Bacterial synthesis of biodegradable polyhydroxyalkanoates (original) (raw)

PRODUCTION OF PHA BY RECOMBINANT ORGANISMS

Polyhydroxyalkanoates (PHA) are biodegradable, thermoplastic polyesters produced from renewable carbon sources by a number of bacteria. However, their application is limited by high production costs. One of the strategies aimed to reduce their costs is the development of recombinant strains able to utilize different carbon sources. Many bacteria are naturally capable of accumulating biopolyesters composed of 3-hydroxy fatty acids as intracellular inclusions, which serve as storage granules. Recently, these inclusions have been considered as nano/ microbeads with surface-attached proteins, which can be engineered to display various protein-based functions that are suitable for biotechnological and biomedical applications. Natural PHA producers have become accustomed to accumulating PHA during evolution; they often have a long generation time, relatively low optimal growth temperature, are often hard to lysis and contain pathways for PHA degradation. This led to the development of recombinant PHA producers, capable of high PHA accumulation and/or free of PHA degradative pathways. This review summarizes the production of PHA by recombinant bacteria as well as some higher organisms in brief.

A New Wave of Industrialization of PHA Biopolyesters

Bioengineering

The ever-increasing use of plastics, their fossil origin, and especially their persistence in nature have started a wave of new innovations in materials that are renewable, offer the functionalities of plastics, and are biodegradable. One such class of biopolymers, polyhydroxyalkanoates (PHAs), are biosynthesized by numerous microorganisms through the conversion of carbon-rich renewable resources. PHA homo- and heteropolyesters are intracellular products of secondary microbial metabolism. When isolated from microbial biomass, PHA biopolymers mimic the functionalities of many of the top-selling plastics of petrochemical origin, but biodegrade in soil, freshwater, and marine environments, and are both industrial- and home-compostable. Only a handful of PHA biopolymers have been studied in-depth, and five of these reliably match the desired material properties of established fossil plastics. Realizing the positive attributes of PHA biopolymers, several established chemical companies an...

Bacterial Production of Hydroxyalkanoates (PHA)

Universal Journal of Microbiology Research, 2016

The dependence of plastic materials is an increasing problem. Although plastics are very useful for humankind many disadvantages derived from the difficulties linked to recycling and disposal are well known. A feasible alternative is the production and use of bioplastics. These compounds have multiple options at the end of his life that can ensure their safety and efficacy of reuse or recovery. For example, raw materials can be returned to the manufacturer for recycling. Bioplastics synthesized through biotechnology include mainly polyhydroxyalkanoates (PHAs), common lipoidic storage materials accumulated by prokaryotes. Some processes for producing PHAs by fermentation using microorganisms have been developed at a different extent. However, biopolymers (PHA) market is under development, and therefore cannot compete with traditional plastics since manufacturing is still more expensive. In this review we have focused on the study of the production processes of bioplastics where bacteria are present, also describing the scaling to industrial level aspects and future trends.

Review of the Developments of Bacterial Medium-Chain-Length Polyhydroxyalkanoates (mcl-PHAs)

Bioengineering

Synthetic plastics derived from fossil fuels—such as polyethylene, polypropylene, polyvinyl chloride, and polystyrene—are non-degradable. A large amount of plastic waste enters landfills and pollutes the environment. Hence, there is an urgent need to produce biodegradable plastics such as polyhydroxyalkanoates (PHAs). PHAs have garnered increasing interest as replaceable materials to conventional plastics due to their broad applicability in various purposes such as food packaging, agriculture, tissue-engineering scaffolds, and drug delivery. Based on the chain length of 3-hydroxyalkanoate repeat units, there are three types PHAs, i.e., short-chain-length (scl-PHAs, 4 to 5 carbon atoms), medium-chain-length (mcl-PHAs, 6 to 14 carbon atoms), and long-chain-length (lcl-PHAs, more than 14 carbon atoms). Previous reviews discussed the recent developments in scl-PHAs, but there are limited reviews specifically focused on the developments of mcl-PHAs. Hence, this review focused on the mcl-...

