Microbial Polyhydroxyalkanoates Research Articles

Bacterial Polyhydroxyalkanoates-based Therapeutics-delivery Nano-systems.

Microbial polyhydroxyalkanoates (PHAs) are bio-based aliphatic biopolyester produced by bacteria as an intracellular storage material of carbon and energy under stressed conditions. PHAs have been paid attention to due to their unique and impressive biological properties including high biodegradability, biocompatibility, low cytotoxicity, and different mechanical properties. Under this context, the development of drug-delivery nanosystems based on PHAs has been revealed to have numerous advantages compared with synthetic polymers that included biocompatibility, biodegradability, non-toxic, and low-cost production, among others. In this review article, we present the available state of the art of PHAs. Moreover, we discussed the potential benefits, weaknesses, and perspectives of PHAs to the develop drug delivery systems.

Valorization of Algal Biomass to Produce Microbial Polyhydroxyalkanoates: Recent Updates, Challenges, and Perspectives.

Biopolymers are highly desirable alternatives to petrochemical-based plastics owing to their biodegradable nature. The production of bioplastics, such as polyhydroxyalkanoates (PHAs), has been widely reported using various bacterial cultures with substrates ranging from pure to biowaste-derived sugars. However, large-scale production and economic feasibility are major limiting factors. Now, using algal biomass for PHA production offers a potential solution to these challenges with a significant environmental benefit. Algae, with their unique ability to utilize carbon dioxide as a greenhouse gas (GHG) and wastewater as feed for growth, can produce value-added products in the process and, thereby, play a crucial role in promoting environmental sustainability. The sugar recovery efficiency from algal biomass is highly variable depending on pretreatment procedures due to inherent compositional variability among their cell walls. Additionally, the yields, composition, and properties of synthesized PHA vary significantly among various microbial PHA producers from algal-derived sugars. Therefore, the microalgal biomass pretreatments and synthesis of PHA copolymers still require considerable investigation to develop an efficient commercial-scale process. This review provides an overview of the microbial potential for PHA production from algal biomass and discusses strategies to enhance PHA production and its properties, focusing on managing GHGs and promoting a sustainable future.

Artificial neural network based optimization of sunflower oil supplementation in polyhydroxyalkanoates production by Cupriavidus necator

The assessment of feeding strategy and availability of alternate carbon source in vegetable oil-supplemented microbial polyhydroxyalkanoates (PHA) production remains largely qualitative. This study aims to model the impact of sunflower oil to sucrose ratio, and feeding strategy on PHA production by Cupriavidus necator. Sets containing oil (20 ml l−1), and oil-sucrose mixture (10 ml l−1, 10 g l−1) resulted in 3.907 g l−1 and 3.342 g l−1 of PHA, much higher than in sucrose-only (2.081 g l−1) set. Shifting sucrose (20 g l−1) pre-grown biomass on into oil (20 ml l−1) containing medium resulted in a substantial increase in polymer than in sets either amended with oil or having an equal proportion sucrose-oil blend. Hyperparameter optimized double-layer (6-3) ANN model for PHA production, developed from factorial design experiment with different sucrose-oil ratios (0.053–19 w/v), inoculum dose (0.853–1.219 g l−1), and time-of-shift (24–72 h), offered reasonably good fitness both on training (R2: 0.960) and cross-validation (R2CV: 0.593). Optimization of the ANN model projected 10.411 g l−1 of PHA from a sucrose-oil ratio of 1.729 (w/v), inoculum dose (0.854 g l−1), and sucrose-to-oil shift after 44 h of incubation.

Pilot scale-up production of poly(3-hydroxybutyrate) (PHB) from starch-based wastewater: A halogen-free process optimization for polymer recovery

