Metabolic Engineering Of Lactococcus Lactis For The Production Of Heparosan

Abstract

Heparosan is a precursor molecule for the widely used anticoagulant heparin, which also has other uses such as certain drug delivery applications and as a scaffold for tissue engineering in biomaterials. Traditionally, pathogenic bacteria such as E.Coli have been used as a host to produce heparosan as an alternative to animal and chemoenzymatic synthesis. Using GRAS status organisms like Lactococcus Lactis as the host for production of heparosan provides a safe alternative as well as being a well-established organism for genetic manipulation and reengineering. In this study, a functional heparosan synthesis pathway was successfully expressed in Lactococcus Lactis by the expression of E.coli K5 genes KfiA and KfiC, along with the overexpression of ugd, glmu and pgma genes present natively in the host organism. The genes were activated using the tightly controlled NICE expression system. The genes were cloned into plasmid p8148 and transformed into two strains, Lactococcus Lactis NZ9000 and Lactococcus Lactis NZ9020, totaling six different recombinant strains were created using these two hosts and various combinations of the heterologous genes. The recombinant Lactococcus Lactis SH6 strain, expressing the genes ugd-KfiA-KfiC-pgma yielded a maximum concentration of 754 mg/l in batch bioreactor experiments and the titer was increased to 1263 mg/l in fed-batch fermentation. NMR imaging successfully determined that the structure of the product derived from Lactococcus Lactis was indeed similar to E.coli heparosan. The molecular weight of heparosan varied from 10-20 KDa, indicating its potential use for chemoenzymatic heparin biosynthesis.