Physiological, biochemical and transcription effects of roxithromycin before and after phototransformation in Chlorella pyrenoidosa.Aquat Toxicol. 2021 Jul 13; 238:105911.AT
Photodegradation is an important transformation pathway for macrolide antibiotics (MCLs) in aquatic environments, but the ecotoxicity of MCLs after phototransformation has not been reported in detail. This study investigated the effects of roxithromycin (ROX) before and after phototransformation on the growth and physio-biochemical characteristics of Chlorella pyrenoidosa, and its toxicity were explored using transcriptomics analysis. The results showed that 2 mg/L ROX before phototransformation (T0 group) inhibited algae growth with inhibition rates of 53.06%, 54.17%, 47.26%, 31.27%, and 28.38% at 3, 7, 10, 14, and 21 d, respectively, and chlorophyll synthesis was also inhibited. The upregulation of antioxidative enzyme activity levels and the malondialdehyde content indicated that ROX caused oxidative damage to C. pyrenoidosa during 21 d of exposure. After phototransformation for 48 h (T48 group), ROX exhibited no significant impact on the growth and physio-biochemical characteristics of the microalgae. Compared with the control group (without ROX and its phototransformation products), 2010 and 2988 differentially expressed genes were identified in the T0 and T48 treatment groups, respectively. ROX significantly downregulated genes related to porphyrin and chlorophyll metabolism, which resulted in the inhibition of chlorophyll synthesis and algae growth. ROX also significantly downregulated genes of DNA replication, suggesting the increased DNA proliferation risks in algae. After phototransformation, ROX upregulated most of the genes associated with the porphyrin and chlorophyll metabolism pathway, which may be the reason that the chlorophyll content in T48 treatment group showed no significant difference from the control group. Almost all light-harvesting chlorophyll a/b (LHCa/b) gene family members were upregulated in both T0 and T48 treatment groups, which may compensate part of the stress of ROX and its phototransformation products.