Established and Emerging Producers of PHA: Redefining the Possibility

Advancements in genetic engineering for enhanced Polyhydroxyalkanoates (PHA) production: a comprehensive review of metabolic pathway manipulation and gene deletion strategies

Polyhydroxyalkanoates (PHA) are bioplastics produced by few bacteria as intracellular lipid inclusions under excess carbon source and nutrient-deprived conditions. These polymers are biodegradable and resemble petroleum-based plastics. The rising environmental concerns have increased the demand for PHA, but the low yield in wild-type bacterial strains limits large-scale production. An improvement in the PHA production can be achieved by genetically engineering the wild-type bacterial strains by removing competitive pathways that divert the metabolites away from PHA biosynthesis, cloning strong promotors to overexpress the genes involved in PHA biosynthesis and constructing non-native metabolic pathways that feed the metabolites for PHA production. The desired monomers in the PHA polymers were obtained by elimination of genes involved in PHA biosynthetic pathway. The chain length degradation specific-gene deletion of β-oxidation pathway resulted in the accumulation of PHA monomers having high carbon chain length. A controlled accumulation of monomers in the PHA polymer was achieved by constructing novel pathways in the bacteria and deleting native genes of competitive pathways from the genome of non-PHA producers. The present review attempts to showcase the novel genetic modification approaches conducted so far to enhance the PHA production with a special focus on metabolic pathway gene deletion in various bacteria.

Plastics of the Future? An Interdisciplinary Review on Biobased and Biodegradable Polymers: Progress in Chemistry, Societal Views, and Environmental Implications

Global demand to reduce polymer waste and microplastics pollution has increased in recent years, prompting further research, development, and wider use of biodegradable and biobased polymers (BBPs). BBPs have emerged as promising alternatives to conventional plastics, with the potential to mitigate the environmental burdens of persistent plastic waste. We provide an updated perspective on their impact, five years after our last article, featuring several recent advances, particularly in exploring broader variety of feedstock, applying novel chemical modifications, and developing new functionalities. Life-cycle assessments reveal that environmental performance of BBPs depends on several factors including feedstock selection, production efficiency, and end-of-life management. Furthermore, the introduction of BBPs in several everyday life products has also influenced consumer perception, market dynamics, and regulatory frameworks. Although offering environmental advantages in specific applications, BBPs also raise concerns regarding their biodegradability under varying environmental conditions, potential microplastic generation, and soil health impacts. We highlight the need for a circular approach considering the entire polymer life cycle, from feedstock sourcing, modification and use, to end-of-life options. Interdisciplinary research, collaborative initiatives, and informed policymaking are crucial to unlocking the full potential of BBPs and exploiting their contribution to create a circular economy and more sustainable future.

From the lab to the field and closer to the market: Production of the biopolymer cyanophycin in plants

A range of studies has investigated the production of biopolymers in plants but a comprehensive assessment of feasibility and environmental safety and consumer acceptance is lacking. This review delivers such an assessment. It describes the establishment of the production in tobacco and potato, the analysis of lead events in the greenhouse and in the field, the establishment and upscaling of effective isolation processes and storage conditions, taking the cyanobacterial storage peptide cyanophycin (CGP) as an example. The paper lists several industrial and medical applications of CGP and its building blocks Arg-Asp-dipeptides. This production is especially interesting because the CGP content can exceed 10% of the dry weight (dw) in the greenhouse and still deliver 4 gram per plant in the field. Furthermore, risk assessment of CGP production in potatoes in vitro, in vivo, in the greenhouse, and in the field showed no relevant differences concerning environment or consumer safety compared with the near isogenic control. A consumer choice analysis in four European countries showed a preference for biodegradable CGP in food-wrapping materials over conventional plastic wrapping. Although data on economic feasibility is lacking, CGP as a renewable, biodegradable and CO2-neutrally produced compound, is preferable over fossil fuels in many applications.

Superlative short chain length and medium chain length polyhydroxyalkanoates microbial producers isolated from Malaysian environment

Plastic waste pollution is escalating globally at an unprecedented pace, with a significant measure of this waste remaining unrecycled. Hence, polyhydroxyalkanoates (PHAs), a biogenic polyester, as a potential alternative to synthetic plastics has been intensively studied over the years. PHAs are biodegradable and biocompatible polyester produced by various microorganisms through the bioprocessing of sustainable sources. Bacterial PHAs show potential as an eco-friendly, biodegradable, and biocompatible alternative to conventional plastics. Malaysian environment, anthropogenic and natural, harbors an enormous diversity of microorganisms as well as various bacteria that produce PHAs. Hence, the current submission highlights on four indigenous PHA producers, isolated from the local environments, namely Cupriavidus malaysiensis USMAA2-4, Cupriavidus malaysiensis USMAA10-20, Cupriavidus malaysiensis USMAHM13, and Pseudomonas putida BET001. The four strains have contributed significantly as a workhorse in advancing PHA research and innovation in Malaysia and globally. Their uniqueness and significance in the PHA investigation, which include biosynthesis, recovery strategies, metabolic pathways involved, characteristics and properties of extracted PHA, biodegradation, and its potential applications are discussed.

