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Abstract
Phytases comprise a group of phosphatases that trim inorganic phosphates from phytic acid (IP6). In this study, we aimed to achieve the efficient secretion of phytase by Bacillus subtilis. B. subtilis laboratory standard strain 168 and its derivatives exhibit no phytase activity, whereas a natto starter secretes phytase actively. The natto phytase gene was cloned into strain RIK1285, a protease-defective derivative of 168, to construct a random library of its N-terminal fusions with 173 different signal peptides (SPs) identified in the 168 genome. The library was screened to assess the efficiency of phytase secretion based on clear zones around colonies on plates, which appeared when IP6 was hydrolyzed. The pbp SP enhanced the secretion of the natto phytase most efficiently, i.e. twice that of the original SP. Thus, the secreted natto phytase was purified and found to remove up to 3 phosphates from IP6.
Graphical abstract
The signal peptide of pbp (C) enhanced the secretion of natto phytase up to twofold more efficiently than the original one of the natto starter.
Notes
Abbreviations: DCI, D-chiro-inositol; IP3, myo-inositol triphosphate; IP5, myo-inositol pentaphosphate; IP6, phytic acid; LB, Luria broth; MI, myo-inositol; SI, scyllo-inositol; SP, signal peptide.
