Dimethylpolysulfides production as the major mechanism behind wheat fungal pathogen biocontrol, by
Arthrobacter
and
Microbacterium
actinomycetes
Authors: Ballot Aline , Dore Jeanne , Rey Marjolaine , Meiffren Guillaume , Langin Thierry , Joly Pierre , Dreux-Zigha Assia , Taibi Ahmed , Prigent-Combaret Claire 
Published: October 2023

Volatile organic compounds (VOCs) produced by plant-associated microorganisms could serve as natural biocontrol compounds. In this work, we investigate the potential of wheat rhizosphere
Microbacterium
and
Arthrobacter
actinomycetes to inhibit the growth of major wheat phytopathogenic fungi,
Fusarium graminearum
and
Zymoseptoria tritici
via production of antifungal VOCs. A correlative analysis between fungal-growth inhibition versus bacterial volatilomic profiles identified four dimethylpolysulfide (DMPS) VOCs as the main active compounds behind their biocontrol potential. Subsequent inhibition assays reveal that DMTriS (dimethyltrisulfide) exhibits the strongest inhibition effects, then dimethyldisulfide (DMDiS). Further investigation focuses on the mechanisms behind
F. graminearum
-growth inhibition by the most active strain
Microbacterium
JM188 in dual culture. Surprisingly, nine interaction-induced VOCs, including two fungal sesquiterpenes, were exclusively detected in dual cultures, suggesting a complex interplay between microbial VOC production and sensing. More importantly, all JM188 VOCs, including antifungal DMPS, were less abundant in dual cultures, suggesting an uptake of bacterial VOCs by the fungus. Quantification of pure DMPS after confrontation with
F. graminearum
confirmed complete and partial uptake by the fungus of DMTriS and DMDiS VOCs, respectively, suggesting a potential link between the fungal uptake level of bacterial VOCs and their toxicity. Finally, we demonstrated that
F. graminearum
growth inhibition leads to a complete depletion of DON (deoxynivalenol) carcinogenic mycotoxins, highlighting a significant modulation of fungal metabolism. Collectively, these results pinpoint DMPS as broad-range fungal-inhibiting VOCs produced by rhizosphere
Microbacterium
and
Arthrobacter
, and emphasize the extensive VOC-mediated interplay between bacterial biocontrol agents and fungal pathogens.

IMPORTANCE

As the management of wheat fungal diseases becomes increasingly challenging, the use of bacterial agents with biocontrol potential against the two major wheat phytopathogens,
Fusarium graminearum
and
Zymoseptoria tritici
, may prove to be an interesting alternative to conventional pest management. Here, we have shown that dimethylpolysulfide volatiles are ubiquitously and predominantly produced by wheat-associated
Microbacterium
and
Arthrobacter
actinomycetes, displaying antifungal activity against both pathogens. By limiting pathogen growth and DON virulence factor production, the use of such DMPS-producing strains as soil biocontrol inoculants could limit the supply of pathogen inocula in soil and plant residues, providing an attractive alternative to dimethyldisulfide fumigant, which has many non-targeted toxicities. Notably, this study demonstrates the importance of bacterial volatile organic compound uptake by inhibited
F. graminearum
, providing new insights for the study of volatiles-mediated toxicity mechanisms within bacteria-fungus signaling crosstalk.