Properties of poly(3-hydroxybutyrate) depolymerase from a marine bacterium, Alcaligenes faecalis AE122

Area of Science:

• Microbiology
• Biochemistry
• Environmental Science

Background:

• Poly(3-hydroxybutyrate) (PHB) is a biodegradable polyester used as a carbon source by various microorganisms.
• Isolation and characterization of novel microbial enzymes are crucial for understanding biodegradation pathways and developing biotechnological applications.

Purpose of the Study:

• To isolate and characterize a novel bacterium capable of utilizing PHB as a sole carbon source.
• To purify and determine the enzymatic properties of PHB depolymerase from the isolated strain.
• To investigate the influence of environmental factors, such as salinity and cations, on enzyme activity.

Main Methods:

• Isolation of Alcaligenes faecalis AE122 from coastal seawater samples.
• Cultivation of the strain using PHB as the sole carbon source.
• Purification of PHB depolymerase using SDS-PAGE.
• Determination of enzyme molecular mass, N-terminal amino acid sequence, optimal pH, and temperature.
• Analysis of hydrolysis products and enzyme inhibition.

Main Results:

• Alcaligenes faecalis AE122 was isolated and demonstrated growth on PHB, requiring seawater or NaCl for optimal conditions.
• A PHB depolymerase was purified to homogeneity, with a monomeric subunit molecular mass of 95.5 kDa.
• The enzyme exhibited optimal activity at pH 9.0 and 55°C, was inhibited by PMSF, and its activity was significantly enhanced by seawater cations.
• Hydrolysis products primarily included dimeric and trimeric esters of 3-hydroxybutyrate.

Conclusions:

• Alcaligenes faecalis AE122 is a novel marine bacterium with the capability to degrade PHB.
• The purified PHB depolymerase is a robust enzyme with potential applications in PHB biodegradation and bioplastic recycling.
• Seawater cations play a significant role in enhancing the activity of this marine PHB depolymerase.