A New Phospholipase D-Producing Bacillus cereus: Taxonomy, Mutagenesis, Fermentation Optimization and Enzyme Characterization

Phospholipase D (PLD) is a valuable enzyme in industrial processes for converting phosphatidylcholine (PC) to phosphatidylserine (PS). In this study, a strain of Bacillus cereus was isolated from soil and identified through 16S rRNA sequencing. To enhance PLD activity, various mutagenesis strategies—including chemical treatment, irradiation, and their combinations—were employed, resulting in four high-activity positive mutants (C-7, I-12, CI 7–12, and IC 13–14). Among these, the CI 7–12 mutant exhibited a significantly higher enzymatic activity, showing a 3.12-fold increase (312.2%) compared to the wild-type strain. Fermentation conditions were optimied using response surface methodology (RSM), achieving a PLD activity of 35 U/mL. The enzyme demonstrated stability over a wide temperature range (30–60°C) and pH range (6–10), with a half-life of 128 days. Kinetic analysis revealed a V _max of 20.04 µmol/h and a K _m of 7.13 µmol/mL, indicating efficient activity. In bioconversion experiments, the PLD-enriched fermentation broth catalyzed the conversion of PC to PS, achieving a 53.0% conversion rate and a 92.3% selectivity for PS in a two-phase system. These findings expand the potential sources of PLD and underscore its applicability for PS production in biotechnological applications.