The novel Ce and F codoped Bi2WO6 samples have been successfully obtained by a facile one-step hydrothermal reaction for the first time. They were characterized by X-ray diffraction patterns (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray photoelectron spectroscopy (XPS), and UV–vis diffuse reflectance spectra (DRS) and photoluminescence (PL) spectra. The presence of Ce3+, Ce4+, and F– dopants in Bi2WO6 was confirmed by XPS. The change of microstructure and optical band gap has also been observed after the doping of Ce and F. Under visible light, the as-synthesized plate-like F–Ce–Bi2WO6 sample exhibits a much better visible-light-responsive photocatalytic performance than pure Bi2WO6 for the degradation of RhB and photocurrent (PC) generation. The mechanism of high photcatalytic activity was also suggested on the basis of the PL spectra, electrochemical impedance spectra (EIS), and active species trapping measurements. The results indicated that the synergistic effect of the Ce and F dopants is responsible for the efficient separation and migration of photoinduced charge carriers, thus resulting in the remarkably improved photocatalytic activity.

BackgroundGreen and blue mold decay, caused by Penicillium digitatum and P. italicum, respectively, are important postharvest diseases of citrus. Biocontrol by microbes is an alternative to synthetic fungicide application. In this study, the antagonistic yeast strain Kloeckera apiculata 34–9 was used to investigate the action mechanisms involved in the biocontrol of postharvest diseases.ResultsAn antifungal substance, 2-phenylethanol (PEA), was isolated from K. apiculata and demonstrated to have antimicrobial activity against selected phytopathogenic fungi. Experiments on P. italicum cells identified the mitochondria and the nucleus as particularly sensitive to inhibition. Regulation of P. italicum gene expression was investigated using RNA-Seq. PEA up-regulated genes involved with the peroxisome, regulation of autophagy, phosphatidylinositol signaling system, protein processing in endoplasmic reticulum, fatty acid metabolism, and inhibited ribosome, RNA polymerase, DNA replication, amino acid biosynthesis, aminoacyl-tRNA biosynthesis and cell cycle. Inhibitory responses revealed by RNA-Seq suggest that PEA might compete for attachment on the active site of phenylalanyl-tRNA synthetase (PheRS).ConclusionThis study provided new insight on the mode of action of biocontrol yeast agents in controlling postharvest pathogenic fungi.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-014-0242-2) contains supplementary material, which is available to authorized users.

BackgroundThe yeast Kloeckera apiculata strain 34–9 is an antagonist that shows biological control activity against the postharvest fungal pathogens of citrus. An antifungal compound, 2-phenylethanol (PEA), has been identified from the extract of K. apiculata. To better understand the molecular processes underlying the response of citrus fruit tissue to K. apiculata, the extract and PEA, microarray analyses were performed on navel oranges using an Affymetrix Citrus GeneChip.ResultsAs many as 801, 339 and 608 differentially expressed genes (DEGs) were identified after the application of K. apiculata, the extract and PEA, respectively. In general, K. apiculata induced the expression of defence-related genes. In addition to chitinase and β-1,3-glucanase, genes involved in ethylene (ET), jasmonic acid (JA), calcium signalling, MAPK signalling and phenylalanine metabolism were induced. In contrast, monodehydroascorbate reductase, superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and carotenoid biosynthesis genes were down-regulated. The expression profiles for the extract- and PEA-treated samples were similar to that found for yeast (sharing 57.4 % DEGs), with a significant increase in the transcript levels of defence-related genes.ConclusionThis study provides a global picture of the gene expression changes in navel oranges after the application of the antagonist yeast K. apiculata, its extract and PEA. The interpretation of the DEGs revealed new insight into the molecular processes that regulate the defence responses in orange tissue.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2333-3) contains supplementary material, which is available to authorized users.

The yeast Kloeckera apiculata strain 34-9 is an antagonist with biological control activity against postharvest diseases of citrus fruit. In a previous study it was demonstrated that K. apiculata produced the aromatic alcohol phenylethanol. In the present study, we found that K. apiculata was able to form biofilm on citrus fruit and embed in an extracellular matrix, which created a mechanical barrier interposed between the wound surface and pathogen. As a quorum-sensing molecule, phenylethanol can promote the formation of filaments by K. apiculata in potato dextrose agar medium, whereas on the citrus fruit, the antagonist remains as yeast after being treated with the same concentration of phenylethanol. It only induced K. apiculata to adhere and form biofilm. Following genome-wide computational and experimental identification of the possible genes associated with K. apiculata adhesion, we identified nine genes possibly involved in triggering yeast adhesion. Six of these genes were significantly induced after phenylethanol stress treatment. This study provides a new model system of the biology of the antagonist-pathogen interactions that occur in the antagonistic yeast K. apiculata for the control of blue mold on citrus caused by Penicillium italicum.

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