Genus-wide analysis of antagonism toward and plant pathogens and the contribution of cellulases to the antagonism.

Parasitism is an important lifestyle in the genus but has not been studied in a genus-wide way toward and hosts. Our approach screened a genus-wide set of 30 species in dual culture assays with two soil-borne and three plant-parasitic species and used exo-proteomic analyses, with the aim to correlate antagonism with potential strategies for attacking and . The spp. showed a wide range of antagonism from strong to weak, but the same strain showed similar levels toward all the and species. The enzymes from strong (, , and ), moderate ( cf. and ), and weak () antagonists were induced by the autoclaved mycelia of one of the screened species, . The variable proportions of putative cellulases, proteases, and redox enzymes suggested diverse as well as shared strategies amongst the antagonists. There was a partial positive correlation between antagonism from microscopy and the cellulase activity induced by autoclaved mycelia in different species. The deletion of the cellulase transcriptional activator XYR1 in led to lower antagonism toward and . The antagonism of and appears to be a generic property of as most of the species were at least moderately antagonistic. While a role for cellulases in the antagonism was uncovered, cellulases did not appear to make a major contribution to antagonism, and other factors are also likely contributing.IMPORTANCE is an important genus widely distributed in nature with broad ecological impacts and applications in the biocontrol of plant diseases. The and genera of fungus-like water molds include many important soil-borne plant pathogens that cause various diseases. Most of the species showed at least a moderate ability to compete with or antagonize the and hosts, and microscopy showed examples of parasitism (a slow type of killing) and predation (a fast type of killing). Hydrolytic enzymes such as cellulases and proteases produced by likely contribute to the antagonism. A mutant deficient in cellulase activity had reduced antagonism. Interestingly, and species contain cellulose in their cell walls (unlike true fungi such as ), and the cellulolytic ability of appears beneficial for antagonism of water molds.