A novel type of hydrolase was purified from culture fluid of Paucimonas (formerly Pseudomonas) lemoignei. Biochemical characterization revealed an unusual substrate specificity of the purified enzyme for amorphous poly((R)-3-hydroxyalkanoates) (PHA) such as native granules of natural poly((R)-3-hydroxybutyrate) (PHB) or poly((R)-3-hydroxyvalerate) (PHV), artificial cholatecoated granules of natural PHB or PHV, atactic poly((R,S)-3-hydroxybutyrate), and oligomers of (R)-3-hydroxybutyrate (3HB) with six or more 3HB units. The enzyme has the unique property to recognize the physical state of the polymeric substrate by discrimination between amorphous PHA (good substrate) and denatured, partially crystalline PHA (no substrate). The pentamers of 3HB or 3HV were identified as the main products of enzymatic hydrolysis of native PHB or PHV, respectively. No activity was found with any denatured PHA, oligomers of (R)-3HB with five or less 3HB units, poly(6-hydroxyhexanoate), substrates of lipases such as tributyrin or triolein, substrates for amidases/nitrilases, DNA, RNA, casein, N-␣-benzoyl-L-arginine-4-nitranilide, or starch. The purified enzyme (M r 36,209) was remarkably stable and active at high temperature (60°C), high pH (up to 12.0), low ionic strength (distilled water), and in solvents (e.g. n-propyl alcohol). The depolymerase contained no essential SH groups or essential disulfide bridges and was insensitive to high concentrations of ionic (SDS) and nonionic (Triton and Tween) detergents. Characterization of the cloned structural gene (phaZ7) and the DNA-deduced amino acid sequence revealed no homologies to any PHB depolymerase or any other sequence of data banks except for a short sequence related to the active site serine of serine hydrolases. A classification of the enzyme into a new family (family 9) of carboxyesterases (Arpigny, J. L., and Jaeger, K.-E. (1999) Biochem. J. 343, 177-183) is suggested.Poly((R)-3-hydroxyalkanoic acids) (PHAs) 1 are a class of storage compounds that are synthesized during unbalanced growth by many bacteria. PHAs are deposited intracellularly in the form of inclusion bodies ("granules") to levels up to 90% of the cellular dry weight. The subject was reviewed recently (1). Poly((R)-3-hydroxybutyric acid) (PHB) is the most abundant polyester in bacteria. Bacterial copolymers containing randomly distributed (R)-3-hydroxybutyric and (R)-3-hydroxyvaleric units (poly(3HB-co-3HV)) have been commercialized for over a decade under the trade name Biopol ® . Any research on the biodegradation of PHA should clearly distinguish between (i) extracellular PHA degradation and (ii) intracellular PHA degradation. (i) Extracellular degradation is the utilization of an exogenous carbon/energy source by a notnecessarily-accumulating microorganism. The source of this extracellular polymer is PHA-released by accumulating cells after death. The ability to degrade PHA is widely distributed among bacteria and depends on the secretion of specific PHA depolymerases that are carboxyesterases (EC 3.1.1) a...

Chronic wounds are often recalcitrant to treatment because of high microbial bioburden and the problem of microbial resistance. Silver is a broad-spectrum natural antimicrobial agent with wide applications extending to proprietary wound dressings. Recently, silver nanoparticles have attracted attention in wound management. In the current study, the green synthesis of nanoparticles was accomplished using a natural reducing agent, curcumin, which is a natural polyphenolic compound that is well-known as a wound-healing agent. The hydrophobicity of curcumin was overcome by its microencapsulation in cyclodextrins. This study demonstrates the production, characterization of silver nanoparticles using aqueous curcumin:hydroxypropyl-β-cyclodextrin complex and loading them into bacterial cellulose hydrogel with moist wound-healing properties. These silver nanoparticle-loaded bacterial cellulose hydrogels were characterized for wound-management applications. In addition to high cytocompatibility, these novel dressings exhibited antimicrobial activity against three common wound-infecting pathogenic microbes Staphylococcus aureus , Pseudomonas aeruginosa , and Candida auris .

Blends of synthetic atactic poly(3-hydroxybutyrate) (a-PHB) with a natural bacterial isotactic copolymer of 3-hydroxybutyrate with 3-hydroxyvalerate (PHBV) containing 10 mol % of 3HV units were prepared using a simple casting procedure. In the range of compositions explored (10−50% a-PHB), blends of bacterial PHBV and synthetic atactic a-PHB were miscible in the melt and solidified with spherulitic morphology. The influence of a-PHB content on the thermal and mechanical properties of the blends was evaluated. The degree of crystallinity decreased with increasing content of a-PHB in the film samples, and the elongation at break for a sample containing 50% of a-PHB was 30-fold that of pure PHBV. Degradation experiments, both hydrolytic (pH = 7.4, T = 70 °C) and enzymatic (PHB-depolymerase A from Pseudomonas lemoignei, Tris-HCl buffer (pH = 8), T = 37 °C), were performed for both polymers and polymer blends. The rate of enzymatic degradation of the blends was higher than that of PHBV and increased with a-PHB content in the blends studied, whereas pure a-PHB did not biodegrade under these conditions. 3-Hydroxybutyric acid and its dimer were identified by HPLC as biodegradation products of both pure PHBV and its blends with a-PHB. Higher oligomers up to heptamer were detected as degradation products of the blends by APCI-MS and ESI-MS.