Effect of PelB signal sequences on Pfe1 expression and omega-hydroxyundec-9-enoic acid biotransformation in recombinant Escherichia coli

Abstract

omega-Hydroxyundec-9-enoic acid (omega-HUA) was reported as a valuable medium-chain fatty acid with industrial potentials. For bioconversion of ricinoleic acid to omega-HUA, in this study, an alcohol dehydrogenase (Adh) from Micrococcus luteus, a Baeyer-Villiger monooxygenase (BVMO) from Pseudomonas putida KT2440 and an esterase (Pfe1) from Pseudomonas fluorescens SIK WI were overexpressed in Escherichia coli BL21(DE3). In order to enhance accessibility of Pfe1 to the (E)-11-(heptanoyloxy) undec-9-enoic acid (11-HOUA) substrate, a truncated PelB signal sequence without the recognition site of signal peptidase (tPelB) was attached to the N-terminus of Pfe1, resulting in the construction of E. coli AB-tPE strain expressing Adh, BVMO and the tPelB-Pfe1 fusion protein. A batch-type biotransformation of ricinoleic acid by E. coli AB-tPE resulted in 1.8- and 2.2-fold increases in omega-HUA conversion yield and productivity, respectively, relative to those for the control strain without the PelB sequence (AB-E). By fed-batch-type biotransformation with glycerol feeding, the AB-tPE strain produced 23.7 mM (equivalent to 4.7 g/L) of omega-HUA with 60.8%(mol/mol) of conversion yield and 1.2 mM/h of productivity, which were 13.2, 2.9, and 2.6 times higher than those in a batch-type biotransformation using the AB-E strain. In conclusion, combination of the truncated PelB-Pfe1 fusion and fed-batch process with glycerol feeding provided the highest efficiency of omega-HUA biotransformation, of which strategies might be applicable for biotransformation of hydrophobic substances.