Insights into Feast-Famine polyhydroxyalkanoate (PHA)-producer selection: Microbial community succession, relationships with system function and underlying driving forces

The Feast-Famine (FF) process has been frequently used to select polyhydroxyalkanoate (PHA)-accumulating mixed cultures (MCs), but there has been little insight into the ecophysiology of the microbial community during the selection process. In three FF systems with well-defined conditions, synchronized variations in higher-order properties of MCs and complicate microbial community succession mainly including enrichment and elimination of non-top competitors and unexpected turnover of top competitors, were observed. Quantification of PHA-accumulating function genes (phaC) revealed that the top competitors maintained the PHA synthesis by playing consecutive roles when the highly dynamic turnover occurred. Due to its specific physiological characteristics during the PHA-accumulating process, Thauera strain OTU 7 was found to be responsible for the fluctuating SVI, which threatened the robustness of the FF system. This trait was also responsible for its later competitive exclusion by the other PHA-producer, Paracoccus strain OTU 1. Deterministic processes dominated the entire FF system, resulting in the inevitable microbial community succession in the acclimation phase and maintenance of the stable PHA-accumulating function in the maturation phase. However, neutral processes, likely caused by predation from bacterial phages, also occurred, which led to the unpredictable temporal dynamics of the top competitors.

Toward flexible regulation of polyhydroxyalkanoate composition based on substrate feeding strategy: Insights into microbial community and metabolic features

The suitable feeding strategy considering both substrate preference (enrichment stage) and flexible regulation (PHA accumulation stage) were investigated, respectively, based on intracellular polymers synthesis peculiarities of the three types of cultures (M-Ac, M-Pr and M-Bu), which were enriched correspondingly using acetic type, propionic type and butyric type substrate. Compared to M-Ac and M-Bu cultures, maximum PHA content (PHA_m) of M-Pr exhibited the most stable responses to varying fractions of propionic acid (f_Pr) of the substrate. The substrate composed of acetic acid and propionic acid (Mix-AP) demonstrated higher efficiency in regulation of polymer composition than that composed of butyric acid and propionic acid (Mix-BP). For the whole process of three-stage MC PHA production, propionic acid-dominated acidification products should be used for the long-term enrichment of PHA producers, and acidification products mainly composed of propionic and acetic acid are preferred considering the regulation of polymer composition in PHA accumulation stage.

Assessing the efficiency and potential for internally reusing nitrogen-containing effluent in the PHA accumulation stage under low C/N conditions in a mixed-culture process

Polyhydroxyalkanoates (PHAs) are biodegradable polyesters poised to replace plastics. Mixed culture (MC)-based three-stage processes are effective for carbon recovery from waste biomass, but the energy-intensive PHA synthesis is negatively affected by ammonia nitrogen, inhibiting PHA yield. This study aims to reuse ammonia nitrogen efficiently to mitigate its impact and prevent secondary pollution. PHA production assays under varying MC types, substrate types, feeding modes, and oxygen levels showed that the butyrate type substrate-enriched, high-load, low-oxygen mode (RBC(4)P(1)O(+)) achieved a PHA conversion ratio of 0.45 g COD/g COD, 1.8 times higher than RBC(2)P(5)O(++), with reduced energy consumption and CO2 emissions. Ammonia uptake was 0.06 g NH3-N/g PHA at a productivity of 4.54 g/L, showing improved nitrogen recycling. Direct recycling of ammonia nitrogen-containing effluent in the PHA-producing MC enrichment system was performed, and no significant decrease was observed in either the physical properties of the MC flocs or the metrics related to PHA synthesis capacity. These results highlight the feasibility of ammonia reuse and indicate that the soluble microbial products in the effluent have minimal impact on MC enrichment.