Production of Polyhydroxybutyrate by halotolerant Halomonas cerina YK44 using sugarcane molasses and soybean flour in tap water

As environmental pollution intensifies, the interest in bioplastics is growing. The bioplastic polyhydroxyalkanoates (PHAs), which are produced and degraded by microorganisms, have received considerable attention. However, the production cost of PHA is still high, and several ways to increase economy of PHA production have been studied. Therefore, as one way of solution, Halomonas species were screened and evaluated with cheap substrates such as molasses and soybean flour. Among tested strains, Halomonas cerina YK44 was selected and used for polyhydroxybutyrate (PHB) production with molasses and soybean flour together, whose combination was not evaluated well before, in tap water. The medium composition optimization showed maximum PHB production at 4 % sugarcane molasses, 2 % NaCl, 0.05 % soybean flour, and pH 8 in tap water (9.2 g/L DCW, 7.3 g/L PHB, and 79.7 % PHB contents). However, cell growth of halotolerant H. cerina YK44 was disturbed by 0.2 % furfural, which existed in biomass based sugars as inhibitors. Physical and thermal analyses revealed that PHB film started from sugarcane molasses and soybean flour was no different from that initiated from simple sugars (Tm was 175.8 °C and 176.2 °C, PDI was 1.29, and 1.31, respectively).

Strategies for producing high value small molecules in microalgae

Eukaryotic microalgae are a diverse group of organisms that can be used for the sustainable production of a wide range of high value compounds, including lipids, flavours and dyes, bioplastics, and cosmetics. Optimising total biomass production often does not lead to optimal product yield and more sophisticated biphasic growth strategies are needed, introducing specific stresses to induce product synthesis. Genetic tools have been used to increase yields of natural products or to introduce new pathways to algae, and wider deployment of these tools offers promising routes for commercial production of high value compounds utilising minimal inputs.

Comprehensive Proteomics Analysis of Polyhydroxyalkanoate (PHA) Biology in Pseudomonas putida KT2440: The Outer Membrane Lipoprotein OprL is a Newly Identified Phasin

Pseudomonas putida KT2440 is an important bioplastic-producing industrial microorganism capable of synthesizing the polymeric carbon-rich storage material, polyhydroxyalkanoate (PHA). PHA is sequestered in discrete PHA granules, or carbonosomes, and accumulates under conditions of stress, for example, low levels of available nitrogen. The pha locus responsible for PHA metabolism encodes both anabolic and catabolic enzymes, a transcription factor, and carbonosome-localized proteins termed phasins. The functions of phasins are incompletely understood but genetic disruption of their function causes PHA-related phenotypes. To improve our understanding of these proteins, we investigated the PHA pathways of P.putida KT2440 using three types of experiments. First, we profiled cells grown in nitrogen-limited and nitrogen-excess media using global expression proteomics, identifying sets of proteins found to coordinately increase or decrease within clustered pathways. Next, we analyzed the protein composition of isolated carbonosomes, identifying two new putative components. We carried out physical interaction screens focused on PHA-related proteins, generating a protein-protein network comprising 434 connected proteins. Finally, we confirmed that the outer membrane protein OprL (the Pal component of the Pal-Tol system) localizes to the carbonosome and shows a PHA-related phenotype and therefore is a novel phasin. The combined datasets represent a valuable overview of the protein components of the PHA system in P.putida highlighting the complex nature of regulatory interactions responsive to nutrient stress.

