Revelation of the ability of Burkholderia sp. USM (JCM 15050) PHA synthase to polymerize 4-hydroxybutyrate monomer

Microbial Biosynthesis of Medium-Chain-Length Polyhydroxyalkanoate (mcl-PHA) from Waste Cooking Oil

Waste cooking oil is a common byproduct in the culinary industry, often posing disposal challenges. This study explores its conversion into the valuable bioplastic material, medium-chain-length polyhydroxyalkanoate (mcl-PHA), through microbial biosynthesis in controlled bioreactor conditions. Twenty-four bacterial isolates were obtained from oil-contaminated soil and waste materials in Mahd Ad-Dahab, Saudi Arabia. The best PHA-producing isolates were identified via 16S rDNA analysis as Neobacillus niacini and Metabacillus niabensis, with the sequences deposited in GenBank (accession numbers: PP346270 and PP346271). This study evaluated the effects of various carbon and nitrogen sources, as well as environmental factors, such as pH, temperature, and shaking speed, on the PHA production titer. Neobacillus niacini favored waste cooking oil and yeast extract, achieving a PHA production titer of 1.13 g/L, while Metabacillus niabensis preferred waste olive oil and urea, with a PHA production titer of 0.85 g/L. Both strains exhibited optimal growth at a neutral pH of 7, under optimal shaking -flask conditions. The bioreactor performance showed improved PHA production under controlled pH conditions, with a final titer of 9.75 g/L for Neobacillus niacini and 4.78 g/L for Metabacillus niabensis. Fourier transform infrared (FT-IR) spectroscopy and gas chromatography-mass spectrometry (GC-MS) confirmed the biosynthesized polymer as mcl-PHA. This research not only offers a sustainable method for transforming waste into valuable materials, but also provides insights into the optimal conditions for microbial PHA production, advancing environmental science and materials engineering.

Current Advances towards 4-Hydroxybutyrate Containing Polyhydroxyalkanoates Production for Biomedical Applications

Polyhydroxyalkanoates (PHA) are polyesters having high promise in biomedical applications. Among different types of PHA, poly-4-hydroxybutyrate (P4HB) is the only polymer that has received FDA approval for medical applications. However, most PHA producing microorganisms lack the ability to synthesize P4HB or PHA comprising 4-hydroxybutyrate (4HB) monomer due to their absence of a 4HB monomer supplying pathway. Thus, most microorganisms require supplementation of 4HB precursors to synthesize 4HB polymers. However, usage of 4HB precursors incurs additional production cost. Therefore, researchers have adopted strategies to reduce the cost, such as utilizing low-cost substrate as well as constructing 4HB monomer supplying pathways in microorganisms. We herein summarize the biomedical applications of P4HB, the natural producers of 4HB polymer, and the various strategies that have been applied in producing 4HB polymers in non-4HB producing microorganisms. It is expected that the readers would gain a vivid idea on the different strategic developments in the field of 4HB polymer production.

Genome, metabolic pathways and characteristics of cometabolism of dibenzothiophene and the biodiesel byproduct glycerol in Paraburkholderia sp. C3

Utilization of glycerol, a biodiesel byproduct, has not been well explored. In the present study, glycerol and the other carbon sources were studied for cometabolism of dibenzothiophene (DBT), a model chemical commonly used in bioremediation studies, by Paraburkholderia sp. C3. This study showed a direct association between rhamnolipids (RLs) biosynthesis and DBT biodegradation induced by different carbon sources in a Paraburkholderia specie. Glycerol can induce the strain C3 produce at least four RLs. The RL precursor is mainly derived from the fatty acid synthesis (FAS II) and β-oxidation pathway. The genome contained two (fabF and fabG) and four (fadA, fadE, fadB and echA) genes involved in FAS II and β-oxidation, respectively. The genome also carried the rhlA and rhlB genes involved in rhamnosyltransferase for RL biosynthesis and two DBT dioxygenase genes (nahAc and catA). The findings suggest a viable approach of using the biodiesel byproduct glycerol to remediate contaminated environments.

