Extremophilic Bacterium Halomonas desertis G11 as a Cell Factory for Poly-3-Hydroxybutyrate-co-3-Hydroxyvalerate Copolymer's Production

Advances and challenges in polyhydroxyalkanoates (PHA) production using Halomonas species: A review

Plastic waste pollution is one of the major threats to sustainable development. Biodegradable polymers and biopolymers such as polyhydroxyalkanoates (PHAs) offer suitable alternatives for replacing synthetic plastics. PHAs are produced by diverse bacteria species and archaea as storage compounds for utilization as carbon and energy sources. Halomonas species have emerged as attractive microbial cell factories for biosynthesis of PHAs due to their metabolic versality, ability to valorize diverse feedstock materials, and tolerance to high salinity and pH that allows fermentation in contamination-resistant conditions. In recent years, there has been great attention to the use of Halomonas species in PHA biosynthesis and genetic engineering efforts for enhanced production. This article provides a discussion of the current state of knowledge on production of polyhydroxyalkanoates by Halomonas species. It includes an overview of PHA biosynthesis mechanisms, fermentation strategies, production with cheap substrates, exploitation of open and unsterile conditions, co-production of PHAs and other products, and advances genetic engineering efforts.

Experimental and Computational Insights into Polyurethane Plastic Waste Conversion to Microbial Bioplastic

In this study, a seven-factor Hoke experimental design and the response surface methodology were used to optimize the fermentation conditions for the maximum polyhydroxyalkanoates (PHA) yield using polyurethane plastic waste (PUPW) as a source of carbon and energy for the microbial growth and biobased polyester production. The highest PHA yield (0.80 g/L ± 0.01) was obtained under a pH of 8; a temperature of 35 °C; a NaCl concentration of 5%; a PUPW concentration of 1%; an inoculum size of 15%, a monoculture of Pseudomonas rhizophila S211; and an incubation time of 6 days. The response values predicted by the Hoke design model at each combination of factor levels aligned with the experimental results, and the analysis of variance demonstrated the predictability and accuracy of the postulated model. In addition to the experimental evidences, P. rhizophila genome was explored to predict the PUPW-degrading enzymes and the associated protein secretion systems. Moreover, physicochemical properties, phylogenetic analysis, and 3D structure of S211 LipA2 polyurethanase were elucidated through an in-silico approach. Taken all together, integrated experimental tests and computational modeling suggest that P. rhizophila S211 has the necessary enzymatic machinery to effectively convert the non-biodegradable PUPW into PHA bioplastics.

Toward Sustainable Polyhydroxyalkanoates: A Next-Gen Biotechnology Approach

Polyhydroxyalkanoates (PHAs) are biodegradable biopolymers synthesized by microorganisms and serve as sustainable alternatives to petroleum-based plastics. While traditional PHA production relies on refined carbon sources and pure cultures, high costs and scalability challenges limit commercial viability. Extremophiles, particularly halophiles, have emerged as promising candidates for cost-effective, large-scale production of PHAs. Their ability to thrive in extreme environments reduces contamination risks, minimizes the need for sterilization, and lowers operational costs. Advancements in metabolic engineering, synthetic biology, and CRISPR-based genome editing have enhanced PHA yields by optimizing metabolic flux and cell morphology. Additionally, utilizing alternative feedstocks such as biowaste, syngas, methane, and CO₂ improves economic feasibility. Next-generation industrial biotechnology integrates extremophilic microbes with AI-driven fermentation and eco-friendly downstream processing to enhance scalability. Industrial-scale production of PHAs using Halomonas spp. and other extremophiles demonstrates significant progress toward commercialization, paving the way for sustainable biopolymer applications in reducing plastic pollution.

Controlled release of trifluralin herbicide using luminescent Vibrio-derived polyhydroxyalkanoate (PHA) microcapsules

The controlled release of herbicides using new and safe materials can mitigate environmental pollution. Polyhydroxyalkanoate (PHA) is a type of biopolymer that can be produced by various bacteria. It has properties that make it suitable for encapsulation and controlled release applications. A luminescent bacterium, Vibrio sp. VLC strain was used as the PHA producer in this study. Initially, the polymer was synthesized by the bacterium following optimization of the culture medium, resulting in an approximate yield of 25 %. Subsequently, the produced polymer was analyzed using TEM, FTIR, and H-NMR techniques. Microcapsules were produced using the emulsion method. FE-SEM imaging revealed spherical microcapsules with an average diameter of 0.5-2 μm. The herbicide loading content and encapsulation efficiency were determined to be 16.64 % and 66.56 %, respectively. The herbicidal effect of the microcapsules containing trifluralin was investigated using Amaranthus retroflexus and Setaria viridis plants, demonstrating a significant reduction in various parameters after application. Furthermore, the impact of encapsulated herbicide on soil microbial population was assessed, revealing a less negative effect compared to its free form. These findings suggest that the PHA from a luminescent vibrio holds promise as an eco-friendly, biodegradable, nontoxic material for the controlled release of herbicides.

