Polyhydroxyalkanoate (PHA) Biopolymer Synthesis by Marine Bacteria of the Malaysian Coral Triangle Region and Mining for PHA Synthase Genes

Polyhydroxyalkanoate (PHA), a biodegradable and plastic-like biopolymer, has been receiving research and industrial attention due to severe plastic pollution, resource depletion, and global waste issues. This has spurred the isolation and characterisation of novel PHA-producing strains through cultivation and non-cultivation approaches, with a particular interest in genes encoding PHA synthesis pathways. Since sea sponges and sediment are marine benthic habitats known to be rich in microbial diversity, sponge tissues (<i>Xestospongia muta</i> and <i>Aaptos aaptos</i>) and sediment samples were collected in this study from Redang and Bidong islands located in the Malaysian Coral Triangle region. PHA synthase (<i>phaC</i>) genes were identified from sediment-associated bacterial strains using a cultivation approach and from sponge-associated bacterial metagenomes using a non-cultivation approach. In addition, phylogenetic diversity profiling was performed for the sponge-associated bacterial community using 16S ribosomal ribonucleic acid (16S rRNA) amplicon sequencing to screen for the potential presence of PHA-producer taxa. A total of three <i>phaC</i> genes from the bacterial metagenome of <i>Aaptos</i> and three <i>phaC</i> genes from sediment isolates (<i>Sphingobacterium mizutaii</i> UMTKB-6, <i>Alcaligenes faecalis</i> UMTKB-7, <i>Acinetobacter calcoaceticus</i> UMTKB-8) were identified. Produced PHA polymers were shown to be composed of 5C to <i>n</i>C monomers, with previously unreported PHA-producing ability of the <i>S. mizutaii</i> strain, as well as a 3-hydroxyvalerate-synthesising ability without precursor addition by the <i>A. calcoaceticus</i> strain.