P(3HB-co-4HB) as high value polyhydroxyalkanoate: its development over recent decades and current advances

Polyhydroxyalkanoate (PHA) is a biogenic polymer that has the potential to substitute synthetic plastic in numerous applications. This is due to its unique attribute of being a biodegradable and biocompatible thermoplastic, achievable through microbial fermentation from a broad utilizable range of renewable resources. Among all the PHAs discovered, poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] stands out as a next generation healthcare biomaterial for having high biopharmaceutical and medical value since it is highly compatible to mammalian tissue. This review provides a critical assessment and complete overview of the development and trend of P(3HB-co-4HB) research over the last few decades, highlighting aspects from the microbial strain discovery to metabolic engineering and bioprocess cultivation strategies. The article also outlines the relevance of P(3HB-co-4HB) as a material for high value-added products in numerous healthcare-related applications.

New insight into poly (3-hydroxybutyrate) production by Azomonas macrocytogenes isolate KC685000: large scale production, kinetic modeling, recovery and characterization

About 24 h incubation of Azomonas (A.) macrocytogenes isolate KC685000 in 14L fermenter produced 22% poly (3-hydroxybutyrate) (PHB) per cell dry weight (CDW) biopolymer using 1 vvm aeration, 10% inoculum size, and initial pH of 7.2. To control the fermentation process, Logistic and Leudeking-Piret models were used to describe the cell growth and PHB production, respectively. These two models were in good agreement with the experimental data confirming the growth associated nature of PHB production. The best method for recovery of PHB was chemical digestion using sodium hypochlorite alone. The characterization of the produced polymer was carried out using FT-IR, ¹HNMR spectroscopy, gel permeation chromatography and transmission electron microscope. The analysis of the nucleotide sequences of PHA synthase enzyme revealed class III identity. The putative tertiary structure of PHA synthase enzyme was analyzed using Modular Approach to Structural class prediction software, Tied Mixture Hidden Markov Model server, and Swiss model software. It was deduced that PHA synthases' structural class was multidomain protein (α/β) containing a conserved cysteine residue and lipase box as characteristic features of α/β hydrolase super family. Taken together, all the results of molecular characterization and transmission electron microscope images supported that the PHB formation was attained by the micelle model. To the best of our knowledge, this is the first report on production of growth associated PHB polymer using A. macrocytogenes isolate KC685000, and its class III PHA synthase.

Physiological characterization of poly-β-hydroxybutyrate accumulation in the moderately thermophilic hydrogen-oxidizing bacterium Hydrogenophilus thermoluteolus TH-1

Hydrogenophilus thermoluteolus strain TH-1 is a thermophilic hydrogen-oxidizing microorganism that has the highest growth rate among autotrophs. Genomic analysis revealed that this strain comprises the complete gene set for poly-β-hydroxybutyrate (PHB) synthesis, i.e., three copies of acetyl-CoA acetyltransferase and polyhydroxyalkanoate synthase and one copy of acetoacetyl-CoA reductase and 3-hydroxyacyl-CoA dehydrogenase/3-hydroxybutyryl-CoA epimerase. An investigation on PHB accumulation in strain TH-1 demonstrated that PHB accumulation was induced by nitrogen limitation under autotrophic as well as heterotrophic conditions. This strain accumulated up to 430.4 ± 14.3 mg L^-1 PHB during a 3-h incubation under nitrogen-limited heterotrophic conditions. The highest PHB accumulation rates under autotrophic and heterotrophic conditions were 38.6% (w/w) of the dry cells after a 6-h induction and 53.8% after 3 h, respectively. Although PHB granules started to accumulate after 15 min of nitrogen limitation under heterotrophic conditions, a drastic decrease of PHB was observed after 9 h of induction.

Bacterial polyhydroxyalkanoates: Still fabulous?

Bacterial polyhydroxyalkanoates (PHA) are polyesters accumulated as carbon and energy storage materials under limited growth conditions in the presence of excess carbon sources. They have been developed as biomaterials with unique properties for the past many years being considered as a potential substitute for conventional non-degradable plastics. Due to the increasing concern towards global climate change, depleting petroleum resource and problems with an utilization of a growing number of synthetic plastics, PHAs have gained much more attention from industry and research. These environmentally friendly microbial polymers have great potential in biomedical, agricultural, and industrial applications. However, their production on a large scale is still limited. This paper describes the backgrounds of PHAs and discussed the current state of knowledge on the polyhydroxyalkanoates. Ability of bacteria to convert different carbon sources to PHAs, the opportunities and challenges of their introduction to global market as valuable renewable products have been also discussed.