Characterization of poly-β-hydroxybutyrate and its biosynthesis in Priestia endophytica UCM B-5715.

Abstract

Background/aim: Polyhydroxyalkanoates (PHAs) are biodegradable biopolymers with promising applications in biotechnology and medicine; however, the diversity of their biosynthesis within the genus Priestia remains poorly characterized. Although Priestia species have been recognized as potential PHA producers, the detailed genomic architecture and physicochemical properties of the polymers synthesized by these bacteria, particularly in the type strain, remain poorly understood. This study aimed to characterize the poly-β-hydroxybutyrate (PHB) produced by Priestia endophytica UCM B-5715 and to investigate the PHB biosynthetic genes across related strains.

Materials and methods: PHB granules were visualized and measured using fluorescence microscopy, transmission electron microscopy, and scanning electron microscopy. Polymer structure and molecular weight were examined using Fourier transform infrared spectroscopy, ¹H nuclear magnetic resonance spectroscopy, and viscometry, whereas thermal behavior was evaluated using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Comparative genomic analysis of 11 P. endophytica strains was performed to reconstruct the PHB biosynthetic pathways and to analyze the evolutionary relationships among PhaC synthases.

Results: Microscopy confirmed the intracellular accumulation of PHB granules ranging in size from 65.35 × 47.77 nm to 1544.39 × 1126.53 nm. DSC analysis revealed a glass transition temperature of 2.3 °C, a crystallization temperature of 74.6 °C, and two melting peaks at 155 °C and 164.5 °C, indicating the presence of distinct crystalline domains. TGA demonstrated high thermal stability, with thermal decomposition initiating at 271 °C. Genomic analysis revealed a complete and conserved pha gene cluster across all examined strains, with the PhaC proteins being classified as Class IV PHA synthases.

Conclusion: This study provides the first comprehensive physicochemical and genomic characterization of PHB synthesized by the type strain Priestia endophytica UCM B-5715, highlighting the potential of this species as a robust microbial source of biotechnologically relevant biopolymers.