Screening of PHA producing bacteria from diverse sources

Synthetic plastics are non-degradable and cause waste disposal problems leading to environmental pollution. Bioplastics (polyhydroxyalkanoates) are considered good substitutes for petroleum derived synthetic plastics because of their similar physical and chemical properties. Main advantage of bioplastics is that they are of biological origin and can get degraded completely to CO2 and water under natural environment by the enzymatic activities of microorganisms. Poly-β-hydroxyalkanoates (PHA) are polyesters of various hydroxyalkanoates, synthesized by numerous bacteria as an intracellular carbon and energy storage compound under limited nutrient conditions and with excess carbon. Poly-βhydroxy butyrate (PHB) is the best known polyhydroxyalkanoate. Considering the industrial interest of PHA, this work has been undertaken for the screening of PHA producing bacteria from diverse sources. In the present study, an attempt was made to isolate efficient PHB producing bacteria from diverse environmental samples. Different industrial wastes and soil samples were screened for bacteria possessing the ability to accumulate poly hydroxyalkanoate (PHA) granules. About 23 bacterial isolates were found to be promising PHA accumulating bacteria. Screening for PHA producers was performed by using E 2 medium. Accumulation of PHB granules in the organisms was analyzed by Sudan black method.

Production of Polyhydroxyalkanoates from Renewable Sources Using Bacteria

Journal of Polymers and the Environment, 2018

Plastics play a very important role in our daily life. They are used for various purposes. But the disposal of these petrochemical-derived plastics causes a risk to the human and marine population, wildlife and environment. Also, due to the eventual depletion of petrochemical sources, there is a need for the development of alternate sources for the production of plastics. Biodegradable polymers produced by microorganisms can be used as substitutes for conventional plastics derived from petrochemical sources since they have similarity in their properties. Polyhydroxyalkanoate (PHA) is one such biopolymer that will be accumulated inside the cells of microorganisms as granules for energy storage under limiting conditions of nutrients and high concentration of carbon. Research on the microbial production of PHA should focus on the identification of costeffective substrates and also identification of a suitable strain of organism for production. The major focus of this review is the production of PHA from various cost-effective substrates using different bacterial species. The review also covers the biosynthetic pathway of PHA, extraction method, characterization technique, and applications of PHA in various sectors.

Recent developments in bioreactor scale production of bacterial polyhydroxyalkanoates

Bioprocess and Biosystems Engineering, 2019

Polyhydroxyalkanoates (PHAs) are biological plastics that are sustainable alternative to synthetic ones. Numerous microorganisms have been identified as PHAs producers they store PHAs as cellular inclusions to use as an energy source backup. They can be produced in shake flasks and in bioreactors under defined fermentation and physiological culture conditions using suitable nutrients. Their production at bioreactor scale depends on various factors such as carbon source, nutrients supply, temperature, dissolved oxygen level, pH and processes. Once produced, PHAs find diverse applications in multiple fields of science and technology particularly in the medical sector. The present review covers some recent developments in sustainable bioreactor scale production of PHAs and identifies some areas in which future research in this field might be focused.

Bacterial Production of PHAs from Lipid-Rich by-Products

2019

Background and Objective: Due to oil shortage and environmental problems, synthetic plastics will surely be replaced by alternative, biodegradable materials. A possible good example could be polyhydroxyalkanoates, and the inexpensive agricultural fatty byproducts could be usefully converted to polyhydroxyalkanoates by properly selected and/or developed microbes. Material and Methods: Among the more common by-products available, a variety of lipid-rich residues have been explored as substrate, such as crude glycerol from biodiesel, biodiesel obtained from fatty residues, and, from slaughterhouse, bacon rind, udder and tallow. In this paper, several new isolates and collection PHA-producing microbes have been screened for both lipolytic activities and polyhydroxyalkanoates production. The soil proved to be the most promising mining place to find new interesting microbial species, even better than more specific and selective environments such as slaughterhouses. Results and Conclusion:...