Polyhydroxyalkanoates: Biodegradable Plastics PDF

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/265726991 Polyhydroxyalkanoates: Biodegradable Plastics for Environmental Conservation Chapter · August 2014 DOI: 10.13140/RG.2.1.4642.5682 CITATIONS...

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/265726991 Polyhydroxyalkanoates: Biodegradable Plastics for Environmental Conservation Chapter · August 2014 DOI: 10.13140/RG.2.1.4642.5682 CITATIONS READS 15 9,434 2 authors: Anna Kynadi Suchithra tv Wiley National Institute of Technology Calicut 8 PUBLICATIONS 65 CITATIONS 60 PUBLICATIONS 959 CITATIONS SEE PROFILE SEE PROFILE All content following this page was uploaded by Anna Kynadi on 27 February 2015. The user has requested enhancement of the downloaded file. Industrial & Environmental Biotechnology Editors (Mrs.) Krishna Pramanik & Jayanta Kumar Patra 2014 Studium Press (India) Pvt. Ltd.  Industrial & Environmental Biotechnology © 2014 This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonable efforts have been made to publish reliable data and information, but the editors and the publisher cannot assume responsibility for the validity of all materials or for the consequences of their use. All rights are reserved under International and Pan-American Copyright Conventions. Apart from any fair dealing for the purpose of private study, research, criticism or review, as permitted under the Copyright Act, 1956, no part of this publication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means–electronic, electrical, chemical, mechanical, optical, photocopying, recording or otherwise–without the prior permission of the copyright owner. ISBN: 978-93-80012-67-4 Published by: Studium Press (India) Pvt. Ltd. 4735/22, 2nd Floor, Prakash Deep Building (Near Delhi Medical Association), Ansari Road, Darya Ganj, New Delhi-110 002 Tel.: + 91-11-43240200-15 (15 lines); Fax: 91-11-43240215 E- mail: [email protected]  Chapter 1 Polyhydroxyalkanoates: Biodegradable Plastics for Environmental Conservation ANNA S. KYNADI AND T.V. SUCHITHRA*  1 Polyhydroxyalkanoates: Biodegradable Plastics for Environmental Conservation ANNA S. KYNADI AND T.V. SUCHITHRA* ABSTRACT Conventional plastics, though widely used have a number of disadvantages like the dependency on depleting fossil fuels for their production, the long time required for decomposition of the material and the associated production of toxic materials. Bio - based plastics are a solution to these problems. Among the many types of Bioplastics, Polyhydroxyalkanoates (PHAs) have been studied widely because of their similarity with conventional plastics and complete biodegradability. Polyhydroxyalkanoates are produced in microorganisms as intracellular storage compounds of energy and carbon under conditions of non-carbon nutrient deficiency.These polymers are generally classified in two categories depending on the number of carbon atoms in their monomer units: small chain length (scl)-PHA when the monomer units contain from 3 to 5 carbon atoms and medium chain length (mcl)-PHA with monomer units possessing from 6 to14 carbon atoms. PHAs, owing to their lipid nature are insoluble in water. The polymers are accumulated as intracellular granules bound by a layer of Phospholipids and some associated proteins. This kind of storage helps in accumulation of large amounts of carbon without disturbing the osmotic balance of the cell. The polymer can be degraded completely using PHA hydrolases and PHA depolymerases thus making it completely compatible with the Carbon cycle and therefore pose no threats to the environment like the conventional plastics. The only limitation in the widespread use of the polymer is the high cost of production in comparison to the conventional plastics. Research on usage of cheaper substrates is being investigated currently to bring down the cost of production. PHAs have been developed to suit a number of School of Biotechnology, National Institute of Technology Calicut, Kozhikode, Kerala – 673601, India *Corresponding author E-mail: [email protected] 2 Industrial and Environmental Biotechnology applications including the medical field. The chapter studies the properties of PHA, the cost cutting strategies that can be incorporated for large scale production of the polymer and the benefits of using PHA over conventional plastics. Key words: Bioplastics, Polyhydroxyalkanoates, Biodegradable plastics, Bio-based plastics, Biopolymers INTRODUCTION The exceptional properties that plastics possess are the reason for their wide usage over wood and other metals. Despite the positives of the material, there are a number of points laid against the widespread use of plastics. Some of them are the dependency on depleting fossil fuels for their production, the long time required for the decomposition of the material and the associated production of toxic materials. Completely biodegradable plastics that are produced from renewable sources are a good alternative for the petroleum based plastics. A number of biodegradable plastic materials, namely Polyhydroxyalkanoates (PHAs), aliphatic polyesters, polylactides, polysaccharides, the