Potential of Streptomyces rochei 8ER183 for poly(lactic acid)-degrading enzyme production, biodegradative capability, and its whole-genome sequence characterization

Abstract

Ninety-eight actinomycetes isolates were screened for poly(lactic acid) (PLA)-degrading abilities using a minimal medium supplemented with emulsified PLA as the substrate. The isolate 8ER183 showed PLA degradation ability after incubation at ambient temperature (30 ± 2 °C) for 96 h. The 16S rRNA gene and whole-genome sequencing identified strain 8ER183 as Streptomyces rochei, and the genome size was 8.4 Mbp with an average G + C content of 72.39%. Genome mining revealed 5,689 proteins with functional assignments. The predicted degradation gene involving PLA-degrading enzymes such as protease and lipase was correlated with the phenotypic investigation. The enzymes involved in PLA degradation produced by 8ER183 strain were evaluated as protease and lipase. For enzyme production, cassava chips and peptone at 1.0 and 5.0 g/L yielded the highest PLA-degrading enzyme production (0.49 ± 0.02 U/mL) at 45 °C with pH 8.0. Scaling up enzyme production in a 3.0 L airlift bioreactor enhanced enzyme yield to 2.57 ± 0.12 U/mL, representing 5.25- and 32.12-fold increases compared to the optimized medium in shaking flasks and the unoptimized medium, respectively. The crude enzyme was most active at pH 9.0 and 50 °C. Electron microscopy and infrared spectroscopy revealed significant differences in the physical and chemical structures of PLA film after degradation by crude enzyme. This research identified and characterized a novel PLA-degrading actinomycetes strain as a solution to reduce bioplastic accumulation in the environment and contribute to a more sustainable future.