Unraveling the intracellular and extracellular self-defense of Chlorella sorokiniana toward highly toxic pyridine stress

•IC50 pyridine caused C. sorokinana photoinhibition and metabolism dysregulation.•Self-defense strategy of C. sorokinana was concentration-dependent.•Low pyridine stress spurred catalase and ascorbate peroxidase for antioxidative.•Elevated calcium signaling and phytohormone responded to high pyridine stress.•More extracellular proteins bound to pyridine by hydrophobic and aromatic stacking.