Production of poly-3-hydroxybutyrate by Bacillus sp. JMa5 cultivated in molasses media

Traditional Chinese medicine residue enzymatic hydrolysates for production of polyhydroxyalkanoate by newly isolated Bacillus altitudinis

Traditional Chinese medicine residue (TCMR) was utilized as an inexpensive carbon source for the production of poly(3-hydroxybutyrate) (PHB) using the newly isolated Bacillus altitudinis HBU-SI7. The results showed that Yu Ping Feng TCMR could be directly hydrolysed by cellulase to obtain a high proportion of glucose (99 % of total sugar) without pretreatment, achieving an enzymatic hydrolysis rate of up to 89.2 %. B. altitudinis could grow and produce PHB when using enzymatically hydrolysed TCMR in a 5-L fermenter. After 20 h of fermentation, the maximum concentration of PHB was 11.2 g/L, and the highest cell dry weight (CDW) was 15.4 g/L, with 72.7 % of the PHB fraction in CDW. Moreover, this strain could utilize enzymatic hydrolysates from various herbal formulas to produce high levels of PHB. This novel approach aims to accumulate PHB from TCMR hydrolysates, offering an effective and environmentally friendly method to reduce production costs and achieve mass production.

Lipid-membranes interaction, structural assessment, and sustainable production of polyhydroxyalkanoate by Priestia filamentosa AZU-A6 from sugarcane molasses

This study presented for the first time the PHA-lipid interactions by circular dichroism (CD) spectroscopy, besides a sustainable PHA production strategy using a cost-effective microbial isolate. About 48 bacterial isolates were selected from multifarious Egyptian sites and screened for PHAs production. The Fe(AZU-A6) was the most potent isolate, and identified genetically as Priestia filamentosa AZU-A6, while the intracellular PHA granules were visualized by TEM. Sugarcane molasses (SCM) was used an inexpensive carbon source and the production conditions were optimized through a Factor-By-Factor strategy and a Plackett-Burman statistical model. The highest production (6.84 g L^-1) was achieved at 8.0 % SCM, pH 8.0, 35 °C, 250 rpm, and 0.5 g L^-1 ammonium chloride after 72 h. The complementary physicochemical techniques (e.g., FTIR, NMR, GC-MS, DSC, and TGA) have ascertained the structural identity as poly-3-hydroxybutyrate (P3HB) with a characteristic melting temperature of 174.5 °C. The circular dichroism analysis investigated the existence of interactions between the PHB and the different lipids, particularly 1,2-dimyristoyl-sn-glycero-3-phosphocholine. The ATR technique for the lipid-PHB films suggested that both the hydrophobic and electrostatic forces control the lipid-PHB interactions that might induce changes in the structuration of PHB.

Formation of polyhydroxyalkanoates using agro and industrial waste as a substrate - a review

In the present scenario, rising environmental concerns of non-biodegradable plastic pollution and depletion of petroleum based raw materials lead to the development of biopolymers. The biodegradability of biopolymers gives them a specific advantage for the environmental concerns. Polyhydroxyalkanoates (PHAs) are a type of biopolymers which are synthesized by microorganisms. Although there are different substrates available in pure forms which are currently used in the production of PHA, 40% of production cost depends on the expensive substrate which is a major disadvantage and make it far from many applications. The use of an inexpensive carbon source which is high in organic matter content such as waste streams of process industries can make this process viable and diminish PHA production cost. This study explores the current research initiatives on various agricultural and industrial waste feedstocks, formulations and processing conditions for producing PHA in a way that is both inexpensive and beneficial to the environment. The creation of fermentation conditions and metabolic engineering techniques for promoting microbial growth and PHA synthesis were also discussed in the review.

