Identification and characterization of a cocoon degradable enzyme from the isolated strain Bacillus subtilis Bs5C

Abstract

A fibroin-degrading bacterium was isolated in a medium containing fibroin as a sole nitrogen source, and then identified and characterized. The strain was designated Bacillus subtilis strain Bs5C, and the culture medium containing the extracellular proteolytic enzymes was found to hydrolyze cocoon fiber. A decomposition rate of 35% was achieved with the culture medium in optimized cocoon-degrading condition. In a second round of decomposition performed on the same fibers with additional culture medium, the decomposition rate reached 45.9%. To investigate the proteolytic enzymes degrading cocoon, the enzymes was purified from culture medium using ion exchange column and identified using LC-MS/MS analysis system. As a result, it was uncovered that the cocoon degradation was due to the neutral protease NprE of the strain Bs5C. Moreover, the cocoon fibers treated with semi-purified NprE enzyme solution were clearly split and degraded, as assessed by SEM, and solubilized peptides from fibroin and sericin were detected by LC-MS/MS. In conclusion, this study is the first report that peptides could be produced from cocoon by cultured medium of B. subtilis, and the newly isolated strain Bs5C and the NprE protease from the strain Bs5C could clearly be valuable for the production of silk peptides, which have various pharmacological and industrial applications. ⓒ 2020, The Korean Society for Biotechnology and Bioengineering and Springer.