Exploring polyhydroxyalkanoates biosynthesis using hydrocarbons as carbon source: a comprehensive review.

Environmental pollution caused by petrochemical hydrocarbons (HC) and plastic waste is a pressing global challenge. However, there is a promising solution in the form of bacteria that possess the ability to degrade HC, making them valuable tools for remediating contaminated environments and effluents. Moreover, some of these bacteria offer far-reaching potential beyond bioremediation, as they can also be utilized to produce polyhydroxyalkanoates (PHAs), a common type of bioplastics. The accumulation of PHAs in bacterial cells is facilitated in environments with high C/N or C/P ratio, which are often found in HC-contaminated environments and effluents. Consequently, some HC-degrading bacteria can be employed to simultaneously produce PHAs and conduct biodegradation processes. Although bacterial bioplastic production has been thoroughly studied, production costs are still too high compared to petroleum-derived plastics. This article aims to provide a comprehensive review of recent scientific advancements concerning the capacity of HC-degrading bacteria to produce PHAs. It will delve into the microbial strains involved and the types of bioplastics generated, as well as the primary pathways for HC biodegradation and PHAs production. In essence, we propose the potential utilization of HC-degrading bacteria as a versatile tool to tackle two major environmental challenges: HC pollution and the accumulation of plastic waste. Through a comprehensive analysis of strengths and weaknesses in this aspect, this review aims to pave the way for future research in this area, with the goal of facilitating and promoting investigation in a field where obtaining PHAs from HC remains a costly and challenging process.

Evaluation of the production and extraction of polyhydroxybutyrate from volatile fatty acids by means of mixed cultures and B. cepacia.

The global consumption of plastics generates accelerated environmental pollution in landfills and marine ecosystems. Biopolymers are the materials with the greatest potential to replace synthetic polymers in the market due to their good biodegradability, however, there are still several disadvantages, mainly related to their production cost. Considering the above, the generation of biodegradable and biocompatible bioplastics stands out as an alternative solution, some of which are made from renewable raw materials, including polyhydroxyalkanoates PHAs. Although much research has been done on bacteria with the capacity for intracellular accumulation of PHAs, among others, it is also possible to produce PHAs using mixed microbial cultures instead of a single microorganism, using natural microbial consortia that have the capacity to store high amounts of PHAs. In this contribution, three methods for the extraction and purification of PHAs produced by fermentation using volatile fatty acids as a carbon source at different concentrations were evaluated, using the pure strain Burkholderia cepacia 2G-57 and the mixed cultures of the activated sludge from the El Salitre WWTP, in order to select the best method from the point of view of environmental sustainability as this will contribute to the scalability of the process. The mixed cultures were identified by sequencing of the 16S gene. A yield of 89% was obtained from the extraction and purification of PHA using acetic acid as a solvent, which according to its properties is "greener" than chloroform. The polymer obtained was identified as polyhydroxybutylated PHB.

Production and characterization of polyhydroxyalkanoates from industrial waste using soil bacterial isolates.

Nowadays when conventional plastic is being looked as a menace, the possibility of it being replaced with polyhydroxyalkanoates (PHAs) which are biodegradable, environment friendly and biocompatible thermoplastics is not remote. PHAs are a fascinating group of biopolyesters stored within the cytoplasm of numerous bacterial cells as energy and carbon reserves. PHAs signify the best promising biological substitute to certain conventional petrochemical plastics which have wide range of applications in different industries such as biomedical sector, packaging, toners for printing, and adhesives for coating, etc. In the present study, PHAs producing bacterial strains were screened by Sudan black B staining and confirmed by Nile blue A staining. Out of forty bacterial strains showing positive results, six bacterial strains exhibited comparatively higher PHAs production. The highest PHAs producing bacterial strain was identified using 16s rRNA sequencing. Optimization of process parameters was performed by using one factor at a time (OFAT) approach. The isolated bacterium was able to synthesize PHAs when various agro-industrial wastes such as domestic kitchen waste, mixed fruit pulp, sugarcane molasses, and waste flour from bread factory were screened as a carbon substrate in the growth medium. The results showed accumulation of 44.5% PHAs of cell dry weight using domestic kitchen waste as carbon substrate. The characterization of biopolymers was performed using FTIR and XRD analysis. The commercial exploitation of results of this study may serve twin purposes of addressing the challenge of high production cost of PHAs being the major constraint in replacing petro-based plastics as well as address the problem of disposal of recurring domestic kitchen waste and other agro-industrial waste.

