The P170 expression system enhances hyaluronan molecular weight and production in metabolically-engineered Lactococcus lactis

• P170 expression system is superior to NICE-system for HA production in L. lactis.
• High initial glucose concentration in batch cultures gives higher MW hyaluronan.
• Hyaluronan MW of 2.94 MDa achieved in batch cultures with P170 system.
• Pulse feeding gives better hyaluronan MW than constant feed in fed-batch processes.

Recombinant Lactococcus lactis strains based on the P170 expression system were developed for hyaluronan (HA) production, by incorporating genes from the has operon of Streptococcus zooepidemicus and compared with nisin-inducible recombinant L. lactis strains containing the hasABC and hasABD constructs. It was found across all batch and fed-batch experimental studies that HA concentration and molecular weight (MW) were higher for the P170 expression systems than the corresponding NICE-based strains. The highest hyaluronan MW was obtained for all constructs in batch studies at 60 g/L initial glucose concentration, the highest being 2.94 MDa for the P170 strains with hasABC construct (L. lactis APJ3). In fed-batch studies with constant feed rate, the L. lactis APJ3 gave better HA yield (0.03 g/g) than the NICE-based strain. A higher hyaluronan MW was obtained for all strains in pulse fed-batch compared to constant feed experiments, the highest being 2.52 MDa for L. lactis APJ3.