A comprehensive review on polyhydroxyalkanoate: Genetic engineering to enhance production and feedstocks assimilation as green alternative for Petrochemical plastics

Microbial polyhydroxyalkanoates (PHA) are promising biopolymers due to their excellent biocompatibility and biodegradability having the potential to be sustainable plastic alternatives for fossil-derived polymers. Carbon flow and energy metabolism divert towards central carbon metabolism, which limits PHA assimilation. Hence genetic engineering strategies target the strains specifically for enhanced PHA synthesis by up-regulating and knocking down operons, thus regulating the biochemical pathway. This review provides an in-depth understanding of genetics in PHA accumulation and briefly discusses its structural properties. Cupriavidus necator is the pioneer bacteria for PHA production; others, such as Pseudomonas sp. and Bacillus sp., avail themselves for the robust PHA production capabilities of genetically modified organisms. Genetic engineering techniques used for PHA production have been detailed and discussed like CRISPR based systems have also served as efficient genome editing tools to improve the efficiency of metabolic modification. The most promising methods to boost the yield were highlighted, along with the metabolic paradigms of PHA-producing bacteria and a summary of the range of inexpensive carbon substrates that are used. It also coveres how metabolic modification can support microbial cell factories that use various fermentation techniques and co-production systems to produce PHA using modified strains. Nevertheless, the high cost of production preventing PHA from being commercialised could be by-passed via., genetically modified strains or enriched Mixed Microbial Culture (MMC) as a cheaper option along with the solvent-free downstream processes appear to be a promising bioroute to lower PHA costs.