The intracellular nature of microbial polyhydroxyalkanoates (PHAs) requires two main steps in their production: bioconversion and extraction. The most widely used method for recovering poly(3-hydroxybutyrate) (PHB) is solvent extraction. Traditional approaches involve the use of halogenated solvents, whose environmental and health hazards are well known. New alternatives advocate the use of sustainable agents, which can be an effective and economical choice. In this work, the bioconversion process of starch-based water into PHB by Cupriavidus necator DSM 545 was first scaled-up using previously optimized conditions. A statistical model was then developed to optimize the best conditions for polymer extraction using NaOH by response surface methodology with a central composite design. The optimized and validated conditions were: 0.05 M NaOH at 29.6 °C for 1 h, resulting in 87.31 ± 0.33 % polymer yield, 104.13 ± 2.22 % polymer purity and 104.76 ± 2.41 % polymer recovery. These conditions were validated for operation at three different biomass-to-NaOH concentrations: 5.7 g/L, 20 g/L and 79.5 g/L, and scaled-up without sacrificing polymer yield, with high levels of PHB purity and recovery. In addition, this work proposed an approach for the scale-up of a halogen-free process for PHB extraction using NaOH, considering parameters that can be easily integrated into the common ranges used in the industry.

A self-stimulating system based on a polyhydroxyalkanoates coupled induction mechanism and its applications for Halomonas

Inducible gene expression systems are vital tools for synthetic biology. This study focused on a microbial polyhydroxyalkanoate (PHA) related inducible expression system, namely, the regulation mechanism of PHA synthesis associated protein PhaR and PhaP1 in Halomonas bluephagenesis which has employed to enhance PHA synthesis under open unsterile conditions. H. bluephagenesis strains ZS19 and ZS49 with one and two copies of the PHA synthesis system (PphaP1*-phaAB) were constructed based on the PHA self-stimulating synthesis mechanism. When grown in a 7-L bioreactor, H. bluephagenesis ZS19 and ZS49 were grown to 97.4 g/L and 89.6 g/L containing 76.3% and 77.1% PHA in the cell dry weights (CDW), with productivity of 2.06 g/L/h and 2.16 g/L/h, respectively. Compared with its control, their CDW, PHB percent and productivity increased by 20.4% and 10.8%, 13.5% and 14.7 %, and 36.4 % and 43.0 %, respectively. Furthermore, H. bluephagenesis ZS97, engineered with an elongated morphology induced by the PHA-mediated PhaR-phaP1 regulatory system, exhibited a 10 % increase in cell dry weight and a morphology approximately 10 times longer than the wild-type strain, allowing easy separation from the culture broth via centrifugation.

Green alternatives to petroleum-based plastics: production of bioplastic from Pseudomonas neustonica strain NGB15 using waste carbon source.

Polyhydroxyalkanoates have attracted great interest as a suitable alternative to petrochemical based plastics due to their outstanding properties such as biodegradability and biocompatibility. However, the biggest problem in the production of microbial polyhydroxyalkanoates is low cost-effectiveness. In this study, polyhydroxyalkanoate production was carried out using waste substrates with local isolates. Culture conditions were optimized to increase the polyhydroxyalkanoate production potential. The produced polyhydroxyalkanoate was characterized by FTIR analyses, and its metabolic pathway was determined by real-time PCR. According to the results, the best polyhydroxyalkanoate producer bacteria was characterized as Pseudomonas neustonica NGB15. The optimal culture conditions were detected as 30g/L banana peel powder, 25°C temperature, pH 8, and 4-day incubation time. Under the optimized conditions, 3.34g/L PHA production was achieved. As a result of FTIR analyses, major peaks were obtained at 1723, 1277, 1261, 1097, 1054, and 993cm-1. These peaks represent that the type of produced polyhydroxyalkanoate was poly-β-hydroxybutyrate. According to gene expression profile of NGB15, it was determined that Pseudomonas neustonica NGB15 produces PHA using the de novo fatty acid synthesis metabolic pathway. In conclusion, poly-β-hydroxybutyrate production by Pseudomonas neustonica NGB15 using a low-cost fermentation medium has been shown to be biotechnologically promising.

Valorization of Cabbage Waste as a Feedstock for Microbial Polyhydroxyalkanoate Production: Optimizing Hydrolysis Conditions and Polyhydroxyalkanoate Production.

