Pseudomonas species from Antarctica and other environments host diverse genes encoding structurally conserved polyhydroxyalkanoate synthases linked with different mobile genetic elements

Polyhydroxyalkanoates (PHAs) are industrial microbial biopolymers offering a sustainable and biodegradable alternative to petroleum-based plastics. The PHA polymerization process is primarily mediated by PHA synthases (PhaCs), which determine the molecular and physical properties of the synthesized polymers. Previous reports have described Antarctic Pseudomonas isolates with unique PhaCs and capabilities for PHA production. However, the genes encoding PhaCs in Pseudomonas from Antarctica and other environments have not been investigated systematically. Here, we studied the diversity and phylogenetic distribution of phaC genes in 186 Pseudomonas species, including 33 isolates from Antarctica. Most species encode two class II PhaCs, with some displaying additional class II and class I enzymes, especially in Antarctic isolates. Different PhaC subclasses were proposed based on this diversity. Some phaC genes are in putative genomic islands, phages, plasmids, or close to insertion sequences, supporting their acquisition by multiple routes of horizontal gene transfer. Remarkably, the Antarctic strain P. frigusceleri MPC6 harbors five PhaCs, including one from a potential novel class. These findings underscore the unique attributes and potential use of Antarctic Pseudomonas for biopolymer production. Future research is essential to elucidate the enzymatic properties of this underexplored PhaC diversity. Impact StatementA few Pseudomonas strains have been widely used to produce polyhydroxyalkanoates (PHAs), biopolymers constituting a sustainable alternative to petroleum-based plastics whose synthesis and properties primarily rely on PHA synthase enzymes (PhaCs). We showed that less-studied Pseudomonas species, especially from Antarctica, host a remarkable diversity of PhaCs, some likely acquired by horizontal transfer, including a potential novel class with yet-to-be-explored functional features and biotechnological potential.