Production and characterization of poly 3-hydroxybutyrate-co-3-hydroxyvalerate in wheat starch wastewater and its potential for nanoparticle synthesis.

Polyhydroxyalkanoates (PHAs) are polymers with biodegradable and biocompatible properties accumulated in a wide variety of bacterial strains. In the present study, active sludge, wheat starch wastewater (WSW), and oil wastewater were used for the isolation and screening of PHA-accumulating bacteria. WSW was then implemented as a cheap and economical culture medium for the production of PHAs by the selected isolate. The extracted PHA was characterized, and the capability of produced biopolymer for preparing nanoparticles was evaluated. Based on the results, 96 different bacterial isolates were obtained, of which the strains isolated from WSW demonstrated the highest PHA-accumulation capability. The maximum PHA content of 3.07 g/l (59.50% of dry cell weight) was obtained by strain N6 in 21 h. The selected strain was identified by molecular approaches as Bacillus cereus. Afterward, the physicochemical characterization of an accumulated biopolymer was specified as a PHBV copolymer. Finally, spherical homogenous PHBV nanoparticles with a size of 137 nm were achieved. The PHBV nanoparticles showed a suitable small size and good zeta potential for medical applications. Hence, it can be concluded that isolated wild strain (B. cereus) has the potential exploitation capability for cost-effective PHBV production using the WSW.

Cyanobacterial Polyhydroxyalkanoates: A Sustainable Alternative in Circular Economy.

Conventional petrochemical plastics have become a serious environmental problem. Its unbridled use, especially in non-durable goods, has generated an accumulation of waste that is difficult to measure, threatening aquatic and terrestrial ecosystems. The replacement of these plastics with cleaner alternatives, such as polyhydroxyalkanoates (PHA), can only be achieved by cost reductions in the production of microbial bioplastics, in order to compete with the very low costs of fossil fuel plastics. The biggest costs are carbon sources and nutrients, which can be appeased with the use of photosynthetic organisms, such as cyanobacteria, that have a minimum requirement for nutrients, and also using agro-industrial waste, such as the livestock industry, which in turn benefits from the by-products of PHA biotechnological production, for example pigments and nutrients. Circular economy can help solve the current problems in the search for a sustainable production of bioplastic: reducing production costs, reusing waste, mitigating CO2, promoting bioremediation and making better use of cyanobacteria metabolites in different industries.

Biosynthesis of polyhydroxyalkanoates from vegetable oil under the co-expression of fadE and phaJ genes in Cupriavidus necator.

The acyl-CoA dehydrogenase (FadE) and (R)-specific enoyl-CoA hydratase (PhaJ) are functionally related to the degradation of fatty acids and the synthesis of polyhydroxyalkanoates (PHAs). To verify this, a recombinant Cupriavidus necator H16 harboring the plasmid -pMPJAS03- with fadE from Escherichia coli strain K12 and phaJ1 from Pseudomonas putida strain KT2440 under the arabinose promoter (araC-PBAD) was constructed. The impact of co-expressing fadE and phaJ genes on C. necator H16/pMPJAS03 maintaining the wild-type synthase on short-chain-length/medium-chain-length PHA formation from canola or avocado oil at different arabinose concentrations was investigated. The functional activity of fadEE.c led to obtaining higher biomass and PHA concentrations compared to the cultures without expressing the gene. While high transcriptional levels of phaJ1P.p, at 0.1% of arabinose, aid the wild-type synthase to polymerize larger-side chain monomers, such as 3-Hydroxyoctanoate (3HO) and 3-Hydroxydecanoate (3HD). The presence of even small amounts of 3HO and 3HD in the co-polymers significantly depresses the melting temperature of the polymers, compared to those composed of pure 3-hydroxybutyrate (3HB). Our data presents supporting evidence that the synthesis of larger-side chain monomers by the recombinant strain relies not only upon the affinity of the wild-type synthase but also on the functionality of the intermediate supplying enzymes.