Establishing a platform for the bioconversion of waste resources into value-added compounds is critical for achieving a sustainable and eco-friendly economy. Herein, we produced polyhydroxyalkanoate via microbial fermentation using cabbage waste as a feedstock and metabolically engineered Escherichia coli. For this, the hydrolysis conditions of cabbage waste were optimized by focusing on parameters such as substrate and enzyme concentrations to enhance the saccharification efficiency. The phaABC operon, which encodes key enzymes responsible for polyhydroxyalkanoate biosynthesis in Ralstonia eutropha H16, was overexpressed in E. coli. Using cabbage hydrolysate as the feedstock, this engineered E. coli strain could produce poly(3-hydroxybutyrate) with a polymer content of 26.0 wt % of dry cell weight. Moreover, malic acid in cabbage hydrolysate significantly enhanced poly(3-hydroxybutyrate) production; the addition of 0.5 g/L malic acid markedly increased poly(3-hydroxybutyrate) content by 59.9%. This study demonstrates the potential of cabbage waste as a promising raw material for the microbial production of polyhydroxyalkanoate.

Dynamic Model Selection and Optimal Batch Design for Polyhydroxyalkanoate (PHA) Production by Cupriavidus necator.

Mathematical modelling of microbial polyhydroxyalkanoates (PHAs) production is essential to develop optimal bioprocess design. Though the use of mathematical models in PHA production has increased over the years, the selection of kinetics and model identification strategies from experimental data remains largely heuristic. In this study, PHA production from Cupriavidus necator utilizing sucrose and urea was modelled using a parametric discretization approach. Product formation kinetics and relevant parameters were established from urea-free experimental sets, followed by the selection of growth models from a batch containing both sucrose and urea. Logistic growth and Luedeking-Piret model for PHA production was selected based on regression coefficient (R2: 0.941), adjusted R2 (0.930) and AICc values (-42.764). Model fitness was further assessed through cross-validation, confidence interval and sensitivity analysis of the parameters. Model-based optimal batch startup policy, incorporating multi-objective desirability, suggests an accumulation of 2.030g l-1 of PHA at the end of 120h. The modelling framework applied in this study can be used not only to avoid over-parameterization and identifiability issues but can also be adopted to design optimal batch startup policies.

Polyhydroxyalkanoate production in Pseudomonas putida from alkanoic acids of varying lengths.

Many studies have been conducted to produce microbial polyhydroxyalkanoates (PHA), a biopolymer, from Pseudomonas sp. fed with various alkanoic acids. Because this previous data was collected using methodologies that varied in critical aspects, such as culture media and size range of alkanoic acids, it has been difficult to compare the results for a thorough understanding of the relationship between feedstock and PHA production. Therefore, this study utilized consistent culture media with a wide range of alkanoic acids (C7-C14) to produce medium chain length PHAs. Three strains of Pseudomonas putida (NRRL B-14875, KT2440, and GN112) were used, and growth, cell dry weight, PHA titer, monomer distribution, and molecular weights were all examined. It was determined that although all the strains produced similar PHA titers using C7-C9 alkanoic acids, significant differences were observed with the use of longer chain feedstocks. Specifically, KT2440 and its derivative GN112 produced higher PHA titers compared to B-14875 when fed longer chain alkanoates. We also compared several analytical techniques for determining amounts of PHA and found they produced different results. In addition, the use of an internal standard had a higher risk of calculating inaccurate concentrations compared to an external standard. These observations highlight the importance of considering this aspect of analysis when evaluating different studies.

Microbial PolyHydroxyAlkanoate (PHA) Biopolymers-Intrinsically Natural.

Global pollution from fossil plastics is one of the top environmental threats of our time. At their end-of-life phase, fossil plastics, through recycling, incineration, and disposal result in microplastic formation, elevated atmospheric CO2 levels, and the pollution of terrestrial and aquatic environments. Current regional, national, and global regulations are centered around banning plastic production and use and/or increasing recycling while ignoring efforts to rapidly replace fossil plastics through the use of alternatives, including those that occur in nature. In particular, this review demonstrates how microbial polyhydroxyalkanoates (PHAs), a class of intrinsically natural polymers, can successfully remedy the fossil and persistent plastic dilemma. PHAs are bio-based, biosynthesized, biocompatible, and biodegradable, and thus, domestically and industrially compostable. Therefore, they are an ideal replacement for the fossil plastics pollution dilemma, providing us with the benefits of fossil plastics and meeting all the requirements of a truly circular economy. PHA biopolyesters are natural and green materials in all stages of their life cycle. This review elaborates how the production, consumption, and end-of-life profile of PHAs are embedded in the current and topical, 12 Principles of Green Chemistry, which constitute the basis for sustainable product manufacturing. The time is right for a paradigm shift in plastic manufacturing, use, and disposal. Humankind needs alternatives to fossil plastics, which, as recalcitrant xenobiotics, contribute to the increasing deterioration of our planet. Natural PHA biopolyesters represent that paradigm shift.

