Bacterial Polyhydroxyalkanoate Granules: Biogenesis, Structure, and Potential Use as Nano-/Micro-Beads in Biotechnological and Biomedical Applications

Embracing Sustainability: The World of Bio-Based Polymers in a Mini Review

The proliferation of polymer science and technology in recent decades has been remarkable, with synthetic polymers derived predominantly from petroleum-based sources dominating the market. However, concerns about their environmental impacts and the finite nature of fossil resources have sparked interest in sustainable alternatives. Bio-based polymers, derived from renewable sources such as plants and microbes, offer promise in addressing these challenges. This review provides an overview of bio-based polymers, discussing their production methods, properties, and potential applications. Specifically, it explores prominent examples including polylactic acid (PLA), polyhydroxyalkanoates (PHAs), and polyhydroxy polyamides (PHPAs). Despite their current limited market share, the growing awareness of environmental issues and advancements in technology are driving increased demand for bio-based polymers, positioning them as essential components in the transition towards a more sustainable future.

Physicochemical characterization of polyhydroxybutyrate (PHB) produced by the rare halophile Brachybacterium paraconglomeratum MTCC 13074

BACKGROUND

Polyhydroxybutyrate is a biopolymer produced by bacteria and archaea under nitrogen-limiting conditions. PHB is an essential polymer in the bioplastic sector because of its biodegradability, eco-friendliness, and adaptability. The characterization of PHB is a multifaceted process for studying the structure and its properties. This entire aspect can assure the long-term viability and performance attributes of the PHB. The characteristics of PHB extracted from the halophile Brachybacterium paraconglomeratum were investigated with the objective of making films for application in healthcare.

RESULTS

This was the first characterization study on PHB produced by a rare halophile, Brachybacterium paraconglomeratum (MTCC 13074). In this study, the strain produced 2.72 g/l of PHB for.5.1 g/l of biomass under optimal conditions. Methods are described for the determination of the physicochemical properties of PHB. The prominent functional groups CH3 and C = O were observed by FT-IR and the actual chemical structure of the PHB was deduced by NMR. GCMS detects the confirmation of four methyl ester derivatives of the extracted PHB in the sample. Mass spectrometry revealed the molecular weight of methyl 3-hydroxybutyric acid (3HB) present in the extract. The air-dried PHB films were exposed to TGA, DSC and a universal testing machine to determine the thermal profile and mechanical stability. Additionally, the essential property of biopolymers like viscosity was also assessed for the extracted PHB.

CONCLUSIONS

The current study demonstrated the consistency and quality of B. paraconglomeratum PHB. Therefore, Brachybacterium sps are also a considerable source of PHB with desired characteristics for industrial production.

In vivo assembly of epitope-coated biopolymer particles that induce anti-tumor responses

There is an unmet need for antigen delivery systems that elicit efficient T cell priming to prevent infectious diseases or for treatment of cancers. Here, we explored the immunogenic potential of biologically assembled biopolymer particles (BPs) that have been bioengineered to display the antigenic MHC I and MHC II epitopes of model antigen ovalbumin (OVA). Purified dendritic cells (DCs) captured BP-OVA and presented the associated antigenic epitopes to CD4+ T cells and CD8+ T cells. Vaccination with BP-OVA in the absence of adjuvant elicited antigen presentation to OVA-specific CD8+ and CD4+ T cells and cross-primed effective cytotoxic T lymphocyte (CTL) killers. BP-OVA induction of CTL killing did not require CD4+ T cell help, with active CTLs generated in BP-OVA vaccinated I-Ab-/- and CD40-/- mice. In contrast, IL-15 and type I IFN were required, with abrogated CTL activity in vaccinated IL-15-/- and IFNAR1-/- mice. cDC1 and/or CD103+ DCs were not essential for BP-OVA specific CTL with immunization eliciting responses in Batf3-/- mice. Poly I:C, but not LPS or CpG, co-administered as an adjuvant with BP-OVA boosted CTL responses. Finally, vaccination with BP-OVA protected against B16-OVA melanoma and Eμ-myc-GFP-OVA lymphoma inoculation. In summary, we have demonstrated that epitope-displaying BPs represent an antigen delivery platform exhibiting a unique mechanism to effectively engage T cell immune responses.

Phages for the treatment of Mycobacterium species

Highly drug-resistant strains are not uncommon among the Mycobacterium genus, with patients requiring lengthy antibiotic treatment regimens with multiple drugs and harmful side effects. This alarming increase in antibiotic resistance globally has renewed the interest in mycobacteriophage therapy for both Mycobacterium tuberculosis complex and non-tuberculosis mycobacteria. With the increasing number of genetically well-characterized mycobacteriophages and robust engineering tools to convert temperate phages to obligate lytic phages, the phage cache against extensive drug-resistant mycobacteria is constantly expanding. Synergistic effects between phages and TB drugs are also a promising avenue to research, with mycobacteriophages having several additional advantages compared to traditional antibiotics due to their different modes of action. These advantages include less side effects, a narrow host spectrum, biofilm penetration, self-replication at the site of infection and the potential to be manufactured on a large scale. In addition, mycobacteriophage enzymes, not yet in clinical use, warrant further studies with their additional benefits for rupturing host bacteria thereby limiting resistance development as well as showing promise in vitro to act synergistically with TB drugs. Before mycobacteriophage therapy can be envisioned as part of routine care, several obstacles must be overcome to translate in vitro work into clinical practice. Strategies to target intracellular bacteria and selecting phage cocktails to limit cross-resistance remain important avenues to explore. However, insight into pathophysiological host-phage interactions on a molecular level and innovative solutions to transcend mycobacteriophage therapy impediments, offer sufficient encouragement to explore phage therapy. Recently, the first successful clinical studies were performed using a mycobacteriophage-constructed cocktail to treat non-tuberculosis mycobacteria, providing substantial insight into lessons learned and potential pitfalls to avoid in order to ensure favorable outcomes. However, due to mycobacterium strain variation, mycobacteriophage therapy remains personalized, only being utilized in compassionate care cases until there is further regulatory approval. Therefore, identifying the determinants that influence clinical outcomes that can expand the repertoire of mycobacteriophages for therapeutic benefit, remains key for their future application.