Evolutionary relationships between the transcriptional repressors of the polyhydroxyalkanoate reserve storage system in prokaryotes: Conserved but phylogenetically heterogeneous.

Bacteria and archaea accumulate cytoplasmic polyhydroxyalkanoate (PHA) granules under nutrient-limited conditions with excess carbon. The transcriptional regulatory (TR) proteins found on the surface of PHA granules act as repressors as well as activators for the expression of major surface proteins called phasins. Until now, detailed information on the evolutionary relationships between these transcription regulators has not been available. Here, we conducted homology searches and analyzed information available for the domains and protein families of the TR proteins through phylogenetic studies. A total of 282 TR proteins were identified and further classified into four distinct subfamilies based upon the presence of conserved motifs: PHB_acc, TetR-like, AbrB-like, and PadR-like. Depending upon the particular family, the DNA-binding domains were located at either the N- or C-terminus. Our results indicated that TR proteins containing the PHB_acc domain are highly conserved within the bacteria, while other TR proteins are present only within archaea (AbrB-like), gram positive bacteria (PadR-like), or the Pseudomonas genera (TetR-like). The repression domains are charged, hydrophobic, and rich in leucine or glutamine. In phylogenetic analyses, many groups of TR proteins were clustered together according to identical domain architectures showing the independent origins of the TR proteins in the PHA reserve storage system. Further analyses revealed that the TR proteins have experienced multiple gene duplications across prokaryotes. Thus, this study investigated the evolutionary framework of TR proteins and has provided a comprehensive catalog of TR proteins for ongoing studies to characterize the functions of these proteins within diverse organisms.

Design and optimization of poly(hydroxyalkanoate)s production plants using alternative substrates.

In this work, we propose a Mixed Integer Nonlinear Programming (MINLP) model to determine the optimal design of a poly(hydroxyalkanoate)s (PHAs) production plant configuration. The superstructure based optimization model considers different carbon sources as raw material: glycerol (crude and purified), corn starch, cassava starch, sugarcane sucrose and sugarcane molasses. The PHA extraction section includes four alternatives: the use of enzyme, solvent, surfactant-NaOCl or surfactant-chelate. Model constraints include detailed capital cost for equipment, mass and energy balances, product specifications and operating bounds on process units. The resulting MINLP model maximizes the project net present value (NPV) as objective function and it is implemented in an equation oriented environment. Optimization results show the sugarcane-enzyme option as the most promising alternative (NPV = 75.01 million USD) for PHAs production with an energy consumption of 22.56 MJ/kg PHA and a production cost of 3.02 USD/kg PHA. Furthermore, an economic sensitivity analysis is performed.

Exploiting the natural poly(3-hydroxyalkanoates) production capacity of Antarctic Pseudomonas strains: from unique phenotypes to novel biopolymers.

Extreme environments are a unique source of microorganisms encoding metabolic capacities that remain largely unexplored. In this work, we isolated two Antarctic bacterial strains able to produce poly(3-hydroxyalkanoates) (PHAs), which were classified after 16S rRNA analysis as Pseudomonas sp. MPC5 and MPC6. The MPC6 strain presented nearly the same specific growth rate whether subjected to a temperature of 4 °C 0.18 (1/h) or 30 °C 0.2 (1/h) on glycerol. Both Pseudomonas strains produced high levels of PHAs and exopolysaccharides from glycerol at 4 °C and 30 °C in batch cultures, an attribute that has not been previously described for bacteria of this genus. The MPC5 strain produced the distinctive medium-chain-length-PHA whereas Pseudomonas sp. MPC6 synthesized a novel polyoxoester composed of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate-co-3-hydroxyoctanoate-co-3-hydroxydecanoate-co-3-hydroxydodecanoate). Batch bioreactor production of PHAs in MPC6 resulted in a titer of 2.6 (g/L) and 1.3 (g/L), accumulating 47.3% and 34.5% of the cell dry mass as PHA, at 30 and 4 °C, respectively. This study paves the way for using Antarctic Pseudomonas strains for biosynthesizing novel PHAs from low-cost substrates such as glycerol and the possibility to carry out the bioconversion process for biopolymer synthesis without the need for temperature control.

