Structural Insights into Polyhydroxyalkanoates Biosynthesis

Enhancing the efficacy of synthesising PHA from nitrogen-limited activated sludge using magnetic field

Polyhydroxyalkanes (PHA) is a biodegradable biopolyester. In this study, we introduced the biological effects of magnetic field into a sequencing batch reactor (SBR) for PHA production to evaluate the effect of different strength of magnetic field on the efficacy of PHA synthesis by activated sludge and used the magnetic field to enhance the PHA synthesis capacity of nitrogen-limited activated sludge and to optimise the percentage of the content of the two monomers in PHA. The results showed that the magnetic field of appropriate strength was favourable to increase the production of PHA and to increase the percentage of PHV. In addition, microbial community analysis showed that there was an obvious succession of key functional bacteria under different strength of magnetic field. The highest PHA accumulation was achieved after the magnetic field of 16 mT, which reached 57.65% of the dry weight of sludge. In addition, the PHV monomers were more sensitive to the response of the magnetic field, and the magnetic field of 8mT and 16mT positively promoted the synthesis of PHV. It is worth noting that too high a magnetic field would have an inhibitory effect on the synthesis of PHA.

Recent advances in synthetic biology toolkits and metabolic engineering of Ralstonia eutropha H16 for production of value-added chemicals

Ralstonia eutropha H16, a facultative chemolithoautotrophic Gram-negative bacterium, demonstrates remarkable metabolic flexibility by utilizing either diverse organic substrates or CO2 as the sole carbon source, with H2 serving as the electron donor under aerobic conditions. The capacity of carbon and energy metabolism of R. eutropha H16 enabled development of synthetic biology technologies and strategies to engineer its metabolism for biosynthesis of value-added chemicals. This review firstly outlines the development of synthetic biology tools tailored for R. eutropha H16, including construction of expression vectors, regulatory elements, and transformation techniques. The availability of comprehensive omics data (i.e., transcriptomic, proteomic, and metabolomic) combined with the fully annotated genome sequence provides a robust genetic framework for advanced metabolic engineering. These advancements facilitate efficient reprogramming metabolic network of R. eutropha. The potential of R. eutropha as a versatile microbial platform for industrial biotechnology is further underscored by its ability to utilize a wide range of carbon sources for the production of value-added chemicals through both autotrophic and heterotrophic pathways. The integration of state-of-the-art genetic and genomic engineering tools and strategies with high cell-density fermentation processes enables engineered R. eutropha as promising microbial cell factories for optimizing carbon fluxes and expanding the portfolio of bio-based products.

Unlocking the potential of microbes: Concomitant production of polyhydroxyalkanoates and carotenoids

The escalating environmental concerns and depletion of crude oil resources have catalyzed interest in biologically derived polymers, particularly biodegradable ones such as polyhydroxyalkanoates. However, the high production costs associated with polyhydroxyalkanoates, driven by raw material expenses, stringent production conditions and low yields, hinder their widespread adoption. A potential strategy to mitigate these costs involves the production of PHAs and other high-value bioproducts, such as carotenoids simultaneously in microbial systems, utilizing shared metabolic pathways. Carotenoids, known for their antioxidant properties and applications in the food, cosmetics and pharmaceutical industries, offer substantial market potential. This review presents a comprehensive overview of the current progress in polyhydroxyalkanoate and carotenoid co-production, explores the co-synthesis pathways, addresses the challenges involved and explores the future prospects of this integrated bioprocess. By diversifying the product portfolio and optimizing microbial production systems, the co-production strategy could pave the way for more sustainable and economically viable bioplastics.

Bioplastic polyhydroxyalkanoate conversion in waste activated sludge

Polyhydroxyalkanoates (PHA) have been proposed as a promising solution for plastic pollution due to their biodegradability and diverse applications. To promote PHA as a competitive commercial product, an attractive alternative is to produce and recover PHA in the use of mixed cultures such as waste activated sludge from wastewater treatment plants. PHA can accumulate in sludge with a potential range of 40%-65% g PHA/g VSS. However, wider challenges with PHA production efficiency, stability, and economic viability still persist for PHA application. This work provides an overview of the current understanding and status of PHA bioconversion in waste sludge with particular attention given to metabolic pathways, operation modes, factors affecting the process, and applications. Challenges and future prospectives for PHA bioconversion in sludge are discussed.

Effect of mutation of phaC on carbon supply, extracellular polysaccharide production, and pathogenicity of Xanthomonas oryzae pv. oryzae

Xanthomonas oryzae pv. oryzae (Xoo) causes bacterial blight in rice. Polyhydroxyalkanoates (PHAs) consitute a diverse group of biopolyesters synthesized by bacteria under nutrient-limited conditions. The phaC gene is important for PHA polymerization. We investigated the effects of phaC gene mutagensis in Xoo strain PXO99A. The phaC gene knock-out mutant exhibited reduced swarming ability relative to that of the wild-type. Under conditions where glucose was the sole sugar source, extracellular polysaccharide (EPS) production by ΔphaC declined by 44.8%. ΔphaC showed weak hypersensitive response (HR) induction in the leaves of non-host Nicotiana tabacum, concomitant with downregulation of hpa1 gene expression. When inoculated in rice leaves by the leaf-clipping method, ΔphaC displayed reduced virulence in terms of lesion length compared with the wild-type strain. The complemented strain showed no significant difference from the wild-type strain, suggesting that the deletion of phaC in Xoo induces significant alterations in various physiological and biological processes. These include bacterial swarming ability, EPS production, transcription of hrp genes, and glucose metabolism. These changes are intricately linked to the energy utilization and virulence of Xoo during plant infection. These findings revealed involvement of phaC in Xoo is in the maintaining carbon metabolism by functioning in the PHA metabolic pathway.

Living in mangroves: a syntrophic scenario unveiling a resourceful microbiome

BACKGROUND

Mangroves are complex and dynamic coastal ecosystems under frequent fluctuations in physicochemical conditions related to the tidal regime. The frequent variation in organic matter concentration, nutrients, and oxygen availability, among other factors, drives the microbial community composition, favoring syntrophic populations harboring a rich and diverse, stress-driven metabolism. Mangroves are known for their carbon sequestration capability, and their complex and integrated metabolic activity is essential to global biogeochemical cycling. Here, we present a metabolic reconstruction based on the genomic functional capability and flux profile between sympatric MAGs co-assembled from a tropical restored mangrove.