Biodegradable blends from bacterial biopolyester PHBV and bio-based PBSA: Study of the effect of chain extender on the thermal, mechanical and morphological properties

Being aware of the global problem of plastic pollution, our society is claiming new bioplastics to replace conventional polymers. Balancing their mechanical performance is required to increase their presence in the market. Brittleness of bacterial poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was attempted to be decreased by melt blending with flexible starch-based poly(butylene succinate-co-butylene adipate) (PBSA). An epoxy-functionalized chain extender was used to enhance interaction between both immiscible biopolyesters. Mechanical performance, morphology, rheology, and crystallization behavior of injection-molded PHBV-PBSA blends (70-30, 50-50, and 30-70 wt%) were assessed in the presence and absence of the chain extender. Crystallization of PHBV was hindered, which was reflected in the improvement of mechanical properties. When PBSA >50 %, the homogeneity of results increased within the same sample while for PHBV-PBSA 70-30 wt% the elongation was 45 % higher. During the flexural test, it changed from brittle to non-breakable. The additive did not change the type of morphology developed by each blend nor the toughening mechanisms, so impact strength was barely affected. However, it reduced the size of dispersed phase domains due to a viscosity change, improving their processability. The higher the PHBV in the blend, the higher the effect of the chain extender.

Nanomaterials in tuberculosis DNA vaccine delivery: historical perspective and current landscape

Vaccinations, especially DNA vaccines that promote host immunity, are the most effective interventions for tuberculosis (TB) control. However, the vaccine delivery system exhibits a significant impact on the protective effects of the vaccine. Recently, effective nanomaterial-based delivery systems (including nanoparticles, nanogold, nanoliposomes, virus-like particles, and virus carriers) have been developed for DNA vaccines to control TB. This review highlights the historical development of various nanomaterial-based delivery systems for TB DNA vaccines, along with the emerging technologies. Nanomaterial-based vaccine delivery systems could enhance the efficacy of TB vaccination; therefore, this summary could guide nanomaterial selection for optimal and safe vaccine delivery, facilitating the design and development of highly effective TB vaccines.

Comparative Genomics of Members of the Genus Defluviicoccus With Insights Into Their Ecophysiological Importance

Members of the genus Defluviicoccus occur often at high abundances in activated sludge wastewater treatment plants designed to remove phosphorus, where biomass is subjected to alternating anaerobic feed/aerobic famine conditions, believed to favor the proliferation of organisms like Ca. Accumulibacter and other phosphate-accumulating organisms (PAO), and Defluviicoccus. All have a capacity to assimilate readily metabolizable substrates and store them intracellularly during the anaerobic feed stage so that under the subsequent famine aerobic stage, these can be used to synthesize polyphosphate reserves by the PAO and glycogen by Defluviicoccus. Consequently, Defluviicoccus is described as a glycogen-accumulating organism or GAO. Because they share a similar anaerobic phenotype, it has been proposed that at high Defluviicoccus abundance, the PAO are out-competed for assimilable metabolites anaerobically, and hence aerobic P removal capacity is reduced. Several Defluviicoccus whole genome sequences have been published (Ca. Defluviicoccus tetraformis, Defluviicoccus GAO-HK, and Ca. Defluviicoccus seviourii). The available genomic data of these suggest marked metabolic differences between them, some of which have ecophysiological implications. Here, we describe the whole genome sequence of the type strain Defluviicoccus vanus^T, the only cultured member of this genus, and a detailed comparative re-examination of all extant Defluviicoccus genomes. Each, with one exception, which appears not to be a member of this genus, contains the genes expected of GAO members, in possessing multiple copies of those for glycogen biosynthesis and catabolism, and anaerobic polyhydroxyalkanoate (PHA) synthesis. Both 16S rRNA and genome sequence data suggest that the current recognition of four clades is insufficient to embrace their phylogenetic biodiversity, but do not support the view that they should be re-classified into families other than their existing location in the Rhodospirillaceae. As expected, considerable variations were seen in the presence and numbers of genes encoding properties associated with key substrate assimilation and metabolic pathways. Two genomes also carried the pit gene for synthesis of the low-affinity phosphate transport protein, pit, considered by many to distinguish all PAO from GAO. The data re-emphasize the risks associated with extrapolating the data generated from a single Defluviicoccus population to embrace all members of that genus.

Polyhydroxyalkanoates, the bioplastics of microbial origin: Properties, biochemical synthesis, and their applications

The rising plastic pollution deteriorates the environment significantly as these petroleum-based plastics are not biodegradable, and their production requires natural fuels (energy source) and other resources. Polyhydroxyalkanoates (PHAs) are bioplastic and a sustainable and eco-friendly alternative to synthetic plastics. PHAs can be entirely synthesized using various microorganisms such as bacteria, algae, and fungi. These value-added biopolymers show promising properties such as enhanced biodegradability, biocompatibility, and other chemo-mechanical properties. Further, it has been established that the properties of PHA polymers depend on the substrates and chemical composition (monomer unit) of these polymers. PHAs hold great potential as an alternative to petroleum-based polymers, and further research for economic production and utilization of these biopolymers is required. The review describes the synthesis mechanism and different properties of microbially synthesized PHAs for various applications. The classification of PHAs and the multiple techniques necessary for their detection and evaluation have been discussed. In addition, the synthesis mechanism involving the genetic regulation of these biopolymers in various microbial groups has been described. This review provides information on various commercially available PHAs and their application in multiple sectors. The industrial production of these microbially synthesized polymers and the different extraction methods have been reviewed in detail. Furthermore, the review provides an insight into the potential applications of this biopolymer in environmental, industrial, and biomedical applications.

Intranasal Delivery of Antigen-Coated Polymer Particles Protects against Pseudomonas aeruginosa Infection

Pseudomonas aeruginosa is an opportunistic human pathogen that is intrinsically resistant to multiple antibiotics, causing severe and persistent infections in immunocompromised individuals. This bacterium has been listed as a priority pathogen by the WHO in 2017, and there is no vaccine available for human use. In this study, 10 vaccine candidate antigens were selected for particulate vaccine design. We engineered Escherichia coli to assemble biopolymer particles (BPs) that were either coated with epitopes (Ag) derived from OprF/I-AlgE proteins or PopB or PopB-Ag or coated with single or double copies of epitopes (10Ag and 10Ag(2x)) derived from OprF, OprI, AlgE, OprL, PopB, PilA, PilO, FliC, Hcp1, and CdrA. Antigen-coated BPs showed a diameter of 0.93-1.16 μm with negative surface charge. Antigens attached to BPs were identified by mass spectrometry. Vaccination with BP-Ag, BP-PopB, BP-PopBAg, PB-10Ag, and BP-10Ag(2x) with and without Alhydrogel adjuvant induced significant antigen-specific humoral and cell-mediated immune responses in mice. All particulate vaccines with Alhydrogel induced protection in an acute pneumonia murine model of P. aeruginosa infection, contributing to up to 80% survival when administered intramuscularly, and the addition of Alhydrogel boosted immunity. The BP-10Ag(2x) vaccine candidate showed the best performance and even induced protective immunity in the absence of Alhydrogel. Intramuscular administration of the BP-10Ag(2x) without Alhydrogel vaccine resulted in 60% survival. Intranasal vaccination induced immunity, contributing to about 90% survival. Overall, our data suggest that vaccination with BPs coated with P. aeruginosa antigens induce protective immunity against P. aeruginosa infections. The possibility of intranasal delivery will strongly facilitate administration and use of BP vaccines.