Recent trends of biotechnological production of polyhydroxyalkanoates from C1 carbon sources

Growing concerns over the use of limited fossil fuels and their negative impacts on the ecological niches have facilitated the exploration of alternative routes. The use of conventional plastic material also negatively impacts the environment. One such green alternative is polyhydroxyalkanoates, which are biodegradable, biocompatible, and environmentally friendly. Recently, researchers have focused on the utilization of waste gases particularly those belonging to C1 sources derived directly from industries and anthropogenic activities, such as carbon dioxide, methane, and methanol as the substrate for polyhydroxyalkanoates production. Consequently, several microorganisms have been exploited to utilize waste gases for their growth and biopolymer accumulation. Methylotrophs such as Methylobacterium organophilum produced highest amount of PHA up to 88% using CH₄ as the sole carbon source and 52-56% with CH₃OH. On the other hand Cupriavidus necator, produced 71-81% of PHA by utilizing CO and CO₂ as a substrate. The present review shows the potential of waste gas valorization as a promising solution for the sustainable production of polyhydroxyalkanoates. Key bottlenecks towards the usage of gaseous substrates obstructing their realization on a large scale and the possible technological solutions were also highlighted. Several strategies for PHA production using C1 gases through fermentation and metabolic engineering approaches are discussed. Microbes such as autotrophs, acetogens, and methanotrophs can produce PHA from CO₂, CO, and CH₄. Therefore, this article presents a vision of C1 gas into bioplastics are prospective strategies with promising potential application, and aspects related to the sustainability of the system.

Microplastics a Novel Substratum for Polyhydroxyalkanoate (PHA)-Producing Bacteria in Aquatic Environments

Polyhydroxyalkanoates (PHA) being biological polymers have attracted great attention. PHA have similar properties to that of synthetic plastic and are biodegradable. To discourage plastic pollution in the environment alternative solutions to the plastic pollution has to be readily available. High cost in production of PHA limits the production of these polymers at industrial scale. Bacteria are screened for PHA from diverse niches to meet the current requirements of cheap PHA production at industrial level. The microbial biofilm formed on the surface of microplastic could be a potential source in providing bacteria of economic importance. This paper is an attempt to search microplastic niche for potential PHA producers. PHA production variation was observed with different parameters such as type of carbon source, nitrogen source concentration and also time of incubation. Bacillus sp. CM27 showed maximum PHA yield up to 32.1% among other isolates at 48 h with 2% glucose as carbon source. Optimization of media leads to increase in PHA yield (37.69%) of CDW in Bacillus sp. CM27. Amino acid sequence of Bacillus sp.CM27 showed the presence of PhaC box with sequence, G-Y-C-M-G-G having cysteine in the middle of the box. The extracted polymer was confirmed by FTIR spectroscopy.

Pure cultures for synthetic culture development: Next level municipal waste treatment for polyhydroxyalkanoates production

Polyhydroxyalkanoates (PHAs), as bio-based plastics, promise a transition from petroleum products to green and sustainable alternatives. However, their commercial production is yet impeded by high production costs. In this study, we assessed synthetic culture in mono and co-culture modes for bacterial PHA production. It was demonstrated that volatile fatty acids (VFAs) derived from food waste and primary sludge are cheap carbon sources for maintaining high production yields in the synthetic cultures. The maximum obtained PHA was 77.54 ± 5.67% of cell dried weight (CDW) (1.723 g/L) from Cupriavidus necator and 54.9 ± 3.66% of CDW (1.088 g/L) from Burkholderia cepacia. The acquired results are comparable to those in literature using sugar substrates. Comparatively, lower PHA productions were obtained from the co-cultivations ranging between 36-45 CDW% (0.39-0.48 g/L). Meanwhile, the 3-hydroxyvalerate content in the biopolymers were increased up to 21%.

