|ZAJC, JANJA - University Of Ljublijana|
|CERNOSA, ANJA - University Of Ljublijana|
|DI FRANCESCO, ALESSANDRA - University Of Bologna|
|CASTORIA, RAFFAELLO - University Of Molise|
|DE CURTIS, FILIPPO - University Of Molise|
|LIMA, GIUSEPPE - University Of Molise|
|BADRI, HANENE - University Of Liege|
|JIJAKLI, HAISSAM - University Of Liege|
|IPPOLITO, ANTONIO - University Of Bari|
|GOSTINCAR, CENE - University Of Ljubljana|
|ZALAR, POLONA - University Of Ljubljana|
|GUNDE-CIMERMAN, NINA - University Of Ljubljana|
Submitted to: Fungal Genomics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2020
Publication Date: 1/22/2020
Citation: Zajc, J., Cernosa, A., Di Francesco, A., Castoria, R., De Curtis, F., Lima, G., Badri, H., Jijakli, H., Ippolito, A., Gostincar, C., Zalar, P., Gunde-Cimerman, N., Janisiewicz, W.J. 2020. Characterization of Aureobasidium pullulans isolates selected as biocontrol agents against fruit decay pathogens. Fungal Genomics and Biology. 10(163):1-13.
Interpretive Summary: The yeast-like fungus, Aureobasidium pullulans, commonly occurs in nature on a wide range of plants. Strains of this fungus were isolated from fruits and leaves in different parts of the world and have effectively controlled various fruit decays before and after harvest. This fungus is used in our PhylloLux technology to control diseases and is applied to strawberry plants after UV-C “sterilization” to fill in microbiological void in order to prevent recolonization by undesirable microbes and increase robustness of the disease control. We characterized 20 strains of this fungus isolated in different parts of Europe, Africa, and North America for some common characteristics which can help in selecting the best strains for biological control and potential commercial use early in the selection process. We found that all strains are closely related genetically and are different from a recently described opportunistic human pathogen belonging to the same fungal genera. In addition, none of the isolates grew at 37°C, human body temperature, which eliminates concern for human safety, a major obstacle in the development of the fungus into a commercial product. All strains grew at 0°C, were tolerant to stress caused by high salt concentration, and produced enzymes important for colonization of fruits. All of these characteristics are beneficial as many fruits are stored at low temperatures and are subjected to stresses during storage and handling in packinghouses. The strains differ in biofilm formation and siderophore production, which have been shown to be beneficial in biological control.
Technical Abstract: The yeast-like fungus, Aureobasidium pullulans, is a commonly occurring natural saprophyte on a wide range of plants. Strains of this fungus, isolated from fruit and leaves in different parts of the world, exhibited strong biocontrol activity against postharvest decays on various fruit, and some were developed into commercial products. We obtained 20 of these strains and characterized them for growth at 37°C and 0°C, tolerance to 50°C, osmotic/salt tolerance, biofilm formation, activity of specific enzymes, production of siderophores and for genetic relatedness. Phylogenetic analyses based on internal transcribed spacer (ITS) and the large subunit of the nuclear ribosomal RNA (rRNA) gene complex (LSU) regions confirmed that all the strains are most closely related to A. pullulans species. All strains grew at 0°C, which is very important to control decays at low storage temperature, and none grew at 37°C, which eliminates concern for human safety. Only two strains survived for 24 h at 50°C, while the other 18 survived for 2 h. Osmotolerance varied; however, all strains grew on medium with 14% NaCl and 14 even with 18% NaCl. Tolerance to high temperature and elevated salinity enables compatibility with postharvest practices. Small differences were observed in enzymatic activity, although some strains did not produce chitinase (8), xylanase (11), or urease (10). Siderophore production on CAS agar was generally low, except for one strain in which it was high and another produced no detectable siderophores. Ability to form biofilm varied widely between the strains. Knowledge of common characteristics of these strains may be very useful in future selection of the best antagonists within this species.