Selective carbon sources influence the microbial community, metabolic pathways, and intracellular carbon storage preference of purple phototrophic bacteria culture

Purple phototrophic bacteria (PPB) has shown great potential for value-added products generation when fed on volatile fatty acid (VFA)-rich fermentation wastewater. However, the composition of VFAs could impact their utilization efficiency and the consistency of final product quality. Potential changes in ecological structure resulting from the selective carbon sources to cultivate mixed PPB culture have rarely been explored. In this work, long-term acclimation was conducted in parallel bioreactors with acetate, propionate, and butyrate as carbon sources. A substantial PPB population (∼70 %) was maintained across all conditions, though a significant shift in the dominant strains was observed in the acetate-fed reactor, changing from Rhodopseudomonas to Rhodoplanes. Butyrate yielded the highest biomass of 1.054 g COD_biomass/g COD_removed, followed by acetate and propionate. Under nutrient-rich conditions, PPB culture achieved a superior uptake rate of 1.812 g COD/g VSS/d using butyrate compared to acetate and propionate as feed. Acetate was primarily used for polyhydroxybutyrate (PHB) synthesis, while propionate tended to favor the production of glycogen and protein, with less polyhydroxyvalerate (PHV) accumulation. Butyrate was mainly used for the PHB and protein production. Apparently, PPB demonstrated the preference of certain substrate transfer and synthesis pathways with different carbon sources. This was also verified by metagenomic sequencing and non-targeted metabolic analysis. This study is expected to improve our understanding of the distinct metabolic pathways and ecological adaptations of PPB under different VFA carbon sources, offering insights into the relationship between carbon source selection, microbial community structure, and value-added product synthesis, and providing guidance for PPB-based resource recovery in practical applications.