Screening And Enzymatic Properties Of A Protease-hyperproducing Strain From The Digestive Tract Of Perinereis Aibuhitensis Grube

Objective The present study was conducted to screen protease-hyperproducing strain from the digestive tract of Perinereis aibuhitensis Grube, and to purify the sought-for microbial extracellular protease as well as analyze its enzymatic properties.Methods Isolates of interest were screened with skim-milk plate and identified based on bioactivities and 16S rDNA sequences analysis. Enzyme producing conditions such as fermental medium, time and temperature were detected and optimized. Sought-for protease was purified to homogeneity by a stepwise procedure including centrifugation, ammonium sulfate precipitation, ion-exchange chromatography and size-exclusion chromatography. Properties of the purified enzyme were studied and two internal peptides were sequenced by ESI-Q-TOF2.Results A strain named D2, with highly proteolytic activity was successfully obtained and identified as S.maltophilia. The production of D2 extracellular protease wasl56.0U/mL, with an optimized fermental condition of pH 7.5 for 48 hours at 25℃. The four-step purification protocol resulted in a 4.9-fold purification with 33% activity recovery. The purified D2 protease exhibited an optimum pH of 9.0, optimum reaction temperature of 60℃and a molecular mass of approximately 42.0 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), with high stability in the pH range from 6.0 to 11.0 for 3 hours and temperature range from 0℃to 60℃for 30 minutes. Its proteolytic activity was simulated by mental ions such as Cu²⁺,Ca²⁺,K⁺,Mg²⁺ and almost completely inhibited by EDTA and PMSF. By means of electrospray ionization tandem mass spectrometry (ESI-MS/MS), amino acid sequence of two selected tryptic peptides was deduced as AHGFLPLTK and APSATGGS ALYPLEFVVGK, respectively.Conclusion The extracellular protease secreted by D2 strain might be a novel source of protease of marine microorganisms.