SciCombinator

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Journal: Applied microbiology and biotechnology

172

ω-3 fatty acid desaturase is a key enzyme for the biosynthesis of ω-3 polyunsaturated fatty acids via the oxidative desaturase/elongase pathways. Here we report the identification of three ω-3 desaturases from oomycetes, Pythium aphanidermatum, Phytophthora sojae, and Phytophthora ramorum. These new ω-3 desaturases share 55 % identity at the amino acid level with the known Δ-17 desaturase of Saprolegnia diclina, and about 31 % identity with the bifunctional Δ-12/Δ-15 desaturase of Fusarium monoliforme. The three enzymes were expressed in either wild-type or codon optimized form in an engineered arachidonic acid producing strain of Yarrowia lipolytica to study their activity and substrate specificity. All three were able to convert the ω-6 arachidonic acid to the ω-3 eicosapentanoic acid, with a substrate conversion efficiency of 54-65 %. These enzymes have a broad ω-6 fatty acid substrate spectrum, including both C18 and C20 ω-6 fatty acids although they prefer the C20 substrates, and have strong Δ-17 desaturase activity but weaker Δ-15 desaturase activity. Thus, they belong to the Δ-17 desaturase class. Unlike the previously identified bifunctional Δ-12/Δ-15 desaturase from F. monoliforme, they lack Δ-12 desaturase activity. The newly identified Δ-17 desaturases could use fatty acids in both acyl-CoA and phospholipid fraction as substrates. The identification of these Δ-17 desaturases provides a set of powerful new tools for genetic engineering of microbes and plants to produce ω-3 fatty acids, such as eicosapentanoic acid and docosahexanoic acid, at high levels.

Concepts: Amino acid, Nutrition, Fatty acid, Enzyme, Fatty acids, Essential fatty acid, Docosahexaenoic acid, Water moulds

164

Apart from being applied as an energy carrier, hydrogen is in increasing demand as a commodity. Currently, the majority of hydrogen (H2) is produced from fossil fuels, but from an environmental perspective, sustainable H2 production should be considered. One of the possible ways of hydrogen production is through fermentation, in particular, at elevated temperature, i.e. thermophilic biohydrogen production. This short review recapitulates the current status in thermophilic biohydrogen production through fermentation of commercially viable substrates produced from readily available renewable resources, such as agricultural residues. The route to commercially viable biohydrogen production is a multidisciplinary enterprise. Microbiological studies have pointed out certain desirable physiological characteristics in H2-producing microorganisms. More process-oriented research has identified best applicable reactor types and cultivation conditions. Techno-economic and life cycle analyses have identified key process bottlenecks with respect to economic feasibility and its environmental impact. The review has further identified current limitations and gaps in the knowledge, and also deliberates directions for future research and development of thermophilic biohydrogen production.

Concepts: Agriculture, Hydrogen, Research, Anaerobic digestion, Fermentative hydrogen production, Hydrogen production, Dark fermentation, Biohydrogen

111

There is increasing interest in the use of beneficial microorganisms as alternatives to chemical pesticides and synthetic fertilisers in agricultural production. Application of beneficial microorganisms to seeds is an efficient mechanism for placement of microbial inocula into soil where they will be well positioned to colonise seedling roots and protect against soil-borne diseases and pests. However, despite the long history of inoculation of legume seeds with Rhizobia spp. and clear laboratory demonstration of the ability of a wide range of other beneficial microorganisms to improve crop performance, there are still very few commercially available microbial seed inoculants. Seed inoculation techniques used for research purposes are often not feasible at a commercial scale and there are significant technical challenges in maintaining viable microbial inocula on seed throughout commercial seed treatment processes and storage. Further research is needed before the benefits of a wide range of environmentally sensitive potential seed inoculants can be captured for use in agriculture, ecosystem restoration and bioremediation. There is no single solution to the challenge of improving the ability of seed inoculants to establish and function consistently in the field. Development of novel formulations that maintain the viability of both inoculant and seed during storage will result from multidisciplinary research in microbial and seed physiology and adjuvant chemistry.

