Insights into the response mechanisms of Tetradesmus obliquus to aged polylactic acid and tetracycline exposure via transcriptome analysis and physiological evaluations

Microplastics (MPs) and antibiotics, identified as emerging pollutants, are extensively prevalent in aquatic environments and display prolonged durability. Unlike conventional plastics, biodegradable plastics are more susceptible to decomposition in the environment, resulting in the generation of microplastics and posing potential risks to the aquatic ecosystems. In this study, we assessed growth inhibition, chlorophyll a content, malondialdehyde content (MDA), and antioxidant enzyme activities. These measurements were integrated with transcriptome analysis to explore the response mechanisms of virgin and aged polylactic acid (vPLA and aPLA) and tetracycline (TC) following 14-day exposure to Tetradesmus obliquus, either individually or in combination. The findings indicated that exposure to vPLA did not significantly impact the growth of T. obliquus. Conversely, aPLA demonstrated growth-promoting effects on T. obliquus, particularly in the latter incubation stages. Moreover, a 14-day exposure significantly increased the chlorophyll a content and the activities of superoxide dismutase (SOD), catalase glutathione (CAT) and glutathione S-transferase (GST) within the algal cells. Apart from 1 mg L, the TC concentrations of 2.5, 5.0, and 10 mg L exhibited significant toxic effects on T. obliquus, including growth inhibition, decreased chlorophyll a content, elevated activities of SOD, CAT, and GST, and increased MDA levels. Exposure to a combination of 300 mg L aPLA and 5.0 mg L TC, compared to solely 5 mg L TC, demonstrated a notable reduction in TC toxicity to T. obliquus in the presence of aPLA. This was indicated by elevated algal cell density and chlorophyll a content, as well as a decrease in MDA content. Transcriptome analysis indicated an enrichment of differentially expressed genes (DEGs) in pathways linked to porphyrin metabolism, photosynthesis, carbon fixation, and metabolism within the aPLA + TC combined exposure. The study aid in expanding our knowledge of the potential ecological risks posed by biodegradable plastics and accompanying pollutants in aquatic environments.