A food-grade expression system for d-psicose 3-epimerase production in Bacillus subtilis using an alanine racemase-encoding selection marker

Bioresources and Bioprocessing

Table 1 Stability of dal-based and neo-based plasmids in different medium

Plasmid	5 Generations (%)	15 Generations (%)	40 Generations (%)	80 Generations (%)
pMA5-RDPE/SR	56	10	3	0
pMA5-RDPE/SR + Kan	100	95	88	85
pMA5-DAL-RDPE/SR	100	100	100	100
pMA5-DAL-RDPE/SR + d-alanine	88	76	54	30

Bacillus subtilis 1A751R harboring pMA5-RDPE and B. subtilis 1A751D2R harboring pMA5-DAL-RDPE were cultivated in selective and nonselective medium. The kanamycin concentration was 50 μg/ml; the d-alanine concentration was 200 μg/ml. The strains were cultivated at 37 °C
Every 10 h, 5 generations passed. The stability of plasmids was calculated by dividing the number of colonies on selective medium with the number of colonies on nonselective medium