Effect of operating conditions on the microbial selection of P(3HB-co-3HV) producers in open continuous culture

From the perspective of producing P(3HB-co-3HV), the selection of PHA accumulating organisms from activated sludge with a feeding incorporating propionate was investigated in open continuous culture under dual carbon and phosphorus limitation conditions. The selected consortia were then harvested in batch cultures with phosphorus (P) deficiency to evaluate their PHA storage potential. Microbial selection exhibited consistent functional stability of PHA production, emphasizing the robustness of this enrichment strategy. A comparison with previous studies revealed that at a given degree of P limitation, the distribution of carbon consumption between cell growth, PHA storage and maintenance reactions was conditioned by the nature of the carbon source. The combination of the nature of the carbon substrate, the degree of P limitation and the dilution rate governs microbial competition. The dominant bacterial genera showed very heterogeneous PHA production capacities. Acinetobacter spp., whose establishment was favored by the presence of acetate, a high dilution rate, and a low C/P ratio, was found to be a poor producer. In contrast, Malikia spp. and Zoogloea spp., mostly selected with butyrate, a lower dilution rate, and strong P limitation, exhibited high specific PHA production rates.