Bioconversion of dairy co-products to polyhydroxyalkanoates by halophilic microbes with salts and nutrients recycling

This study presented the cultivation of Haloferax mediterranei for polyhydroxyalkanoates (PHA) production from dairy co-products with spent salts recycling and provided the first insights of dissolved oxygen (DO) in regulating PHA biosynthesis by halophiles. PHA had yields up to 0.40 ± 0.02 g/g substrate from whey sugar and up to 0.17 ± 0.12 g/g substrate from delactosed permeate. A higher log-phase DO led to faster biosynthesis, but a lower final PHA production (2.0 ± 0.3 g/L) compared to lower DO levels (3.0 ± 0.1 g/L). This was later elucidated through mathematical modelling by the kinetic parameters and metabolic reaction rates. A novel approach was established to recycle up to 90 % salts and nutrients in the system and achieved consistent production and product quality. This study develops a sustainable biotechnology of converting dairy co-products to biomaterials, improve the economics of PHA and has the potential scalability for industrial applications.