Poly (L-lactic acid)-degrading activity from endophytic Micromonospora spp. and catalytic analysis using surface plasmon resonance

Abstract

Poly (L-lactic acid) (PLA) is one of the biodegradable plastics that has been favorably consumed in substitution of petroleum-based plastics. PLA can be degraded by microorganisms including actinomycetes. In an attempt to seek for PLA degradable actinomycetes, three of the 164 strains of endophytic actinomycetes from the Genetics-Microbiology Kasetsart University (GMKU) culture collection showed clear zone formation on PLA-emulsified agar. 16S rRNA gene sequencing of the positive strains revealed that they belonged to the genus Micromonospora. After incubation of these strains on PLA film in basal medium for 2 wk, the films had clearly deteriorated when viewed under a scanning electron microscope. The degradation of the PLA by crude enzymes of these strains was investigated using surface plasmon resonance (SPR) analysis. A crude enzyme (Micromonospora sp. GMKU 358) produced the highest activity with a specific activity of 0.22 mg/hr/mg crude enzyme at pH 10 without ionic strength (no sodium chloride). This was the first report of the PLA-degrading activity of an endophytic Micromonospora characterized using SPR.