Resistance of Postharvest Biocontrol Yeasts to Oxidative Stress: A Possible New Mechanism of Action

Abstract

We detected the generation of the reactive oxygen species (ROS) superoxide anion ( O.(-) (2)) and hydrogen peroxide (H(2)O(2)) in apple wounds 2 immediately after wounding, and assessed the relationships between (i) timely colonization of apple wounds by biocontrol yeasts, (ii) resistance of these microorganisms to oxidative stress caused by ROS, and (iii) their antagonism against postharvest wound pathogens. We analyzed a model system consisting of two yeasts with higher (Cryptococcus laurentii LS-28) or lower (Rhodotorula glutinis LS-11) antagonistic activity against the postharvest pathogens Botrytis cinerea and Penicillium expansum. LS-28 exhibited faster and greater colonization of wounds than LS-11. In contrast to LS-28, the number of LS-11 cells dropped 1 and 2 h after application, and then increased only later. In vitro, LS-28 was more resistant to ROS-generated oxidative stress. The combined application of biocontrol yeasts and ROS-deactivating enzymes in apple wounds prevented the decrease in number of LS-11 cells mentioned above, and enhanced colonization and antagonistic activity of both biocontrol yeasts against B. cinerea and P. expansum. Polar lipids of LS-11 contained the more unsaturated and oxidizable alpha-linolenic acid, which was absent in LS-28. Resistance to oxidative stress could be a key mechanism of biocontrol yeasts antagonism against postharvest wound pathogens.

Modulation of Antioxidant Defense in Aspergillus parasiticus Is Involved in Aflatoxin Biosynthesis: a Role for the Ap yapA Gene

“…The isolates were incubated on potato dextrose agar (PDA; Difco) for 7 days at 30°C, before use. Twenty-five milliliters of potato dextrose broth (PDB; Difco) (which is aflatoxin conducive) in 50-ml Erlenmeyer flasks was inoculated with the WT, ⌴, and CM strains, using 0.2 ml of conidial suspension (ϳ10 6 conidia) for each flask; incubation was performed at 30°C for different time periods (10,12,14,18,21,24,30,36,42,48,60,72,96,120,144, and 168 h). In other experiments, 50 ml of Czapek Dox (CD) broth (Difco) (which is low-conducive for aflatoxins) was inoculated with the WT and M strains; after 4 days of incubation at 30°C, 1 mM cumene hydroperoxide (CH), 0.5 mM menadione (Men), and 1 mM and 10 mM hydrogen peroxide (H 2 O 2 ) were added to test the strain's sensitivity to oxidant stressors.…”

“…In Aspergillus nidulans, the presence of the fatty-acid DOXs PpoA, -B, and -C has been reported (63). In Aspergillus, compounds produced by LOXs and DOXs, such as hydroperoxyoctadecadienoic acid (HPODE) and precocious sexual inducer factors, which consist of a mixture of hydroxylated oleic, linoleic, and linolenic acids, have all been shown to stimulate conidiogenesis, and in Aspergillus flavus this occurrence is related to aflatoxin biosynthesis (7,10,12,13). In A. nidulans, ROS can also steer the production of mitospores and meiospores in the regulation of the asexual and sexual phases in development (25,63).…”

Responses of Yeast Biocontrol Agents to Environmental Stress

“…It has been reported that peroxidases and superoxide dismutase in grapefruit were induced by application of the yeast M. fructicola, based on transcriptome analysis (56). Castoria et al (39) investigated the relationship between oxidative stress resistance and the fitness of the postharvest biocontrol yeasts Cryptococcus laurentii LS-28 and Rhodotorula glutinis LS-11 (39). C. laurentii LS-28, which had higher resistance to ROS-generated oxidative stress than R. glutinis LS-11, exhibited greater colonization and better biocontrol efficacy on apple fruit.…”

Two rapid assays for screening of patulin biodegradation

“…In some cases, biotransformation leads to less toxic or non-toxic products and is considered to be a detoxification (He et al 2010;Karlovsky 1999;Wu et al 2009). The yeast R. kratochvilovae (formerly Rhodotorula glutinis) strain LS11 is an excellent biocontrol agent of P. expansum (Castoria et al 2003(Castoria et al , 2005Lima et al 2003, …”