Comparative Characterization and Identification of Poly-3-hydroxybutyrate Producing Bacteria with Subsequent Optimization of Polymer Yield

In this work, the strains Bacillus megaterium RAZ 3, Azotobacter chrocococcum Az 3, Bacillus araybhattay RA 5 were used as an effective producer of poly-3-hydroxybutyrate P(3HB). The purpose of the study was to isolate and obtain an effective producer of P(3HB) isolated from regional chestnut soils of northern Kazakhstan. This study demonstrates the possibility of combining the protective system of cells to physical stress as a way to optimize the synthesis of PHA by strains. Molecular identification of strains and amplification of the phbC gene, transmission electron microscope (TEM), extracted and dried PHB were subjected to Fourier infrared transmission spectroscopy (FTIR). The melting point of the isolated P(3HB) was determined. The optimal concentration of bean broth for the synthesis of P(3HB) for the modified type of Bacillus megaterium RAZ 3 was 20 g/L, at which the dry weight of cells was 25.7 g/L⁻¹ and P(3HB) yield of 13.83 g/L⁻¹, while the percentage yield of P(3HB) was 53.75%. The FTIR spectra of the extracted polymer showed noticeable peaks at long wavelengths. Based on a proof of concept, this study demonstrates encouraging results.

Insightful Advancement and Opportunities for Microbial Bioplastic Production

Impetuous urbanization and population growth are driving increased demand for plastics to formulate impeccable industrial and biomedical commodities. The everlasting nature and excruciating waste management of petroleum-based plastics have catered to numerous challenges for the environment. However, just implementing various end-of-life management techniques for assimilation and recycling plastics is not a comprehensive remedy; instead, the extensive reliance on finite resources needs to be reduced for sustainable production and plastic product utilization. Microorganisms, such as bacteria and algae, are explored substantially for their bioplastic production repertoire, thus replacing fossil-based plastics sooner or later. Nevertheless, the utilization of pure microbial cultures has led to various operational and economical complications, opening the ventures for the usage of mixed microbial cultures (MMCs) consisting of bacteria and algae for sustainable production of bioplastic. The current review is primarily focuses on elaborating the bioplastic production capabilities of different bacterial and algal strains, followed by discussing the quintessence of MMCs. The present state-of-the-art of bioplastic, different types of bacterial bioplastic, microalgal biocomposites, operational factors influencing the quality and quantity of bioplastic precursors, embracing the potential of bacteria-algae consortia, and the current global status quo of bioplastic production has been summarized extensively.

Absence of KpsM (Slr0977) Impairs the Secretion of Extracellular Polymeric Substances (EPS) and Impacts Carbon Fluxes in Synechocystis sp. PCC 6803

Many cyanobacteria produce extracellular polymeric substances (EPS), composed mainly of heteropolysaccharides, that play a variety of physiological roles, being crucial for cell protection, motility, and biofilm formation. However, due to their complexity, the EPS biosynthetic pathways as well as their assembly and export mechanisms are still far from being fully understood. Here, we show that the absence of a putative EPS-related protein, KpsM (Slr0977), has a pleiotropic effect on Synechocystis sp. strain PCC 6803 physiology, with a strong impact on the export of EPS and carbon fluxes. The kpsM mutant exhibits a significant reduction of released polysaccharides and a smaller decrease of capsular polysaccharides, but it accumulates more polyhydroxybutyrate (PHB) than the wild type. In addition, this strain shows a light/cell density-dependent clumping phenotype and exhibits an altered protein secretion capacity. Furthermore, the most important structural component of pili, the protein PilA, was found to have a modified glycosylation pattern in the mutant compared to the wild type. Proteomic and transcriptomic analyses revealed significant changes in the mechanisms of energy production and conversion, namely, photosynthesis, oxidative phosphorylation, and carbon metabolism, in response to the inactivation of slr0977 Overall, this work shows for the first time that cells with impaired EPS secretion undergo transcriptomic and proteomic adjustments, highlighting the importance of EPS as a major carbon sink in cyanobacteria. The accumulation of PHB in cells of the mutant, without affecting significantly its fitness/growth rate, points to its possible use as a chassis for the production of compounds of interest.IMPORTANCE Most cyanobacteria produce extracellular polymeric substances (EPS) that fulfill different biological roles depending on the strain/environmental conditions. The interest in the cyanobacterial EPS synthesis/export pathways has been increasing, not only to optimize EPS production but also to efficiently redirect carbon flux toward the production of other compounds, allowing the implementation of industrial systems based on cyanobacterial cell factories. Here, we show that a Synechocystis kpsM (slr0977) mutant secretes less EPS than the wild type, accumulating more carbon intracellularly, as polyhydroxybutyrate. Further characterization showed a light/cell density-dependent clumping phenotype, altered protein secretion, and modified glycosylation of PilA. The proteome and transcriptome of the mutant revealed significant changes, namely, in photosynthesis and carbon metabolism. Altogether, this work provides a comprehensive overview of the impact of kpsM disruption on Synechocystis physiology, highlighting the importance of EPS as a carbon sink and showing how cells adapt when their secretion is impaired, and the redirection of the carbon fluxes.

