S45: Low pH lactic acid production: A new approach to an old fermentation through biotechnology

Poly Lactic Acid (PLA) is a green alternative to petroleum derived plastics that is derived from annually renewable substrates.  NatureWorks LLC, a wholly-owned subsidiary of Cargill, is the market leader in PLA.  Successful commercialization of PLA requires a lactic acid feedstock that simultaneously achieves a low production cost as well as high chemical and chiral purity.  To meet these criteria, the Biotechnology Development Center at Cargill has developed an innovative, yeast biocatalyst and fermentation process.  Rather than relying on the traditional host strains of biotechnology with known benefits and known limitations, we decided to look for an entirely new host that was better suited to our target process conditions.  Employing an extensive screening process, we identified a new yeast host which is substantially improved over conventional yeasts in the parameters that were important to our fermentation:  robustness, high tolerance to organic acids, and high sugar consumption rates.  Through mutagenesis and selection, genetic engineering and evolution we have developed this yeast into an efficient producer of lactic acid.  At a process pH below the pka of lactic acid, we are able to achieve commercially relevant rates and yields as well as titers in excess of 100 g/L.  This low pH fermentation results in substantial savings over conventional, near-neutral pH bacterial fermentations as well as significant improvement in the overall environmental footprint.  Through significant collaboration between Cargill’s R&D  and production teams, this new yeast fermentation was successfully implemented at full commercial scale at the Blair lactic acid plant in 2008.