Concepts: Agriculture, Improve, Microbiology, Chemistry, Nitrogen, Fabaceae, Seed, Legume

28

Cyclodextrins (CD) are cyclic α-1,4-glucans composed of glucose units, and they have multiple applications in food, pharmaceuticals, cosmetics, agriculture, chemicals, etc. CD are usually produced by cyclodextrin glycosyltransferase (CGTase) from starch. In the present study, a simultaneous conversion approach was developed to improve the yield of CD from starch by conjunction use of isoamylase with α-CGTase. The isoamylase of Thermobifida fusca was cloned and expressed in Escherichia coli BL21(DE3). The biochemical characterization of the enzyme showed that the optimum temperature and pH of the recombinant enzyme was 50 °C and 5.5, respectively, and it maintained 60 %, 85 % and 78 % relative activity at 30 °C, 40 °C and 60 °C, respectively. When the recombinant isoamylase and α-CGTase were used simultaneously to convert potato starch (15 %, w/v) into CD, the optimum conditions were found to be: 10 U of α-CGTase and 48 U of isoamylase per gram of substrate, with reaction temperature of 30 °C and pH 5.6. On the optimum condition, the total yield of CD reached 84.6 % (w/w) after 24 h, which was 31.2 % higher than transformation with α-CGTase alone. This is the first report of synchronous bioconversion of CD by both α-CGTase and isoamylase, and represents the highest efficiency of CD production reported so far.

Concepts: Molecular biology, Enzyme, Glucose, Escherichia coli, Starch, Potato, Cyclodextrin, Cyclodextrin glycosyltransferase

28

Haloarchaeal alcohol dehydrogenases are exciting biocatalysts with potential industrial applications. In this study, two alcohol dehydrogenase enzymes from the extremely halophilic archaeon Haloferax volcanii (HvADH1 and HvADH2) were homologously expressed and subsequently purified by immobilized metal-affinity chromatography. The proteins appeared to copurify with endogenous alcohol dehydrogenases, and a double Δadh2 Δadh1 gene deletion strain was constructed to prevent this occurrence. Purified HvADH1 and HvADH2 were compared in terms of stability and enzymatic activity over a range of pH values, salt concentrations, and temperatures. Both enzymes were haloalkaliphilic and thermoactive for the oxidative reaction and catalyzed the reductive reaction at a slightly acidic pH. While the NAD(+)-dependent HvADH1 showed a preference for short-chain alcohols and was inherently unstable, HvADH2 exhibited dual cofactor specificity, accepted a broad range of substrates, and, with respect to HvADH1, was remarkably stable. Furthermore, HvADH2 exhibited tolerance to organic solvents. HvADH2 therefore displays much greater potential as an industrially useful biocatalyst than HvADH1.

Concepts: Protein, Alcohol, Metabolism, Enzyme, Ethanol, Catalysis, PH, Alcohol dehydrogenase

28

The nanopattern on the surface of Clanger cicada (Psaltoda claripennis) wings represents the first example of a new class of biomaterials that can kill bacteria on contact based solely on its physical surface structure. As such, they provide a model for the development of novel functional surfaces that possess an increased resistance to bacterial contamination and infection. Their effectiveness against a wide spectrum of bacteria, however, is yet to be established. Here, the bactericidal properties of the wings were tested against several bacterial species, possessing a range of combinations of morphology and cell wall type. The tested species were primarily pathogens, and included Bacillus subtilis, Branhamella catarrhalis, Escherichia coli, Planococcus maritimus, Pseudomonas aeruginosa, Pseudomonas fluorescens, and Staphylococcus aureus. The wings were found to consistently kill Gram-negative cells (i.e., B. catarrhalis, E. coli, P. aeruginosa, and P. fluorescens), while Gram-positive cells (B. subtilis, P. maritimus, and S. aureus) remained resistant. The morphology of the cells did not appear to play any role in determining cell susceptibility. The bactericidal activity of the wing was also found to be quite efficient; 6.1 ± 1.5 × 10(6) P. aeruginosa cells in suspension were inactivated per square centimeter of wing surface after 30-min incubation. These findings demonstrate the potential for the development of selective bactericidal surfaces incorporating cicada wing nanopatterns into the design.

Concepts: Bacteria, Antibiotic resistance, Escherichia coli, Pseudomonas aeruginosa, Cell wall, Bacillus, Gram negative bacteria, Firmicutes

