Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) biodegradation by a novel thermophilic Actinomadura sp. SCN-SB with microbial upcycling potential

Abstract

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is a biodegradable and biocompatible biopolymer with promising applications in food packaging and biomedical fields. However, its degradation under uncontrolled composting conditions remains relatively slow. To address this limitation, this study aimed to isolate and characterize thermophilic bacteria capable of producing extracellular hydrolytic enzymes involved in PHBV degradation. A total of 131 bacterial strains were isolated from soil samples, among which isolate 93 showed the highest PHBV-degrading activity on agar plates. Based on 16S rRNA gene sequencing, isolate 93 shared 98.19 % similarity with Actinomadura adrarensis ACD12. Whole-genome analysis revealed closer relatedness to A. vinacea JCM 3325, with digital DNA–DNA hybridization (dDDH) and average nucleotide identity (ANIb) values of 25.40 % and 80.07 %, respectively, suggesting that isolate 93 is a novel species, designated Actinomadura sp. SCN-SB. Gene annotation confirmed the presence of extracellular short-chain-length PHA (scl-PHA) depolymerase genes. Functional assays demonstrated a maximum clear zone of 28.0 ± 2.9 mm on PHBV agar plates at 50 °C and a 50.4 ± 4.7 % weight loss of PHBV films in submerged cultivation. Higher degradation rates were observed in YP medium compared to MSM, regardless of the C/N ratio. The crude scl-PHA depolymerase, purified via 80 % ammonium sulfate precipitation, exhibited optimal activity (0.27 ± 0.01 U/mL) at pH 9.0 and 50 °C. These findings identify Actinomadura sp. SCN-SB as a novel thermophilic bacterium with significant potential for enzymatic PHBV degradation, biological recycling, and upcycling in high-temperature composting and landfill conditions.