Use Intein Cleavable Polyhydroxyalkanoate Synthase Fusions to Improve Protein Solubility

Recombinant E. coli producing intein-cleavable polyhydroxyalkanoate synthase fusions mediates the intracellular formation of polyhydroxyalkanoate (PHA) particles densely coated with intein-cleavable target protein fusion. These PHA particles can be efficiently purified from lysed cells. The self-cleaving intein performs as a bio-linker between the PHA synthase and the target protein. The tagless target protein can be released as pure soluble protein from the PHA particles by a simple pH reduction to 6.0. Here we describe that PHA particles serve as bioseparation resin for purification of soluble target proteins with pharmaceutical grade purity, similar to commercial affinity separation technologies. This cost-effective technique does not involve multiple complicated protein purification procedures, and we have exploited this approach to purify six target proteins: green fluorescent protein (GFP) from A. victoria, antigen Rv1626 from M. tuberculosis, the immunoglobulin G (IgG) binding ZZ domain of protein A derived from Staphylococcus aureus, human tumor necrosis factor alpha (TNFα), human granulocyte colony-stimulating factor (G-CSF), and human interferon alpha 2b (IFNα2b).

PHA Production from Cheese Whey and "Scotta": Comparison between a Consortium and a Pure Culture of Leuconostoc mesenteroides

It is urgent to expand the market of biodegradable alternatives to oil-derived plastics owing to (i) increasingly limited oil availability/accessibility, and (ii) the dramatic impact of traditional plastics on aquatic life, the food chain, all Earth ecosystems, and ultimately, human health. Polyhydroxyalkanoates (PHAs) are promising biodegradable polymers that can be obtained through microbial fermentation of agro-industrial byproducts, e.g., milk and cheese whey. Here, the PHA-accumulating efficiency of a mixed microbial culture (MMC, derived from activated sludges) grown on dairy byproducts (cheese and scotta whey) was measured. Bioreactor tests featuring temperature and pH control showed that both scotta and pre-treated Toma cheese whey could be used for PHA production by MMC, although scotta cheese whey supported higher PHA yield and productivity. The advantages of open MMCs include their plasticity and versatility to fast changing conditions; furthermore, no growth-medium sterilization is needed prior to fermentation. However, the use of pure cultures of efficient PHA producers may support better metabolic performances. Therefore, PHA-producing strains were isolated from a MMC, leading to the satisfactory identification of two bacterial strains, Citrobacter freundii and Leuconostoc spp., whose ability to accumulate PHAs in synthetic media was confirmed. A more detailed investigation by mass spectrometry revealed that the strain was L. mesenteroides. Although the validation of L. mesenteroides potential to produce PHA through fermentation of agro-industrial byproducts requires further investigations, this is the first study reporting PHA production with the Leuconostoc genus.

Engineering Antigens to Assemble into Polymer Particle Vaccines for Prevention of Streptococcus suis Infection

Streptococcus suis is a zoonotic pathogen affecting pigs and humans. This bacterium causes severe economic losses in the swine industry and poses a serious threat to public health and food safety. There is no effective commercial vaccine available for pigs or humans. In this study, we applied the biopolymer particle (BP) vaccine technology to incorporate seven conserved S. suis antigens (38 kDa protein (38), enolase (Enol), SSU1915, SSU1355, SSU0185, SSU1215, and SSU1773 (SSU1 and SSU2)). Two combinations of these antigens (38 and Enol; all SSU antigens designated as SSU1 and SSU2) were engineered to mediate production of BPs coated with either antigens 38 and Enol or SSU1 and SSU2 inside recombinant Escherichia coli. The isolated and purified empty BPs, 38-BP-Enol and SSU1-BP-SSU2, showed size ranges of 312-428 nm and 292-344 nm with and without the QuilA® adjuvant, respectively, and all showed a negative surface charge. Further characterization of purified BPs confirmed the presence of the expected antigen-comprising fusion proteins as assessed by tryptic peptide fingerprinting analysis using quadrupole time-of-flight mass spectrometry and immunoblotting. Vaccination with 38-BP-Enol and SSU1-BP-SSU2 formulated with and without QuilA® adjuvant induced significant antigen-specific humoral immune responses in mice. Antigen-coated BPs induced significant and specific Ig (IgM + IgG) and IgG immune responses (1.0 × 106-1.0 × 107) when compared with mice vaccinated with empty BPs. Functionality of the immune response was confirmed in challenge experiments using an acute murine S. suis infection model, which showed 100% survival of the 38-BP-Enol and SSU1-BP-SSU2 vaccinated mice compared to 70% survival when vaccinated with empty BPs. Overall, our data suggest that S. suis antigen-coated BPs could be developed into particulate vaccines that induce protective immunity against S. suis infections.

PHA granule formation and degradation by Cupriavidus necator under different nutritional conditions

Polyhydroxyalkanoates (PHA) are polymers produced by microorganisms with increasing commercialization potential; Cupriavidus necator has been the model microorganism to research PHA production. Despite many contributions concerning the formation and degradation of PHA granules, as well as the morphological changes in cells, these phenomena have not been univocally explained yet. Thus, this study aims to integrate the microscopic and analytical analysis to characterize changes in bacterial cell/PHA granules morphology, PHA content, and yield coefficients under different cultivation strategies of C. necator ATCC 17697. The cell size and morphology, granule size and amount, residual biomass, and PHA concentration along the fermentation and degradation depend greatly on nutritional conditions and cultivation time of C. necator. It was proposed to calculate a yield coefficient for the residual biomass production in the PHA utilization stage, related to the bacteria's ability to survive without a carbon source in the culture medium by utilizing the accumulated PHA previously. Maximum granule length reached 1.07 µm after 72 h of PHA accumulation stage under optimum nutritional conditions. This value is twice the values previously reported for C. necator. It is important since the larger PHA granules facilitate the recovery of PHA and different application development.