Recent advances in polyhydroxyalkanoate production: Feedstocks, strains and process developments

Polyhydroxyalkanoates (PHAs) have been actively studied in academia and industry for their properties comparable to petroleum-derived plastics and high biocompatibility. However, the major limitation for commercialization is their high cost. Feedstock costs, especially carbon costs, account for the majority of the final cost. Finding cheap feedstocks for PHA production and associated process development are critical for a cost-effective PHA production. In this study, waste materials from different sources, particularly lignocellulosic biomass, were proposed as suitable feedstocks for PHA production. Strains involved in the conversion of these feedstocks into PHA were reviewed. Newly isolated strains were emphasized. Related process development, including the factors that affect PHA production, fermentation modes and downstream processing, was elaborated upon.

Response surface method for polyhydroxybutyrate (PHB) bioplastic accumulation in Bacillus drentensis BP17 using pineapple peel

Polyhydroxybutyrate (PHB) is a biodegradable biopolymer which is useful for various applications including packing, medical and coating materials. An endospore-forming bacterium (strain BP17) was isolated from composted soil and evaluated for PHB production. Strain BP17, taxonomically identified as Bacillus drentensis, showed enhanced PHB accumulation and was selected for further studies. To achieve maximum PHB production, the culture conditions for B. drentensis BP17 were optimized through response surface methodology (RSM) employing central composite rotatable design (CCRD). The final optimum fermentation conditions included: pineapple peel solution, 11.5% (v/v); tryptic soy broth (TSB), 60 g/L; pH, 6.0; inoculum size, 10% (v/v) and temperature, 28°C for 36 h. This optimization yielded 5.55 g/L of PHB compared to the non-optimized condition (0.17 g/L). PHB accumulated by B. drentensis BP17 had a polydispersity value of 1.59 and an average molecular weight of 1.15x105 Da. Thermal analyses revealed that PHB existed as a thermally stable semi-crystalline polymer, exhibiting a thermal degradation temperature of 228°C, a melting temperature of 172°C and an apparent melting enthalpy of fusion of 83.69 J/g. It is evident that B. drentensis strain BP17 is a promising bacterium candidate for PHB production using agricultural waste, such as pineapple peel as a low-cost alternative carbon source for PHB production.

A glimpse of biodegradable polymers and their biomedical applications

Over the past two decades, biodegradable polymers (BPs) have been widely used in biomedical applications such as drug carrier, gene delivery, tissue engineering, diagnosis, medical devices, and antibacterial/antifouling biomaterials. This can be attributed to numerous factors such as chemical, mechanical and physiochemical properties of BPs, their improved processibility, functionality and sensitivity towards stimuli. The present review intended to highlight main results of research on advances and improvements in terms of synthesis, physical properties, stimuli response, and/or applicability of biodegradable plastics (BPs) during last two decades, and its biomedical applications. Recent literature relevant to this study has been cited and their developing trends and challenges of BPs have also been discussed.