copolymer or blends of these, have been studied and developed to replace conventional plastics (Chang, 1994; Lee, 1996). These biobased plastics offer solution to plastic waste management problems and in some cases, are a good substitute for conventional plastic where mechanical properties are desired (Lee, 1996; Steinbüchel and Fuchtenbusch, 1995). Among these, PHAs, the polymer produced by microorganisms have been studied widely because of their similarity to conventional plastics and complete biodegradability (Steinbüchel and Fuchtenbusch, 1998). Study on production of PHA, cost reduction strategies etc have been part of main stream research for quite some time now. Based on their biodegradable characteristics the biopolymers can be broadly classified into three groups. The first group consists of biopolymers having biodegradable or compostable properties. But these are normally not bio-based. Some of the synthetic polymers that come in this group are aliphatic–aromatic copolyesters like polybutylene terephthalate succinate and polybutylene terephthalate adipate. The second group includes polymers that are not only biodegradable but are also of biological origin, for example Polyhydroxyalkanoates, polylactides, starch or cellulose based materials, and blends of these compounds. The third group includes non-biodegradable polymers, but produced from biological sources and engineered into non-biodegradable forms. Corn sugar and bioethanol are engineered to produce 1, 3 propanediol and linear low-density polyethylene respectively (Averous, 2004). Polyhydroxyalkanoates: Biodegradable Plastics for Environmental Conservation 3 HISTORY OF PHA There are about 250 strains of microbe that have the capacity to produce Polyhydroxyalkanoates. Out of these very few strains have been studied for industrial production. The most commonly used strain is Cupriavidus necator. It was formerly known as Ralstonia eutropha or Alcaligenes eutrophus Poly(3-hydroxybutyrate) is the most commonly seen PHA and its presence was first reported by the French Scientist Lemoigne. Since this discovery, many strains of microbes have been found to accumulate PHB both aerobically and anaerobically. They include archae bacteria, gram positive as well as gram negative bacteria, photosynthetic bacteria etc. It was then found out that the PHA accumulation begins when the ratio of Carbon to nitrogen available to the Bacillus megaterium is high and that when there is depletion in carbon sources, there is degradation of the polymer. Earlier it was thought that the only monomer present in PHB is HB. But that notion changed after other types of monomers were discovered. In 1974 it was reported that the apart from the 3-hydroxybutyrate as monomer there existed some major and minor constituents like 3-hydroxyvalerate, 3-hydroxyhexanoate and 3- hydroxyheptanoate. In 1983 the presence of a new type of monomer, 3- hydroxyoctanoate was discovered in the strain Pseudomonas oleovorans when the carbon source was n-octane. This led to the conclusion that the type of PHA produced is not just based on the microbial species, but also on the type of substrate used. About 150 types of monomers have been found out till date. They include a wide variety with R group being straight, branched, aromatic etc. Nature and Types of PHA The general structure of PHAs consists of 3-hydroxy fatty acids as shown in Fig. 1. The monomer differs with the difference in pendant group R varying from methyl (C1) to tridecyl (C13). The most common polymers and their varying R groups are shown in Table 1. O R H O n Fig. 1: Poly(3-hydroxyalkanoates) PHAs are generally classified in two categories depending on the number of carbon atoms in their monomer units: small chain length (scl)-PHA when the monomer units contain 5 or a lower number of carbon atoms and medium 4 Industrial and Environmental Biotechnology chain length (mcl)-PHA when the monomer units possess more than 5 carbon atoms. Table 1: Different types of PHAs R Group Full name Short CH3 Poly(3-hydroxybutyrate) PHB CH2CH3 Poly(3-hydroxyvalerate) PHV CH2CH2CH3 Poly(3-hydroxyhexanoate) PHHx A wide range of molecular masses (MM) are exhibited by PHA from different microorganisms and also from different stages and conditions of cultivation. The largest reported MM value for biologically synthesized PHA is about 20 MDa (Kusaka et al., 1997). In the same report, it was also shown that the pH of the culture medium can greatly affect the MM of the PHA produced. Also, the type and concentration of the carbon source supplied can affect the MM of the PHA produced. PHA Storage in Cell PHAs are polymers which are usually lipid in nature. They are accumulated as energy storage materials helping microbial sustenance under conditions of stress related to nutritional depletion. The type of PHA, the number of granules per organism, the size of the cell and other characteristics of the granule are normally dependent upon the organism involved (Ha et al., 2002). PHAs, owing to their lipid nature are insoluble in water and therefore the polymers are accumulated as intracellular granules. This kind of storage also helps the