A Pseudomonas aeruginosa-Derived Particulate Vaccine Protects against P. aeruginosa Infection

Despite numerous efforts to develop an effective vaccine against Pseudomonas aeruginosa, no vaccine has yet been approved for human use. This study investigates the utility of the P. aeruginosa inherently produced polyhydroxyalkanaote (PHA) inclusions and associated host-cell proteins (HCP) as a particulate vaccine platform. We further engineered PHA inclusions to display epitopes derived from the outer membrane proteins OprF/OprI/AlgE (Ag) or the type III secretion system translocator PopB. PHA and engineered PHA beads induced antigen-specific humoral, cell-mediated immune responses, anti-HCP and anti-polysaccharide Psl responses in mice. Antibodies mediated opsonophagocytic killing and serotype-independent protective immunity as shown by 100% survival upon challenge with P. aeruginosa in an acute pneumonia murine model. Vaccines were stable at 4 °C for at least one year. Overall, our data suggest that vaccination with subcellular empty PHA beads was sufficient to elicit multiple immune effectors that can prevent P. aeruginosa infection.

Bioengineered Polymer Nanobeads for Isolation and Electrochemical Detection of Cancer Biomarkers

Early sensitive diagnosis of cancer is critical for enhancing treatment success. We previously bioengineered multifunctional core-shell structures composed of a poly-3-hydroxybutyrate (PHB) core densely coated with protein functions for uses in bioseparation and immunodiagnostic applications. Here, we report bioengineering of Escherichia coli to self-assemble PHB inclusions that codisplay a ferritin-derived iron-binding peptide and the protein A-derived antibody-binding Z domain. The iron-binding peptide mediated surface coating with a ferrofluid imparting superparamagnetic properties, while the Z domain remained accessible for binding of cancer biomarker-specific antibodies. We demonstrated that these nanobeads can specifically bind biomarkers in complex mixtures, enabling efficient magnetic separation toward enhanced electrochemical detection of cancer biomarkers such as methylated DNA and exosomes from cancer cells. Our study revealed that superparamagnetic core-shell structures can be derived from biological self-assembly systems for uses in sensitive and specific electrochemical detection of cancer biomarkers, laying the foundation for engineering advanced nanomaterials for diverse diagnostic approaches.

Metabolic circuits and gene regulators in polyhydroxyalkanoate producing organisms: Intervention strategies for enhanced production

Worldwide worries upsurge concerning environmental pollutions triggered by the accumulation of plastic wastes. Biopolymers are promising candidates for resolving these difficulties by replacing non-biodegradable plastics. Among biopolymers, polyhydroxyalkanoates (PHAs), are natural polymers that are synthesized and accumulated in a range of microorganisms, are considered as promising biopolymers since they have biocompatibility, biodegradability, and other physico-chemical properties comparable to those of synthetic plastics. Consequently, considerable research have been attempted to advance a better understanding of mechanisms related to the metabolic synthesis and characteristics of PHAs and to develop native and recombinant microorganisms that can proficiently produce PHAs comprising desired monomers with high titer and productivity for industrial applications. Recent developments in metabolic engineering and synthetic biology applied to enhance PHA synthesis include, promoter engineering, ribosome-binding site (RBS) engineering, development of synthetic constructs etc. This review gives a brief overview of metabolic routes and regulators of PHA production and its intervention strategies.

Biomedical applications of environmental friendly poly-hydroxyalkanoates

Biological polyesters of hydroxyacids are known as polyhydroxyalkanoates (PHA). They have proved to be an alternative, environmentally friendly and attractive candidate for the replacement of petroleum-based plastics in many applications. Many bacteria synthesize these compounds as an intracellular carbon and energy compound usually under unbalanced growth conditions. Biodegradability and biocompatibility of different PHA has been studied in cell culture systems or in an animal host during the last few decades. Such investigations have proposed that PHA can be used as biomaterials for applications in conventional medical devices such as sutures, patches, meshes, implants, and tissue engineering scaffolds as well. Moreover, findings related to encapsulation capability and degradation kinetics of some PHA polymers has paved their way for development of controlled drug delivery systems. The present review discusses about bio-plastics, their characteristics, examines the key findings and recent advances highlighting the usage of bio-plastics in different medical devices. The patents concerning to PHA application in biomedical field have been also enlisted that will provide a brief overview of the status of research in bio-plastic. This would help medical researchers and practitioners to replace the synthetic plastics aids that are currently being used. Simultaneously, it could also prove to be a strong step in reducing the plastic pollution that surged abruptly due to the COVID-19 medical waste.

PLAN-M; Mycobacteriophage Endolysins Fused to Biodegradable Nanobeads Mitigate Mycobacterial Growth in Liquid and on Surfaces

The Mycobacteria are a genus of Actinobacteria that include human pathogens such as Mycobacterium tuberculosis (TB). Active TB disease can spread by airborne transmission to healthcare workers and to their community. The HHMI SEA-PHAGES program has contributed to discovering bacteriophages that are able to infect M. smegmatis MC² 155, a close relative of M. tuberculosis. This collection of diverse Mycobacteriophages is an excellent resource for trialling bacteriophage-sourced enzymes in novel applications. Herein we measured the ability Mycobacteriophage endolysins to lyse their host strain when functionally fused to biodegradable polyhydroxyalkanoate (PHA) nanobeads. PHA nanobeads facilitate both the expression and the application of enzymes to surfaces and have been demonstrated to stabilize a wide array of proteins for practical applications whilst eliminating the challenges of traditional protein purification. We selected two Lysin A and six Lysin B homologs to be functionally fused to the polyhydroxyalkanoate synthase C (PhaC). Expression of these constructs resulted in functional lysins displayed on the surface of PHA nanobeads. The lysins thus directionally displayed on nanobeads lysed up to 79% of the M. smegmatis MC² 155 population using 80 mg/mL of nanobeads in pure culture. In order to determine whether the nanobeads would be effective as a protective layer in PPE we adapted a fabric-based test and observed a maximum of 1 log loss of the cell population after 5 h of exposure on a textile (91% cell lysis). Lysin B enzymes performed better than the Lysin A enzymes as a protective barrier on textiles surface assays. These results suggest that bacterial endolysins are efficient in their action when displayed on PHA nanobeads and can cause significant population mortality in as little as 45 min. Our results provide the proof-of-principle that Mycobacteriophage endolysins can be used on functionalized nanobeads where they can protect surfaces such as personal protective equipment (PPE) that routinely come into contact with aerosolised bacteria.

