Toxic effects of amoxicillin on the photosystem II of Synechocystis sp. characterized by a variety of in vivo chlorophyll fluorescence tests.

Amoxicillin is one of the widely used antibiotics of environmental concern. This study shows that amoxicillin has toxic effects on the photosynthesis of Synechocystis sp. Its inhibitory effects on photosystem II (PSII) of Synechocystis sp. were investigated by using a variety of in vivo chlorophyll fluorescence tests. The inhibitory effects of amoxicillin on PSII activity of Synechocystis sp. are concentration-dependent. Amoxicillin exposure leads to slowing down of electron transport on both donor side and acceptor side and causes accumulation of P680(+). Q(A)(-) reoxidation test revealed that amoxicillin hinders electron transfer from Q(A)(-) to Q(B)/Q(B)(-) and more Q(A)(-) is oxidized through S(2)(Q(A)Q(B))(-) charge recombination. Analysis of PSII heterogeneity demonstrated that an exposure to amoxicillin increases the proportion of inactive PSII (PSII(X)) centers and the proportion of PSII centers with small antenna (PSIIbeta). These changes finally result in deterioration of full photosynthesis performance.