Optimization of Ralstonia solanacearum cell growth using a central composite rotational design for the P(3HB) production: Effect of agitation and aeration

The intracellular accumulation of polyhydroxyalkanoates (PHAs) normally occurs after cell growth, during the second fermentation stage and under nutrient-limited conditions in the presence of a carbon excess. However, some microorganisms are able to accumulate PHAs as poly(3-hydroxybutyrate) [P(3HB)] during the first fermentation stage, the cell growth phase, without nutrient limitation, once they have been reported to utilize type II metabolism during the polymer accumulation phase. This study evaluated the effect of aeration and agitation on cell growth and P(3HB) accumulation in Ralstonia solanacearum RS, performed in a bioreactor for 24h at 32°C. A 2² central composite rotational design (CCRD) was used, with agitation (150 to 250 rpm) and aeration (0.3 to 1 vvm) as independent variables and optical density (OD_600nm), dry cell weight (DCW), and P(3HB) yield as dependent variables. A significant polymer accumulation, until 70% of P(3HB), was observed, proving that R. solanacearum RS exhibited metabolism type II, regardless of the aeration process. The best results were obtained for 1 vvm and 250 rpm (+1, +1), with values of OD_600nm (18.04) and DCW (4.82 g.L^-1).

Carbon flux to growth or polyhydroxyalkanoate synthesis under microaerophilic conditions is affected by fatty acid chain-length in Pseudomonas putida LS46

Economical production of medium-chain length polyhydroxyalkanoates (mcl-PHA) is dependent on efficient cultivation processes. This work describes growth and mcl-PHA synthesis characteristics of Pseudomonas putida LS46 when grown on medium-chain length fatty acids (octanoic acid) and lower-cost long-chain fatty acids (LCFAs, derived from hydrolyzed canola oil) in microaerophilic environments. Growth on octanoic acid ceased when the oxygen uptake rate was limited by the oxygen transfer rate, and mcl-PHA accumulated to 61.9% of the cell dry mass. From LCFAs, production of non-PHA cell mass continued at a rate of 0.36 g L^-1 h^-1 under oxygen-limited conditions, while mcl-PHA accumulated simultaneously to 31% of the cell dry mass. The titer of non-PHA cell mass from LCFAs at 14 h post-inoculation was double that obtained from octanoic acid in bioreactors operated with identical feeding and aeration conditions. While the productivity for octanoic acid was higher by 14 h, prolonged cultivation on LCFAs achieved similar productivity but with twice the PHA titer. Simultaneous co-feeding of each substrate demonstrated the continued cell growth under microaerophilic conditions characteristic of LCFAs, and the resulting polymer was dominant in C8 monomers. Furthermore, co-feeding resulted in improved PHA titer and volumetric productivity compared to either substrate individually. These results suggest that LCFAs improve growth of P. putida in oxygen-limited environments and could reduce production costs since more non-PHA cell mass, the cellular factories required to produce mcl-PHA and the most oxygen-intensive cellular process, can be produced for a given oxygen transfer rate.

Efficient polyhydroxybutyrate production from Bacillus juice substrate thuringiensis using sugarcane

The present study focused on the screening and optimization of biopolymer polyhydroxybutyrate (PHB) production by Bacillus spp. using cost-effective substrates. Among 602 local Bacillus isolates, Bacillus thuringiensis B417-5 produced the highest amount of PHB (2.278 g/L, 60.07% of dry cell weight, DCW). 1H NMR and FTIR analyses of the extracted polymer revealed the characteristic peaks of PHB. The optimization results showed that the highest PHB accumulation (2.768 g/L, 72.08% of DCW) was achieved when culturing B. thuringiensis B417-5 in a nitrogen-deficient medium containing 1% total sugar from sugarcane juice and 0.5% yeast extract, with a pH of 7.0 and an incubation temperature of 37 °C for 48 h. B. thuringiensis B417-5 can thus be considered a good candidate for large-scale production of PHB. We are reporting for the first time that sugarcane juice is a promising carbon source for economical PHB production by B. thuringiensis.

