Purification and characterization of two extracellular polyhydroxyalkanoate depolymerases from Pseudomonas mendocina

Area of Science:

• Microbiology
• Biochemistry
• Enzymology

Background:

• Polyhydroxyalkanoates (PHAs) are biodegradable polyesters with diverse applications.
• Efficient enzymatic degradation of PHAs is crucial for their sustainable management and recycling.
• Pseudomonas mendocina DS04-T is known for its PHA-degrading capabilities.

Purpose of the Study:

• To purify and characterize two key polyhydroxyalkanoate depolymerases (PHAases) from Pseudomonas mendocina DS04-T.
• To investigate the enzymatic properties and substrate specificities of the purified PHAases.
• To understand the factors influencing the activity and stability of these enzymes.

Main Methods:

• Homogeneous purification of PHAase I and PHAase II using chromatography techniques.
• Determination of molecular masses via SDS-PAGE.
• Enzyme activity assays across a range of pH and temperature conditions.
• Substrate degradation studies using PHB, PHBV, and P(3HB-co-4HB).
• Analysis of the effects of various chemical agents (Na+, K+, EDTA, mercaptoethanol, H2O2) on enzyme activity.

Main Results:

• Two PHA depolymerases, PHAase I (59.4 kDa) and PHAase II (33.8 kDa), were successfully purified.
• Optimal activity for both enzymes was observed at 50°C.
• PHAase I and II exhibited optimal activity at pH 8.5 and 8.0, respectively.
• Both enzymes demonstrated degradation capabilities for poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)).
• Na+ and K+ ions slightly enhanced PHAase II activity, while EDTA significantly inhibited it.
• Mercaptoethanol and hydrogen peroxide inhibited the activity of both PHAases.

Conclusions:

• Pseudomonas mendocina DS04-T produces effective extracellular PHA depolymerases.
• The characterized PHAases exhibit distinct properties regarding molecular mass, optimal pH, and sensitivity to inhibitors.
• These enzymes show potential for biotechnological applications in PHA biodegradation and recycling.
• Understanding the specific activity and inhibition profiles is key for optimizing enzymatic PHA degradation processes.