Identification of a toxic serralysin family protease with unique thermostable property from S. marcescens FS14

A serralysin family protease (Serralysin-like protease B, SPB) with unique V-shaped thermostable property was isolated and identified from the Serratia marcescens FS14 by biochemical and molecular biological methods. It is the first time to report the isolation of a native serralysin family protease directly from Serratia species except the well-studied serralysin. SPB has an optimum pH at 8.0 and an optimum temperature at 37 °C. It shows high proteolytic activities after pretreated at 4–50 °C for 10 min respectively and almost no detectable activity after pretreated at 60 °C. Surprisingly, increasing activities were observed after pretreated at 70–90 °C respectively. Further study revealed that the reason behind this phenomenon may be the self-digestion property of SPB with an optimum temperature around 60 °C. This self-digestion property may expand the SPB future application in industry. The bioassay using the healthy cotton bollworm Helicoverpa armigera larvae demonstrated that the serralysin and SPB from FS14 are toxic to the H. armigera larvae. This result implied that FS14 strain and/or the SPB and serralysin in FS14 might have a potential application in insect control.