Functional redundancy ensures performance robustness in 3-stage PHA-producing mixed cultures under variable feed operation

Polyhydroalkanoates (PHA) are biopolymers that can be produced by mixed microbial cultures using wastes or industrial by-products, which represent an economical and environmental advantage over pure culture processes. The use of alternate feedstocks enables using seasonal by-products, providing that the system is resilient to transient conditions. The mixed microbial communities of a 3-stage PHA producing system fed initially with molasses and then cheese whey were investigated through amplicon sequencing of the 16S rRNA gene. The transition in feedstock resulted in an adaptation of the acidogenic community, where Actinobacteria dominated with sugarcane molasses and Firmicutes, with cheese whey. The resulting fermentation products profile also changed, with a higher fraction of HV precursors in the former case. As for the PHA storing culture, Azoarcus, Thauera and Paracoccus where enriched with fermented molasses. Later, fermented cheese whey fostered a higher diversity, including some less characterised PHA-storers such as Paenibacillus and Lysinibacillus. Although the microbial structure was significantly affected by the feedstock shift, the acidogenic and PHA storing performance of the 3-stage system was very similar once a pseudo steady state was attained, showing that a reliable level of functional redundancy was attained in both mixed cultures.