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).