Standardization of biopolymer production from seaweed associative bacteria

Polyhydroxyalkanoate (PHA) is the biodegradable plastic, which is shown the similar properties to the synthetic plastic. Production of PHA is expensive when compared with petrochemical based plastics costs and also hazardous to ecosystem. In order to overcome these drawbacks, some cheaper commercially available carbon sources like rice bran, coconut cake, palm jaggary, etc. can be used. The present study aimed to identify the potential PHA producing bacterial strains from different seaweeds. Based on PHA production and crotonic acid assay, two bacterial strains were screened and designated as M3 and S6 which were found to be efficient PHA producers. Potential PHA producers of M3 and S6 were identified as Bacillus cereus RBL6 and Pseudomonas pseudoalcaligens RBL7 by 16S rRNA gene sequencing. The physical and nutritional parameters such as pH, temperature, incubation period, substrate, carbon and nitrogen concentration have been used for enhancing PHA production which was served as precursor. The purified PHA had been chemically characterized by FT-IR, GC-MS and viewed through SEM.

Lipid accumulation in prokaryotic microorganisms from arid habitats

This review shall provide support for the suitability of arid environments as preferred location to search for unknown lipid-accumulative bacteria. Bacterial lipids are attracting more and more attention as sustainable replacement for mineral oil in fuel and plastic production. The development of prokaryotic microorganisms in arid desert habitats is affected by its harsh living conditions. Drought, nutrient limitation, strong radiation, and extreme temperatures necessitate effective adaption mechanisms. Accumulation of storage lipids as energy reserve and source of metabolic water represents a common adaption in desert animals and presumably in desert bacteria and archaea as well. Comparison of corresponding literature resulted in several bacterial species from desert habitats, which had already been described as lipid-accumulative elsewhere. Based on the gathered information, literature on microbial communities in hot desert, cold desert, and humid soil were analyzed on its content of lipid-accumulative bacteria. With more than 50% of the total community size in single studies, hot deserts appear to be more favorable for lipid-accumulative species then humid soil (≤20%) and cold deserts (≤17%). Low bacterial lipid accumulation in cold deserts is assumed to result from the influence of low temperatures on fatty acids and the increased necessity of permanent adaption methods.

Class IV polyhydroxyalkanoate (PHA) synthases and PHA-producing Bacillus

This review highlights the recent investigations of class IV polyhydroxyalkanoate (PHA) synthases, the newest classification of PHA synthases. Class IV synthases are prevalent in organisms of the Bacillus genus and are composed of a catalytic subunit PhaC (approximately 40 kDa), which has a PhaC box sequence ([GS]-X-C-X-[GA]-G) at the active site, and a second subunit PhaR (approximately 20 kDa). The representative PHA-producing Bacillus strains are Bacillus megaterium and Bacillus cereus; the nucleotide sequence of phaC and the genetic organization of the PHA biosynthesis gene locus are somewhat different between these two strains. It is generally considered that class IV synthases favor short-chain-length monomers such as 3-hydroxybutyrate (C4) and 3-hydroxyvalerate (C5) for polymerization, but can polymerize some unusual monomers as minor components. In Escherichia coli expressing PhaRC from B. cereus YB-4, the biosynthesized PHA undergoes synthase-catalyzed alcoholytic cleavage using endogenous and exogenous alcohols. This alcoholysis is thought to be shared among class IV synthases, and this reaction is useful not only for the regulation of PHA molecular weight but also for the modification of the PHA carboxy terminus. The novel properties of class IV synthases will open up the possibility for the design of new PHA materials.