RESULTS

Eleven MAGs were assigned to six Bacteria phyla, all distantly related to the available reference genomes. The metabolic reconstruction showed several potential coupling points and shortcuts between complementary routes and predicted syntrophic interactions. Two metabolic scenarios were drawn: a heterotrophic scenario with plenty of carbon sources and an autotrophic scenario with limited carbon sources or under inhibitory conditions. The sulfur cycle was dominant over methane and the major pathways identified were acetate oxidation coupled to sulfate reduction, heterotrophic acetogenesis coupled to carbohydrate catabolism, ethanol production and carbon fixation. Interestingly, several gene sets and metabolic routes similar to those described for wastewater and organic effluent treatment processes were identified.

CONCLUSION

The mangrove microbial community metabolic reconstruction reflected the flexibility required to survive in fluctuating environments as the microhabitats created by the tidal regime in mangrove sediments. The metabolic components related to wastewater and organic effluent treatment processes identified strongly suggest that mangrove microbial communities could represent a resourceful microbial model for biotechnological applications that occur naturally in the environment.

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.

Unveiling the repressive mechanism of a PPS-like regulator (PspR) in polyhydroxyalkanoates biosynthesis network

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is a type of polyhydroxyalkanoates (PHA) that exhibits numerous outstanding properties and is naturally synthesized and elaborately regulated in various microorganisms. However, the regulatory mechanism involving the specific regulator PhaR in Haloferax mediterranei, a major PHBV production model among Haloarchaea, is not well understood. In our previous study, we showed that deletion of the phosphoenolpyruvate (PEP) synthetase-like (pps-like) gene activates the cryptic phaC genes in H. mediterranei, resulting in enhanced PHBV accumulation. In this study, we demonstrated the specific function of the PPS-like protein as a negative regulator of phaR gene expression and PHBV synthesis. Chromatin immunoprecipitation (ChIP), in situ fluorescence reporting system, and in vitro electrophoretic mobility shift assay (EMSA) showed that the PPS-like protein can bind to the promoter region of phaRP. Computational modeling revealed a high structural similarity between the rifampin phosphotransferase (RPH) protein and the PPS-like protein, which has a conserved ATP-binding domain, a His domain, and a predicted DNA-binding domain. Key residues within this unique DNA-binding domain were subsequently validated through point mutation and functional evaluations. Based on these findings, we concluded that PPS-like protein, which we now renamed as PspR, has evolved into a repressor capable of regulating the key regulator PhaR, and thereby modulating PHBV synthesis. This regulatory network (PspR-PhaR) for PHA biosynthesis is likely widespread among haloarchaea, providing a novel approach to manipulate haloarchaea as a production platform for high-yielding PHA. KEY POINTS: • The repressive mechanism of a novel inhibitor PspR in the PHBV biosynthesis was demonstrated • PspR is widespread among the PHA accumulating haloarchaea • It is the first report of functional conversion from an enzyme to a trans-acting regulator in haloarchaea.

Computational Analysis of the Tripartite Interaction of Phasins (PhaP4 and 5)-Sigma Factor (σ24)-DNA of Azospirillum brasilense Sp7

Azospirillum brasilense Sp7 produces PHB, which is covered by granule-associated proteins (GAPs). Phasins are the main GAPs. Previous studies have shown phasins can regulate PHB synthesis. When A. brasilense grows under stress conditions, it uses sigma factors to transcribe genes for survival. One of these factors is the σ24 factor. This study determined the possible interaction between phasins and the σ24 factor or phasin-σ24 factor complex and DNA. Three-dimensional structures of phasins and σ24 factor structures were predicted using the I-TASSER and SWISS-Model servers, respectively. Subsequently, a molecular docking between phasins and the σ24 factor was performed using the ClusPro 2.0 server, followed by molecular docking between protein complexes and DNA using the HDOCK server. Evaluation of the types of ligand-receptor interactions was performed using the BIOVIA Discovery Visualizer for three-dimensional diagrams, as well as the LigPlot server to obtain bi-dimensional diagrams. The results showed the phasins (Pha4Abs7 or Pha5Abs7)-σ24 factor complex was bound near the -35 box of the promoter region of the phaC gene. However, in the individual interaction of PhaP5Abs7 and the σ24 factor, with DNA, both proteins were bound to the -35 box. This did not occur with PhaP4Abs7, which was bound to the -10 box. This change could affect the transcription level of the phaC gene and possibly affect PHB synthesis.

Genetic and process engineering for polyhydroxyalkanoate production from pre- and post-consumer food waste

Biopolymers produced as microbial carbon storage systems, such as polyhydroxyalkanoates (PHAs), offer potential to be used in place of petrochemically derived plastics. Low-value organic feedstocks, such as food waste, have been explored as a potential substrate for the microbial production of PHAs. In this review, we discuss the biosynthesis, composition and producers of PHAs, with a particular focus on the genetic and process engineering efforts to utilise non-native substrates, derived from food waste from across the entire supply chain, for microbial growth and PHA production. We highlight a series of studies that have achieved impressive advances and discuss the challenges of producing PHAs with consistent composition and properties from mixed and variable food waste and by-products.

Polyhydroxyalkanoates for Sustainable Aquaculture: A Review of Recent Advancements, Challenges, and Future Directions

Polyhydroxyalkanoates (PHA) are biodegradable biopolymers produced by prokaryotic microbes, which, at the same time, can be applied as single-cell proteins (SCPs), growing on renewable waste-derived substrates. These PHA polymers have gained increasing attention as a sustainable alternative to conventional plastics. One promising application of PHA and PHA-rich SCPs lies within the aquaculture food industry, where they hold potential as feed additives, biocontrol agents against diseases, and immunostimulants. Nevertheless, the cost of PHA production and application remains high, partly due to expensive substrates for cultivating PHA-accumulating SCPs, costly sterilization, energy-intensive SCPs harvesting techniques, and toxic PHA extraction and purification processes. This review summarizes the current state of PHA production and its application in aquaculture. The structure and classification of PHA, microbial sources, cultivation substrates, biosynthesis pathways, and the production challenges and solutions are discussed. Next, the potential of PHA application in aquaculture is explored, focusing on aquaculture challenges, common and innovative PHA-integrated farming practices, and PHA mechanisms in inhibiting pathogens, enhancing the immune system, and improving growth and gut health of various aquatic species. Finally, challenges and future research needs for PHA production and application in aquaculture are identified. Overall, this review paper provides a comprehensive overview of the potential of PHA in aquaculture and highlights the need for further research in this area.