28

Three probiotic Lactobacillus strains, Lactobacillus acidophilus, Lactobacillus plantarum, and Lactobacillus delbrueckii, were tested for their ability to assimilate and metabolize glycerol. Biodiesel-derived glycerol was used as the main carbon and energy source in batch microaerobic growth. Here, we show that the tested strains were able to assimilate glycerol, consuming between 38 and 48 % in approximately 24 h. L. acidophilus and L. delbrueckii showed a similar growth, higher than L. plantarum. The highest biomass reached was 2.11 g L(-1) for L. acidophilus, with a cell mass yield (Y (X/S)) of 0.37 g g(-1). L. delbrueckii and L. plantarum reached a biomass of 2.06 and 1.36 g L(-1). All strains catabolize glycerol mainly through glycerol kinase (EC 2.7.1.30). For these lactobacillus species, kinetic parameters for glycerol kinase showed Michaelis-Menten constant (K (m)) ranging from 1.2 to 3.8 mM. The specific activities for glycerol kinase in these strains were in the range of 0.18 to 0.58 U mg protein(-1), with L. acidophilus ATCC 4356 showing the maximum specific activity after 24 h of cultivation. Glycerol dehydrogenase activity was also detected in all strains studied but only for the reduction of glyceraldehyde with NADPH (K (m) for DL-glyceraldehyde ranging from 12.8 to 32.3 mM). This enzyme shows a very low oxidative activity with glycerol and NADP(+) and, most likely, under physiological conditions, the oxidative reaction does not occur, supporting the assumption that the main metabolic flux concerning glycerol metabolism is through the glycerol kinase pathway.

Concepts: Metabolism, Enzyme, Microbiology, Probiotic, Lactobacillus, Lactobacillus plantarum, Lactobacillus acidophilus, Lactobacillaceae

28

India is the fifth largest primary energy consumer and fourth largest petroleum consumer after USA, China, and Japan. Despite the global economic crisis, India’s economy is expected to grow at 6 to 8 %/year. There is an extreme dependence on petroleum products with considerable risks and environmental issues. Petroleum-derived transport fuels are of limited availability and contribute to global warming, making renewable biofuel as the best alternative. The focus on biogas and biomass-based energy, such as bioethanol and biohydrogen, will enhance cost-effectiveness and provide an opportunity for the rural community. Among all energy sources, microalgae have received, so far, more attention due to their facile adaptability to grow in the photobioreactors or open ponds, high yields, and multiple applications. Microalgae can produce a substantial amount of triacylglycerols as a storage lipid under photooxidative stress or other adverse environmental conditions. In addition to renewable biofuels, they can provide different types of high-value bioproducts added to their advantages, such as higher photosynthetic efficiency, higher biomass production, and faster growth compared to any other energy crops. The viability of first-generation biofuels production is, however, questionable because of the conflict with food supply. In the future, biofuels should ideally create the environmental, economic, and social benefits to the communities and reflect energy efficiency so as to plan a road map for the industry to produce third-generation biofuels.

Concepts: Petroleum, Anaerobic digestion, Biogas, Biofuel, Renewable energy, Ethanol fuel, Biomass, Fuels

28

Frustules, the silica shells of diatoms, have unique porous architectures with good mechanical strength. In recent years, biologists have learned more about the mechanism of biosilica shells formation; meanwhile, physicists have revealed their optical and microfluidic properties, and chemists have identified ways to modify them into various materials while maintaining their hierarchical structures. These efforts have provided more opportunities to use biosilica structures in microsystems and other commercial products. This review focuses on the preparation of biosilica structures and their applications, especially in the development of microdevices. We discuss existing methods of extracting biosilica from diatomite and diatoms, introduce methods of separating biosilica structures by shape and sizes, and summarize recent studies on diatom-based devices used for biosensing, drug delivery, and energy applications. In addition, we introduce some new findings on diatoms, such as the elastic deformable characteristics of biosilica structures, and offer perspectives on planting diatom biosilica in microsystems.

Concepts: Structure, Silicon, Strength of materials, Diatom, Diatoms, Silicic acid, Frustule, Diatomaceous earth

28

Root colonization by antagonistic bacteria is a prerequisite for successful biological control, and the instability of colonization under varying environmental conditions has accentuated the need to improve the colonization activity. Root colonization by Bacillus spp. is mainly determined by chemotaxis and biofilm formation, and both functions are negatively controlled by the global transcription regulator AbrB. Here, we disrupted the gene abrB in Bacillus amyloliquefaciens SQR9, which has been proven to be a promising biocontrol agent of cucumber and watermelon wilt disease. Chemotaxis, biofilm formation, and colonization activities as well as biocontrol efficiency were measured and compared between the wild-type strain of SQR9 and the abrB mutant. The data presented in this article demonstrate that the colonization and biocontrol activity of B. amyloliquefaciens SQR9 could be significantly improved by abrB gene disruption. The results offer a new strategy to enhance the biocontrol efficacy of B. amyloliquefaciens SQR9.

Concepts: DNA, Gene, Archaea, Bacteria, Microbiology, Bacillus, Biological pest control, Bacillus amyloliquefaciens