Comparative genome analysis of completely sequenced Cupriavidus genomes provides insights into the biosynthetic potential and versatile applications of Cupriavidus alkaliphilus ASC-732.

The genome analysis of microorganisms provides valuable information to endorse more extensive research on their potential applications. In this paper, the genome of Cupriavidus alkaliphilus ASC-732, isolated from agave rhizosphere in northeastern Mexico, was analyzed and compared with the genomes of other Cupriavidus species to gain better insight into the parts in the genetic makeup responsible for essential metabolic pathways and others of biotechnological importance. Here, the key genes related to glycolysis, pentose phosphate, and the Entner-Doudoroff and tricarboxylic acid cycle pathways were predicted. Comparative genome analysis revealed that the key genes for hydrogenotrophic growth and carbon fixation pathway, i.e., those coding for hydrogenase and enzymes Calvin-Benson-Bassham cycle, are absent in C. alkaliphilus ASC-732. Furthermore, capabilities for producing polyhydroxyalkanoates and extracellular polysaccharide matrix and degrading xenobiotics were found, and the related pathways are explained. Moreover, biofilm formation and the production of exopolysaccharides and polyhydroxyalkanoates were corroborated with crystal violet staining, calcofluor, and Nile red fluorochromes, confirming the presence of the products of the active genes in these pathways and their related metabolic routes, respectively. Additionally, a large group of genes essential for the resistance and detoxification of several heavy metals were also found. Thus, the present study demonstrates that this strain can respond to various environmental signals, such as energy source, nutrient limitations, virulence, and extreme metals concentration, indicating the possibility to foster C. alkaliphilus ASC-732 in diverse biotechnological applications.

Role of ß-oxidation and de novo fatty acid synthesis in the production of rhamnolipids and polyhydroxyalkanoates by Pseudomonas aeruginosa.

Pseudomonas aeruginosa are ubiquitous γ-proteobacteria capable of producing the biosurfactant rhamnolipids (RL) and the polymer polyhydroxyalkanoate (PHA). RL are glycolipids with high biotechnological potential, whereas PHA is used for the production of biodegradable plastics. It has been proposed that the ß-oxidation pathway provides intermediates for RL biosynthesis, even when using a non-fatty acid carbon source for growth, while an intermediate of de novo fatty acid biosynthesis (FASII) pathway [(R)-3-hydroxyacyl-ACP] is used for PHA biosynthesis. The aim of this work is to study the inter-relationship of the RL and PHA biosynthetic pathways in a culture medium with a non-fatty acid carbon source, focusing on the role of FASII and ß-oxidation in supplying the substrates for the first step in RL and PHA synthesis, carried out by the RhlA and PhaG enzymes, respectively. The PHA synthases (PhaC1 and PhaC2) are only able to use CoA-linked 3-hydroxy acids and the PhaG enzyme catalyzes the conversion of (R)-3-hydroxyacyl-ACP to (R)-3-hydroxyacyl-CoA, the substrate of PhaC1 and PhaC2. RhlA in turn catalyzes the synthesis of the RL precursor 3-(3-hydroxyalkanoyloxy) alkanoic acids (HAA) by the dimerization of two 3-hydroxyalkanoic acid molecules (that have been shown to be also (R)-3-hydroxyacyl-ACP). In this work, we show that RhlA can produce both RL and PHA precursors (presumably CoA-linked HAA), that the blockage of carbon flux through ß-oxidation pathway does not decrease RL titer, and that the enoyl-CoA hydratase RhlY and enoyl-CoA hydratase/isomerase RhlZ produce the main fatty acids precursor of RL using as substrate also a FASII intermediate (presumably (S)-3-hydroxyacyl-CoA).

