Recovery of polyhydroxyalkanoate from the newly identified strain Enterobacter sp. MPLSI-2 isolated from a plastic waste landfill

Synthetic plastic waste poses a severe environmental threat due to its persistence and accumulation. As a result, producing biodegradable alternatives like polyhydroxyalkanoates (PHAs) is essential to replace conventional plastics and mitigate this pollution crisis. We isolated a novel Enterobacter sp. (MPLSI-2, PV029923) from a plastic waste landfill, a stress-rich and underexplored niche for identifying PHA producers. This study reports the first bioproduction of a novel seven-monomer medium- and long-chain copolymer, P(3HHxD-co-3HHxDe-co-3HOD-co-3HODe-co-3HTeD-co-3HTrD-co-3HHeD), by Enterobacter sp. MPLSI-2. Notably, the complex PHA was synthesized directly from glucose as the sole carbon source. The isolate identified via 16S rRNA sequencing as Enterobacter sp. MPLSI-2 (GenBank accession number: PV029923). Phylogenetic analysis and nucleotide homology confirmed the strain shares 99.44% sequence similarity with Enterobacter bugandensis EB-247 (FYBI01000003). The isolate is a Gram-negative, non-spore-forming rod, positive for citrate utilization and for amylase and protease production. Initial screening using Sudan Black B, Nile Blue A, and PHA-selective media revealed intracellular PHA granules, which were confirmed by microscopic observation. Using a One-Factor-At-A-Time (OFAT) design, culture conditions (temperature, pH) and carbon sources were optimized. Maximum PHA accumulation occurred at 37 °C and pH 7 using glucose (52.1 ± 1.87% DCW), followed by molasses (37.9 ± 0.66% DCW). The achieved productivity highlights the viability of molasses as an alternative substrate. Among recovery methods tested, SDS pretreatment followed by solvent extraction gave the highest extraction yield (74.7 ± 3.72%). While FTIR analysis suggested the characteristic ester carbonyl and alkyl bands indicative of PHAs, complementary GC–MS profiling definitively identified the polymer as a complex seven-monomer copolymer consisting of P(3HHxD-co-3HHxDe-co-3HOD-co-3HODe-co-3HTeD-co-3HTrD-co-3HHeD). These results indicate that Enterobacter sp. MPLSI-2 can produce substantial PHA from both pure and agro-industrial substrates and that optimized recovery improves overall yield.