Abstract
Fungal pathogens in fruits and vegetables cause significant losses during handling, transportation, and storage. Biological control with microbial antagonists replacing the use of chemical fungicides is a major approach in postharvest disease control, and several products based on single antagonists have been developed but have limitations related to reduced and inconsistent performance under commercial conditions. One possible approach to enhance the biocontrol efficacy is to broaden the spectrum of the antagonistic action by employing compatible microbial consortia. Here, we explore commercial kefir grains, a natural probiotic microbial consortium, by culture-dependent and metagenomic approaches and observed a rich diversity of co-existing yeasts and bacterial population. We report effective inhibition of the postharvest pathogen Penicillium expansum on apple by using the grains in its fresh commercial and milk-activated forms. We observed few candidate bacteria and yeasts from the kefir grains that grew together over successive enrichment cycles, and these mixed fermentation cultures showed enhanced biocontrol activities as compared to the fresh commercial or milk-activated grains. We also report several individual species of bacteria and yeasts with biocontrol activities against Penicillium rots on apple and grapefruit. These species with antagonistic properties could be further exploited to develop a synthetic consortium to achieve enhanced antagonistic effects against a wide range of postharvest pathogens.
Highlights
Fungal pathogens are the main cause of postharvest losses in fruits and vegetables during storage, shipment, and post-consumer purchase [1,2]
Studies have shown that the microorganisms present in probiotic water kefir have a capacity to act biocontrol agents in stored grains [38]
The microbial analysis of the kefir grains revealed the coexistence of a stable population of a consortium of yeasts and bacteria, their distribution and abundance varied between the kefir grains obtained from different commercial kefir-grain products
Summary
Fungal pathogens are the main cause of postharvest losses in fruits and vegetables during storage, shipment, and post-consumer purchase [1,2]. Chemical-based control approaches have been under mounting scrutiny by the public and regulatory authorities due to their negative effects on human and animal health, as well as the environment in general [3] This concern has been the main driving force of research to identify effective and more eco-friendly methods for the management of postharvest fungal diseases [1,4]. The discovery and development of these biocontrol agents have been based on the paradigm of isolating a single antagonist that is effective against several different postharvest pathogens and was expected to be effective on different commodities that vary in their genetic background, physiology, pathogen susceptibility, and pre- and postharvest management practices This paradigm has resulted in several limitations, including inconsistent efficacy and a narrow range of biocontrol activity on specific hosts or pathogens. The use of a consortium in biocontrol systems would have several advantages over the use of a single species, including the potential for a wider range of biocontrol efficacy, robustness, resilience to environmental stress, and modularity [10]
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