Biodegradable materials with plastic or elastomeric properties are in great demand for a variety of applications. Polyhydroxyalkanoates (PHAs), polyesters synthesized by microorganisms, possess such desired features. Industrial production of PHAs is currently achieved using recombinant Escherichia coli. Nevertheless, recent research on halophiles, salt requiring microorganisms, has shown a remarkable potential for biotechnological production of PHAs. The halophilic archaeon Haloferax mediterranei accumulates a co-polymer, i.e., poly(3-hydroxybutyrate-co-3-hydroxyvalerate) in large amounts using glucose, starch, and hydrolyzed whey as carbon sources. Chemical composition and molecular weight of PHAs produced by H. mediterranei can be modified depending on the substrate utilized as precursor. Phylogenetic studies on haloarchaeal enzymes able to polymerize the components of PHAs (i.e., PHA synthases) reveal a novel cluster, with a close relationship with PHA polymerases of bacteria and archaea found in marine-related niches. On the other hand, sequences of PHA synthases of two halophilic bacteria are more closely affiliated to synthases of Proteobacteria. Several bacterial species of the family Halomonadaceae accumulate PHAs. Halomonas boliviensis reached PHA yields and volumetric productivities close to the highest reported so far. Furthermore, H. boliviensis and other Halomonas species are able to co-produce PHA and osmolytes, i.e., ectoines and hydroxyectoine, in one process.

Synthesis and production of polyhydroxyalkanoates by halophiles: current potential and future prospects

This paper aims to develop a model for simulating the electric double layer dynamics in CV measurements while simultaneously accounting for transport phenomena in both the electrode and the electrolyte. It also aims (i) to identify the dimensionless parameters that govern the CV measurements, (ii) to provide a physical interpretation of the shape of CV curves, and (iii) to investigate the effect of the electrode electrical conductivity on the predicted double layer capacitance. The transient double layer dynamics was simulated using the modified Poisson–Nernst–Planck (MPNP) model with a Stern layer and accounting for the presence of the electrode. A dimensional analysis was performed and four dimensionless numbers governing the CV measurements were identified. This study established that the hump in CV curves for electrodes with large radius of curvature was due to the saturation of ion concentration near the electrode surface before reaching the maximum potential. It also demonstrates that CV curves became symmetric for large ion diffusion coefficient due to rapid ion transport. This study confirmed that the EDL capacitance retrieved from CV measurements is constant for low scan rates and corresponds to the capacitance under equilibrium conditions. Larger ion diffusion coefficient and electrode electrical conductivity led to larger EDL capacitance at large scan rates corresponding to better charging performance.

Physical Interpretation of Cyclic Voltammetry for Measuring Electric Double Layer Capacitances

Plastic pollution is a severe threat to our environment which necessitates implementation of bioplastics to realize sustainable development for a green world. Polyhydroxyalkanoates (PHA) represent one of the potential candidates for these bioplastics. However, a major challenge faced by PHA is the high production cost which limits its commercial application. Halophiles are considered to be a promising cell factory for PHA synthesis due to its several unique characteristics including high salinity requirement preventing microbial contamination, high intracellular osmotic pressure allowing easy cell lysis for PHA recovery, and capability to utilize wide spectrum of low-cost substrates. Optimization of fermentation parameters has made it plausible to achieve large-scale production at low cost by using halophiles. Further deeper insights into halophiles have revealed the existence of diversified and even novel PHA synthetic pathways within different halophilic species that greatly affects PHA type. Thus, precise metabolic engineering of halophiles with the help of advanced tools and strategies have led to more efficient microbial cell factory for PHA production. This review is an endeavour to summarize the various research achievements in these areas which will help the readers to understand the current developments as well as the future efforts in PHA research.

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Current developments on polyhydroxyalkanoates synthesis by using halophiles as a promising cell factory.

Production and characterization of a biodegradable poly (hydroxybutyrate-co-hydroxyvalerate) (PHB-co-PHV) copolymer by moderately haloalkalitolerant Halomonas campisalis MCM B-1027 isolated from Lonar Lake, India.

Polyhydroxyalkanoates (PHA) from Halomonas pacifica ASL10 and Halomonas salifodiane ASL11 isolated from Mariout salt lakes.

