3.5. Time-dependent l-PA production with different substrate concentrations
After optimization, we conducted the whole-cell reaction with the optimal conditions (strain: yhPA004; fermentation conditions: TB broth, 30 °C, 0.1 mM IPTG; reaction conditions: pH 7.5, 150 mM phosphate buffer, 20 mM FeSO4, and 0.1% Triton X-100 with gently mixing), and we monitored the time-dependent l-PA production according to l-lysine concentrations for 6 days. The l-lysine concentration ranged from 400 mM to 1 M. l-PA production increased for 5 days for all substrate concentrations and showed the highest conversion at day 6, except for 1 M l-lysine which showed the highest production at day 5 (Fig. 6A). The highest production and conversion from each concentration are shown in Figure 6B. Production was 317 mM, 473 mM, 673 mM, and 724 mM from 400 mM, 600 mM, 800 mM, and 1 M l-lysine, respectively, and conversions were 79.3%, 78.8%, 84.1%, and 72.4%, respectively. The highest conversion yield was demonstrated with 800 mM l-lysine (84.1%); however, the concentration of l-PA produced was highest with 1 M l-lysine (93.5 g/L; 72.4% conversion). Comparing the productivity between 800 mM and 1 M l-lysine, productivity was 0.63 g/L/h from 800 mM and 0.78 g/L/h from 1 M l-lysine. As mentioned above, agitation was essential to enhance LCD activity in this system. Faster agitation speed promoted higher productivity; however, vigorous agitation (1300 rpm) caused whole-cell activity to be lost after 2 days (Supplementary Fig. 3).