SUMMARY
Background: Poly(DL-lactic acid), or PDLLA, is a biodegradable polymer that can be hydrolyzed by various types of
enzymes. The protease produced by Actinomadura keratinilytica strain T16-1 was previously reported to have
PDLLA depolymerase activity. However, few studies have reported on PDLLA-degrading enzyme production
by bacteria. Therefore, the aims of this study were to determine a suitable immobilization material for
PDLLA-degrading enzyme production and optimize PDLLA-degrading enzyme production by using
immobilized A. keratinilytica strain T16-1 under various fermentation process conditions in a stirrer fermenter.
Results: Among the tested immobilization materials, a scrub pad was the best immobilizer, giving an enzyme
activity of 30.03 U/mL in a shake-flask scale. The maximum enzyme activity was obtained at aeration
0.25 vvm, agitation 170 rpm, 45°C, and 48 h of cultivation time. Under these conditions, a PDLLA-degrading
enzyme production of 766.33 U/mL with 15.97 U/mL·h productivity was observed using batch fermentation in
a 5-L stirrer fermenter. Increased enzyme activity and productivity were observed in repeated-batch
(942.67 U/mL and 19.64 U/mL·h) and continuous fermentation (796.43 U/mL and 16.58 U/mL·h) at a dilution
rate of 0.013/h. Scaled-up production of the enzyme in a 10-L stirrer bioreactor using the optimized conditions
showed a maximum enzyme activity of 578.67 U/mL and a productivity of 12.06 U/mL·h.
Conclusions: This research successfully scaled-up the enzyme production to 5 and 10 L in a stirrer fermenter and is
helpful for many applications of poly(lactic acid).