Engineering Halomonas TD01 for the low-cost production of polyhydroxyalkanoates

The halophile Halomonas TD01 and its derivatives have been successfully developed as a low-cost platform for the unsterile and continuous production of chemicals. Therefore, to increase the genetic engineering stability of this platform, the DNA restriction/methylation system of Halomonas TD01 was partially inhibited. In addition, a stable and conjugative plasmid pSEVA341 with a high-copy number was constructed to contain a LacI(q)-Ptrc system for the inducible expression of multiple pathway genes. The Halomonas TD01 platform, was further engineered with its 2-methylcitrate synthase and three PHA depolymerases deleted within the chromosome, resulting in the production of the Halomonas TD08 strain. The overexpression of the threonine synthesis pathway and threonine dehydrogenase made the recombinant Halomonas TD08 able to produce poly(3-hydroxybutyrate-co-3-hydroxyvalerate) or PHBV consisting of 4-6 mol% 3-hydroxyvalerate or 3 HV, from various carbohydrates as the sole carbon source. The overexpression of the cell division inhibitor MinCD during the cell growth stationary phase in Halomonas TD08 elongated its shape to become at least 1.4-fold longer than its original size, resulting in enhanced PHB accumulation from 69 wt% to 82 wt% in the elongated cells, further promoting gravity-induced cell precipitations that simplify the downstream processing of the biomass. The resulted Halomonas strains contributed to further reducing the PHA production cost.

clpC operon regulates cell architecture and sporulation in Bacillus anthracis

The clpC operon is known to regulate several processes such as genetic competence, protein degradation and stress survival in bacteria. Here, we describe the role of clpC operon in Bacillus anthracis. We generated knockout strains of the clpC operon genes to investigate the impact of CtsR, McsA, McsB and ClpC deletion on essential processes of B. anthracis. We observed that growth, cell division, sporulation and germination were severely affected in mcsB and clpC deleted strains, while none of deletions affected toxin secretion. Growth defect in these strains was pronounced at elevated temperature. The growth pattern gets restored on complementation of mcsB and clpC in respective mutants. Electron microscopic examination revealed that mcsB and clpC deletion also causes defect in septum formation leading to cell elongation. These vegetative cell deformities were accompanied by inability of mutant strains to generate morphologically intact spores. Higher levels of polyhydroxybutyrate granules accumulation were also observed in these deletion strains, indicating a defect in sporulation process. Our results demonstrate, for the first time, the vital role played by McsB and ClpC in physiology of B. anthracis and open up further interest on this operon, which might be of importance to success of B. anthracis as pathogen.

Microbial synthesis of functional homo-, random, and block polyhydroxyalkanoates by β-oxidation deleted Pseudomonas entomophila

Functional polyhydroxyalkanoates (PHAs) allow chemical modifications to widen PHA diversity, promising to increase values of these biodegradable and biocompatible polyesters. Among functional PHAs, unsaturated PHA site chains can be easily grafted to add chemical groups, and to cross-link with other PHA polymer chains. However, it has been very difficult to obtain structurally controllable functional homo-, random, or block PHA. For the first time, a β-oxidation deleted Pseudomonas entomophila was used to successfully synthesize random copolymers of 3-hydroxydodecanoate (3HDD) and 3-hydroxy-9-decenoate (3H9D). Compositions of the random copolymers P(3HDD-co-3H9D) can be adjusted by ratios of dodecanoic acid (DDA) to 9-decenol (9DEO) fed to the culture of P. entomophila. Homopolymer P3H9D was formed when only 9DEO was added to the culture. Diblock copolymers of P3HDD-b-P3H9D were produced by feeding DDA as the first precursor to form a P3HDD block followed by adding 9DEO as the second precursor to form a second P3H9D block. It was demonstrated that random copolymers P(3HDD-co-3H9D) could be crossed-linked under UV-radiation due to the presence of the unsaturated bonds. Thermal and mechanical characterizations of the above homo-, random, and diblock PHA polymers were conducted. It was found that the diblock polymer P3HDD-b-P3H9D increased at least 2-fold on Young's modulus compared with its random copolymers consisting of similar 3HDD/3H9D ratios. This study demonstrates that PHA functionality could be controlled to meet various requirements.

