Identification and characterization of novel poly(DL-lactic acid) depolymerases from metagenome

Area of Science:

• Biotechnology
• Environmental Science
• Polymer Science

Background:

• Culture-based methods have identified poly(lactic acid) (PLA)-degrading microorganisms.
• The potential of unculturable microorganisms for PLA degradation remains unexplored.

Purpose of the Study:

• To identify and characterize novel PLA-degrading enzymes from unculturable microorganisms using metagenomic approaches.
• To investigate the enzymatic activity and substrate specificity of newly discovered PLA depolymerases.

Main Methods:

• Construction of a metagenomic library from DNA extracted from PLA disks in compost.
• Identification of PLA-degrading genes encoding lipase or hydrolase.
• Purification and characterization of the encoded enzymes, including substrate specificity and optimal activity conditions.

Main Results:

• Three PLA-degrading genes encoding enzymes with esterase activity were identified.
• The enzymes degraded PLA, other aliphatic polyesters, tributyrin, and p-nitrophenyl esters.
• One enzyme, PlaM4, demonstrated thermophilic properties, with optimal activity at 70°C and stability at 50°C, showing degradation of solid PLA at 60°C.
• Two other enzymes, PlaM7 and PlaM9, were not classifiable into known lipase or esterase families based on amino acid sequences.

Conclusions:

• This study reports the first identification and characterization of PLA depolymerases from a metagenome.
• The discovered enzymes, particularly the thermophilic PlaM4, show significant potential for industrial applications in PLA biodegradation.
• Metagenomic analysis is a powerful tool for uncovering novel enzymes from unculturable microbial communities.