Polyhydroxyalkanoates consisting of α-methylated monomers: current progress in biosynthesis, material properties, and biodegradation

Abstract This review focuses on the biosynthesis, material properties, and potential applications of α-methylated polyhydroxyalkanoates (PHAs), a subclass of biodegradable polyesters produced by microbial fermentation. Emphasis is placed on monomers such as 3-hydroxy-2-methylbutyrate (3H2MB), 3-hydroxy-2-methylpropionate (3H2MP), 3-hydroxypivalate (3HPi), and α-methylated thioester 3-methyl-2-mercaptopropionate (3M2MP), which contribute to the unique properties of these polymers. The incorporation of α-methyl groups into PHA monomers enhances thermal stability and mechanical strength compared to non-substituted PHAs, while maintaining their biodegradability, making them attractive candidates for sustainable bioplastics. This review also summarizes the known microbial pathways and enzymatic mechanisms responsible for synthesizing these α-methylated PHAs, highlighting key enzymes and metabolic routes. These advancements suggest that α-methylated PHAs can overcome some limitations of conventional PHAs, such as brittleness and low thermal stability, thereby expanding their potential industrial applications in packaging, biomedical devices, and other fields. Overall, this review provides an updated overview of α-methylated PHA biosynthesis and properties, underscoring their importance in developing environmentally friendly alternatives to petroleum-based plastics.