3-Hydroxybutyrate as a Metabolite and a Signal Molecule Regulating Processes of Living Organisms

3-hydroxybutyrate (3-HB) as a very important metabolite occurs in animals, bacteria and plants. It is well known that in animals, 3-HB is formed as a product of the normal metabolism of fatty acid oxidation and can therefore be used as an energy source in the absence of sufficient blood glucose. In microorganisms, 3-HB mainly serves as a substrate for the synthesis of polyhydroxybutyrate, which is a reserve material. Recent studies show that in plants, 3-HB acts as a regulatory molecule that most likely influences the expression of genes involved in DNA methylation, thereby altering DNA methylation levels. Additionally, in animals, 3-HB is not only an intermediate metabolite, but also an important regulatory molecule that can influence gene expression, lipid metabolism, neuronal function, and overall metabolic rate. Some of these effects are the direct effects of 3-HB itself, while others are indirect effects, regulated by the metabolites into which 3-HB is converted. One of the most important regulatory functions of 3-HB is the inhibition of the activity of histone deacetylases and thus the epigenetic regulation of many genes. Due to the number of functions of this compound, it also shows promising therapeutic properties.

Recovery of Polyhydroxyalkanoates From Single and Mixed Microbial Cultures: A Review

An overview of the main polyhydroxyalkanoates (PHA) recovery methods is here reported, by considering the kind of PHA-producing bacteria (single bacterial strains or mixed microbial cultures) and the chemico-physical characteristics of the extracted polymer (molecular weight and polydispersity index). Several recovery approaches are presented and categorized in two main strategies: PHA recovery with solvents (halogenated solvents, alkanes, alcohols, esters, carbonates and ketones) and PHA recovery by cellular lysis (with oxidants, acid and alkaline compounds, surfactants and enzymes). Comparative evaluations based on the recovery, purity and molecular weight of the recovered polymers as well as on the potential sustainability of the different approaches are here presented.

Halophilic archaea and their potential to generate renewable fuels and chemicals

Lignocellulosic biofuels and chemicals have great potential to reduce our dependence on fossil fuels and mitigate air pollution by cutting down on greenhouse gas emissions. Chemical, thermal, and enzymatic processes are used to release the sugars from the lignocellulosic biomass for conversion to biofuels. These processes often operate at extreme pH conditions, high salt concentrations, and/or high temperature. These harsh treatments add to the cost of the biofuels, as most known biocatalysts do not operate under these conditions. To increase the economic feasibility of biofuel production, microorganisms that thrive in extreme conditions are considered as ideal resources to generate biofuels and value-added products. Halophilic archaea (haloarchaea) are isolated from hypersaline ecosystems with high salt concentrations approaching saturation (1.5-5 M salt concentration) including environments with extremes in pH and/or temperature. The unique traits of haloarchaea and their enzymes that enable them to sustain catalytic activity in these environments make them attractive resources for use in bioconversion processes that must occur across a wide range of industrial conditions. Biocatalysts (enzymes) derived from haloarchaea occupy a unique niche in organic solvent, salt-based, and detergent industries. This review focuses on the use of haloarchaea and their enzymes to develop and improve biofuel production. The review also highlights how haloarchaea produce value-added products, such as antibiotics, carotenoids, and bioplastic precursors, and can do so using feedstocks considered "too salty" for most microbial processes including wastes from the olive-mill, shell fish, and biodiesel industries.

Novel Nanocomposites Based on Bacterial Polyester/LDH-SDS Clay for Stem Cells Delivery in Modern Wound Healing Management

Nanocomposite materials based on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) and modified mineral clay layered double hydroxides (LDH-SDS) were explored as novel nanostructured materials for potential tissue engineering applications. The mineral clay inorganic phase was modified with an anionic long-chain structure of carbon atoms, such as sodium dodecyl sulfate, in order to increase the compatibility between the two phases. The melt intercalation method used for nanocomposite fabrication ensures a good dispersion of the modified LDH-SDS within the polymer matrix without using a toxic solvent (chloroform). The nanocomposites were found to have an intercalated/exfoliated structure with an enhanced Young modulus and increased stiffness. This could allow them to be considered for autologous stem cells dressings in the view of efficient wound healing applications.

Bioengineered Polyhydroxyalkanoates as Immobilized Enzyme Scaffolds for Industrial Applications

Enzymes function as biocatalysts and are extensively exploited in industrial applications. Immobilization of enzymes using support materials has been shown to improve enzyme properties, including stability and functionality in extreme conditions and recyclability in biocatalytic processing. This review focuses on the recent advances utilizing the design space of in vivo self-assembled polyhydroxyalkanoate (PHA) particles as biocatalyst immobilization scaffolds. Self-assembly of biologically active enzyme-coated PHA particles is a one-step in vivo production process, which avoids the costly and laborious in vitro chemical cross-linking of purified enzymes to separately produced support materials. The homogeneous orientation of enzymes densely coating PHA particles enhances the accessibility of catalytic sites, improving enzyme function. The PHA particle technology has been developed into a remarkable scaffolding platform for the design of cost-effective designer biocatalysts amenable toward robust industrial bioprocessing. In this review, the PHA particle technology will be compared to other biological supramolecular assembly-based technologies suitable for in vivo enzyme immobilization. Recent progress in the fabrication of biological particulate scaffolds using enzymes of industrial interest will be summarized. Additionally, we outline innovative approaches to overcome limitations of in vivo assembled PHA particles to enable fine-tuned immobilization of multiple enzymes to enhance performance in multi-step cascade reactions, such as those used in continuous flow bioprocessing.

