Bacterial predation of a fungal wheat pathogen: Prelude to experimental evolution of enhanced biocontrol agents

Abstract

AbstractResearch to identify appropriate biological agents for controlling pathogens might exploit experimental evolution to select for enhanced antagonism against pathogens. We developed an experimental regime facilitating this approach, featuring the bacterial broad‐spectrum predator Myxococcus xanthus and the fungal wheat pathogen Zymoseptoria tritici. We demonstrate that Z. tritici, a major cause of crop loss and fungicide use worldwide, both fuels growth of and is killed by M. xanthus on wheat straw, a probable source of seedling infection. M. xanthus was found capable of growth on moistened straw alone, unaided by Z. tritici, in a manner dependent on both M. xanthus initial density and on how long straw was moistened before M. xanthus inoculation. Such growth of non‐cellulolytic myxobacteria on plant detritus may have implications for understanding their roles in nutrient cycling. However, straw with Z. tritici was found to fuel greater M. xanthus growth than straw alone under many conditions. After shorter moistening periods, growth by low‐density M. xanthus populations was found to be fully dependent on Z. tritici. Such pathogen‐dependent M. xanthus populations could be sustained with population replacement over five 1‐week growth cycles, indicating the feasibility of conducting long‐term experimental evolution with this system. Furthermore, M. xanthus was found to kill majorities of Z. tritici populations on both buffered agar and straw. Our results suggest that myxobacteria may serve as effective biocontrol agents of Z. tritici and are amenable to long‐term experimental selection for enhanced killing of this pathogen, an approach broadly applicable to many potential biocontrol agents and target pathogens.