Menaquinone production in genetically engineered E. coli.

Menaquinone (MK) is an important electron transporter in Escherichia coli. This isoprenoid quinone can transfer electrons to many terminal acceptors, such as fumarate and nitrate, which helps this organism survive under diverse and challenging conditions. As isoprenoid quinones with various lengths of isoprenyl tail are widely distributed in nature, the heterologous expression of polyprenyl diphosphate synthases (PDSs) has been investigated using its counterpart, ubiquinone (UQ). In this study, we investigated the MK production by the expression of various heterologous PDS genes from prokaryotic and eukaryotic species, including Saccharomyces cerevisiae COQ1 (hexa-PDS), Haemophilus influenzae hi0881 (hepta-PDS), Synechocystis sp. strain PCC6803 slr0611 (nona-PDS), and Gluconobacter suboxydans ddsA (deca-PDS) in E. coli. We detected specific isoforms of MK, including MK7, MK9, and MK10, via the expression of HI0881, Slr0611, and DdsA respectively, but barely detected MK6 via the expression of Coq1. As UQ6 was detected in E. coli harboring COQ1, the acceptance of the side chain lengths by MenA (prenyl transferase for MK) was narrower than UbiA (prenyl transferase for UQ). We also identified a mutation in menA in the E. coli AN386 strain and a transposon insertion of IS186 in menC in E. coli KO229 (∆ispB) and its parental strain FS1576. Taken together, these results elucidate the different nature of MenA from UbiA.