Advanced liquid biopsy technologies for circulating biomarker detection

Liquid biopsy is a new diagnostic concept that provides important information for monitoring and identifying tumor genomes in body fluid samples. Detection of tumor origin biomolecules like circulating tumor cells (CTCs), circulating tumor specific nucleic acids (circulating tumor DNA (ctDNA), circulating tumor RNA (ctRNA), microRNAs (miRNAs), long non-coding RNAs (lnRNAs)), exosomes, autoantibodies in blood, saliva, stool, urine, etc. enables cancer screening, early stage diagnosis and evaluation of therapy response through minimally invasive means. From reliance on painful and hazardous tissue biopsies or imaging depending on sophisticated equipment, cancer management schemes are witnessing a rapid evolution towards minimally invasive yet highly sensitive liquid biopsy-based tools. Clinical application of liquid biopsy is already paving the way for precision theranostics and personalized medicine. This is achieved especially by enabling repeated sampling, which in turn provides a more comprehensive molecular profile of tumors. On the other hand, integration with novel miniaturized platforms, engineered nanomaterials, as well as electrochemical detection has led to the development of low-cost and simple platforms suited for point-of-care applications. Herein, we provide a comprehensive overview of the biogenesis, significance and potential role of four widely known biomarkers (CTCs, ctDNA, miRNA and exosomes) in cancer diagnostics and therapeutics. Furthermore, we provide a detailed discussion of the inherent biological and technical challenges associated with currently available methods and the possible pathways to overcome these challenges. The recent advances in the application of a wide range of nanomaterials in detecting these biomarkers are also highlighted.

In vivo immobilization of an organophosphorus hydrolyzing enzyme on bacterial polyhydroxyalkanoate nano-granules

Background

Polyhydroxyalkanoate (PHA) are nano-granules naturally produced by bacteria. Two types of proteins, PHA synthase (PhaC) and phasins (PhaPs), are attached to the PHA surface by covalent and hydrophobic interactions. Utilizing these anchored proteins, functionalized PHA nano-granules displaying proteins of interest can be easily prepared by fermentation.

Results

In this study, a one-step fabrication method was developed for stable and efficient immobilization of an organophosphorus degrading enzyme on PHA nano-granules. The nano-biocatalysts were produced in recombinant Escherichia coli cells into which the polyhydroxyalkanoate synthesis pathway from Cupriavidus necator had been introduced. Two different strategies, covalent attachment and hydrophobic binding, were investigated by fusing bacterial organophosphorus anhydride hydrolase (OPAA4301) with PhaC and PhaP, respectively. Using both methods, the tetrameric enzyme successfully self-assembled and was displayed on the PHA surface. The display density of the target fused enzyme was enhanced to 6.8% of total protein on decorated PHA by combination of covalent and non-covalent binding modes. Immobilization of the enzyme on PHA granules resulted in higher catalytic efficiency, increased stability and excellent reusability. The k_cat values of the immobilized enzymes increased by threefold compared to that of the free enzyme. The pH stability under acidic conditions was significantly enhanced, and the immobilized enzyme was stable at pH 3.0–11.0. Furthermore, more than 80% of the initial enzyme activity retained after recycling ten times.

Conclusions

This study provides a promising approach for cost-efficient in vivo immobilization of a tetrameric organophosphorus degrading enzyme. The immobilization process expands the utility of the enzyme, and may inspire further commercial developments of PHA nano-biocatalysts. As revealed by our results, combination of covalent and non-covalent binding is recommended for display of enzymes on PHA granules.

Functionalized polyhydroxyalkanoate nano-beads as a stable biocatalyst for cost-effective production of the rare sugar d-allulose

d-Allulose is a promising low-calorie sweetener especially for diabetes and obesity patients. The functionalized polyhydroxyalkanoate (PHA) nano-beads decorated with d-tagatose 3-epimerase (DTE) was produced in recombinant endotoxin-free ClearColi, whereby the expression, purification, and immobilization of the active DTE were efficiently combined into one step. The immobilized DTE exhibited remarkable enzyme activity of 649.3 U/g beads and extremely high stability at a harsh working condition (pH 7.0-8.0, 65 °C). When DTE-PHA beads were subjected to enzymatic synthesis of d-allulose, a maximum conversion rate of 33% can be achieved at pH 7.0 and 65 °C for 3 h, and DTE-PHA beads retained about 80% of its initial activity after 8 continuous cycles. Moreover, the d-allulose/d-fructose binary mixture can be simply separated by a single cation exchange resin-equipped chromatography. Taken together, DTE-PHA beads are promising and robust nano-biocatalysts that will remarkably simplify the production procedures of d-allulose, contributing to its cost-effective production.

Formation of an Organic-Inorganic Biopolymer: Polyhydroxybutyrate-Polyphosphate

A considerable variety of different biopolymers is formed by the entirety of organisms present on earth. Most of these compounds are organic polymers such as polysaccharides, polyamino acids, polynucleotides, polyisoprenes or polyhydroxyalkanoates (PHAs), but some biopolymers can consist of solely inorganic monomers such as phosphate in polyphosphates (polyPs). In this contribution, we describe the formation of an organic-inorganic block copolymer consisting of poly(3-hydroxybutyrate) (PHB) and polyP. This was achieved by the expression of a fusion of the polyP kinase gene (ppk2c) with the PHB synthase gene (phaC) of Ralstonia eutropha in a polyP-free and PHB-free mutant background of R. eutropha. The fusion protein catalyzed both the formation of polyP by its polyP kinase domain and the formation of PHB by its PHB synthase domain. It was also possible to synthesize the polyP-PHB polymer in vitro with purified Ppk2c-PhaC, if the monomers, adenosine triphosphate (ATP) and 3-hydroxybutyryl-CoA (3HB-CoA), were provided. Most likely, the formed block copolymer (polyP-protein-PHB) turns into a blend of polyP and PHB after release from the enzyme.

Polyhydroxyalkanoate (PHA): applications in drug delivery and tissue engineering

INTRODUCTION

The applications of naturally obtained polymers are tremendously increased due to them being biocompatible, biodegradable, environmentally friendly and renewable in nature. Among them, polyhydroxyalkanoates are widely studied and they can be utilized in many areas of human life research such as drug delivery, tissue engineering, and other medical applications.

AREAS COVERED

This review provides an overview of the polyhydroxyalkanoates biosynthesis and their possible applications in drug delivery in the range of micro- and nano-size. Moreover, the possible applications in tissue engineering are covered considering macro- and microporous scaffolds and extracellular matrix analogs.

EXPERT COMMENTARY

The majority of synthetic plastics are non-biodegradable so, in the last years, a renewed interest is growing to develop alternative processes to produce biologically derived polymers. Among them, PHAs present good properties such as high immunotolerance, low toxicity, biodegradability, so, they are promisingly using as biomaterials in biomedical applications.

