title: Antifungal Rhizosphere Bacteria Can increase as Response to the Presence of Saprotrophic Fungi.
abstract: Knowledge on the factors that determine the composition of bacterial communities in the vicinity of roots (rhizosphere) is essential to understand plant-soil interactions. Plant species identity, plant growth stage and soil properties have been indicated as major determinants of rhizosphere bacterial community composition. Here we show that the presence of saprotrophic fungi can be an additional factor steering rhizosphere bacterial community composition and functioning. We studied the impact of presence of two common fungal rhizosphere inhabitants (Mucor hiemalis and Trichoderma harzianum) on the composition of cultivable bacterial communities developing in the rhizosphere of Carex arenaria (sand sedge) in sand microcosms. Identification and phenotypic characterization of bacterial isolates revealed clear shifts in the rhizosphere bacterial community composition by the presence of two fungal strains (M. hiemalis BHB1 and T. harzianum PvdG2), whereas another M. hiemalis strain did not show this effect. Presence of both M. hiemalis BHB1 and T. harzianum PvdG2 resulted in a significant increase of chitinolytic and (in vitro) antifungal bacteria. The latter was most pronounced for M. hiemalis BHB1, an isolate from Carex roots, which stimulated the development of the bacterial genera Achromobacter and Stenotrophomonas. In vitro tests showed that these genera were strongly antagonistic against M. hiemalis but also against the plant-pathogenic fungus Rhizoctonia solani. The most likely explanation for fungal-induced shifts in the composition of rhizosphere bacteria is that bacteria are being selected which are successful in competing with fungi for root exudates. Based on the results we propose that measures increasing saprotrophic fungi in agricultural soils should be explored as an alternative approach to enhance natural biocontrol against soil-borne plant-pathogenic fungi, namely by stimulating indigenous antifungal rhizosphere bacteria.
authors.affiliation: Department of Microbial Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, 6708 PB, the Netherlands; Department of Soil Quality, Wageningen University, Wageningen, 6708 PB, the Netherlands.
authors.forename: Wietse
authors.initials: W
authors.lastname: de Boer
authors.affiliation: Department of Microbial Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, 6708 PB, the Netherlands.
authors.forename: Maria P J
authors.initials: MP
authors.lastname: Hundscheid
authors.affiliation: Department of Microbial Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, 6708 PB, the Netherlands.
authors.forename: Paulien J A
authors.initials: PJ
authors.lastname: Klein Gunnewiek
authors.affiliation: Department of Microbial Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, 6708 PB, the Netherlands.
authors.forename: Annelies S
authors.initials: AS
authors.lastname: de Ridder-Duine
authors.affiliation: School of Biological Science, University of Aberdeen, Aberdeen, AB24 3UU, United Kingdom.
authors.forename: Cecile
authors.initials: C
authors.lastname: Thion
authors.affiliation: Department of Microbial Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, 6708 PB, the Netherlands; Insititute of Biology, Leiden University, Leiden, 2333 BE, the Netherlands.
authors.forename: Johannes A
authors.initials: JA
authors.lastname: van Veen
authors.affiliation: Department of Microbial Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, 6708 PB, the Netherlands.
authors.forename: Annemieke
authors.initials: A
authors.lastname: van der Wal
mesh_terms: D000898:Antibiosis / Q000502:physiology; D001419:Bacteria / Q000145:classification / Q000235:genetics / Q000254:growth & development*; D031255:Carex Plant / Q000382:microbiology; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004271:DNA, Fungal / Q000737:chemistry / Q000235:genetics; D005658:Fungi / Q000145:classification / Q000235:genetics / Q000502:physiology*; D064307:Microbiota / Q000235:genetics / Q000502:physiology; D008954:Models, Biological; D008969:Molecular Sequence Data; D009089:Mucor / Q000235:genetics / Q000502:physiology; D018517:Plant Roots / Q000382:microbiology*; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D058441:Rhizosphere; D017422:Sequence Analysis, DNA; D012988:Soil Microbiology; D014242:Trichoderma / Q000235:genetics / Q000502:physiology
chemical_list: D004269:DNA, Bacterial; D004271:DNA, Fungal; D012336:RNA, Ribosomal, 16S