Production of poly-3-hydroxybutyrate (PHB) nanoparticles using grape residues as the sole carbon source

The production of poly-3-hydroxybutyrate (PHB) on an industrial scale remains a major challenge due to its higher production cost compared to petroleum-based plastics. As a result, it is necessary to develop efficient fermentative processes using low-cost substrates and identify high-value-added applications where biodegradability and biocompatibility properties are of fundamental importance. In this study, grape residues, mainly grape skins, were used as the sole carbon source in Azotobacter vinelandii OP cultures for PHB production and subsequent nanoparticle synthesis based on the extracted polymer. The grape residue pretreatment showed a high rate of conversion into reducing sugars (fructose and glucose), achieving up to 43.3 % w w-1 without the use of acid or external heat. The cultures were grown in shake flasks, obtaining a biomass concentration of 2.9 g L-1 and a PHB accumulation of up to 37.7 % w w-1. PHB was characterized using techniques such as Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The formation of emulsified PHB nanoparticles showed high stability, with a particle size between 210 and 240 nm and a zeta potential between -12 and - 15 mV over 72 h. Owing to these properties, the produced PHB nanoparticles hold significant potential for applications in drug delivery.

Unlocking growth potential in Halomonas bluephagenesis for enhanced PHA production with sulfate ions

The mutant strain Halomonas bluephagenesis (TDH4A1B5P) was found to produce PHA under low-salt, non-sterile conditions, but the yield was low. To improve the yield, different nitrogen sources were tested. It was discovered that urea was the most effective nitrogen source for promoting growth during the stable stage, while ammonium sulfate was used during the logarithmic stage. The growth time of H. bluephagenesis (TDH4A1B5P) and its PHA content were significantly prolonged by the presence of sulfate ions. After 64 hr in a 5-L bioreactor supplemented with sulfate ions, the dry cell weight (DCW) of H. bluephagenesis weighed 132 g/L and had a PHA content of 82%. To promote the growth and PHA accumulation of H. bluephagenesis (TDH4A1B5P), a feeding regimen supplemented with nitrogen sources and sulfate ions with ammonium sodium sulfate was established in this study. The DCW was 124 g/L, and the PHA content accounted for 82.3% (w/w) of the DCW, resulting in a PHA yield of 101 g/L in a 30-L bioreactor using the optimized culture strategy. In conclusion, stimulating H. bluephagenesis (TDH4A1B5P) to produce PHA is a feasible and suitable strategy for all H. bluephagenesis.

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.

Untargeted metabolomics elucidated biosynthesis of polyhydroxyalkanoate by mixed microbial cultures from waste activated sludge under different pH values

Waste activated sludge has been frequently used as mixed substrate to produce polyhydroxyalkanoate (PHA). However, insufficient research on microbial metabolism has led to difficulties in regulating PHA accumulation in mixed microbial cultures (MMCs). To explore the variation of functional genes during domestication and the effect of different pH conditions on metabolic pathways during PHA accumulation, MMCs were domesticated by adding acetate and propionate with aerobic dynamic feeding strategy for 60 days. As the domestication progressed, the microbial community diversity declined and PHA-producing bacteria, Brevundimonas, Dechloromonas and Hyphomonas, were enriched. Through bacterial function prediction by PICRUSt the gene rpoE involved in starvation resistance of bacteria was enriched after the domestication. The pH value of 8.5 was the best condition for PHA accumulation in MMCs, under which a maximum PHA content reached 23.50% and hydroxybutyric (HB)/hydroxyvaleric (HV) reached 2.22. Untargeted metabolomics analysis exhibited that pH conditions of 7 and 8.5 could promote the up-regulation of significant differential metabolites, while higher alkaline conditions caused the inhibition of metabolic activity. Functional annotation showed that pH condition of 8.5 significantly affected Pyrimidine metabolism, resulting in an increase in PHA production. Regarding the pathways of PHA biosynthesis, acetoacetate was found to be significant in the metabolism of hydroxybutyric, and the alkaline condition could restrain the conversion from hydroxybutyric (HB) to the acetoacetate to protect PHB accumulation in MMCs compared with neutral condition. Taken together, the present results can advance the fundamental understanding of metabolic function in PHA accumulation under different pH conditions.