Halomonas marina HMA 103 (MTCC 8968), the moderately halophilic bacterium isolated and characterized from the solar saltern of Orissa, India, grows optimally at 10% (w/v) NaCl in culture medium and is able to synthesize poly(3-hydroxybutyrate) [P(3HB)] during growth. This study is an attempt to optimize the cultural conditions for efficient production of P(3HB) by H. marina in batch cultivation. Growth of the organism under shake-flask culture using 2% (w/v) glucose resulted in P(3HB) accumulation accounting for more than 59% of cell dry weight after 50 h of incubation. The optimum P(3HB) production was attained with a combined supply of NH4Cl and yeast extract as N-source, 0.01% (w/v) phosphate, 1.5% (w/v) sulphate and 10% (w/v) NaCl. Qualitative and quantitative 1HNMR and FT-IR analysis of cells grown in alkanoic acids (C3-C6) as sole source of carbon and co-substrates revealed synthesis of PHA co-polymers composed of 3-hydroxybutyric acid and 3-hydroxyvaleric acid [P(3HB-co-3HV)]. In two-step cultivation, accumulation of the co-polymer was significantly improved (80% CDW) in glucose medium supplemented with valerate (0.1%, w/v) as co-substrate and the polymer contained 88.1 and 12.8 mol% 3HB and 3HV monomers, respectively.

Production of poly-3-hydroxyalkanoic acids by a moderately halophilic bacterium, Halomonas marina HMA 103 isolated from solar saltern of Orissa, India.

High-rank coals are generally more floatable than low rank or oxidized coals due to their higher hydrophobicity. Surface oxidation of coals due to the exposure to atmospheric oxygen renders the sur...

Synergistic Effect of Polar Group Containing Collectors and Synthesized Frother on Flotation Performance of Oxidized Coal

Organic fluorescent semiconducting nanomaterials have gained widespread research interest owing to their potential applications in the arena of high-tech devices. We designed two pyrazaacene-based compounds, their stacked system, and the role of gluing interactions to fabricate nanomaterials, and determined the prospective band gaps utilizing the density functional theory calculation. The two pyrazaacene derivatives containing complementary amide linkages (-CONH and -NHCO) were efficiently synthesized. The synthesized compounds are highly soluble in common organic solvents as well as highly fluorescent and photostable. The heterocycles and their mixture displayed efficient solvent dependent fluorescence in the visible region of the solar spectrum. Notably, the compounds were associated through complementary NH•••O = C type hydrogen bonding, π-π stacking, and hydrophobic interactions, and thereby afforded nanomaterials with a low band gap. Fascinatingly, the fabricated stacked nanomaterial system exhibited resistive switching behavior, leading to the fabrication of an efficient write-once-read-many-times memory device of crossbar structure.

Complementary amide-based donor-acceptor with unique nano-scale aggregation, fluorescence, and band gap-lowering properties: a WORM memory device.

The author considers the problem of finding designs insensitive to the presence of an outlier in a treatment-control block design setup for estimating the set of elementary contrasts between the effects of each test treatment and a control treatment. The criterion of robustness suggested by Mandal (1989) in block design setup for estimating a full set of orthonormal treatment contrasts is adapted. A new class viz. partially balanced treatment incomplete block designs (PBTIBD) is introduced and it is shown that balanced treatment incomplete block designs (BTIBD) and PBTIB designs, under certain conditions, are robust in the previous sense. Such designs are important in the sense that the inference on the treatment contrasts under consideration remain unaffected by the presence of an outlier.

Block Designs Robust Against the Presence of an Aberration in a Treatment-Control Setup

Energy plays a key role in the development of modern civilization. The power generation and power consumption problems are solved by the energy-storage device technologies. Many capacitors, supercapacitors are already used for energy-storage devices, but our modern civilization demands low cost and environmentally friendly nanomaterials for high-tech devices. Recently, eco-friendly way to use sustainable energy is an important phase for modern energy economy. Continuous use of electronic devices is essential in the daily life of the highly demanding modern society. An essential requirement of fresh and proficient energy-storage technology will give us a substitute solution. Herein we discuss the low-cost eco-friendly nanomaterials for effective energy-storage devices, charge–discharge capacity as supercapacitors to help in daily human life.

Amrita Biswas

Papers

Production of poly-3-hydroxyalkanoic acids by a moderately halophilic bacterium, Halomonas marina HMA 103 isolated from solar saltern of Orissa, India.

Synergistic Effect of Polar Group Containing Collectors and Synthesized Frother on Flotation Performance of Oxidized Coal

Complementary amide-based donor-acceptor with unique nano-scale aggregation, fluorescence, and band gap-lowering properties: a WORM memory device.

Block Designs Robust Against the Presence of an Aberration in a Treatment-Control Setup

Eco-friendly cost-effective energy-storage device for the benefit of society