bacteria to store large amounts of carbon as the osmotic balance of the cell system is not disturbed. The granule also hinders any interaction between the cell structures and PHAs thereby eliminating any damage to the cell or the polymer. Within bacteria, PHAs are accumulated to levels as high as 90% (w/w) of the dry cell mass (Fig. 2). PHAs are accumulated intracellularly as granules of different sizes. The polymer molecules are surrounded by a phospholipid monolayer and some associated proteins to form granules. Though the function of the envelope has not been studied completely, it is assumed that the presence of the membrane is required to avoid the contact of PHAs with water (preventing the transition of the polyester from the amorphous liquid state to a more stable crystalline form) (Sudesh et al., 2000) and that it acts as a protective barrier (avoiding cellular damage caused by the interaction of PHAs with internal structures or with cytosolic proteins) (Garcia et al., 1999). Phasins, a class of proteins, are the predominant compounds in the interface of a granule. The phasins influence the number and size of PHA granules (Fig. 3) (Potter and Steinbuchel, 2005). Biosynthesis of PHA The first PHA to be discovered and therefore the most studied is PHB. Bacteria produce acetyl-coenzyme-A (acetyl-CoA), which is converted into PHB by three biosynthetic enzymes. In the first step, 3-ketothiolase (PhaA) Polyhydroxyalkanoates: Biodegradable Plastics for Environmental Conservation 5 Fig. 2: Transmission electron micrograph of thin sections of recombinant R. eutropha PHB24 cells containing large amounts (90% of the dry cell weight) of P(3HB-co-5 mol% 3HHx). Bar represents 0.5 mm (Sudesh et al., 2000). Fig. 3: A model attempting to show the structure of in vivo PHA inclusions (Not drawn to actual scale) (Sudesh et al., 2000). combines two molecules of acetyl-CoA to form acetoacetyl-CoA. Acetoacetyl-CoA reductase (PhaB) allows the reduction of acetoacetyl-CoA by NADH to 3- hydroxybutyryl-CoA. Finally, PHB synthase (PhaC) polymerizes 3-hydroxybutyryl- CoA to PHB, coenzyme-A being liberated. The carboxyl group of one monomer forms an ester bond with the hydroxyl group of the neighboring monomer. Under culture conditions promoting normal bacterial 6 Industrial and Environmental Biotechnology growth the free coenzyme-A produced in Kreb’s cycle inhibits the 3-ketothiolase. Non-carbon nutrient limitation will restrict the entry of acetyl-CoA from Glycolysis into Kreb’s cycle the molecule is lead to the PHB biosynthesis pathway. PHA Producing Microbes Cupriavidus necator is well known to produce small chain length PHAs. The monomers found in these PHAs are 3HV, 3HB and 4HB (Doi, 1990; Kunioka et al., 1998; Saito et al., 1996). The (scl )PHA are more commonly produced industrially in comparison to (mcl)PHA. This is because, the former are easily produced while the large scale production for latter has not been established till now. The common microbes producing (mcl)PHA are Pseudomonas oleovorans and Pseudomonas putida. The major constituents of these polymers are 3-hydroxyoctanoate and 3-hydroxydecanoate. In 1980, a glucose utilizing mutant of C. necator was used to produce PHA by imperial chemical industries (UK). The polymer [P(3-HB)co(3-HV)] was sold under the name Biopol. The mutants are better than the natural PHA producers when it comes to commercial production because they can be designed to attain a high cell density utilizing very simple substrates. Low Cost Substrates for PHA Production Despite the initial success, the commercial production of the polymer is very limited. The main reason for this lag is the high cost of production. The cost of production cannot be compared to that of conventional plastics since cost of production of polyethylene and polypropylene are as low as 1US$ per kg. There are different types of production processes studied for PHA synthesis. The two-stage fed-batch process (Doi, 1990) utilizes a first stage that has nutritionally enriched medium for sufficient growth followed by a second stage for product formation by depleting nitrogen. Single stage fermentation is less preferred since accumulation of biomass is lesser and therefore product formation is also lesser (Katircioglu et al., 2003). The feast and famine method involves culturing of microbes in a nutrient limited media for a long time and then sudden transfer to a nutrient rich medium. This causes a sudden accumulation of PHA (Dias et al., 2005). Substantial effort is being put in to reduce the cost of production by developing better strains, modified fermentation processes and better recovery processes. The major cost incurring area is the cost of substrates used for the polymer production. Therefore using simple, cheap and renewable resources is the first step to cost cutting. But the material used should support microbial growth and PHA production simultaneously. Microorganisms are capable of producing PHA from a large variety of carbon sources like complex waste effluents, plant oils, alkanes, fatty acids and so Polyhydroxyalkanoates: Biodegradable Plastics for Environmental Conservation 7 