Background: Streptolysin O (SLO) from Streptococcus pyogenes could oligomerize to form large pores on the membrane of some eukaryotic cells. Because of the action, SLO had multifaceted applications in animal cell biology and medicine science. In the previous researches, the highest yield of recombinant expressed SLO might be no more than 124 mg/L medium. Objectives: A fusion protein of pectate lyase and streptolysin O (PEL-SLO) was highly expressed with the pectate lyase (PEL, from