Recent Biotechnological Applications of Polyhydroxyalkanoates (PHA) in the Biomedical Sector-A Review

Petroleum-derived plastics are materials of great importance for the contemporary lifestyle, and are widely used commercially because they are low cost, resistant, malleable, and weightless, in addition to their hydrophobic character. However, some factors that confer the qualities of these materials also cause problems, mainly environmental, associated with their use. The COVID-19 pandemic aggravated these impacts due to the high demand for personal protective equipment and the packaging sector. In this scenario, bioplastics are environmentally positive alternatives to these plastics due to their applicability in several areas ranging from packaging, to biomedicine, to agriculture. Polyhydroxyalkanoates (PHAs) are biodegradable biopolymers usually produced by microorganisms as an energy reserve. Their structural variability provides a wide range of applications, making them a viable option to replace polluting materials. PHAs can be applied in various biotechnology sectors, such as producing drug carriers and scaffolds for tissue engineering. This review aimed to survey works published in the last five years on the study and biotechnological application of PHAs in the biomedical sector, exploring the versatility and advantages of their use and helping to understand how to enhance their application.

Pseudomonas umsongensis GO16 as a platform for the in vivo synthesis of short and medium chain length polyhydroxyalkanoate blends

Polyhydroxyalkanoates (PHAs) are biological polyesters, viewed as a replacement for petrochemical plastic. However, they suffer from suboptimal physical and mechanical properties. Here, it was shown that a metabolically versatile Pseudomonas umsongensis GO16 can synthesise a blend of short chain length (scl) and medium chain length (mcl)-PHA. A defined mix of butyric (BA) and octanoic acid (OA) in different ratios was used. The PHA monomer composition varied depending on the feeding strategy. When OA and BA were fed at 80:20 ratio it showed 14, 8, 77 and 1 mol% of (R)-3-hydroxybutyrate, (R)-3-hydroxyhexanoate, (R)-3-hydroxyoctanoate and (R)-3-hydroxydecanoate respectively. The polymer characterisation clearly shows that polyhydroxybutyrate (PHB) and mcl-PHA are produced individually. The two polymers are blended on the PHA granule level, as demonstrated by fluorescence microscopy and yeast two-hybrid assay. The resulting blend has a specific viscoelasticity compared to PHB and PHO. Mcl-PHA acts as a plasticiser and reduces PHB brittleness.

Production of polyhydroxyalkanoates as a feasible alternative for an integrated multiproduct lignocellulosic biorefinery

Polyhydroxyalkanoates (PHAs) are considered an alternative to fossil fuel-based plastics. However, in spite of their interesting properties and their multiple applications, PHAs have not taken off as an industrial development. The reason is mainly due to the associated high-production costs, which represent a significant constraint. In recent years, the interest in lignocellulosic biomass (LCB) derived from crop, forestry or municipal waste by-products has been growing, since LCB is plentiful, cheap, renewable and sustainable. On this matter, the valorization of LCB into PHAs represents a promising route within circular economy strategies. However, much effort still needs to be made to improve the bioconversion yields and to enhance PHA production efficiency. So, this review focuses on reviewing the different options for PHA synthesis from LCB, stressing the progress in biomass deconstruction, enzymatic hydrolysis and microbial conversion. In addition, some of the current biological strategies for improving the process of bioconversion are discussed.

Effect of composition of volatile fatty acids on yield of polyhydroxyalkanoates and mechanisms of bioconversion from activated sludge

Polyhydroxyalkanoates (PHA) is green biodegradable natural polymer. Here PHA production from volatile fatty acids (VFAs) was investigated in sequential batch reactors inoculated with activated sludge. Single or mixed VFAs ranging from acetate to valerate were evaluated, and the dominant VFA concentration was 2 times of that of the others in the tests. Results showed that mixed substrates achieved about 1.6 times higher yield of PHA production than single substrate. The butyrate-dominated substrates maximized PHA content at 72.08% of VSS, and the valerate-dominated substrates were followed with PHA content at 61.57%. Metabolic flux analysis showed the presence of valerate in the substrates caused a more robust PHA production. There was at least 20% of 3-hydroxyvalerate in the polymer. Hydrogenophaga and Comamonas were the main PHA producers. As VFAs could be produced in anaerobic digestion of organic wastes, the methods and data here could be referred for efficient green bioconversion of PHA.

A (S)-3-Hydroxybutyrate Dehydrogenase Belonging to the 3-Hydroxyacyl-CoA Dehydrogenase Family Facilitates Hydroxyacid Degradation in Anaerobic Bacteria

Ketone bodies, including acetoacetate, 3-hydroxybutyrate, and acetone, are produced in the liver of animals during glucose starvation. Enzymes for the metabolism of (R)-3-hydroxybutyrate have been extensively studied, but little is known about the metabolism of its enantiomer (S)-3-hydroxybutyrate. Here, we report the characterization of a novel pathway for the degradation of (S)-3-hydroxybutyrate in anaerobic bacteria. We identify and characterize a stereospecific (S)-3-hydroxylbutyrate dehydrogenase (3SHBDH) from Desulfotomaculum ruminis, which catalyzes the reversible NAD(P)H-dependent reduction of acetoacetate to form (S)-3-hydroxybutyrate. 3SHBDH also catalyzes oxidation of d-threonine (2R, 3S) and l-allo-threonine (2S, 3S), consistent with its specificity for β-(3S)-hydroxy acids. Isothermal calorimetry experiments support a sequential mechanism involving binding of NADH prior to (S)-3-hydroxybutyrate. Homologs of 3SHBDH are present in anaerobic fermenting and sulfite-reducing bacteria, and experiments with Clostridium pasteurianum showed that 3SHBDH, acetate CoA-transferase (YdiF), and (S)-3-hydroxybutyryl-CoA dehydrogenase (Hbd) are involved together in the degradation of (S)-3-hydroxybutyrate as a carbon and energy source for growth. (S)-3-hydroxybutyrate is a human metabolic marker and a chiral precursor for chemical synthesis, suggesting potential applications of 3SHBDH in diagnostics or the chemicals industry. IMPORTANCE (R)-3-hydroxybutyrate is well studied as a component of ketone bodies produced by the liver and of bacterial polyesters. However, the biochemistry of its enantiomer (S)-3-hydroxybutyrate is poorly understood. This study describes the identification and characterization of a stereospecific (S)-3-hydroxylbutyrate dehydrogenase and its function in a metabolic pathway for the degradation of (S)-3-hydroxybutyrate as a carbon and energy source in anaerobic bacteria. (S)-3-hydroxybutyrate is a mammalian metabolic marker and a precursor for chemical synthesis and bioplastics, suggesting potential applications of these enzymes in diagnostics and biotechnology.