on. Each year, a large amount of waste materials are discharged from agricultural and food processing industries and these wastes represent a potential renewable feedstock for PHA production. If these waste materials are utilized for PHA production, then the cost of production will be reduced drastically and also methods for waste disposal will be formulated. There are a variety of low cost substrates being used to bring down the cost of production of PHAs. Plant oils such as soybean oil, palm oil and corn oil are good materials for PHA production. They are much cheaper than the commercially available sugars and also provide a product yield better than that by the sugars. Glucose gives a yield of 0.3 to 0.4 gm PHB per gm glucose while in the case of plant oils the yield rises to 0.6 to 0.8 gm. This is because the plant oils contain higher carbon content per weight when compared to the sugars (Akiyama et al., 2003). Using soybean oil as the sole carbon source, a product yield of about 80% dry cell mass has been attained from C. necator H16 strain (Kahar et al., 2004). Similar results were obtained on using palm oil too. Burkholderia cepecia and Comamonas testosteroniare two common strains that are capable of PHA production from plant oils. P. putida cannot utilize plant oils in form of triglycerides due to lack of lipase activity. A saponification added to the procedure step can solve this issue. A two stage fed-batch fermentation of P. putida with octane as feed in the first stage provided good microbial growth and at the same time induced good mcl PHA yield (Kim et al., 1997). C. testosteroni has the ability to produce mcl PHA from a variety of vegetable oils (Thakor et al. , 2005). A product yield of about 80% dry cell mass has been attained using the vegetable oils. Glycerol is a byproduct of palm oil refining process. This is a very interesting carbon source for certain microbes. Glycerol can be used to produce PHB from Burkholderia sp (Chee et al., 2012; Zhu et al., 2010) Similarly mixed culture of P. oleovorans and P. corrugata was used to produce a mix of PHB and some mcl PHAs. This is because though the two stains have similar growth requirements the PHA produced are different from the same substrate. The most abundant carbon source of the environment is Carbon dioxide. Since plants can take up Carbon dioxide, the prospect of using crop plants for PHA production gained acceptance. Arabidopsis thaliana was genetically modified to carry genes from C. necator and thereby synthesize PHA (Poirier et al. , 1992). Similarly Cyanobacteria and other oxygen evolving bacteria have the enzymes required for PHA production (Sudesh et al., 2002). But so far only PHB synthesis has been noticed in cyanobacteria. Recovery of PHA from Broth Separation and purification of PHA is as important as the production process. Since PHA is an intracellular product, the product recovery is also quite 8 Industrial and Environmental Biotechnology complex and expensive. The most common method of separation of PHA from biomass used is solvent extraction (Table 2). Extraction using chloroform gives good product yield without any degradation of the polymer (Hahn and Chang, 1995). Other solvents used for the purpose are dichlorethane, chloropropane, dichloromethane etc. but usage of solvent extraction for large scale production can be hazardous to the environment. Another simple method of extraction is the treatment of biomass using sodium hypochlorite. This will lyse the cells. The PHA granules can be separated later by centrifugation (Berger et al., 1989). The down side of this method is that severe degradation of the polymer occurs, leading to a lower molecular mass. But hypochlorite extraction combined with a surfactant pretreatment can be used to address this issue (Ramsay et al., 1989). While the PHA molecular weight from surfactant-hypochlorite extraction is 730000-790000 gm/mol with a yield of 97 to 98%, that from simple hypochlorite extraction is only about 680000 gm/mol. (Hahn and Chang, 1995). Table 2: Comparison of various PHA recovery methods Method Advantages Disadvantages Solvent extraction Removal of endotoxin Not environmental friendly Useful for medical Consumption of large volume applications of toxic and volatile solvents High purity Negligible/limited degradation High capital and operation to the polymer cost Higher molecular weight Difficulty in extracting PHA from solution containing more than 5% (w/v) P(3HB) Lengthy process Native order of polymer chains in PHA granules might be disrupted Sodium hypochlorite Higher purity of PHA can be Severe reduction in digestion obtained molecular weight of the extracted polymer Hypochlorite and High purity of PHA Not environment friendly chloroform extraction Reduced viscosity of solvent Consumption of large volume phase due to digestion of non- of toxic and volatile polymer cellular material compounds (NPCM) by sodium hypochlorite Enzymatic separation Mild operation conditions Higher recovery cost Good recovery with good Complex process quality High cost of enzymes Extraction using non- Mild operating conditions Not optimized halogenated solvents Not