Screening of antagonistic yeast strains for postharvest control of Penicillium expansum causing blue mold decay in table grape.

Blue mold decay caused by Penicillium expansum is one of the most important postharvest diseases of grapes, leading to considerable economic losses. Regarding the increasing demand for pesticide-free foods, this study aimed to find potential yeast strains for biological control of blue mold on table grapes. A total of 50 yeast strains were screened for antagonistic activity against P. expansum using the dual culture method and six strains significantly inhibited the fungal growth. All six yeast strains (Coniochaeta euphorbiae, Auerobasidium mangrovei, Tranzscheliella sp., Geotrichum candidum, Basidioascus persicus, and Cryptococcus podzolicus) reduced the fungal growth (29.6-85.0%) and the decay degree of wounded grape berries inoculated with P. expansum while G. candidum was found to be the most efficient biocontrol agent. On the basis of antagonistic activity, the strains were further characterized by in vitro assays involving inhibition of conidial germination, production of volatile compounds, iron competition, production of hydrolytic enzymes, biofilm-forming capacity, and exhibited three or more putative mechanisms. To our knowledge, the yeasts are reported for the first time as potential biocontrol agents against the blue mold of grapes but more study is required to evaluate their efficiency related to field application.

Bioactive exopolysaccharide from Neopestalotiopsis sp. strain SKE15: Production, characterization and optimization.

Fungal exopolysaccharides are powerful resources of medicinal applications. Neopestalotiopsis sp. SKE15 was isolated and identified according to phenotypical and genotypical analyses (GenBank Accession No. MG649986). The exopolysaccharide (EPS) was produced by cultivation of mycelia in broth culture and extracted. The production was optimized to 2.02 g/l after selection of agitation, temperature, FeSO4 and K2HPO4 concentrations as the most influencing factors using Placket-Burman design and then by applying response surface methodology. Analytical Tools showed that the EPS is composed of a polysaccharide (1.5-2.1 × 106 Da) and its probable low molecular weight derivatives, in a wide range of chain lengths, among them an oligosaccharide of about 1970 Da was dominant. GC-MS (Gas chromatography-mass spectrometry) analysis revealed the EPS was mainly constructed from d-glucose, sorbitol and D-galactose. The EPS showed antibacterial activity against Staphylococcus aureus ATCC 25923, Bacillus subtilis ATCC 6633 and Pseudomonas aeruginosa ATCC 27853. DPPH (1,1-diphenyl-2-picryl-hydrazyl) and hydroxyl radical scavenging activity assays showed strong antioxidant activity of the EPS. A challenge with three different cancerous cell lines showed cytotoxic activity of the EPS at final concentration of 100 and 200 µg/ml. Further investigation on medicinal applications of the biopolymer is promising.

Starmerella orientalis f.a., sp. nov., an ascomycetous yeast species isolated from flowers.

Four strains of a novel ascomycetous yeast species were isolated from flowers in Iran and China. Phylogenetic analysis of the sequences of the ITS region (including 5.8S rRNA gene) and the LSU rRNA gene D1/D2 domains indicated that these strains belong to the Starmerella clade and show divergence from previously described species in this clade. Growth reactions on carbon and nitrogen sources were similar to those observed in related species of the Starmerella clade. Sexual reproduction was not observed after mating tests on different sporulation media. Based on physiological characteristics and phylogeny of rRNA gene sequences, the novel species is most closely related to Candida (iter. nom. Starmerella) powellii and Candida (iter. nom. Starmerella) floricola. It is therefore assigned to the genus Starmerella and described as Starmerella orientalis f.a., sp. nov. The type strain is SAM09T ( = IBRC-M 30204T = CBS 14142T). The MycoBank accession number is MB 814379.

Enterobacterial repetitive intergenic consensus (ERIC) PCR based genetic diversity of Xanthomonas spp. and its relation to xanthan production.

BACKGROUND AND OBJECTIVE: The genus Xanthomonas is composed of phytopathogenic bacterial species. In addition to causing crops diseases, most of the Xanthomonas species especially Xanthomonas campestris produce xanthan gum via an aerobic fermentation process. Xanthan gum is, an important exopolysaccharide from Xanthomonas campestris, mainly used in the food, petroleum and other industries. the purpose of this study was assessment of relationship between genetic diversity and xanthan production in Xanthomonas spp. MATERIALS AND METHODS: In this study 15 strains of Xanthomonas spp. which had previously been isolated from soils of vegetable farms, were discriminated from each other using Enterobacterial Repetitive Intergenic Consensus (ERIC) PCR and 16S rDNA sequencing methods. Xanthan production of strains was measured in 250 ml flask. The results of ERIC PCR and xanthan production was compared. RESULTS: ERIC-PCR patterns not only could differentiate all Xanthomonas campestis from the control i.e. Xanthomonas translucent but also discriminate strains of Xanthomonas to three clusters with 40% similarity based on Jaccard's coefficient. This clustering of the strains was in agreement with other characteristics including xanthan production and biochemical features. DISCUSSION: The results showed that genomic fingerprinting conferred adequate genetic data for discriminating between strains of the species Xanthomonas campestris. The data indicated a partial relationship between ERIC-PCR patterns and xanthan production by the strains. CONCLUSION: Further development of experiments may result in making good prediction about xanthan production capability of the Xanthomonas strains on the basis of ERIC-PCR method.