Application of Immersed Membrane Bioreactor for Semi-Continuous Production of Polyhydroxyalkanoates from Organic Waste-Based Volatile Fatty Acids.

Volatile fatty acids (VFAs) appear to be an economical carbon feedstock for the cost-effective production of polyhydroxyalkanoates (PHAs). The use of VFAs, however, could impose a drawback of substrate inhibition at high concentrations, resulting in low microbial PHA productivity in batch cultivations. In this regard, retaining high cell density using immersed membrane bioreactor (iMBR) in a (semi-) continuous process could enhance production yields. In this study, an iMBR with a flat-sheet membrane was applied for semi-continuous cultivation and recovery of Cupriavidus necator in a bench-scale bioreactor using VFAs as the sole carbon source. The cultivation was prolonged up to 128 h under an interval feed of 5 g/L VFAs at a dilution rate of 0.15 (d-1), yielding a maximum biomass and PHA production of 6.6 and 2.8 g/L, respectively. Potato liquor and apple pomace-based VFAs with a total concentration of 8.8 g/L were also successfully used in the iMBR, rendering the highest PHA content of 1.3 g/L after 128 h of cultivation. The PHAs obtained from both synthetic and real VFA effluents were affirmed to be poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with a crystallinity degree of 23.8 and 9.6%, respectively. The application of iMBR could open an opportunity for semi-continuous production of PHA, increasing the feasibility of upscaling PHA production using waste-based VFAs.

Rapid Enrichment of Cupriavidus necator in Mixed Microbial Cultures Using Autotrophic Growth: Mixed Microbial Cultures for Biodegradable Polymer Production Using CO2 and Organic Wastes

Polyhydroxyalkanoate (PHA) is a biodegradable polymer that can replace petroleum-based plastics. Cupriavidus necator has been extensively utilized in industrial PHA production because the bacterium can grow and accumulate high amounts of PHA in their cells under heterotrophic and/or autotrophic growth conditions. Microbial PHA production using mixed cultures reduces the high PHA production costs and allows for the utilization of waste organics as carbon sources. However, C. necator cultivation in mixed microbial cultures has not been investigated before. In this work, we developed innovative methods for rapid and selective enrichment of C. necator in mixed cultures, utilizing the unique metabolic characteristics of C. necator (i.e., the ability to grow heterotrophically and/or autotrophically). Three enrichment methods were proposed: autotrophic-only, alternating autotrophic–heterotrophic, and heterotrophic-only cycles. These methods were examined with two wastewater sources as initial mixed mixtures. In the autotrophic-only method, the fraction of C. necator exceeded 92% of the total microbial population in only 60 h, whereas the alternating autotrophic–heterotrophic cycles showed >81.3% selection of C. necator. However, the heterotrophic-only method resulted in practically no enrichment of C. necator after five repeated feast–famine cycles. When tested for PHA accumulation, enriched cultures using the autotrophic and alternating cycles accumulated significant amounts of PHA, confirming the selective and rapid enrichment of C. necator over other microorganisms. Based on the experimental results, the autotrophic-based enrichment is a potential approach for the cost-effective cultivation of C. necator, which can reduce PHA production costs.

Polyhydroxyalkanoates (PHAs) from Endophytic Bacterial Strains as Potential Biocontrol Agents against Postharvest Diseases of Apples.

Due to the increasing use and accumulation of petrochemical plastics in the environment and the rapid depletion of natural resources, microbial polyhydroxyalkanoates have great potential to replace them. This study provides new insights in the field of obtaining of polyhydroxyalkanoates (PHAs) from endophytic bacterial strains and applying them as potential biocontrol agents against postharvest diseases of apples. Two strains-Pseudomonas flavescens D5 and Bacillus aerophilus A2-accumulated PHAs in amounts ranging from 2.77 to 5.9 g L-1. The potential to use low-cost substrates such as beet molasses and soapstock for PHA accumulation was shown. The PHAs produced by the Ps. flavescens D5 strain had pronounced antagonistic activity against Penicillium expansum (antifungal property = 62.98-73.08%). The use of PHAs as biocontrol agents significantly reduced the severity of apple blue mold, especially in the preventive treatment option.

