Polyhydroxyalkanoate production by Paramecium caudatum isolated from industrial wastewater: a micro eukaryotic host for bioplastic accumulation.

Paramecium caudatum is a well-known ecotoxicological indicator for monitoring heavy metal pollution, including lead contamination. This study investigates P. caudatum's stress response to lead nitrate through the accumulation of polyhydroxyalkanoates (PHAs), biopolymers with potential applications in sustainable bioplastic production. The effect of lead nitrate stress (23.1 g/L) on PHA synthesis was compared with glucose supplementation (180 g/L) and unsupplemented controls. PHA was extracted at 24, 48, and 72 h from both glucose- and metal-treated cultures. Intracellular PHA granules were visualized using Sudan Black B and Nile Blue A staining. Extracted polymers were characterized by FTIR and GC-MS, confirming their chemical identity and structural similarity to poly(3-hydroxybutyrate) (PHB). Scanning electron microscopy (SEM) was used to examine the polymer microstructure. Lead nitrate treatment induced the highest PHA yield (4.8 g/L) after 24 h, significantly exceeding glucose-supplemented (3.8 g/L) and control (1.8 g/L) cultures. FTIR spectra revealed characteristic O-H, C-H, and ester carbonyl (C = O) absorption bands typical of PHB, while GC-MS identified 3-hydroxybutyrate as the dominant monomer along with minor medium-chain-length components. SEM imaging showed a porous, pseudospherical, and interconnected polymer morphology. P. caudatum responds to heavy metal stress by enhancing PHA accumulation, producing high-quality biopolymers structurally comparable to PHB. These findings highlight the dual potential of P. caudatum for bioplastic production and environmental remediation, offering a novel green biotechnology approach to valorize pollutant stress responses.