Submitted to: International Journal of Food Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/14/2012
Publication Date: 4/20/2012
Citation: Sui, Y., Liu, U., Wisniewski, M.E., Droby, S., Norelli, J.L., Hershkovitz, V. 2012. Pretreatment of the yeast antagonist, Candida oleophila with glycine betaine increases oxidative stress tolerance in the microenvironment of apple wounds. International Journal of Food Microbiology. 157:45-51. Interpretive Summary: Developing alternative approaches to disease control is a critical objective of NP-303, Plant Diseases, due to consumer demands to lower exposure to chemicals and reduces the impact of agriculture on the environment. In the past decade, USDA-ARS has identified several species of yeasts that can be used as biocontrol agents against postharvest diseases of fruit. At least one of these yeast species was previously commercialized and other international research programs and commercial companies have also developed postharvest biocontrol products. 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 variable and often adverse environmental conditions. Our previous studies have demonstrated that different additives or sub-lethal stresses can make the yeast more tolerant to oxidative stresses. However, this increased tolerance was only demonstrated in vitro (i.e. in petri dishes in the lab). In the present study, we exposed the yeast, Candida oleophila, to a potential stress-ameliorating compound, glycine betaine, to determine if that would improve their stress tolerance when they were in apple wounds. Results indicated that exposure to glycine betaine, increased the stress tolerance of the biocontrol agent, C. oleophila, even after they were administered to apple wounds. The glycine betaine induced the yeast to express stress tolerance genes while in the apple wounds, grow faster, and exhibit better biocontrol activity. 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: In response to wounding, harvested fruit tissues of apple and citrus exhibit the production of reactive oxygen species (ROS). ROS production is greater when yeast antagonists used as biocontrol agents are applied in the wounds. These phenomena result in an oxidative stress environment for the yeast antagonists. It has been demonstrated that pre-exposure of some of these yeast antagonists to sublethal abiotic stress (heat or hydrogen peroxide), or stress-ameliorating compounds such as glycine betaine (GB) can induce subsequent oxidative stress tolerance in the antagonistic yeast. The increased level of oxidative stress tolerance has been demonstrated in vitro and is characterized by higher levels of antioxidant gene expression, increased production of trehalose, and lower levels of ROS when yeast are exposed to a subsequent oxidative stress. The current study determined whether or not the effects of glycine betaine on yeast antagonists determined in vitro persist and are present in planta when yeast are applied to wounded apples. The effect of exogenous GB on the production of ROS in the yeast antagonist, Candida oleophila, was determined after the yeast was placed in apple wounds. Oxidative damage to yeast cells recovered from apple wounds was also monitored. Results indicated that GB treatment improved the adaptation of C. oleophila to apple fruit wounds. Compared to untreated control yeast cells, GB-treated cells recovered from the oxidative stress environment of apple wounds exhibited less accumulation of ROS and lower levels of oxidative damage to cellular proteins and lipids. Additionally, GB-treated yeast exhibited greater biocontrol activity against Penicillium expansum and Botrytis cinerea, and faster growth in wounds of apple fruits compared to untreated yeast. The expression of major antioxidant genes, including peroxisomal catalase, peroxiredoxin TSA1, and glutathione peroxidase was elevated in the yeast by GB treatment. This study supports the premise that activation of antioxidant response in bicontrol yeast can improve biocontrol efficacy.