harmful to Purity low environment Cost effective Polyhydroxyalkanoates: Biodegradable Plastics for Environmental Conservation 9 Using hypochlorite and chloroform together also helps in lowering the product degradation. This is because as soon as the cells degrade, the PHA is dissolved in chloroform, there by stopping its contact with the aqueous phase (Ramsay et al. , 1990). The reduction in molecular weight is about 17% with a very high product yield of about 98% (Hahn and Chang, 1995). Another interesting type of separation is the enzymatic separation of PHA. It is very gentle, selective, causes minimal product damage and gives high yield. The enzymes normally used are proteases, cellulases and lysozyme (de Koning and Witholt, 1997). But for the extraction to be proper, a prior heat treatment is required to rupture cells and denature nucleic acids which otherwise will make the broth very viscous (Kapritchkoff et al., 2006). Addition of chemicals like Sodium dodecyl sulfate (SDS) and ethylene diamine tetra acetic acid (EDTA) helps to enhance the efficiency of the extraction. Extraction using non-halogenated solvents is also being developed and optimized these days (Mitra Mohammadi et al., 2012). Degradation of PHA An important characteristic of PHAs is their biodegradability. Micro-organisms in nature are able to degrade PHAs by using PHA hydrolases and PHA depolymerases. Microorganisms then metabolize these degradation products into water and carbon dioxide. The activities of these enzymes may vary and depend on the composition of the polymer and the environmental conditions. PHAs have been proved biocompatible, which means they have no toxic effects in living organisms. Within mammals the polymer is hydrolyzed, but only slowly. There are two types of PHA depolymerases based on the type of PHA it acts upon and the site of action. Intracellular degradation is the active degradation (mobilization) of an endogenous storage reservoir by the accumulating bacterium itself. This happens in case of nutrient depletion. Enzymes catalyzing the intracellular degradation of PHA are intracellular PHA depolymerases (e-PHA depolymerases). Conversely, extracellular degradation is the utilization of extracellular PHA by an organism that need not be the microorganism that accumulated the polymer. These depolymerases are the extracellular depolymerases (e-PHA depolymerases). The extracellular PHA is that which is released by the accumulating cells. The importance of the two types of PHAs will become clear on study of the difference between the nature of PHA inside and outside the cell. PHA within intracellular granules with intact surface layer are in the amorphous state and are called native PHA or nPHA. PHAs outside the cell are normally partially crystalline and are denatured PHA or dPHA. The same notation is used to differentiate PHA depolymerases according to their ability to hydrolyze nPHA (nPHA depolymerases) or dPHA (dPHA depolymerases). When mentioning degradation of PHA in this study, it is about the 10 Industrial and Environmental Biotechnology degradation of the Bioplastic form that is the dPHA form. PHA-degrading bacteria differ in respect to the type of polyester they can degrade. Most bacteria that have been studied specifically produce either dPHA(scl) or dPHA(mcl). However, some bacteria reveal broad polyester specificities too and are found to degrade most types of PHAs (Schirmer et al., 1995). Such bacteria have the broad spectrum ability due to synthesis of more than one PHA depolymerases, each acting upon its specific target substrate. Renewable Nature of PHA Not only are the Polyhydroxyalkanoates biodegradable, they are also produced from renewable biological sources unlike the fossil fuel based plastics (Braunegg et al., 2004). Fermentative production of PHAs uses agricultural feeds such as sugars and fatty acids as carbon and energy sources (Kadouri et al., 2005). Thus PHAs are produced from naturally available carbon sources and also can be microbiologically degrades into non toxic products. We can confidently say that the life cycle of PHAs is completely compatible with the carbon. Biodegradability is crucial for certain applications. But more than that the lower impact on the natural resources available has been a big factor contributing to the attention, this class of polymer has been enjoying (Gavrilescu et al., 2005). Polyhydroxyalkanoates produced from plants are not energy efficient as the energy required in the entire process ranging from crop growing to molding of the final plastic product is very tedious and the quantity obtained is very scanty in comparison. Fermentative production from microbes is a very good option, but the process has not yet been optimized enough to be able to compete with the cost of production of the conventional plastics (Gerngross, 1999; Dove, 2000; Kim and Dale, 2005). BIOTECHNOLOGICAL APPLICATIONS Industrial production of PHA was started with Biopol1 by ICI Ltd in 1982. Initially, the bioplastics were used for the fabrication of bottles, fibers, latex and several products of agricultural, commercial or packaging interest (Angelova et al., 