Decoupled carbon-and-nutrient feed boosts efficient polyhydroxyalkanoates production by mixed microbial cultures...

Conventional anaerobically/aerobically alternating operated mixed microbial cultures (MMC) for polyhydroxyalkanoates (PHA) production requests high energy for aeration, restricting its technological scale-up and industrialization. MMC-based PHA production under anoxic conditions was studied in two sequencing batch reactors with decoupled and coupled carbon-and-nutrient feed (designated as D-SBR and C-SBR, respectively) to develop energy-saving PHA production. D-SBR obtained cellular PHAs of 50.6% in 27 days and further displayed robust PHA production of 45.7±8.1% with a peak value of 64.2%. C-SBR gained lower cellular PHAs of 10.9±3.4% during a two-month elaborated operation. Both SBRs produced PHAs with high-content 3-hydroxyvalerate, i.e., 32.6% for D-SBR and 45.8% for C-SBR. 16S rRNA V4 gene amplicon analysis revealed that the SBRs proliferated discrepant PHA producers. C-SBR was dominated by Pandoraea, Thauera, and Leptolyngbya; while Brachymonas, Defluviicoccus, Pseudomonas, Comamonas, and Thauera (in total, 53.3%) responded to PHA production in D-SBR. Full-length 16S rRNA gene analysis corroborated the dominances of Defluviicoccus vanus, Thauera aminoaromatica, and Brachymonas denitrificans in D-SBR. Nutrient limitation and feast/famine selection were proposed to boost efficient PHA production in D-SBR. Anoxic MMC favored propionate-to-3-hydroxyvalerate biosynthesis, properly due to its metabolically and energetical advantages over acetate-to-3-hydroxybutyrate under the ATP deficiency. This work for the first time validated the efficacy of MMC-based PHA production under anoxic conditions, which promises possible cost reduction in PHA production and thus encourages continual efforts on developing anoxic PHA production.