Genome-centric polyhydroxyalkanoate reconciliation reveals nutrient enriched growth dependent biosynthesis in Bacillus cereus IBA1

Microbiological polyhydroxyalkanoates (PHAs) are rooted as the most promising bio-replacements of synthetic polymers. Inherent properties of these PHAs further expand their applicability in numerous industrial, environmental, and clinical sectors. To propel these, a new environmental, endotoxin free gram-positive bacterium i.e., Bacillus cereus IBA1 was identified to harbor advantageous PHA producer characteristics through high-throughput omics mining approaches. Unlike traditional fermentations, nutrient enriched strategy was used to enhance PHA granular concentrations by ∼2.3 folds to 2.78 ± 0.19 g/L. Additionally, this study is the first to confirm an underlying growth dependent PHA biogenesis through exploring PHA granule associated operons which harbour constitutively expressing PHA synthase (phaC) coupled with differentially expressing PHA synthase subunit (phaR) and regulatory protein (phaP, phaQ) amid different growth phases. Moreover, the feasibility of this promising microbial phenomenon could propel next-generation biopolymers, and increase industrial applicability of PHAs, thereby significantly contributing to the sustainable development.

The degradation of single-use plastics and commercially viable bioplastics in the environment: A review

Plastics have become an integral part of human life. Single-use plastics (SUPs) are disposable plastics designed to be used once then promptly discarded or recycled. This SUPs range from packaging and takeaway containers to disposable razors and hotel toiletries. Synthetic plastics, which are made of non-renewable petroleum and natural gas resources, require decades to perpetually disintegrate in nature thus contribute to plastic pollution worldwide, especially in marine environments. In response to these problems, bioplastics or bio-based and biodegradable polymers from renewable sources has been considered as an alternative. Understanding the mechanisms behind the degradation of conventional SUPs and biodegradability of their greener counterpart, bioplastics, is crucial for appropriate material selection in the future. This review aims to provide insights into the degradation or disintegration of conventional single-use plastics and the biodegradability of the different types of greener-counterparts, bioplastics, their mechanisms, and conditions. This review highlights on the biodegradation in the environments including composting systems. Here, the various types of alternative biodegradable polymers, such as bacterially biosynthesised bioplastics, natural fibre-reinforced plastics, starch-, cellulose-, lignin-, and soy-based polymers were explored. Review of past literature revealed that although bioplastics are relatively eco-friendly, their natural compositions and properties are inconsistent. Furthermore, the global plastic market for biodegradable plastics remains relatively small and require further research and commercialization efforts, especially considering the urgency of plastic and microplastic pollution as currently critical global issue. Biodegradable plastics have potential to replace conventional plastics as they show biodegradation ability under real environments, and thus intensive research on the various biodegradable plastics is needed to inform stakeholders and policy makers on the appropriate response to the gradually emerging biodegradable plastics.

Engineering Vibrio alginolyticus as a novel chassis for PHB production from starch

Vibrio alginolyticus LHF01 was engineered to efficiently produce poly-3-hydroxybutyrate (PHB) from starch in this study. Firstly, the ability of Vibrio alginolyticus LHF01 to directly accumulate PHB using soluble starch as the carbon source was explored, and the highest PHB titer of 2.06 g/L was obtained in 18 h shake flask cultivation. Then, with the analysis of genomic information of V. alginolyticus LHF01, the PHB synthesis operon and amylase genes were identified. Subsequently, the effects of overexpressing PHB synthesis operon and amylase on PHB production were studied. Especially, with the co-expression of PHB synthesis operon and amylase, the starch consumption rate was improved and the PHB titer was more than doubled. The addition of 20 g/L insoluble corn starch could be exhausted in 6-7 h cultivation, and the PHB titer was 4.32 g/L. To the best of our knowledge, V. alginolyticus was firstly engineered to produce PHB with the direct utilization of starch, and this stain can be considered as a novel host to produce PHB using starch as the raw material.

Enzyme catalyzes ester bond synthesis and hydrolysis: The key step for sustainable usage of plastics

Petro-plastic wastes cause serious environmental contamination that require effective solutions. Developing alternatives to petro-plastics and exploring feasible degrading methods are two solving routes. Bio-plastics like polyhydroxyalkanoates (PHAs), polylactic acid (PLA), polycaprolactone (PCL), poly (butylene succinate) (PBS), poly (ethylene furanoate) s (PEFs) and poly (ethylene succinate) (PES) have emerged as promising alternatives. Meanwhile, biodegradation plays important roles in recycling plastics (e.g., bio-plastics PHAs, PLA, PCL, PBS, PEFs and PES) and petro-plastics poly (ethylene terephthalate) (PET) and plasticizers in plastics (e.g., phthalate esters, PAEs). All these bio- and petro-materials show structure similarity by connecting monomers through ester bond. Thus, this review focused on bio-plastics and summarized the sequences and structures of the microbial enzymes catalyzing ester-bond synthesis. Most of these synthetic enzymes belonged to α/β-hydrolases with conserved serine catalytic active site and catalyzed the polymerization of monomers by forming ester bond. For enzymatic plastic degradation, enzymes about PHAs, PBS, PCL, PEFs, PES and PET were discussed, and most of the enzymes also belonged to the α/β hydrolases with a catalytic active residue serine, and nucleophilically attacked the ester bond of substrate to generate the cleavage of plastic backbone. Enzymes hydrolysis of the representative plasticizer PAEs were divided into three types (I, II, and III). Type I enzymes hydrolyzed only one ester-bond of PAEs, type II enzymes catalyzed the ester-bond of mono-ester phthalates, and type III enzymes hydrolyzed di-ester bonds of PAEs. Divergences of catalytic mechanisms among these enzymes were still unclear. This review provided references for producing bio-plastics, and degrading or recycling of bio- and petro-plastics from an enzymatic point of view.

