Novel L-lysine α-oxidase from marine streptomyces: production, optimization and potent antibacterial activity against drug-resistant pathogens

This study reported the optimization, purification and characterization of a novel L-lysine α-oxidase (LLO) from marine-derived Streptomyces griseobrunneus strain S15. Among the twenty-two Streptomyces isolates, S15 showed the highest production of LLO (8 U/mg) after 96 h of cultivation. Molecular identification via 16S rRNA sequencing confirmed its phylogenetic relationship to S. griseobrunneus (GenBank PQ416578). Optimization of LLO production using response surface methodology enhanced the enzyme production by about five-fold compared to the control. Purification of LLO resulted in a yield of 49.99% and 2.356-fold purification through a single-step Sephacryl S-300 column. The purified homodimeric enzyme (115 kDa native, 58 kDa subunit) exhibited optimal activity at pH 6.4 and 50 °C, with exceptional thermal stability at physiological temperatures. According to kinetic studies, the enzyme has a high substrate affinity (Km 0.050 mM for L-lysine) and a broad specificity for basic and hydrophobic amino acids. Moreover, the enzyme showed potent antibacterial effects against multidrug-resistant pathogens (MIC 1.99–5.33 U/mL), demonstrated comparable or enhanced antibacterial activity relative to tested antibiotics. The unique combination of catalytic efficiency, stability, and antimicrobial activity makes this LLO a promising candidate for therapeutic and industrial applications.