1999). It is expected that the PHAs can be used to replace the conventional plastics. Applications mainly looked into are containers, films etc. normally used for packaging (Bucci and Tavares, 2005). Use of these plastics in personal hygiene articles such as diapers to make them biodegradable also has been studied (Noda, 2001). PHAs have also been used in toners for printing applications as well as adhesives for coating applications (Madison and Huisman, 1999). Currently, there are a lot of medical applications for these plastics. Some of the applications are in sutures, implants, urological stents, neural- and cardiovascular- tissue engineering, fracture fixation, treatment of narcolepsy and alcohol addiction, drug-delivery vehicles, cell microencapsulation, Polyhydroxyalkanoates: Biodegradable Plastics for Environmental Conservation 11 support of hypophyseal cells, or as precursors of molecules with anti-rheumatic, analgesic, radiopotentiator, chemopreventive, antihelmintic or anti-tumuoral properties (those containing aromatic monomers or those linked to nucleosides) (Williams and Martin , 2002; Madison and Huisman, 1999). However, PHA use for contact with human blood has some extra specifications to be followed. Therefore not all types of PHA can be used in human body (Vert, 2005). PHA used in contact with blood has to be microbial endotoxin free and so has to undergo quite expensive and tedious purification procedures (Sevastianov et al., 2003). Main applications of PHAs Agricultural Medical and Commercial Pharmaceutical Biodegradable carriers for Sutures and implants Packaging materials in long-term dosage of Urological stents various industries agricultural commodities Neural- and cardiova- including food industry like insecticides, or scular-tissue engineering, Disposable items such as fertilizers, seedling Fracture fixation razors, utensils, diapers, containers and plastic Treatment of narcolepsy feminine hygiene sheaths for protecting and alcohol addiction products. saplings Drug-delivery vehicle Toners for printing Biodegradable carrier for Cell microencapsulation applications drug release in veterinary and support of hypophy- Adhesives for coating medicine, and tubing for seal cells applications crop irrigation Precursors of pharmaco- logically important molecules Effect of PHA on Enviroment and Improvement Strategies Apart from bringing down the cost of production, the impact PHAs and the production process on the society and the environment also has to be taken into consideration. The Life Cycle Assessment (LCA) is a well-established approach for identifying best practices within the complexity of choices confronting society and industry. The LCA is an objective procedure for evaluating the environmental impacts associated with a product through every step of its life cycle starting from procurement of raw materials, production process, marketing and sale, usage at various consumer levels, disposal and recycling into a new product. It was found that although LCA usually leads to a definite conclusion, its results can easily be reversed under different environmental impacts, different inventory parameters and/ or different boundaries of the study (Giudice et al., 2006). Under the current manufacturing technology, a number of LCA reports have indicated that 12 Industrial and Environmental Biotechnology petrochemical polymers can have equivalent or better eco-profiles than PHAs. The main factors influencing this assessment were energy for polymer manufacture, the effects of the number of recycling loops, and end-of-life disposal (especially methane generation in landfill). However, PHA manufacturing is not in large scale currently. It is hoped that as the scale increases and the techniques improve, the eco- profiles also will become better. At this stage, PHAs could contribute to sustainability and help engage the public in environmental awareness. To make the eco-profiles of PHA better bioplastic production has three major hurdles to cross. Primarily, since the product is formed under conditions of stress, the biomass production is also affected adversely. The unbalanced nutritional content in the media will slow down microbial growth. Secondly, the cost of production is currently high. Extensive studies are now going on for making the production process more cost effective. That can be done by utilizing cheaper substrates. The third and final hurdle is the high cost for product recovery. Currently since the biosynthetic pathway for PHA production has been studied, recombinant organisms are also being developed to synthesize bioplastics from cheaper carbon sources. The recombinant strains not only have a higher production capacity, but also packs the PHA granules more closely and efficiently (Sujatha and Shenbagarathai, 2006). At present, traditional fermentations carried out with recombinant bacteria and transgenic plants cannot compete with the conventional industrial production of synthetic plastics. Enzymatic synthesis of bioplastics is a production strategy that is in use under laboratory conditions presently. 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