Biogeochemical properties of blue carbon sediments influence the distribution and monomer composition of bacterial polyhydroxyalkanoates (PHA)

Coastal wetlands are highly efficient 'blue carbon' sinks which contribute to mitigating climate change through the long-term removal of atmospheric CO2 and capture of carbon (C). Microorganisms are integral to C sequestration in blue carbon sediments and face a myriad of natural and anthropogenic pressures yet their adaptive responses are poorly understood. One such response in bacteria is the alteration of biomass lipids, specifically through the accumulation of polyhydroxyalkanoates (PHAs) and alteration of membrane phospholipid fatty acids (PLFA). PHAs are highly reduced bacterial storage polymers that increase bacterial fitness in changing environments. In this study, we investigated the distribution of microbial PHA, PLFA profiles, community structure and response to changes in sediment geochemistry along an elevation gradient from intertidal to vegetated supratidal sediments. We found highest PHA accumulation, monomer diversity and expression of lipid stress indices in elevated and vegetated sediments where C, nitrogen (N), PAH and heavy metals increased, and pH was significantly lower. This was accompanied by a reduction in bacterial diversity and a shift to higher abundances of microbial community members favouring complex C degradation. Results presented here describe a connection between bacterial PHA accumulation, membrane lipid adaptation, microbial community composition and polluted C rich sediments.

Graphical Abstract

Geochemical, microbiological and polyhydroxyalkanoate (PHA) gradient in a blue carbon zone.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10533-022-01008-5.

Genotypic and Phenotypic Detection of Polyhydroxyalkanoate Production in Bacterial Isolates from Food

Polyhydroxyalkanoates (PHAs) are widely used in medical and potentially in other applications due to their biocompatibility and biodegradability. Understanding PHA biosynthetic pathways may lead to the detection of appropriate conditions (substrates) for producing a particular PHA type by a specific microbial strain. The aim of this study was to establish a method enabling potentially interesting PHA bacterial producers to be found. In the study, all four classes of PHA synthases and other genes involved in PHA formation (fabG, phaA, phaB, phaG, and phaJ) were detected by PCR in 64 bacterial collection strains and food isolates. Acinetobacter, Bacillus, Cupriavidus, Escherichia, Klebsiella, Lelliottia, Lysinibacillus, Mammaliicoccus, Oceanobacillus, Pantoea, Peribacillus, Priestia, Pseudomonas, Rahnella, Staphylococcus, and Stenotrophomonas genera were found among these strains. Fructose, glucose, sunflower oil, and propionic acid were utilized as carbon sources and PHA production was detected by Sudan black staining, Nile blue staining, and FTIR methods. The class I synthase and phaA genes were the most frequently found, indicating the strains' ability to synthesize PHA from carbohydrates. Among the tested bacterial strains, the Pseudomonas genus was identified as able to utilize all tested carbon sources. The Pseudomonas extremorientalis strain was determined as a prospect for biotechnology applications.

Valorization of agro-industrial wastes into polyhydroxyalkanoates-rich single-cell proteins to enable a circular waste-to-feed economy

Recovering and converting carbon and nutrients from waste streams into healthy single-cell proteins (SCPs) can be an effective strategy to address costly waste management and support the increasing animal feed demand for the global food supply. Recently, SCPs rich in polyhydroxybutyrate (PHB) have been identified as an effective biocontrol healthy feed to replace conventional antibiotics-supplemented aquaculture feed. PHB, an intercellular polymer of short-chain-length (SCL) hydroxy-fatty acids, is a common type of polyhydroxyalkanoates (PHA) that can be microbially produced from various organics, including agro-industrial wastes. The complex chemical properties of agro-industrial wastes might produce SCPs containing PHA with SCL and/or medium chain-length (MCL) hydroxy-fatty acids. However, the effects of MCL-PHA-containing SCPs on aqua species' health and disease-fighting ability remains poorly understood. This study investigated the feasibility of producing various PHA-containing SCPs from renewable agro-industrial wastes/wastewaters, the effectiveness of SCL- and MCL-PHA as biocontrol agents, and the effects of these PHA-rich SCPs on the growth and disease resistance of an aquaculture animal model, brine shrimp Artemia. Zobellella denitrificans ZD1 and Pseudomonas oleovorans were able to grow on different pure substrates and agro-industrial wastes/wastewaters to produce various SCL- and/or MCL-PHA-rich SCPs. Low doses of MCL-fatty acids (i.e., PHA intermediates) efficiently suppressed the growth of aquaculture pathogens. Moreover, MCL-PHA-rich SCPs served as great food/energy sources for Artemia and improved Artemia's ability to fight pathogens. This study offers a win-win approach to address the challenges of wastes/wastewater management and feed supply faced by the aquaculture industry.

Novel Production Methods of Polyhydroxyalkanoates and Their Innovative Uses in Biomedicine and Industry

Polyhydroxyalkanoate (PHA), a biodegradable polymer obtained from microorganisms and plants, have been widely used in biomedical applications and devices, such as sutures, cardiac valves, bone scaffold, and drug delivery of compounds with pharmaceutical interests, as well as in food packaging. This review focuses on the use of polyhydroxyalkanoates beyond the most common uses, aiming to inform about the potential uses of the biopolymer as a biosensor, cosmetics, drug delivery, flame retardancy, and electrospinning, among other interesting uses. The novel applications are based on the production and composition of the polymer, which can be modified by genetic engineering, a semi-synthetic approach, by changing feeding carbon sources and/or supplement addition, among others. The future of PHA is promising, and despite its production costs being higher than petroleum-based plastics, tools given by synthetic biology, bioinformatics, and machine learning, among others, have allowed for great production yields, monomer and polymer functionalization, stability, and versatility, a key feature to increase the uses of this interesting family of polymers.

Recovery of value-added products from biowaste: A review

This review provides an update on the state-of-the art technologies for the valorization of solid waste and its mechanism to generate various bio-products. The organic content of these wastes can be easily utilized by the microbes and produce value-added compounds. Microbial fermentation techniques can be utilized for developing waste biorefinery processes. The utilization of lignocellulosic and plastics wastes for the generation of carbon sources for microbial utilization after pre-processing steps will make the process a multi-product biorefinery. The C1 and C2 gases generated from different industries could also be utilized by various microbes, and this will help to control global warming. The review seeks to expand expertise about the potential application through several perspectives, factors influencing remediation, issues, and prospects.

