The aim of this work was to develop green and bioactive films with sodium alginate incorporating guava leaf extracts. Seven formulations were performed with a different sodium alginate: Guava leaf water extract (WE)/ethanolic extract (EE) proportions (100:0, 90:10, 85:15, 80:20), and glycerol were used as a plasticizer. The HPLC-PDA analysis showed the main phenolic compounds in WE were gallic acid, ellagic acid, quercetin-3-O-β-D-xylopyranoside, avicularin and quercetin. The main polyphenols in EE were rutin, isoquercitrin, quercetin-3-O-β-D-xylopyranoside, avicularin, quercitrin, quercetin and kaempferol. Guava leaf extracts could greatly enhance the antioxidant activity, antibacterial activity, tensile strength and water solubility of the sodium alginate film as well as the water barrier property, while inducing a decrease in the moisture content and elongation at the break. The FTIR and SEM analyses indicated that intermolecular hydrogen bonding between the guava leaf extract and sodium alginate resulted in a more compact structure in the composite films. These results indicated that sodium alginate-guava leaf extract films might be developed into antiradical and antimicrobial food packaging materials.
In2O3 is of particular interest as a wide-gap
transparent semiconductor oxide, in which the shallow donor defect
of the oxygen vacancy plays an important role in electronic properties.
Herein, we focus on the oxygen vacancy with various concentrations
in In2O3, where the distribution is found to
be crucial to the structural stabilities. For a specific supercell,
the formation energies of oxygen-vacancy pairs remarkably depend on
the distance between the two vacancies, which can be used to determine
the oxygen-vacancy distribution in the nonstoichiometric In2O3 structure. Interestingly, when two oxygen vacancies
share a same In atom, the structures are approximately stabilized
with the decreasing of distance. However, when two oxygen vacancies
are not attached to the same In atom, the structures become more stable
with the increasing of distance between vacancies. In addition, the
gap states induced by oxygen vacancies move toward the valence band
maximum (VBM) when the nearest distance between the two vacancies
decreases, which will have a great effect on the conductivity.
Rice blast caused by Magnaporthe oryzae severely impacts global rice yield stability. The rice endophyte Streptomyces sporocinereus OsiSh-2, with strong antagonistic activity towards M. oryzae, has been reported in our previous study. To decipher the model of the antagonistic action of OsiSh-2 towards M. oryzae, we compared the iron-capturing abilities of these two strains. The cultivation of OsiSh-2 and a M. oryzae strain under iron-rich and iron-starved conditions showed that M. oryzae depended more on iron supplementation for growth and development than did OsiSh-2. Genomic analysis of the S. sporocinereus and M. oryzae species strains revealed that they might possess different iron acquisition strategies. The actinobacterium OsiSh-2 is likely to favor siderophore utilization compared to the fungus M. oryzae. In addition, protein annotations found that OsiSh-2 contains the highest number of the siderophore biosynthetic gene clusters among the 13 endophytic actinomycete strains and 13 antifungal actinomycete strains that we compared, indicating the prominent siderophore production potential of OsiSh-2. Additionally, we verified that OsiSh-2 could excrete considerably more siderophores than Guy11 under iron-restricted conditions and displayed greater Fe-reducing activity during iron-supplemental conditions. Measurements of the iron mobilization between the antagonistic OsiSh-2 and Guy11 showed that the iron concentration is higher around OsiSh-2 than around Guy11. In addition, adding iron near OsiSh-2 could decrease the antagonism of OsiSh-2 towards Guy11. Our study revealed that the antagonistic capacity displayed by OsiSh-2 towards M. oryzae was related to the competition for iron. The highly efficient iron acquisition system of OsiSh-2 may offer valuable insight for the biocontrol of rice blast.
BackgroundLignocellulolytic bacteria have revealed to be a promising source for biofuel production, yet the underlying mechanisms are still worth exploring. Our previous study inferred that the highly efficient lignocellulose degradation by bacterium Pantoea ananatis Sd-1 might involve Fenton chemistry (Fe2+ + H2O2 + H+ → Fe3+ + OH· + H2O), similar to that of white-rot and brown-rot fungi. The aim of this work is to investigate the existence of this Fenton-based oxidation mechanism in the rice straw degradation process of P. ananatis Sd-1.ResultsAfter 3 days incubation of unpretreated rice straw with P. ananatis Sd-1, the percentage in weight reduction of rice straw as well as its cellulose, hemicellulose, and lignin components reached 46.7, 43.1, 42.9, and 37.9 %, respectively. The addition of different hydroxyl radical scavengers resulted in a significant decline (P < 0.001) in rice straw degradation. Pyrolysis gas chromatography–mass spectrometry and Fourier transform infrared spectroscopy analysis revealed the consistency of chemical changes of rice straw components that exists between P. ananatis Sd-1 and Fenton reagent treatment. In addition to the increased total iron ion concentration throughout the rice straw decomposition process, the Fe3+-reducing capacity of P. ananatis Sd-1 was induced by rice straw and predominantly contributed by aromatic compounds metabolites. The transcript levels of the glucose-methanol-choline oxidoreductase gene related to hydrogen peroxide production were significantly up-regulated (at least P < 0.01) in rice straw cultures. Higher activities of GMC oxidoreductase and less hydrogen peroxide concentration in rice straw cultures relative to glucose cultures may be responsible for increasing rice straw degradation, which includes Fenton-like reactions.ConclusionsOur results confirmed the Fenton chemistry-assisted degradation model in P. ananatis Sd-1. We are among the first to show that a Fenton-based oxidation mechanism exists in a bacteria degradation system, which provides a new perspective for how natural plant biomass is decomposed by bacteria. This degradative system may offer an alternative approach to the fungi system for lignocellulosic biofuels production.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0623-x) contains supplementary material, which is available to authorized users.
Rice blast, caused by the fungus Magnaporthe oryzae, can result in notable yield losses in rice production. The objective of this study was to investigate the potential of a rice endophytic isolate, Streptomyces albidoflavus OsiLf‐2, on the control of rice blast and the possible mechanisms involved. In vitro assays displayed a variety of antagonistic effects of OsiLf‐2 against different physiological races of M. oryzae, with peak mycelial growth inhibition ranging from 74.1% to 83.0%. In vivo tests of OsiLf‐2 showed 18.0% and 19.6% reduction in disease index in greenhouse and field conditions, respectively. The stable active metabolites in its cell‐free culture filtrate inhibited the mycelial growth, spore germination and appressorial formation of M. oryzae in a dose‐dependent manner. They also possessed strong antifungal capacities toward various phytopathogens in vitro. OsiLf‐2 secreted multiple antimicrobial compounds, cell wall degradation enzymes, siderophore, plant hormones, and 1‐aminocyclopropane‐1‐carboxylate deaminase, which might function in direct or indirect resistance to M. oryzae. In addition, a variety of defence responses were induced in OsiLf‐2‐treated rice, including hydrogen peroxide (H2O2) accumulation, callose deposition, defence‐related enzymes activation, and elevated expression of salicylic acid (SA) and jasmonic acid (JA) pathways genes, which might contribute in resisting pathogen attack. The significant biological control activity and host defence‐stimulation ability of OsiLf‐2 suggest that this endophytic actinobacterial strain could be a promising candidate in the management of rice blast disease.
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