Statistical optimization of lipase production from Sphingobacterium sp. strain S2 and evaluation of enzymatic depolymerization of Poly(lactic acid) at mesophilic temperature

The current study focuses on the production of poly (lactic acid) (PLA) degrading enzyme from Sphingobacterium sp. strain S2 under optimized conditions. The important variables influencing lipase production were identified by Plackett–Burman Design (PBD) and Central Composite Design (CCD). The results demonstrated NH4Cl as significant independent variable while mutual interaction between CaCl2.2H2O and yeast extract, NaCl and yeast extract and olive oil and MgSO4.7H2O showed highest regression coefficient, thus more influential towards the enzyme activity. The analysis suggested the following optimized production medium constituents [g/L; Na2HPO4·2H2O 6.0, Olive Oil 15, Yeast extract 4, NH4Cl 2.3, NaCl 3.0, MgSO4.7H2O 0.8, CaCl2.2H2O 3.0]. The predicted values were in agreement with experimental values and coefficient of determination R2 as 0.9943. The enzyme was purified to homogeneity and molecular size was determined as 40 kDa. The purified lipase was found stable at wide range of temperature (30–45 °C) and pH (3.0–10.0). The degradation of PLA was further evaluated using scanning electron microscopy (SEM) and Fourier Transform Infrared (FTIR) Spectroscopy. The PLA degradation products of PLA were determined through liquid-chromatography mass-spectrometry (LC-MS). Purified lipase depolymerized PLA films at 37 °C producing lactic acid oligomers of different chain lengths ranging from (3–12 oligomers long) that confirms the biodegradation potential of Sphingobacterium sp. against PLA. The results demonstrate that the lipase from Sphingobacterium sp. strain S2 could be applied for the treatment of PLA waste in a simulated system or using biochemical recovery process. •Production of poly (lactic acid) (PLA) degrading enzyme from Sphingobacterium sp. strain S2.•Physico-chemical parameters have been optimized through Plackett–Burman Design and Central Composite Design.•Lipase was purified to homogeneity and its molecular size was determined as approximately 40 kDa.•The purified lipase was stable to wide range of temperature and pH.•Short and long chain oligomers were detected upon degradation of PLA by strain S2 through LC-MS.