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

Abstract

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 (Xestospongia muta and Aaptos aaptos) and sediment samples were collected in this study from Redang and Bidong islands located in the Malaysian Coral Triangle region. PHA synthase (phaC) 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 phaC genes from the bacterial metagenome of Aaptos and three phaC genes from sediment isolates (Sphingobacterium mizutaii UMTKB-6, Alcaligenes faecalis UMTKB-7, Acinetobacter calcoaceticus UMTKB-8) were identified. Produced PHA polymers were shown to be composed of 5C to nC monomers, with previously unreported PHA-producing ability of the S. mizutaii strain, as well as a 3-hydroxyvalerate-synthesising ability without precursor addition by the A. calcoaceticus strain.

Polyhydroxyalkanoate Production by Actinobacterial Isolates in Lignocellulosic Hydrolysate

“…They are suited to a variety of applications, including food packaging materials, medical devices, cosmetics, agricultural films, and biofuels [1][2][3][4][5]. Microorganisms typically synthesize PHAs as carbonaceous storage polymers when the concentrations of essential nutrients, such as oxygen (O2), and/or nitrogen (N), and/or phosphorus (P) are depleted [3,[6][7][8]. These biopolymers are classified as either short chain length (SCL), medium chain length (MCL), or long chain length (LCL) according to their hydroxyalkanoic monomeric composition [7].…”

“…Microorganisms typically synthesize PHAs as carbonaceous storage polymers when the concentrations of essential nutrients, such as oxygen (O2), and/or nitrogen (N), and/or phosphorus (P) are depleted [3,[6][7][8]. These biopolymers are classified as either short chain length (SCL), medium chain length (MCL), or long chain length (LCL) according to their hydroxyalkanoic monomeric composition [7]. The SCL, MCL, and LCL PHAs consist of three to five carbon (C) atoms, six to fourteen C atoms, and over fifteen C atoms, respectively [2,6,7].…”

“…These biopolymers are classified as either short chain length (SCL), medium chain length (MCL), or long chain length (LCL) according to their hydroxyalkanoic monomeric composition [7]. The SCL, MCL, and LCL PHAs consist of three to five carbon (C) atoms, six to fourteen C atoms, and over fifteen C atoms, respectively [2,6,7]. Polymers containing the SCL monomer, polyhydroxybutyrate (PHB), are ubiquitous in nature.…”

“…Polymers containing the SCL monomer, polyhydroxybutyrate (PHB), are ubiquitous in nature. The homopolymeric form of PHB is brittle, with a low impact strength, but the structural integrity can be improved by polymerization with other SCL or MCL monomers to form heteropolymers, such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) or 3HB and (R)-3-hydroxy-hexanoate (3HHx), P(3HB-co-3HHx) [1,3,7].…”