PHA-Based Bioplastic: a Potential Alternative to Address Microplastic Pollution

Petroleum-derived plastics are linked to a variety of growing environmental issues throughout their lifecycle, including emission of greenhouse gases, accumulation in terrestrial and marine habitats, pollution, among others. There has been a lot of attention over the last decade in industrial and research communities in developing and producing eco-friendly polymers to deal with the current environmental issues. Bioplastics preferably are a fast-developing family of polymeric substances that are frequently promoted as substitutes to petroleum-derived plastics. Polyhydroxyalkanoates (PHAs) have a number of appealing properties that make PHAs a feasible source material for bioplastics, either as a direct replacement of petroleum-derived plastics or as a blend with elements derived from natural origin, fabricated biodegradable polymers, and/or non-biodegradable polymers. Among the most promising PHAs, polyhydroxybutyrates (PHBs) are the most well-known and have a significant potential to replace traditional plastics. These biodegradable plastics decompose faster after decomposing into carbon dioxide, water, and inorganic chemicals. Bioplastics have been extensively utilized in several sectors such as food-processing industry, medical, agriculture, automobile industry, etc. However, it is also associated with disadvantages like high cost, uneconomic feasibility, brittleness, and hydrophilic nature. A variety of tactics have been explored to improve the qualities of bioplastics, with the most prevalent being the development of gas and water barrier properties. The prime objective of this study is to review the current knowledge on PHAs and provide a brief introduction to PHAs, which have drawn attention as a possible potential alternative to conventional plastics due to their biological origin, biocompatibility, and biodegradability, thereby reducing the negative impact of microplastics in the environment. This review may help trigger further scientific interest to thoroughly research on PHAs as a sustainable option to greener bioplastics.

Recent advancements in hydrocarbon bioremediation and future challenges: a review

Petrochemicals are important hydrocarbons, which are one of the major concerns when accidently escaped into the environment. On one hand, these cause soil and fresh water pollution on land due to their seepage and leakage from automobile and petrochemical industries. On the other hand, oil spills occur during the transport of crude oil or refined petroleum products in the oceans around the world. These hydrocarbon and petrochemical spills have not only posed a hazard to the environment and marine life, but also linked to numerous ailments like cancers and neural disorders. Therefore, it is very important to remove or degrade these pollutants before their hazardous effects deteriorate the environment. There are varieties of mechanical and chemical methods for removing hydrocarbons from polluted areas, but they are all ineffective and expensive. Bioremediation techniques provide an economical and eco-friendly mechanism for removing petrochemical and hydrocarbon residues from the affected sites. Bioremediation refers to the complete mineralization or transformation of complex organic pollutants into the simplest compounds by biological agents such as bacteria, fungi, etc. Many indigenous microbes present in nature are capable of detoxification of various hydrocarbons and their contaminants. This review presents an updated overview of recent advancements in various technologies used in the degradation and bioremediation of petroleum hydrocarbons, providing useful insights to manage such problems in an eco-friendly manner.

Production and Properties of Microbial Polyhydroxyalkanoates Synthesized from Hydrolysates of Jerusalem Artichoke Tubers and Vegetative Biomass

One of the major challenges in PHA biotechnology is optimization of biotechnological processes of the entire synthesis, mainly by using new inexpensive carbon substrates. A promising substrate for PHA synthesis may be the sugars extracted from the Jerusalem artichoke. In the present study, hydrolysates of Jerusalem artichoke (JA) tubers and vegetative biomass were produced and used as carbon substrate for PHA synthesis. The hydrolysis procedure (the combination of aqueous extraction and acid hydrolysis, process temperature and duration) influenced the content of reducing substances (RS), monosaccharide contents, and the fructose/glucose ratio. All types of hydrolysates tested as substrates for cultivation of three strains—C. necator B-10646 and R. eutropha B 5786 and B 8562—were suitable for PHA synthesis, producing different biomass concentrations and polymer contents. The most productive process, conducted in 12-L fermenters, was achieved on hydrolysates of JA tubers (X = 66.9 g/L, 82% PHA) and vegetative biomass (55.1 g/L and 62% PHA) produced by aqueous extraction of sugars at 80 °C followed by acid hydrolysis at 60 °C, using the most productive strain, C. necator B-10646. The effects of JA hydrolysates on physicochemical properties of PHAs were studied for the first time. P(3HB) specimens synthesized from the JA hydrolysates, regardless of the source (tubers or vegetative biomass), hydrolysis conditions, and PHA producing strain employed, exhibited the 100–120 °C difference between the T_melt and T_degr, prevailing of the crystalline phase over the amorphous one (C_x between 69 and 75%), and variations in weight average molecular weight (409–480) kDa. Supplementation of the culture medium of C. necator B-10646 grown on JA hydrolysates with potassium valerate and ε-caprolactone resulted in the synthesis of P(3HB-co-3HV) and P(3HB-co-4HB) copolymers that had decreased degrees of crystallinity and molecular weights, which influenced the porosity and surface roughness of polymer films prepared from them. The study shows that JA hydrolysates used as carbon source enabled productive synthesis of PHAs, comparable to synthesis from pure sugars. The next step is to scale up PHA synthesis from JA hydrolysates and conduct the feasibility study. The present study contributes to the solution of the critical problem of PHA biotechnology—finding widely available and inexpensive substrates.