank after the same cultivation. A single time sonication treatment achieved better inhibition efficiency than the multiple times modes when their total sonication time was equal. The inhibition mechanism for the photosynthetic activity of Synedra sp. by sonication can be concluded as follows: at the early stage, the thylakoids membrane expansion and oscillation can lead to the structure damage of thylakoids; subsequently, OH oxidation is responsible for the chlorophyll-a degradation.