Rapid combinatorial rewiring of metabolic networks for enhanced poly(3-hydroxybutyrate) production in Corynebacterium glutamicum

BackgroundThe disposal of plastic waste is a major environmental challenge. With recent advances in microbial genetic and metabolic engineering technologies, microbial polyhydroxyalkanoates (PHAs) are being used as next-generation biomaterials to replace petroleum-based synthetic plastics in a sustainable future. However, the relatively high production cost of bioprocesses hinders the production and application of microbial PHAs on an industrial scale.ResultsHere, we describe a rapid strategy to rewire metabolic networks in an industrial microorganism, Corynebacterium glutamicum, for the enhanced production of poly(3-hydroxybutyrate) (PHB). A three-gene PHB biosynthetic pathway in Rasltonia eutropha was refactored for high-level gene expression. A fluorescence-based quantification assay for cellular PHB content using BODIPY was devised for the rapid fluorescence-activated cell sorting (FACS)-based screening of a large combinatorial metabolic network library constructed in C. glutamicum. Rewiring metabolic networks across the central carbon metabolism enabled highly efficient production of PHB up to 29% of dry cell weight with the highest cellular PHB productivity ever reported in C. glutamicum using a sole carbon source.ConclusionsWe successfully constructed a heterologous PHB biosynthetic pathway and rapidly optimized metabolic networks across central metabolism in C. glutamicum for enhanced production of PHB using glucose or fructose as a sole carbon source in minimal media. We expect that this FACS-based metabolic rewiring framework will accelerate strain engineering processes for the production of diverse biochemicals and biopolymers.

Systematizing Microbial Bioplastic Production for Developing Sustainable Bioeconomy: Metabolic Nexus Modeling, Economic and Environmental Technologies Assessment.

The excessive usage of non-renewable resources to produce plastic commodities has incongruously influenced the environment's health. Especially in the times of COVID-19, the need for plastic-based health products has increased predominantly. Given the rise in global warming and greenhouse gas emissions, the lifecycle of plastic has been established to contribute to it significantly. Bioplastics such as polyhydroxy alkanoates, polylactic acid, etc. derived from renewable energy origin have been a magnificent alternative to conventional plastics and reconnoitered exclusively for combating the environmental footprint of petrochemical plastic. However, the economically reasonable and environmentally friendly procedure of microbial bioplastic production has been a hard nut to crack due to less scouted and inefficient process optimization and downstream processing methodologies. Thereby, meticulous employment of computational tools such as genome-scale metabolic modeling and flux balance analysis has been practiced in recent times to understand the effect of genomic and environmental perturbations on the phenotype of the microorganism. In-silico results not only aid us in determining the biorefinery abilities of the model microorganism but also curb our reliance on equipment, raw materials, and capital investment for optimizing the best conditions. Additionally, to accomplish sustainable large-scale production of microbial bioplastic in a circular bioeconomy, extraction, and refinement of bioplastic needs to be investigated extensively by practicing techno-economic analysis and life cycle assessment. This review put forth state-of-the-art know-how on the proficiency of these computational techniques in laying the foundation of an efficient bioplastic manufacturing blueprint, chiefly focusing on microbial polyhydroxy alkanoates (PHA) production and its efficacy in outplacing fossil based plastic products.