Food Packaging Materials with Special Reference to Biopolymers-Properties and Applications

Food is an important material for survival. The increasing world population, urbanization, and globalization are responsible for more food. This has increased challenges in food storage and safety. Therefore, it is necessary to preserve food by suitable packaging materials. The packaging materials are useful for giving longer life to the food and improving quality during transportation, storage and distribution. Innovations and developments in food packaging, have become very important in the food industry. Variety of packaging materials such as plastics, paper, metal, and glass are used in food packaging. Most widely used packaging materials are non-biodegradable plastics but these are harmful to environment and human health. Therefore, the food industry is in search of environment friendly replacement of non-biodegradable plastics by biodegradable plastics. However, no systematic literature is available on the subject, so there is a need to summarise the available information in a systematic way. Polymer packaging materials with special reference to biodegradable plastics have been discussed in detail. Different type of biodegradable plastics with their functionality and applications in food packaging have been summarised. Literature available has shown that biodegradable plastics are much better for food packaging as compared to other packaging materials. Increasing fundamental research in the use of biodegradable polymers in food packaging and effort to protect the environment, requires deep understanding and there are lot of challenges for commercialization, which are to be tackled. All these aspects have been discussed in this review article.

Optimization of nitrogen feeding strategies for improving polyhydroxybutyrate production from biogas by Methylocystis parvus str. OBBP in a stirred tank reactor

The design of efficient cultivation strategies to produce bioplastics from biogas is crucial for the implementation of this biorefinery process. In this work, biogas-based polyhydroxybutyrate (PHB) production and CH₄ biodegradation performance was investigated for the first time in a stirred tank bioreactor inoculated with Methylocystis parvus str. OBBP. Decreasing nitrogen loading rates in continuous mode and alternating feast:famine regimes of 24 h-cycles, and alternating feast:famine regimes of 24 h:24 h and 24 h:48 h were tested. Continuous N feeding did not support an effective PHB production despite the occurrence of nitrogen limiting conditions. Feast-famine cycles of 24 h:24 h (with 50% stoichiometric nitrogen supply) supported the maximum PHB production (20 g-PHB m^-3 d^-1) without compromising the CH₄-elimination capacity (25 g m^-3 h^-1) of the system. Feast:famine ratios ≤1:2 entailed the deterioration of process performance at stoichiometric nitrogen inputs ≤60%.

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.

Tyrosinase-functionalized polyhydroxyalkanoate bio-beads as a novel biocatalyst for degradation of bisphenol analogues

Bisphenol compounds are emerging contaminants of high concerns with known endocrine-disrupting effects. Biocatalysis provides a green chemistry alternative for advanced treatment in water reclamation. This study createda novel biocatalyst through genetically immobilizing the Bacillus megaterium tyrosinase enzyme (BmTyr) on the surface ofself-assembled polyhydroxyalkanoate (PHA) biopolymer beads (termed PHA-BmTyr) by using synthetic biology techniques and demonstrated one-pot in vivo production of the biocatalyst for effective degradation and detoxification of various bisphenol analogues for the first time. The degradation pathway of bisphenols was determined to be mediated by the monophenolase and diphenolase activity of BmTyr. Notably, biocatalytic bisphenol degradation by PHA-BmTyr could substantially reduce or eliminate estrogenic activity of the contaminants, and the degradation products had remarkably lower acute and chronic toxicity than their parent compounds. Furthermore, the PHA-BmTyr biocatalyst had high reusability for multiple bisphenol degradation reaction cycles and showed excellent stability that retained 100% and 86.6% of the initial activity when stored at 4 °C and room temperature, respectively for 30 days. Also, the PHA-BmTyr biocatalyst could efficiently degrade bisphenol analogues in real wastewater effluent matrix. This study provides a promising approach to develop innovative biocatalysis technologies for sustainable water reclamation.

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.

Developing Microbial Co-Culture System for Enhanced Polyhydroxyalkanoates (PHA) Production Using Acid Pretreated Lignocellulosic Biomass

In the growing polymer industry, the interest of researchers is captivated by bioplastics production with biodegradable and biocompatible properties. This study examines the polyhydroxyalkanoates (PHA) production performance of individual Lysinibacillus sp. RGS and Ralstonia eutropha ATCC 17699 and their co-culture by utilizing sugarcane bagasse (SCB) hydrolysates. Initially, acidic (H₂SO₄) and acidified sodium chlorite pretreatment was employed for the hydrolysis of SCB. The effects of chemical pretreatment on the SCB biomass assembly and its chemical constituents were studied by employing numerous analytical methods. Acidic pretreatment under optimal conditions showed effective delignification (60%) of the SCB biomass, leading to a maximum hydrolysis yield of 74.9 ± 1.65% and a saccharification yield of 569.0 ± 5.65 mg/g of SCB after enzymatic hydrolysis. The resulting SCB enzymatic hydrolysates were harnessed for PHA synthesis using individual microbial culture and their defined co-culture. Co-culture strategy was found to be effective in sugar assimilation, bacterial growth, and PHA production kinetic parameters relative to the individual strains. Furthermore, the effects of increasing acid pretreated SCB hydrolysates (20, 30, and 40 g/L) on cell density and PHA synthesis were studied. The effects of different cost-effective nutrient supplements and volatile fatty acids (VFAs) with acid pretreated SCB hydrolysates on cell growth and PHA production were studied. By employing optimal conditions and supplementation of corn steep liquor (CSL) and spent coffee waste extracted oil (SCGO), the co-culture produced maximum cell growth (DCW: 11.68 and 11.0 g/L), PHA accumulation (76% and 76%), and PHA titer (8.87 and 8.36 g/L), respectively. The findings collectively suggest that the development of a microbial co-culture strategy is a promising route for the efficient production of high-value bioplastics using different agricultural waste biomass.

