Effects of nitrogen and phosphorous concentrations on PHA synthesis by PNSB enriched phototrophic mixed microbial culture

Global economic burden due to plastic pollution is estimated to be over $3 trillion annually. Bioplastics derived from bacteria-synthesized biopolymers like polyhydroxyalkanoates (PHAs), are a remarkably versatile sustainable alternative. Research on optimal growth-conditions for microbial PHA-synthesis fed-on sustainable substrates, particularly by phototrophic-mixed-cultures (PMC) enriched with purple non-sulphur bacteria (PNSB) is essential. This study intends to understand the effect of nitrogen and phosphorus concentrations on PHA-production by PMC grown using fuel synthesis wastewater (FSW) (organic by-product of Fischer-Tropsch process) as substrate. Stoichiometric quantification and 16 S metagenomic sequencing followed by statistical and bioinformatic analysis were done. High PHA-production (65–82% of biomass) is observed to be induced by Low-Nitrogen conditions enriching Rhodopseudomonas, Paludibacter and Pleomorphomonas and a Low-Phosphorus condition enriching Rhodopseudomonas, Rhodoplanes and Lentimicrobium. Analysis of metabolic-potential revealed 16 enzymes (of 8 different PHA-synthesis-pathways) inherent within the genomes of bacteria enriched by these culture conditions. This study identifies optimal nitrogen and phosphorus concentrations and the corresponding microbial-composition of FSW substrate-grown PMC-system to maximize PHA-production in a laboratory-scale bioprocess.