Biochemistry, genetics and biotechnology of glycerol utilization in Pseudomonas species

The use of renewable waste feedstocks is an environment‐friendly choice contributing to the reduction of waste treatment costs and increasing the economic value of industrial by‐products. Glycerol (1,2,3‐propanetriol), a simple polyol compound widely distributed in biological systems, constitutes a prime example of a relatively cheap and readily available substrate to be used in bioprocesses. Extensively exploited as an ingredient in the food and pharmaceutical industries, glycerol is also the main by‐product of biodiesel production, which has resulted in a progressive drop in substrate price over the years. Consequently, glycerol has become an attractive substrate in biotechnology, and several chemical commodities currently produced from petroleum have been shown to be obtained from this polyol using whole‐cell biocatalysts with both wild‐type and engineered bacterial strains. Pseudomonas species, endowed with a versatile and rich metabolism, have been adopted for the conversion of glycerol into value‐added products (ranging from simple molecules to structurally complex biopolymers, e.g. polyhydroxyalkanoates), and a number of metabolic engineering strategies have been deployed to increase the number of applications of glycerol as a cost‐effective substrate. The unique genetic and metabolic features of glycerol‐grown Pseudomonas are presented in this review, along with relevant examples of bioprocesses based on this substrate – and the synthetic biology and metabolic engineering strategies implemented in bacteria of this genus aimed at glycerol valorization.

Microalgae as source of polyhydroxyalkanoates (PHAs) - A review

Polyhydroxyalkanoates (PHA) are biopolymers synthesized by different microorganisms and considered substitute powers for petroleum-based plastics because they have similar mechanical properties as synthetic polymers, can be processed in a similar way and are fully biodegradable. Currently commercial PHAs are produced in fermenters using bacteria and large amounts of organic carbon sources and salts in the culture media, accounting for approximately 50% of the total production costs. A greater commercial application of the PHA is limited to a decrease in the cost of production. Several studies suggest that microalgae are a type of microorganisms that can be used to obtain PHAs at a lower cost because they have minimum nutrient requirements for growth and are photoautotrophic in nature, i.e. they use light and CO₂ as their main sources of energy. Thus, this work aims to provide a review on the production of PHAs of different microalgae, focusing on the properties and composition of biopolymers, verifying the potential of using these bioplastics instead of petroleum based plastics. Studies of stimulation PHA synthesis by microalgae are still considered incipient. Still, it is clear that microalgae have the potential to produce biopolymers with lower cost and can play a vital role in the environment.

Innovative antigen carrier system for the development of tuberculosis vaccines

A major obstacle to tuberculosis (TB)-subunit-vaccine development has been the induction of inadequate levels of protective immunity due to the limited breadth of antigen in vaccine preparations. In this study, immunogenic mycobacterial fusion peptides Ag85B-TB10.4 and Ag85B-TB10.4-Rv2660c were covalently displayed on the surface of self-assembled polyester particles. This study investigated whether polyester particles displaying mycobacterial antigens could provide augmented immunogenicity (i.e., offer an innovative vaccine formulation) when compared with free soluble antigens. Herein, polyester particle-based particulate vaccines were produced in an endotoxin-free Escherichia coli strain and emulsified with the adjuvant dimethyl dioctadecyl ammonium bromide. C57BL/6 mice were used to study the immunogenicity of formulated particulate vaccines. The result of humoral immunity showed the antibodies only interacted with target antigens and not with PhaC and the background proteins of the production host. The analysis of T helper 1 cellular immunity indicated that a relatively strong production of cellular immunity biomarkers, IFN-γ and IL-17A cytokines, was induced by particulate vaccines when compared with the respective soluble controls. This study demonstrated that polyester particles have the potential to perform as a mycobacterial antigen-delivery agent to induce augmented antigen-specific immune responses in contrast to free soluble vaccines.-Chen, S., Sandford, S., Kirman, J. R., Rehm, B. H. A. Innovative antigen carrier system for the development of tuberculosis vaccines.

Calcium Involved Directional Organization of Polymer Chains in Polyester Nanogranules in Bacterial Cells

Soil bacteria accumulate polyesters (typically poly([R]-3-hydroxybutyrate (PHB), in which one end of the chain terminates with a carboxyl group) in the form of hydrated, amorphous nanogranules in cells. However, it is not clear what drives the structure of these biomaterials inside bacterial cells. Here, we determined that calcium guides intracellular formation of PHB nanogranules. Our systematic study using the surface zeta potential measurement and the carboxyl-specific SYTO-62 dye binding assay showed that the terminal carboxyl is not exposed to the granule surface but is buried inside native “unit-granules” comprising the mature granule. Extracellular Ca²⁺ was found to mediate the formation of these PHB unit-granules, with uptaken Ca²⁺ stored inside the granules. Comparative [Ca²⁺]-dependent fluorescence spectroscopy revealed that the native granules in Cupriavidus necator H16 act as a Ca²⁺ storage system, presumably for the regulation of its cytosolic Ca²⁺ level, but those from recombinant Escherichia coli do not. This study reveals intimate links between Ca²⁺ and native granule formation, and establishes a novel mechanism that intracellular PHB granules function as Ca²⁺ storage in order to relieve soil bacteria from Ca²⁺ stress.

Valorization of polyhydroxyalkanoates production process by co-synthesis of value-added products

Polyhydroxyalkanoates (PHAs) are the only polyesters that are completely synthesized biologically and possess features equivalent to petroleum-based plastics besides being biodegradable. PHA based materials may certainly prove helpful in addressing the concerns caused due to the indiscriminate use of synthetic plastics. However, the cost of producing these polymers on a large scale is still uneconomical. Various approaches have been developed to tackle this issue through usage of agro-industrial wastes, co-production of high market value products, polymer extraction using green solvents, etc. The advent of recombineering and CRISPR technologies has broadened the scope of constructing a microbe capable of synthesizing multiple products with economic feasibility. Quite a few high-market value chemicals are possible to synthesize along with the favorable accumulation of PHA. The present article attempts to review all PHA polymer co-production processes with other chemicals reported till date and discusses the opportunities for their large-scale operation in future.

Inhibition of Rumen Methanogens by a Novel Archaeal Lytic Enzyme Displayed on Tailored Bionanoparticles

Methane is a potent greenhouse gas, 25 times more efficient at trapping heat than carbon dioxide. Ruminant methane emissions contribute almost 30% to anthropogenic sources of global atmospheric methane levels and a reduction in methane emissions would significantly contribute to slowing global temperature rises. Here we demonstrate the use of a lytic enyzme, PeiR, from a methanogen virus that infects Methanobrevibacter ruminantium M1 as an effective agent inhibiting a range of rumen methanogen strains in pure culture. We determined the substrate specificity of soluble PeiR and demonstrated that the enzyme is capable of hydrolysing the pseudomurein cell walls of methanogens. Subsequently, peiR was fused to the polyhydroxyalkanoate (PHA) synthase gene phaC and displayed on the surface of PHA bionanoparticles (BNPs) expressed in Eschericia coli via one-step biosynthesis. These tailored BNPs were capable of lysing not only the original methanogen host strain, but a wide range of other rumen methanogen strains in vitro. Methane production was reduced by up to 97% for 5 days post-inoculation in the in vitro assay. We propose that tailored BNPs carrying anti-methanogen enzymes represent a new class of methane inhibitors. Tailored BNPs can be rapidly developed and may be able to modulate the methanogen community in vivo with the aim to lower ruminant methane emissions without impacting animal productivity.

