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Browsing by Author "Vasebi, Yalda"

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    Comprehensive characterization of an aspen (Populus tremuloides) leaf litter sample that maintained ice nucleation activity for 48 years
    Vasebi, Yalda; Mechan Llontop, Marco Enrique; Hanlon, Regina; Schmale, David G. III; Schnell, Russell; Vinatzer, Boris A. (European Geosciences Union, 2019-04-24)
    Decaying vegetation was determined to be a potentially important source of atmospheric ice nucleation particles (INPs) in the early 1970s. The bacterium Pseudomonas syringae was the first microorganism with ice nucleation activity (INA) isolated from decaying leaf litter in 1974. However, the ice nucleation characteristics of P. syringae are not compatible with the characteristics of leaf litter-derived INPs since the latter were found to be sub-micron in size, while INA of P. syringae depends on much larger intact bacterial cells. Here we determined the cumulative ice nucleation spectrum and microbial community composition of the historic leaf litter sample 70-S-14 collected in 1970 that conserved INA for 48 years. The majority of the leaf litter-derived INPs were confirmed to be sub-micron in size and to be sensitive to boiling. Culture-independent microbial community analysis only identified Pseudomonas as potential INA. Culture-dependent analysis identified one P. syringae isolate, two isolates of the bacterial species Pantoea ananatis, and one fungal isolate of Mortierella alpina as having INA among 1170 bacterial colonies and 277 fungal isolates, respectively. Both Pa. ananatis and M. alpina are organisms that produce heat-sensitive sub-micron INPs. They are thus both likely sources of the INPs present in sample 70-S-14 and may represent important terrestrial sources of atmospheric INPs, a conclusion that is in line with other recent results obtained in regard to INPs from soil, precipitation, and the atmosphere.
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    Expression of pathogenicity and virulence related genes in Pseudomonas syringae pv. syringae under copper stress
    Vasebi, Yalda; Khakvar, Reza; Faghihi, Mohammad Mehdi; Vinatzer, Boris A. (2020-01)
    Stone fruit bacterial canker is one of the most destructive diseases of apricot in Iran. Copper-based compounds are widely used to protect plants against bacterial diseases, but pathogens frequently evolve resistance against copper (Cu). This study was conducted to investigate the genetic diversity of the Cu resistance gene copA among strains of the causal agent of canker disease of stone fruits Pseudomonas syringae pv. syringae (Pss), isolated from apricot trees in East Azarbaijan province of Iran. The phylogenic trees based on copA and rpoD are very similar to each other revealing no evidence of recombination. To test the hypothesis that pathogenicity- and virulence-related genes may be induced by Cu in Pss strains, quantitative real-time polymerase chain reaction (qRT-PCR) was used to evaluate the expression of genes algD, copA, fliC, hrpA, syrB and tatC, in the Cu sensitive Pss 170 strain upon exposure to Cu. Among the tested genes, the algD and copA involved in alginate synthesis and Cu resistance, respectively, showed the highest increase in expression compared to a non-copper (control): 4.75-fold and 2.68-fold, respectively. Based on these results and on the conservation of genes algD and copA in Pseudomonas pathovars, antimicrobials that target AlgD and CopA proteins should be developed to use in combination with Cu to increase control efficiency.
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    Genomic and pathogenic properties of Pseudomonas syringae pv. syringae strains isolated from apricot in East Azerbaijan province, Iran
    Vasebi, Yalda; Khakvar, Reza; Faghihi, Mohammad Mehdi; Vinatzer, Boris A. (2019-05)
    Strains of Pseudomonas syringae pv. syringae (Pss) were isolated from P. armeniaca in different geographic areas in East Azerbaijan province, Iran, and studied for genetic diversity and host preference. Results of morphological, physiological and biochemical tests showed no differences among strains and syrB gene was determined to be present in all strains by PCR using gene-specific primers. Results of antibiotic assays showed that all strains were resistant to ceftriaxone and erythromycin, while tetracycline induced the strongest growth inhibition. In pathogenicity tests, all strains incited progressive necrotic lesions on apricot twigs at inoculated sites. Severity of symptoms was variable on mango leaves, lemon fruits, bean pods and tomato seedlings. To assess genetic diversity among strains, clustering of strains was performed based on partial sequences of the 16S rRNA and the rpoD housekeeping genes and DNA fingerprinting using IS50-PCR analysis. Cluster analysis was performed using the Unweighted Pair Group Method with Arithmetic (UPGMA) method and Jaccard's similarity coefficients. High genetic diversity was detected among strains. All Pss strains were divided into two distinct clusters at the 37% similarity level. In summary, this study indicates that Pss strains isolated from apricot in East Azerbaijan province in Iran, are genetically diverse, do not display host specificity, but are heterogeneous in regard to aggressiveness.