Submitted to: FEMS Microbiology Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/14/2010
Publication Date: 1/28/2011
Citation: Liu, J., Wisniewski, M.E., Droby, S., Tian, S., Tworkoski, T. 2011. Effect of heat shock treatment on stress tolerance and biocontrol efficacy of Metschnikowia fructicola. FEMS Microbiology Ecology. 76:145-155. Interpretive Summary: Developing alternative approaches to disease control is critical due to consumer demands to lower exposure to chemicals and reduce 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. In the present study, we exposed the yeast, M. fructicola, to a mild heat shock (40 C for 30 min) to determine if that would improve their stress tolerance. Results indicated that a mild heat shock improved the viability of the yeast when they were subjected to a subsequent high temperature stress and also stressful oxidative conditions that were simulated with the use of hydrogen peroxide. The improvement was partially due to the induction of the protective sugar, trehalose, in response to the mild heat shock. Importantly, yeast cells of M. fructicola that were exposed to a mild heat shock also performed better as a bicontrol agent against a postharvest rot of apple caused by Penicillium expansum compared to untreated cells. The use of heat shock treated cells resulted in lower disease incidence and reduced lesion size, apparently due to the ability of these cells to grow more rapidly in the wound site during the first two days after application. 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: Several different species of yeasts have been used as biocontrol agents against postharvest diseases of fruits and vegetables. Our current research is directed to develop a better understanding of yeast biology in relation to biocontrol activity and to develop strategies to improve the efficacy of their biocontrol activity. In the present study, we have examined the effect of abiotic stress on the biology and performance of the yeast antagonist, Metschnikowia fructicola. High temperatures and oxidative stress had a significant effect on survival of M. fructicola. The effect of a mild heat shock (HS) pretreatment (30 min at 40 deg C) on the tolerance of M. fructicola to subsequent high temperature (45 deg C) and oxidative stress (0.4 mol l-1 H2O2) was evaluated. The viability of M. fructicola subjected to both stresses was enhanced by the pretreatment. Correspondingly, the HS yeast cells showed markedly less accumulation of reactive oxygen species (ROS) in response to both stresses. Additionally, the HS yeast showed better biocontrol efficacy against Penicillium expansum and higher population on apple fruits stored at 25 deg C compared to the performance of untreated yeast cells. The expression of a trehalose-6-phosphate synthase gene (TPS1) was upregulated in response to HS, and trehalose content in M. fructicola also increased. Results indicate that induction of trehalose content by HS pretreatment may contribute to improvement in ROS scavenging and stress tolerance, population dynamics and biocontrol efficacy of M. fructicola.