Exploiting Cheese Whey for Efficient Selection of Polyhydroxyalkanoates-Storing Bacteria

Agroindustrial by-products hold an enormous potential to be bioconverted into high-value-added products such as polyhydroxyalkanoates (PHA), a cost-effective alternative to conventional plastics. In this study, cheese whey, a highly abundant side stream of the cheese making process, was explored as a feasible substrate for the selection of a mixed culture highly enriched in PHA-storing bacteria using a sequencing batch reactor under an aerobic dynamic feeding regime. For that, the absence/presence of thiourea, magnesium and iron, as well as the application of two different organic loading rates (OLR), i.e., 60 and 80 CmM d⁻¹, were tested. The results showed an improved culture selection when thiourea, magnesium and iron were added to the culture medium as well as when the highest OLR was applied. Under these conditions, the biomass achieved a maximum PHA storage of 54% and a PHA production rate of 4.81 Cmmol-PHA L⁻¹ h⁻¹. Additionally, the study of the microbial community showed that during this period of maximum productivity, the biomass was enriched in <i>Azoarcus</i> and <i>Amaricoccus</i> bacterial species. Conclusively, cheese whey can be considered a good feedstock to efficiently select a mixed culture with high potential to accumulate PHA and a good way to give this by-product added value.