Hyperproduction of PHA copolymers containing high fractions of 4-hydroxybutyrate (4HB) by outer membrane-defected Halomonas bluephagenesis grown in bioreactors

Bacterial outer membrane (OM) is a self‐protective and permeable barrier, while having many non‐negligible negative effects in industrial biotechnology. Our previous studies revealed enhanced properties of Halomonas bluephagenesis based on positive cellular properties by OM defects. This study further expands the OM defect on membrane compactness by completely deleting two secondary acyltransferases for lipid A modification in H. bluephagenesis, LpxL and LpxM, and found more significant advantages than that of the previous lpxL mutant. Deletions on LpxL and LpxM accelerated poly(3‐hydroxybutyrate) (PHB) production by H. bluephagenesis WZY229, leading to a 37% increase in PHB accumulation and 84‐folds reduced endotoxin production. Enhanced membrane permeability accelerates the diffusion of γ‐butyrolactone, allowing H. bluephagenesis WZY254 derived from H. bluephagenesis WZY229 to produce 82wt% poly(3‐hydroxybutyrate‐co‐23mol%4‐hydroxybutyrate) (P(3HB‐co‐23mol%4HB)) in shake flasks, showing increases of 102% and 307% in P(3HB‐co‐4HB) production and 4HB accumulation, respectively. The 4HB molar fraction in copolymer can be elevated to 32 mol% in the presence of more γ‐butyrolactone. In a 7‐l bioreactor fed‐batch fermentation, H. bluephagenesis WZY254 supported a 84 g l⁻¹ dry cell mass with 81wt% P(3HB‐co‐26mol%4HB), increasing 136% in 4HB molar fraction. This study further demonstrated that OM defects generate a hyperproduction strain for high 4HB containing copolymers.

Strategies for Biosynthesis of C1 Gas-derived Polyhydroxyalkanoates: A review

Biosynthesis of polyhydroxyalkanoates (PHAs) from C1 gases is highly desirable in solving problems such as climate change and microplastic pollution. PHAs are biopolymers synthesized in microbial cells and can be used as alternatives to petroleum-based plastics because of their biodegradability. Because 50% of the cost of PHA production is due to organic carbon sources and salts, the utilization of costless C1 gases as carbon sources is expected to be a promising approach for PHA production. In this review, strategies for PHA production using C1 gases through fermentation and metabolic engineering are discussed. In particular, autotrophs, acetogens, and methanotrophs are strains that can produce PHA from CO₂, CO, and CH₄. In addition, integrated bioprocesses for the efficient utilization of C1 gases are introduced. Biorefinery processes from C1 gas into bioplastics are prospective strategies with promising potential and feasibility to alleviate environmental issues.

Metabolic cascade of complex organic wastes to medium-chain carboxylic acids: A review on the state-of-the-art multi-omics analysis for anaerobic chain elongation pathways

Medium-chain carboxylic acid (MCCA) production from organic wastes has attracted much attention because of their higher energy contents and diverse applications. Anaerobic reactor microbiomes are stable and resilient and have resulted in efficient performance during many years of operation for thousands of full-scale anaerobic digesters worldwide. The method underlying how the relevant microbial pathways contribute to elongate carbon chains in reactor microbiomes is important. In particular, the reverse β-oxidation pathway genes are critical to upgrading short-chain fermentation products to MCCAs via a chain elongation (CE) process. Diverse genomics and metagenomics studies have been conducted in various fields, ranging from intracellular metabolic pathways to metabolic cascades between different strains. This review covers taxonomic approach to culture processes depending on types of organic wastes and the deeper understanding of genome and metagenome-scale CE pathway construction, and the co-culture and multi-omics technology that should be addressed in future research.

Installing a Green Engine To Drive an Enzyme Cascade: A Light-Powered In Vitro Biosystem for Poly(3-hydroxybutyrate) Synthesis

Many existing in vitro biosystems harness power from the chemical energy contained in substrates and co-substrates, and light or electric energy provided from abiotic parts, leading to a compromise in atom economy, incompatibility between biological and abiotic parts, and most importantly, incapability to spatiotemporally co-regenerate ATP and NADPH. In this study, we developed a light-powered in vitro biosystem for poly(3-hydroxybutyrate) (PHB) synthesis using natural thylakoid membranes (TMs) to regenerate ATP and NADPH for a five-enzyme cascade. Through effective coupling of cofactor regeneration and mass conversion, 20 mM PHB was yielded from 50 mM sodium acetate with a molar conversion efficiency of carbon of 80.0 % and a light-energy conversion efficiency of 3.04 %, which are much higher than the efficiencies of similar in vitro PHB synthesis biosystems. This suggests the promise of installing TMs as a green engine to drive more enzyme cascades.

Integrated analysis of Whole genome sequencing and life cycle assessment for polyhydroxyalkanoates production by Cupriavidus sp. ISTL7

The current study demonstrates the enhanced production capability of strain Cupriavidus sp. ISTL7 for polyhydroxyalkanoates (PHA) using acetate and glucose (4.93 ± 0.4571 g L^-1) which was characterised analytically by GC-MS, FTIR and NMR analysis. Whole genome sequencing of strain ISTL7 unveiled an array of PHA metabolism genes which included phaA, phaB and phaC. Life cycle assessment of the protocol established that the production was most sustainable with the carbon source acetate. + Glucose as compared to acetate/glucose alone. It also concluded that solvent extraction of PHA and energy consumption during the process requires optimization to sustain the production on ecological fronts. Additionally, acetoacetyl-CoA reductase (phaB) gene was molecularly cloned, expressed and purified (27 KDa, 2.63 mg/ml). Conclusively, Cupriavidus sp. ISTL7 is a potential strain for PHA production with a scope of improvement on energy fronts which would transform the production environmentally and economically appealing.

An updated overview on the regulatory circuits of polyhydroxyalkanoates synthesis

Polyhydroxyalkanoates (PHA) are a promising and sustainable alternative to the petroleum‐based synthetic plastics. Regulation of PHA synthesis is receiving considerable importance as engineering the regulatory factors might help developing strains with improved PHA‐producing abilities. PHA synthesis is dedicatedly regulated by a number of regulatory networks. They tightly control the PHA content, granule size and their distribution in cells. Most PHA‐accumulating microorganisms have multiple regulatory networks that impart a combined effect on PHA metabolism. Among them, several factors ranging from global to specific regulators, have been identified and characterized till now. This review is an attempt to categorically summarize the diverse regulatory circuits that operate in some important PHA‐producing microorganisms. However, in several organisms, the detailed mechanisms involved in the regulation of PHA synthesis is not well‐explored and hence further research is needed. The information presented in this review might help researcher to identify the prevailing research gaps in PHA regulation.

