Submitted to: FEMS Microbiology Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/26/2012
Publication Date: 3/9/2012
Citation: Wisniewski, M.E., Norelli, J.L., Liu, J., Tian, S., Droby, S., Hershkovitz, V., Farrell, R. 2012. Increase in antioxidant-defense gene transcripts, stress tolerance and biocontrol efficacy of Candida oleophila following sublethal oxidative stress exposure. FEMS Microbiology Ecology. 80:578-590. Interpretive Summary: Consumer demands to lower exposure to chemicals and the need to minimize the impact of agriculture on the environment are important drivers for developing alternative approaches to disease control by chemicals. Development of effective biocontrol strategies is a critical objective. USDA-ARS and other international research programs and commercial companies. Despite these options, use of these products remains limited partly due to variable performance. Therefore, there is a need to find strategies that will increase the efficacy of these bicontrol agents and allow them to perform more reliably under the variable conditions found in packing houses. In the present study, we exposed the ability of a sublethal oxidative stress to improve the overall stress tolerance and biocontrol performance of the yeast, Candida oleophila. Results indicated that a brief exposure to a low-level of hydrogen peroxide (oxidative stress) resulted in yeast cultures that were more tolerant (could survive better) when exposed to subsequent lethal heat, oxidative, and pH stresses. Postharvest biocontrol activity was increased and the yeast grew faster once they were applied to wounded fruit. The increase in stress tolerance in the yeast was associated with the upregulation of several antioxidant-defense genes which most likely contributed to the increased ability of the yeast to survive adverse environmental conditions and grow faster at the low pH found in the apple wounds. The use of this strategy to improve the efficacy of bicontrol agents will be explored for other species and on a larger scale to determine if it can be incorporated into the manufacturing process or at the time of application in a packing house.
Technical Abstract: Candida oleophila is one of several yeast species that have been used as bicontrol agents to manage postharvest diseases of fruits and vegetables. Current research is aimed at improving the tolerance of various antagonistic yeasts to environmental stresses in order to improve their efficacy. We examined the adaptive effect of sublethal oxidative stress on gene expression, subsequent stress tolerance, and biocontrol efficacy of C. oleophila. Results showed that a pretreatment of the yeast with a sublethal oxidative stress (5 mM hydrogen peroxide for 30 min) increased its tolerance to subsequent oxidative stress (50 mM hydrogen peroxide), high temperature (40 degrees C), and low pH (pH 4). Additionally, the sublethal oxidative stress treatment enhanced the ability of C. oleophila to control postharvest rot in apple caused by the wound-pathogen, Penicillium expansum. Population growth rate in wounds of apple fruits stored at 25 degrees C also increased compared to untreated yeast. Suppression subtractive hybridization (SSH) analysis was used to identify genes expressed in yeast in response to sublethal oxidative stress. Transcript levels were confirmed using semi-quantitative PCR. Data indicated that antioxidant-defense genes, such as peroxisomal catalase, cytochrome c peroxidase, peroxiredoxin TSA1, thioredoxin reductase, glutathione peroxidase, glutathione reductase and glucose-6-phosphate dehydrogenase were upregulated. The elevated expression of these genes contributed to less ROS accumulation and a lower level of protein oxidation under subsequent oxidative and heat stresses. Collectively, results indicated oxidative stress adaptation contributed to improvement in subsequent stress tolerance and biocontrol efficacy of C. oleophila by a mechanism that involves the activation of antioxidant-defense gene expression.