Colonization and degradation of polyhydroxyalkanoates by lipase-producing bacteria

Area of Science:

• Microbiology
• Polymer Science
• Biotechnology

Background:

• Polyhydroxyalkanoates (PHAs) are biodegradable polyesters with diverse applications.
• Understanding microbial degradation pathways is crucial for PHA recycling and environmental management.
• Limited information exists on the specific enzymes responsible for PHA breakdown by certain bacterial species.

Purpose of the Study:

• To investigate the biodegradation capabilities of *Pseudomonas chlororaphis* and *Acinetobacter lwoffii* on short-chain-length (scl-PHAs) and medium-chain-length (mcl-PHAs).
• To identify and characterize the enzymes involved in PHA depolymerization by these bacteria.
• To explore the genetic basis of PHA degradation in *P. chlororaphis* and *A. lwoffii*.

Main Methods:

• Culturing *P. chlororaphis* and *A. lwoffii* with PHA films as the sole carbon source.
• Assessing lipase activity using *p*-nitrophenyl octanoate substrate.
• Analyzing PHA film mass loss and surface morphology using scanning electron microscopy (SEM).
• Identifying and analyzing genes encoding secretory lipases in bacterial genomes.

Main Results:

• Both bacterial species exhibited depolymerization activity against scl-PHAs and mcl-PHAs, indicated by clear zones on agar plates.
• Significant mass loss (5%-18%) of PHA films was observed after 7 days of incubation.
• SEM revealed bacterial colonization, cracks, and pitting on the surface of degraded PHA films.
• Degradation products included 3-hydroxyhexanoate, 3-hydroxyoctanoate, and 3-hydroxydecanoate monomers.
• Genes for secretory lipases with conserved lipase box and oxyanion hole motifs were identified, showing low homology to known PHA depolymerases.

Conclusions:

• *Pseudomonas chlororaphis* and *Acinetobacter lwoffii* possess the enzymatic machinery to biodegrade both scl-PHAs and mcl-PHAs.
• The identified lipases represent novel enzymes for PHA degradation, distinct from previously characterized PHA depolymerases.
• These findings contribute to understanding microbial PHA catabolism and offer potential for biotechnological applications in PHA waste management.