Engineering potassium activation into biosynthetic thiolase

Activation of enzymes by monovalent cations (M+) is a widespread phenomenon in biology. Despite this, there are few structure-based studies describing the underlying molecular details. Thiolases are a ubiquitous and highly conserved family of enzymes containing both K+-activated and K+-independent members. Guided by structures of naturally occurring K+-activated thiolases, we have used a structure-based approach to engineer K+-activation into a K+-independent thiolase. To our knowledge, this is the first demonstration of engineering K+-activation into an enzyme, showing the malleability of proteins to accommodate M+ ions as allosteric regulators. We show that a few protein structural features encode K+-activation in this class of enzyme. Specifically, two residues near the substrate-binding site are sufficient for K+-activation: A tyrosine residue is required to complete the K+ coordination sphere, and a glutamate residue provides a compensating charge for the bound K+ ion. Further to these, a distal residue is important for positioning a K+-coordinating water molecule that forms a direct hydrogen bond to the substrate. The stability of a cation-π interaction between a positively charged residue and the substrate is determined by the conformation of the loop surrounding the substrate-binding site. Our results suggest that this cation-π interaction effectively overrides K+-activation, and is, therefore, destabilised in K+-activated thiolases. Evolutionary conservation of these amino acids provides a promising signature sequence for predicting K+-activation in thiolases. Together, our structural, biochemical and bioinformatic work provide important mechanistic insights into how enzymes can be allosterically activated by M+ ions.

Established and Emerging Producers of PHA: Redefining the Possibility

The polyhydroxyalkanoate was discovered almost around a century ago. Still, all the efforts to replace the traditional non-biodegradable plastic with much more environmentally friendly alternative are not enough. While the petroleum-based plastic is like a parasite, taking over the planet rapidly and without any feasible cure, its perennial presence has made the ocean a floating island of life-threatening debris and has flooded the landfills with toxic towering mountains. It demands for an immediate solution; most resembling answer would be the polyhydroxyalkanoates. The production cost is yet one of the significant challenges that various corporate is facing to replace the petroleum-based plastic. To deal with the economic constrain better strain, better practices, and a better market can be adopted for superior results. It demands for systems for polyhydroxyalkanoate production namely bacteria, yeast, microalgae, and transgenic plants. Solely strains affect more than 40% of overall production cost, playing a significant role in both upstream and downstream processes. The highly modifiable nature of the biopolymer provides the opportunity to replace the petroleum plastic in almost all sectors from food packaging to medical industry. The review will highlight the recent advancements and techno-economic analysis of current commercial models of polyhydroxyalkanoate production. Bio-compatibility and the biodegradability perks to be utilized highly efficient in the medical applications gives ample reason to tilt the scale in the favor of the polyhydroxyalkanoate as the new conventional and sustainable plastic.

Developing Bioprospecting Strategies for Bioplastics Through the Large-Scale Mining of Microbial Genomes

The accumulation of petroleum-based plastic waste has become a major issue for the environment. A sustainable and biodegradable solution can be found in Polyhydroxyalkanoates (PHAs), a microbially produced biopolymer. An analysis of the global phylogenetic and ecological distribution of potential PHA producing bacteria and archaea was carried out by mining a global genome repository for PHA synthase (PhaC), a key enzyme involved in PHA biosynthesis. Bacteria from the phylum Actinobacteria were found to contain the PhaC Class II genotype which produces medium-chain length PHAs, a physiology until now only found within a few Pseudomonas species. Further, several PhaC genotypes were discovered within Thaumarchaeota, an archaeal phylum with poly-extremophiles and the ability to efficiently use CO2 as a carbon source, a significant ecological group which have thus far been little studied for PHA production. Bacterial and archaeal PhaC genotypes were also observed in high salinity and alkalinity conditions, as well as high-temperature geothermal ecosystems. These genome mining efforts uncovered previously unknown candidate taxa for biopolymer production, as well as microbes from environmental niches with properties that could potentially improve PHA production. This in silico study provides valuable insights into unique PHA producing candidates, supporting future bioprospecting efforts toward better targeted and relevant taxa to further enhance the diversity of exploitable PHA production systems.

Engineering the permeability of Halomonas bluephagenesis enhanced its chassis properties

Bacterial outer membrane (OM), an asymmetric lipid bilayer functioning as a self-protective barrier with reduced permeability for Gram-negative bacteria, yet wasting nutrients and energy to synthesize, has not been studied for its effect on bioproduction. Here we construct several OM-defected halophile Halomonas bluephagenesis strains to investigate the effects of OM on bioproduction. We achieve enhanced chassis properties of H. bluephagenesis based on positive cellular properties among several OM-defected strains. The OM-defected H. bluephagenesis WZY09 demonstrates better adaptation to lower salinity, increasing 28%, 30% and 12% on dry cell mass (DCM), poly(3-hydroxybutyrate) (PHB) accumulation and glucose to PHB conversion rate, respectively, including enlarged cell sizes and 21-folds reduced endotoxin. Interestingly, a poly(3-hydroxybutyrate-co-21mol%4-hydroxybutyrate) (P(3HB-co-21mol%4HB)) is produced by H. bluephagenesis WZY09 derivate WZY249, increasing 60% and 260% on polyhydroxyalkanoate (PHA) production and 4HB content, respectively. Furthermore, increased electroporation efficiency, more sensitive isopropyl β-D-1-thio-galactopyranoside (IPTG) induction, better oxygen uptake, enhanced antibiotics sensitivity and ectoine secretion due to better membrane permeability are observed if OM defected, demonstrating significant OM defection impacts for further metabolic engineering, synthetic biology studies and industrial applications.

Production of polyhydroxyalkanoates from propylene oxide saponification wastewater residual sludge using volatile fatty acids and bacterial community succession

The active sludge treating propylene oxide saponification wastewater has heavy salt concentration and is hard to treat. The integration of the residual sludge treatment with polyhydroxyalkanoates (PHA) production may provide an economic and environment friendly solution. PHA production was therefore studied in two sequencing biological reactors with effective volume of 30 L using the active sludge. The two reactors, named as SBR-I and SBR-II, were fed with acetic acid, and a mixture of acetic acid and propionic acid respectively. PHA was obtained with a yield of 9.257 g/L in SBR-II. Also, the proportion of 3-hydroxyvalarate was enhanced from 5% to 30% in comparison to SBR-I (5.471 g/L). Illumina MiSeq and Pacific Biosciences sequencing platforms were used to evaluate the community structure, which revealed that the bacterial genera showed a high degree of diversity in the PHA accumulating microbial community. Azoarcus was the most dominant PHA accumulating microorganism after acclimation.