Genome characteristics dictate poly-R-(3)-hydroxyalkanoate production in Cupriavidus necator H16.

Cupriavidus necator H16 is a well-recognized enterprise with efficient manufacturing machineries to produce diverse polymers belonging to polyhydroxyalkanoates (PHAs) family. The genome fingerprints, including PHA machinery proteins and fatty acid metabolism, had educated engineering strategies to enhance PHAs production. This outstanding progress has enlightened us to present an exhaustive examination of the ongoing research, addressing the great potential design of genome features towards PHA production and furthermore, we show how those acquired knowledge have been explored in other biotechnological applications. This updated-review concludes that the combination of an optimal strain selection, suitable metabolic engineering and a large-scale fermentation on oil substrates is critical to endow the ability of incorporating mcl-PHAs monomers in this organism.

Production of Polyhydroxyalkanoates Copolymers by Recombinant Pseudomonas in Plasmid- and Antibiotic-Free Cultures.

Three different polyhydroxyalkanoate (PHA) synthase genes (Ralstonia eutropha H16, Aeromonas sp. TSM81 or Aeromonas hydrophila ATCC7966 phaC) were introduced into the chromosome of two Pseudomonas strains: a native medium-chain-length 3-polyhydroxyalkanoate (PHAMCL) producer (Pseudomonas sp. LFM046) and a UV-induced mutant strain unable to produce PHA (Pseudomonas sp. LFM461). We reported for the first time the insertion of a chromosomal copy of phaC using the transposon system mini-Tn7. Stable antibiotic marker-free and plasmid-free recombinants were obtained. Subsequently, P(3HB-co-3HAMCL) was produced by these recombinants using glucose as the sole carbon source, without the need for co-substrates and under antibiotic-free conditions. A recombinant harboring A. hydrophila phaC produced a terpolyester composed of 84.2 mol% of 3-hydroxybutyrate, 6.3 mol% of 3-hydroxyhexanoate, and 9.5 mol% of 3-hydroxydecanoate from only glucose. Hence, we were successful in increasing the industrial potential of Pseudomonas sp. LFM461 strain by producing PHA copolymers containing 3HB and 3HAMCL using an unrelated carbon source, for the first time in a plasmid- and antibiotic-free bioprocess.

Heterologous expression of phaC2 gene and poly-3-hydroxyalkanoate production by recombinant Cupriavidus necator strains using canola oil as carbon source.

Many heterologous transformation studies have been carried out using the Cupriavidus necator PHB-4 strain to investigate the expression characteristics of various polyhydroxyalkanoate (PHA) synthase enzymes. In this study, we generated a recombinant C. necator PHB-4 strain by transforming a plasmid (pMRC03) harbouring the synthetic phaC2 gene of Pseudomonas putida CA-3. Under conditions favourable for expression of the phaC2 P.putCA-3 gene, canola oil was used as carbon source for the synthesis of PHAs. The expressed synthase polymerised monomers of 3-hydroxybutyrate (3-HB), 3-hydroxyvalerate (3-HV) and 3-hydroxyhexanoate (3-HHx) in the recombinant C. necator PHB-4 (pMRC03) strain. We then co-expressed the phaC2P.putCA-3 gene with the native phaC1C.ne gene in wild type Cupriavidus necator H16 (C. necator H16 (pMRC03)). This co-expression produced a PHA blend of 3-HB, 3-HV, 3-HHx and 3-hydroxyoctanoate (3-HO) monomers in the presence of canola oil. Gas chromatography analysis revealed the presence of 94mol% 3-HB, 1mol% 3-HV, 4mol% 3-HHx and 1mol% 3-HO in a tetra-polymer. Thus, we confirmed that a synthetic phaC2 gene encoding the synthase enzyme is functionally active with substrates ranging from short to medium chain length PHAs.

Perspectives on the production, structural characteristics and potential applications of bioplastics derived from polyhydroxyalkanoates.

