Effective whole cell biotransformation of arginine to a four-carbon diamine putrescine using engineered Escherichia coli

Abstract

The rising awareness of environmental protection has triggered bio-based materials to replace the traditional petrochemical plastics. Putrescine as 1,4-diaminobutane is an important monomer of polyamide (PA) and uses in the sustainable chemical industry. Herein, a time-effective whole cell bioconversion of L-arginine to putrescine was developed, which has applied the key enzymes (i.e., SpeA and SpeB) from the arginine decarboxylase (ADC) pathway. The synergetic collaboration of both enzymes was examined from the different combination of plasmids among 4 Escherichia coli chassis. The optimal reaction condition was at pH 9 with 1 mM pyridoxal-5′-phosphate (PLP) and 10 mM magnesium, thus 90% conversion was obtained using an all-in-one plasmid with equal protein of SpeA and SpeB in BL21(DE3). The enzymatic kinetics demonstrated the higher kcat of SpeA (1212 s−1) than that of SpeB (418 s−1), while severe inhibition of putrescine on SpeA (KI = 8.61 mM), thus it was disadvantage using the surface display of enzyme. To prevent the feedback-inhibition by product, a 2-step enzymatic reaction with cold treatment was conducted. Finally, the putrescine was achieved 17.1 g/L with the productivity of 8.56 g/L/h under 86% conversion of 50 g/L L-arginine-HCl, which is an effective approach to obtain high putrescine titer.