Pseudomonas rhizophila S211 as a microbial cell factory for direct bioconversion of waste cooking oil into medium-chain-length polyhydroxyalkanoates

The present study examines the use of waste cooking oil (WCO) as a substrate for medium-chain-length polyhydroxyalkanoates (mcl-PHA) production by Pseudomonas rhizophila S211. The genome analysis revealed that the S211 strain has a mcl-PHA cluster (phaC1ZC2DFI) encoding two class II PHA synthases (PhaC1 and PhaC2) separated by a PHA depolymerase (PhaZ), a transcriptional activator (PhaD) and two phasin-like proteins (PhaFI). Genomic annotation also identified a gene encoding family I.3 lipase that was able to hydrolyze plant oils and generate fatty acids as favorable carbon sources for cell growth and PHA synthesis via β-oxidation pathway. Using a three-variable Doehlert experimental design, the optimum conditions for mcl-PHA accumulation were achieved in 10% of WCO-based medium with an inoculum size of 10% and an incubation period of 48 h at 30 °C. The experimental yield of PHA from WCO was 1.8 g/L close to the predicted yield of 1.68 ± 0.14 g/L. Moreover, 1H nuclear magnetic resonance spectroscopy analysis confirmed the extracted mcl-PHA. Overall, this study describes P. rhizophila as a cell factory for biosynthesis of biodegradable plastics and proposes green and efficient approach to cooking oil waste management by decreasing the cost of mcl-PHA production, which can help reduce the dependence on petroleum-based plastics.

Halomonas alkaliantarctica as a platform for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) production from biodiesel-derived glycerol

Polyhydroxyalkanoates (PHAs) are biodegradable polyesters produced by a wide range of microorganisms, including extremophiles. These unique microorganisms have gained interest in PHA production due to their ability to utilise low-cost carbon sources under extreme conditions. In this study, Halomonas alkaliantarctica was examined with regards to its potential to produce PHAs using crude glycerol from biodiesel industry as the only carbon source. We found that cell dry mass concentration was not dependent on the applying substrate concentration. Furthermore, our data confirmed that the analysed halophile was capable of metabolising crude glycerol into poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer within 24 h of the cultivation without addition of any precursors. Moreover, crude glycerol concentration affects the repeat units content in the purified PHAs copolymers and their thermal properties. Nevertheless, a differential scanning calorimetric and thermogravimetric analysis showed that the analysed biopolyesters have properties suitable for various applications. Overall, this study described a promising approach for the valorisation of crude glycerol as a future strategy of industrial waste management to produce high value microbial biopolymers.

Commercialization potential of agro-based polyhydroxyalkanoates biorefinery: A technical perspective on advances and critical barriers

The exponential increase in the use and careless discard of synthetic plastics has created an alarming concern over the environmental health due to the detrimental effects of petroleum based synthetic polymeric compounds. Piling up of these plastic commodities on various ecological niches and entry of their fragmented parts into soil and water has clearly affected the quality of these ecosystems in the past few decades. Among the many constructive strategies developed to tackle this global issue, use of biopolymers like polyhydroxyalkanoates as sustainable alternatives for synthetic plastics has gained momentum. Despite their excellent material properties and significant biodegradability, polyhydroxyalkanoates still fails to compete with their synthetic counterparts majorly due to the high cost associated with their production and purification thereby limiting their commercialization. Usage of renewable feedstocks as substrates for polyhydroxyalkanoates production has been the thrust area of research to attain the sustainability tag. This review work attempts to provide insights about the recent developments in the production of polyhydroxyalkanoates using renewable feedstock along with various pretreatment methods used for substrate preparation for polyhydroxyalkanoates production. Further, the application of blends based on polyhydroxyalkanoates, and the challenges associated with the waste valorization based polyhydroxyalkanoates production strategy is elaborated in this review work.