Three novel proteins co-localise with polyhydroxybutyrate (PHB) granules in Rhodospirillum rubrum S1

Polyhydroxybutyrate (PHB), a biodegradable polymer accumulated by bacteria is deposited intracellularly in the form of inclusion bodies often called granules. The granules are supramolecular complexes harbouring a varied number of proteins on their surface, which have specific but incompletely characterised functions. By comparison with other organisms that produce biodegradable polymers, only two phasins have been described to date for Rhodosprillum rubrum, raising the possibility that more await discovery. Using a comparative proteomics strategy to compare the granules of wild-type R. rubrum with a PHB-negative mutant housing artificial PHB granules, we identified four potential PHB granules' associated proteins. These were: Q2RSI4, an uncharacterised protein; Q2RWU9, annotated as an extracellular solute-binding protein; Q2RQL4, annotated as basic membrane lipoprotein; and Q2RQ51, annotated as glucose-6-phosphate isomerase. In silico analysis revealed that Q2RSI4 harbours a Phasin_2 family domain and shares low identity with a single-strand DNA-binding protein from Sphaerochaeta coccoides. Fluorescence microscopy found that three proteins Q2RSI4, Q2EWU9 and Q2RQL4 co-localised with PHB granules. This work adds three potential new granule associated proteins to the repertoire of factors involved in bacterial storage granule formation, and confirms that proteomics screens are an effective strategy for discovery of novel granule associated proteins.

Engineering Bacillus megaterium for production of functional intracellular materials

BACKGROUND

Over the last 10-15 years, a technology has been developed to engineer bacterial poly(3-hydroxybutyrate) (PHB) inclusions as functionalized beads, for applications such as vaccines, diagnostics and enzyme immobilization. This has been achieved by translational fusion of foreign proteins to the PHB synthase (PhaC). The respective fusion protein mediates self-assembly of PHB inclusions displaying the desired protein function. So far, beads have mainly been produced in recombinant Escherichia coli, which is problematic for some applications as the lipopolysaccharides (LPS) co-purified with such inclusions are toxic to humans and animals.

RESULTS

In this study, we have bioengineered the formation of functional PHB inclusions in the Gram-positive bacterium Bacillus megaterium, an LPS-free and established industrial production host. As B. megaterium is a natural PHB producer, the PHB-negative strain PHA05 was used to avoid any background PHB production. Plasmid-mediated T7 promoter-driven expression of the genes encoding β-ketothiolase (phaA), acetoacetyl-CoA-reductase (phaB) and PHB synthase (phaC) enabled PHB production in B. megaterium PHA05. To produce functionalized PHB inclusions, the N- and C-terminus of PhaC was fused to four and two IgG binding Z-domains from Staphylococcus aureus, respectively. The ZZ-domain PhaC fusion protein was strongly overproduced at the surface of the PHB inclusions and the corresponding isolated ZZ-domain displaying PHB beads were found to purify IgG with a binding capacity of 40-50 mg IgG/g beads. As B. megaterium has the ability to sporulate and respective endospores could co-purify with cellular inclusions, a sporulation negative production strain was generated by disrupting the spoIIE gene in PHA05. This strain did not produce spores when tested under sporulation inducing conditions and it was still able to synthesize ZZ-domain displaying PHB beads.

CONCLUSIONS

This study provides proof of concept for the successful genetic engineering of B. megaterium as a host for the production of functionalized PHB beads. Disruption of the spoIIE gene rendered B. megaterium incapable of sporulation but particularly suitable for production of functionalized PHB beads. This sporulation-negative mutant represents an improved industrial production strain for biotechnological processes otherwise impaired by the possibility of endospore formation.

Immunological properties and protective efficacy of a single mycobacterial antigen displayed on polyhydroxybutyrate beads

In 2015, there were an estimated 10.4 million new tuberculosis (TB) cases and 1.4 million deaths worldwide. Bacille Calmette-Guérin (BCG), an attenuated strain of Mycobacterium bovis, is the vaccine available against TB, but it is insufficient for global TB control. This study evaluated the immunogenicity of the Mycobacterium tuberculosis antigen Rv1626 in mice while assessing the effect of co-delivering either Cpe30 (immunostimulatory peptide), CS.T3378-395 (promiscuous T helper epitope) or flagellin (TLR5 agonist) or a combination of all three immunostimulatory agents. Rv1626 and the respective immunostimulatory proteins/peptides were co-displayed on polyhydroxybutyrate beads assembled inside an engineered endotoxin-free mutant of Escherichia coli. Mice vaccinated with these beads produced immune responses biased towards Th1-/Th17-type responses, but inclusion of Cpe30, CS.T3378-395 and flagellin did not enhance immunogenicity of the Rv1626 protein. This was confirmed in a M. bovis challenge experiment in mice, where Rv1626 beads reduced bacterial cell counts in the lungs by 0.48 log10 compared with the adjuvant alone control group. Co-delivery of immunostimulatory peptides did not further enhance protective immunity.

Polyhydroxyalkanoates: Properties and chemical modification approaches for their functionalization

Polyhydroxyalkanoates (PHAs) have become an attractive biomaterial in research in the past few years due to their extensive potential industrial applications. Being long chain hydroxyl fatty acid molecules, the PHAs are hydrophobic in nature, and have less functional groups. These features limit their applications in various areas. To enhance their usage, these polymers may need to be modified including surface and chemical modifications. Such modifications may alter their mechanical properties, surface structure, amphiphilic character and rate of degradation to fulfil the requirements for their future applications. Chemical modifications allow incorporation of functional groups to PHAs that could not be introduced through biotechnological methods. These chemically reformed PHAs, with enhanced properties, could be used for broad range of applications. This review aims to introduce different chemical modification approaches including some recent methods that had not been explored or discussed so far for PHAs as possible technologies for widening the range of product and application potentials. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:29-41, 2018.