Effects of Bacterial Infections under Heatwaves on Chinese Soft-Shelled Turtles and Their Single-Cell Transcriptomic Landscapes

The intensification of global warming could precipitate the widespread dissemination of opportunistic pathogens, exerting a bidirectional strain on wildlife populations and potentially hastening the process of species extinction. In this study, we integrated indicators from peripheral blood single-cell transcriptome, behavior, and physiological indices in Chinese soft-shelled turtles (Pelodiscus sinensis) to explore the impact of dual stress caused by bacterial infections and/or heatwaves on the turtles. Turtles were randomly divided into four groups based on constant temperature at 28 °C and heatwave exposure, as well as whether they were infected with bacteria (Bacillus cereus). Principal component analysis-based cell clustering revealed that the 14 cell clusters were classified into seven distinct cell types: erythrocytes, monocytes, thrombocytes, T cells, B cells, basophils, and heterophils. All cell types participated in the host immune response to heatwaves and bacterial infection, but these cells exhibited significant group-specific differences in their gene expression patterns. Bacterial infections and heatwaves altered turtle behavior and physiology indexes. The dual stresses inhibited the expression of antioxidant enzymes and immune genes, potentially jeopardizing turtle survival. Overall, this study provides valuable insights into peripheral blood cell profiles of Chinese soft-shelled turtles under different environmental conditions, enhancing the understanding of their immune responses and potential stressors.