Synthesis and biodegradation of polymer blends of poly(3-hydroxybutyrate) and natural rubber

Microbial polyhydroxyalkanoates (PHAs) as an ideal choice of biomaterial for specific applications. In this study, PHA was synthesized and purified from Pseudomonas mendocina PSU. These obtained PHA was then determined its monomer composition and found that 3-hydroxybutyrate (3HB) was a major component, in addition, the molecular weight were also investigated. The average Mw was 8.39 ×104 when grown in MSM supplemented with glycerol whereas the melting temperature was 172 °C. To improve mechanical and biodegradation properties of PHB, blending with suitable well defined polymers such as natural rubbers (NR) has been performed by blending poly(3-hydroxybutyrate) [(PHB)] with and epoxidized natural rubber (ENR) using two different blending methods e.g. solvent blending and melting blending in a ratio of PHB to ENR of 70:30. The polymer blends were further investigated their biodegradation by soil burial test and rubber-degrading consortium. The results clearly showed that in soil burial test, the most rapid biodegradation was PHB from P. mendocina PSU which reached to 34.10%weight loss whereas the biodegradation of polymers by rubber-degrading bacteria, interestingly the highest percentages of weight loss about 13% was obtained in PHB-ENR blend films from melt blending followed by PHB-ENR blend films from solvent blending, NR, PHB from P. mendocina PSU and ENR, respectively. In addition, the physical changes in all tested samples were observed.

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

Resorbable Nanomatrices from Microbial Polyhydroxyalkanoates: Design Strategy and Characterization.

From a series of biodegradable natural polymers of polyhydroxyalkanoates (PHAs)-poly-3-hydroxybutyrate (P(3HB) and copolymers containing, in addition to 3HB monomers, monomers of 3-hydroxyvalerate (3HV), 3-hydroxyhexanoate (3HHx), and 4-hydroxybutyrate (4HB), with different ratios of monomers poured-solvent casting films and nanomembranes with oriented and non-oriented ultrathin fibers were obtained by electrostatic molding. With the use of SEM, AFM, and measurement of contact angles and energy characteristics, the surface properties and mechanical and biological properties of the polymer products were studied depending on the method of production and the composition of PHAs. It has been shown in cultures of mouse fibroblasts of the NIH 3T3 line and diploid human embryonic cells of the M22 line that elastic films and nanomembranes composed of P(3HB-co-4HB) copolymers have high biocompatibility and provide adhesion, proliferation and preservation of the high physiological activity of cells for up to 7 days. Polymer films, namely oriented and non-oriented nanomembranes coated with type 1 collagen, are positively evaluated as experimental wound dressings in experiments on laboratory animals with model and surgical skin lesions. The results of planimetric measurements of the dynamics of wound healing and analysis of histological sections showed the regeneration of model skin defects in groups of animals using experimental wound dressings from P(3HB-co-4HB) of all types, but most actively when using non-oriented nanomembranes obtained by electrospinning. The study highlights the importance of nonwoven nanomembranes obtained by electrospinning from degradable low-crystalline copolymers P(3HB-co-4HB) in the effectiveness of the skin wound healing process.

Microbial Polyhydroxyalkanoates (PHAs): A Review on Biosynthesis, Properties, Fermentation Strategies and Its Prospective Applications for Sustainable Future

Microbial Polyhydroxyalkanoates (PHAs): A Review on Biosynthesis, Properties, Fermentation Strategies and Its Prospective Applications for Sustainable Future

Structural variability, implementational irregularities in mathematical modelling of polyhydroxyalkanoates (PHAs) production—A state‐of‐the‐art review

The rate and extent of microbial polyhydroxyalkanoates (PHAs) production rely on the availability of substrates, growth of microbial biomass, and intracellular accumulation of polymer under nitrogen-limited conditions. The dynamics of PHAs production captured through various structured or unstructured models can be extended to design an optimal feeding strategy for process intensification. Large variability in process assumptions, choices of kinetics, and model complexity is expected depending on substrate(s), microbial metabolism, and discretization of the process under consideration. This communication attempts to review the estimation of stoichiometric yield coefficients, metabolic modelling, and choices of unstructured kinetics in microbial PHA production. Implementational irregularities in parameter estimation and quality check in modelling exercises have also been reviewed. It is observed that the scope of the majority of the "modelling" studies is confined to the estimation of stoichiometric parameters with limited utility. In dynamic models, microbial growth is often described using either Monod or logistic variants, while PHAs production adopts a Luedeking-Piret expression with or without substrate inhibition. Though model selection, regression with experimental data, parameter estimation, and model validation are integral parts of the exercise, very few provide sufficient coverage on all those aspects. Application of the model to control or optimize the bioprocess has rarely been attempted.