Since the last two decades, the use of synthetic materials has increased and become more frequent in this capitalist system. Polymers used as raw materials are usually disposed very rapidly and considered serious damages when they return to the environment. Because of this behaviour, there was an increasing in the global awareness by minimizing the waste generated, in addition to the scientific community concern for technological alternatives to solve this problem. Alternatively, biodegradable polymers are attracting special interest due to their inherent properties, which are similar to the ones of the conventional plastics. Bioplastics covers plastics made from renewable resources, including plastics that biodegrade under controlled conditions at the end of their use phase. Polyhydroxyalkanoates (PHAs) are polyesters composed of hydroxy acids, synthesized by a variety of microorganisms as intracellular carbon and energy storage. These environmentally friendly biopolymers have excellent potential in domestic, agricultural, industrial and medical field, however their production on a large scale is still limited. This review considered the most recent scientific publications on the production of bioplastics based on PHAs, their structural characteristics and the exploitation of different renewable sources of raw materials. In addition, there were also considered the main biotechnological applications of these biopolymers.

Variation analysis of bacterial polyhydroxyalkanoates production using saturated and unsaturated hydrocarbons

ABSTRACT Polyhydroxyalkanoates (PHA) are efficient, renewable and environment friendly polymeric esters. These polymers are synthesized by a variety of microbes under stress conditions. This study was carried out to check the suitability of waste frying oil in comparison to other oils for economical bioplastic production. Six bacterial strains were isolated and identified as Bacillus cereus (KF270349), Klebsiella pneumoniae (KF270350), Bacillus subtilis (KF270351), Brevibacterium halotolerance (KF270352), Pseudomonas aeruginosa (KF270353), and Stenotrophomonas rhizoposid (KF270354) by ribotyping. All strains were PHA producers so were selected for PHA synthesis using four different carbon sources, i.e., waste frying oil, canola oil, diesel and glucose. Extraction of PHA was carried out using sodium hypochlorite method and maximum amount was detected after 72 h in all cases. P. aeruginosa led to maximum PHA production after 72 h at 37 °C and 100 rpm using waste frying oil that was 53.2% PHA in comparison with glucose 37.8% and cooking oil 34.4%. B. cereus produced 40% PHA using glucose as carbon source which was high when compared against other strains. A significantly lesser amount of PHA was recorded with diesel as a carbon source for all strains. Sharp Infrared peaks around 1740-1750 cm-1 were present in Fourier Transform Infrared spectra that correspond to exact position for PHA. The use of waste oils and production of poly-3hydroxybutyrate-co-3hydroxyvalerate (3HB-co-3HV) by strains used in this study is a good aspect to consider for future prospects as this type of polymer has better properties as compared to PHBs.

Evaluation of short-chain-length polyhydroxyalkanoate accumulation in Bacillus aryabhattai

Abstract This study was focused on the polyhydroxybutyrate (PHB) accumulation property of Bacillus aryabhattai isolated from environment. Twenty-four polyhydroxyalkanoate (PHA) producers were screened out from sixty-two environmental bacterial isolates based on Sudan Black B colony staining. Based on their PHA accumulation property, six promising isolates were further screened out. The most productive isolate PHB10 was identified as B. aryabhattai PHB10. The polymer production maxima were 3.264 g/L, 2.181 g/L, 1.47 g/L, 1.742 g/L and 1.786 g/L in glucose, fructose, maltose, starch and glycerol respectively. The bacterial culture reached its stationary and declining phases at 18 h and 21 h respectively and indicated growth-associated PHB production. Nuclear Magnetic Resonance (NMR) spectra confirmed the material as PHB. The material has thermal stability between 30 and 140 °C, melting point at 170 °C and maximum thermal degradation at 287 °C. The molecular weight and poly dispersion index of the polymer were found as 199.7 kDa and 2.67 respectively. The bacterium B. aryabhattai accumulating PHB up to 75% of cell dry mass utilizing various carbon sources is a potential candidate for large scale production of bacterial polyhydroxybutyrate.

Variation analysis of bacterial polyhydroxyalkanoates production using saturated and unsaturated hydrocarbons.

