Primary Photosynthetic Processes of Thalassiosira weissflogii under the Effect of Ciprofloxacin

Fluoroquinolone antibiotics, such as ciprofloxacin, have been actively used in medical practice, including the COVID-19 pandemic, to suppress adverse bacterial infections. Widespread application and improper disposal have resulted in the ubiquity of antibiotics in the environment, which can affect natural aquatic life, including phytoplankton. The effect of fluoroquinolone antibiotics on the photosynthetic processes of marine diatoms, which are the main producers in marine ecosystems, has been little studied. In this work, the effect of the antibiotic ciprofloxacin on the primary photosynthetic processes in the marine diatom Thalassiosira weissflogii has been studied. It was shown that ciprofloxacin affects the functioning of PSII, preventing the transfer of absorbed energy from the excited antenna chlorophyll molecules to the PSII RC (φ Do ). Under the influence of ciprofloxacin, a decrease in the efficiency of electron donation to P680 + (F V /F O ), inhibition of the quantum yield of PSII (F V /F M ), a decrease in the proportion of active RCs (ABS/RC), and an increase in the dissipation of absorbed energy in RCs (DI 0 /RC) were revealed. It was shown that the mechanism of ciprofloxacin’s action is associated with damage to the PSII RCs. Ciprofloxacin enhances the photosensitivity of microalgae and causes an increase in lipid peroxidation products. It is proposed to use the parameters of chlorophyll fluorescence to analyze the effect of antibiotics on microalgae.