3.5 High‑level production of Oml1, Oml7 and ApxⅡ by fed‑batch
cultivation
To achieve high-level production of Oml1, Oml7, and ApxII in E.
coli , fed-batch cultivation was performed for each protein in a 5 L
bioreactor with a 2 L working volume. As shown in Fig. 6A-6C ,
the trend of cell growth and protein accumulation was similar for all
three antigens, and the highest cell density and maximum yield were all
observed at 30 h after inoculation. The maximum OD600 of
Oml1, Oml7, and ApxII were 98, 110, and 80, respectively, and the
corresponding protein yield reached 2.43 g/L, 2.59 g/L, and 1.21 g/L.
Unlike continuous protein accumulation observed in secretory
expression,[12,32] there was a significant
correlation between protein accumulation and cell density, protein
accumulation ceased when the cell density stopped increasing. Next, the
recombinant antigens Oml1, Oml7, and ApxII were purified using a HisTrap
HP affinity column. As shown in Fig. 6D-6F , after simple
purification steps, all three proteins were successfully purified with
high purity (>90%). This allows us to further explore
whether these three recombinant antigens are biologically active.