Microplastics and tetracycline affecting apoptosis, enzyme activities and metabolism processes in the Aurelia aurita polyps: Insights into combined pollutant effects

Xuandong Wu ^1,2 Xiaoyong Zhang ³ Hongze Liao ² Jie Guo ⁴ Zhenhua Ma ⁵ Zhilu Fu ^2,6*

• ¹ Guangxi Key Laboratory of Marine Natural Products and Combinatorial Biosynethesis Chemistry , Guangxi Academy of Sciences, Nanning, Guangxi Zhuang Region, China
• ² Guangxi Key Laboratory for Polysaccharide Materials and Modifications, Guangxi University for Nationalities, Nanning, Guangxi Zhuang Region, China
• ³ University Joint Laboratory of Guangdong Province, Hong Kong and Macao Region on Marine Bioresource Conservation and Exploitation, College of Marine Sciences, South China Agricultural University,, Guangzhou, China
• ⁴ Key Laboratory of Marine Environmental Science, Guangxi Academy of Sciences, Nanning, Guangxi Zhuang Region, China
• ⁵ Key Laboratory of South China Sea Fishery Resources Exploitation and Utilization, South China Sea Fisheries Research Institute (CAFS), Guangzhou, China
• ⁶ Guangxi Key Laboratory of Marine Natural Products and Combinatorial Biosynethesis Chemistry, Guangxi Academy of Sciences, Nanning, Guangxi Zhuang Region, China

Microplastics and tetracycline, are prevalent in marine ecosystems and cumulatively affect marine life, especially benthic organisms. However, the mechanisms remain unclear. In this study, Aurelia aurita polyps were subjected to 7 days exposure to microplastics (1 mg/L) and tetracycline (5 mg/L) to test the apoptosis rate. Next, a new patch of polyps were exposed to short-term treatments with microplastics (10 mg/L) and tetracycline (5 mg/L) for 72 hours. The water was changed after 72 hours and the culture was continued until 288 hours. Samples were collected at 0, 1, 6, 24, 72, 96, 144, and 288 hours, and various biochemical indicators were measured, including CAT, GSH, GSH-PX, SOD, MDA, and T-AOC. The study was to observe whether the damage caused by short-term high-concentration stimulation to the A. aurita would recover after water change. Finally, polyps were exposed to microplastics and tetracycline at environmentally relevant concentrations over a prolonged period (185 days), and samples (n ≥ 100 for each replicate) were collected for metabolomics analysis. TUNEL assay results showed that there was no significant difference in cell apoptosis rate between single microplastics, single microplastics, and control groups, while the cell apoptosis rate of the microplastics combined with tetracycline group was significantly higher than the other three groups (P < 0.05). Antioxidant capacity test results indicated that even after 288 hours, the polyps in the single microplastic treatment group exhibited significant oxidative damage. In the combined pollutant treatment group, physiological indicators showed varying responses, and high concentrations of tetracycline hydrochloride did not consistently exert harmful effects. Bioinformatics analysis revealed that the two pollutants induced distinct metabolite changes, suggesting that the jellyfish employed different physiological strategies to cope with each pollutant. A variety of antioxidants, neurotransmitters, and other metabolites were affected, with multiple metabolic pathways, including ABC transporters and protein digestion and absorption, implicated in the response. This study demonstrates the need for further investigation of the long-term ecological effects of microplastics and associated pollutants, such as tetracycline, to enhance marine ecosystem protection