Shifts in the composition of the microbiota of stored wheat grains in response to fumigation

Authors: SOLANKI, MANOJ KUMAR - Volcani Center (ARO); ABDELFATTAH, AHMED - Stockholm University; BRITZI, MALKA - Kimron Veterinary Institute; ZAKIN, VARDA - Volcani Center (ARO); Wisniewski, Michael; DROBY, SAMIR - Volcani Center (ARO); SIONOV, EDWARD - Volcani Center (ARO)

Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2019
Publication Date: 5/17/2019
Citation: Solanki, M., Abdelfattah, A., Britzi, M., Zakin, V., Wisniewski, M.E., Droby, S., Sionov, E. 2019. Shifts in the composition of the microbiota of stored wheat grains in response to fumigation. Frontiers in Microbiology. https://doi.org/10.3389/fmicb.2019.01098.
DOI: https://doi.org/10.3389/fmicb.2019.01098

Interpretive Summary: Wheat is one of the most important cultivated cereals produced and consumed globally. It provides, on average, about 20% of the daily caloric requirement and about 21% of the daily protein intake in the human diet. The availability of high-quality wheat grains is essential for maintaining the stability of the world’s food supply and for global food security. Wheat grains are colonized by complex microbial communities that play different roles in grain quality and susceptibility to disease. A better knowledge of the composition and dynamics of wheat-grain associated microbiota is needed to identify novel beneficial microorganisms that may improve crop health and suppress the growth of potential pathogens in a sustainable manner. The objective of the present study was to characterize the composition of the fungal and bacterial communities in stored wheat grains, which produced annually for human and animal consumption, and to determine the impact of phosphine fumigation on the wheat grain microbiome. The results of the study demonstrated that phosphine fumigation had a significant impact on microbial community composition in stored wheat grain. The shifts in bacterial and yeast populations, coincident with the fumigant application, may have also led to changes in the functional diversity of those communities. A better understanding of the interactions that occur among the different members of the microbial community of stored wheat grains at specific timepoints (e.g., before and/or after fumigant application) can assist in the prediction of fungal disease incidence and mycotoxin production, as well as in the development of novel approaches for controlling mycotoxin contamination in grains and managing crop diseases in general.

Technical Abstract: While the wheat-associated microbiome is of major agricultural importance, little is known about the alterations in wheat grain microbial community composition during storage. Characterization of the bacterial and fungal communities in stored wheat grains revealed the impact of phosphine fumigation, one of the most effective methods to eliminate insects in stored commodities, on the composition of the wheat grain microbiome. High-throughput amplicon sequencing of the bacterial 16S rRNA gene and fungal internal transcribed spacer (ITS) region was used to analyze the wheat grain microbiome at different times over a 6-month-period of storage. Higher bacterial diversity was found across the samples during the first (immediately after harvest) and second (3 months later) time points, with a predominance of Proteobacteria, Firmicutes, Actinobacteria, Bacteroidetes and Planctomycetes. A two-fold decrease in the number of bacterial operational taxonomic units (OTUs) was observed in wheat grains at the last time point (6 months later), following phosphine treatment. In contrast to the effect of phosphine on bacteria, it did not affect fungal diversity in stored grains. The majority of fungal sequences were assigned to Ascomycota, followed by Basidiomycota, Glomeromycota, and unidentified fungi, which were evenly distributed throughout the storage period. Alpha and beta diversity analyses were confirmed by examination of the cultured microbial taxa obtained from the stored wheat grains. Mycotoxinanalysis of wheat grains collected after phosphine fumigation revealed the presence of Fusarium toxins, primarily deoxynivalenol (DON). Several mycotoxigenic Fusariumspp. were also detected in the same samples. Results of the present study indicate that microbiome of stored, whole wheat grains was strongly affected by phosphinefumigation, which changed the structure of the microbial community leading to shifts in species composition toward mycotoxigenic strains. A better understanding of the complex interactions within the microbial communities of stored grains will assist in the development of novel biocontrol strategies to overcome mycotoxin contamination.