Poly β-hydroxybutyrate production by Bacillus subtilis NG220 using sugar industry waste water

The production of poly β-hydroxybutyrate (PHB) by Bacillus subtilis NG220 was observed utilizing the sugar industry waste water supplemented with various carbon and nitrogen sources. At a growth rate of 0.14 g h(-1) L(-1), using sugar industry waste water was supplemented with maltose (1% w/v) and ammonium sulphate (1% w/v); the isolate produced 5.297 g/L of poly β-hydroxybutyrate accumulating 51.8% (w/w) of biomass. The chemical nature of the polymer was confirmed with nuclear magnetic resonance, Fourier transform infrared, and GC-MS spectroscopy whereas thermal properties were monitored with differential scanning calorimetry. In biodegradability study, when PHB film of the polymer (made by traditional solvent casting technique) was subjected to degradation in various natural habitats like soil, compost, and industrial sludge, it was completely degraded after 30 days in the compost having 25% (w/w) moisture. So, the present study gives insight into dual benefits of conversion of a waste material into value added product, PHB, and waste management.

Polyhydroxybutyrate production in Bacillus mycoides DFC1 using response surface optimization for physico-chemical process parameters

The production of polyhydroxybutyrate (PHB) by Bacillus sp. is most often growth associated and is influenced by various physico-chemical parameters. Imbalanced nutrient conditions were often found to result in sporulation and low PHB production in Bacillus sp. In the present investigation, Bacillus mycoides DFC1 strain isolated from garden soil was studied for PHB production in glucose–peptone broth. The effect of glucose/peptone ratio on biomass yield, PHB production and sporulation was investigated. Central composite rotatable design was used to study the interactive effects of three variables: glucose, peptone and pH on cell growth and PHB production. The optimized medium conditions with the constraint ‘to maximize’ cell growth and PHB content were glucose 17.34 g/l, peptone 7.03 g/l at pH 7.3. A maximum dry cell weight of 4.35 g/l and PHB yield of 3.32 g/l amounting to 76.32 % (w/w) of dry cell weight with negligible sporulation at the end of 72 h resulted in a significant increase (1.83–3.32 g/l or 1.82-fold) in the production of PHB in comparison to the medium used in preliminary studies.

Utilization of molasses spentwash for production of bioplastics by waste activated sludge

Present study describes the treatment of molasses spentwash and its use as a potential low cost substrate for production of biopolymer polyhydroxybutyrate (PHB) by waste activated sludge. Fluorescence microscopy revealed the presence of PHB granules in sludge biomass which was further confirmed by fourier transform-infra-red spectroscopy (FT-IR) and (13)C nuclear magnetic resonance (NMR). The processing of molasses spentwash was carried out for attaining different ratios of carbon and nitrogen (C:N). Highest chemical oxygen demand (COD) removal and PHB accumulation of 60% and 31% respectively was achieved with raw molasses spentwash containing inorganic nitrogen (C:N ratio=28) followed by COD removal of 52% and PHB accumulation of 28% for filtered molasses containing inorganic nitrogen (C:N ratio=29). PHB production yield (Y(p/s)) was highest (0.184 g g(-1) COD consumed) for deproteinized spentwash supplemented with nitrogen. In contrast, the substrate consumption and product formation were higher in case of raw spentwash. Though COD removal was lowest from deproteinized spentwash, evaluation of kinetic parameters suggested higher rates of conversion of available carbon to biomass and PHB. Thus the process provided dual benefit of conversion of two wastes viz. waste activated sludge and molasses spentwash into value-added product-PHB.

Bacillus subtilis as potential producer for polyhydroxyalkanoates

Polyhydroxyalkanoates (PHAs) are biodegradable polymers produced by microbes to overcome environmental stress. Commercial production of PHAs is limited by the high cost of production compared to conventional plastics. Another hindrance is the brittle nature and low strength of polyhydroxybutyrate (PHB), the most widely studied PHA. The needs are to produce PHAs, which have better elastomeric properties suitable for biomedical applications, preferably from inexpensive renewable sources to reduce cost. Certain unique properties of Bacillus subtilis such as lack of the toxic lipo-polysaccharides, expression of self-lysing genes on completion of PHA biosynthetic process – for easy and timely recovery, usage of biowastes as feed enable it to compete as potential candidate for commercial production of PHA.