Polyhydroxyalkanoates (PHA) are efficient, renewable and environment friendly polymeric esters. These polymers are synthesized by a variety of microbes under stress conditions. This study was carried out to check the suitability of waste frying oil in comparison to other oils for economical bioplastic production. Six bacterial strains were isolated and identified as Bacillus cereus (KF270349), Klebsiella pneumoniae (KF270350), Bacillus subtilis (KF270351), Brevibacterium halotolerance (KF270352), Pseudomonas aeruginosa (KF270353), and Stenotrophomonas rhizoposid (KF270354) by ribotyping. All strains were PHA producers so were selected for PHA synthesis using four different carbon sources, i.e., waste frying oil, canola oil, diesel and glucose. Extraction of PHA was carried out using sodium hypochlorite method and maximum amount was detected after 72h in all cases. P. aeruginosa led to maximum PHA production after 72h at 37°C and 100rpm using waste frying oil that was 53.2% PHA in comparison with glucose 37.8% and cooking oil 34.4%. B. cereus produced 40% PHA using glucose as carbon source which was high when compared against other strains. A significantly lesser amount of PHA was recorded with diesel as a carbon source for all strains. Sharp Infrared peaks around 1740-1750cm-1 were present in Fourier Transform Infrared spectra that correspond to exact position for PHA. The use of waste oils and production of poly-3hydroxybutyrate-co-3hydroxyvalerate (3HB-co-3HV) by strains used in this study is a good aspect to consider for future prospects as this type of polymer has better properties as compared to PHBs.

Evaluation of short-chain-length polyhydroxyalkanoate accumulation in Bacillus aryabhattai.

This study was focused on the polyhydroxybutyrate (PHB) accumulation property of Bacillus aryabhattai isolated from environment. Twenty-four polyhydroxyalkanoate (PHA) producers were screened out from sixty-two environmental bacterial isolates based on Sudan Black B colony staining. Based on their PHA accumulation property, six promising isolates were further screened out. The most productive isolate PHB10 was identified as B. aryabhattai PHB10. The polymer production maxima were 3.264g/L, 2.181g/L, 1.47g/L, 1.742g/L and 1.786g/L in glucose, fructose, maltose, starch and glycerol respectively. The bacterial culture reached its stationary and declining phases at 18h and 21h respectively and indicated growth-associated PHB production. Nuclear Magnetic Resonance (NMR) spectra confirmed the material as PHB. The material has thermal stability between 30 and 140°C, melting point at 170°C and maximum thermal degradation at 287°C. The molecular weight and poly dispersion index of the polymer were found as 199.7kDa and 2.67 respectively. The bacterium B. aryabhattai accumulating PHB up to 75% of cell dry mass utilizing various carbon sources is a potential candidate for large scale production of bacterial polyhydroxybutyrate.

Simultaneous Biosynthesis of Polyhydroxyalkanoates and Extracellular Polymeric Substance (EPS) from Crude Glycerol from Biodiesel Production by Different Bacterial Strains.

Simultaneous synthesis of polyhydroxyalkanoates (PHAs) and polyglutamic acid (PGA) was investigated in cultures of Cupriavidus necator IPT 026, C. necator IPT 027, C. necator IPT 029, and Bacillus megaterium INCQS 425 strains in a medium containing 2.0 % sucrose or crude glycerol from biodiesel (CGB), in an orbital shaker (35 °C, 180 rpm, 72 h). All the strains tested simultaneously produced PHA and PGA in a medium containing CGB. The C. necator IPT026 culture provided higher molecular mass PHA and PGA (1128.55 and 835.56 kDa, respectively). B. megaterium INCQS 425 promoted PGA production (1.90 g L-1) with higher crystalline melting temperature (84.04 °C) and higher initial decomposition temperature (247.10 °C). Furthermore, the latter culture promoted the production of medium- and long-chain PHA (0.78 g L-1) with high crystalline melting temperatures (∼170 °C) and high initial decomposition temperature (307.53 °C) and low degree of crystallinity (20.2 %). These characteristics render these PHAs more appropriate and suitable for processes that require high temperatures, such as extrusion, increasing the possibility of industrial applications, especially in the packaging sector.