Upcycling depolymerized PET waste into polyhydroxyalkanoates and triacylglycerols by a newly isolated Rhodococcus sp. strain

The use of post-consumer polyethylene terephthalate (PET) wastes, which often contain various additives and contaminants such as metals and pigments that make mechanical recycling and reusability difficult, as feedstocks for microbial synthesis of value-added bio-based products is an emerging sustainable strategy for managing such wastes. This study evaluated the ability of a strain isolated from a plastic-contaminated site, Rhodococcus sp. isolate Ave7, to use terephthalic acid (TPA) obtained by chemically depolymerizing PET waste, as sole feedstock for cell growth and production of polyhydroxyalkanoates (PHAs) and triacylglycerols (TAGs) as intracellular storage compounds. The fed-batch bioreactor cultivation resulted in a cell dry weight production of 3.85 g/L, with PHA and TAG contents of 15.0 wt.% and 15.4 wt.%, respectively. Overall, the culture consumed 16.5 g/L TPA over a period of 73 h. The produced PHA was mainly composed of 3-hydroxyvalerate (3HV) monomers (> 90 wt.%). The accumulated TAGs presented a fatty acids profile rich in octadecenoic acid (C18:1; 52 wt.%), hexadecanoic acid (C16:0; 32 wt.%) and octadecanoic acid (C18:0; 12 wt.%). Overall, the strain Rhodococcus sp. Ave7 demonstrated a high capacity for TPA removal, converting it into cell biomass, PHA and TAGs, thus rendering this bioprocess a promising solution to reduce the plastic waste burden, in a circular and sustainable approach.