ABSTRACT
There is increasing evidence that microbial volatile organic compounds (mVOCs) play an important role in interactions between microbes in soils. In this minireview, we zoom in on the ...possible role of mVOCs in the suppression of plant-pathogenic soil fungi. In particular, we have screened the literature to see what the actual evidence is that mVOCs in soil atmospheres can contribute to pathogen suppression. Furthermore, we discuss biotic and abiotic factors that influence the production of suppressive mVOCs in soils. Since microbes producing mVOCs in soils are part of microbial communities, community ecological aspects such as diversity and assembly play an important role in the composition of produced mVOC blends. These aspects have not received much attention so far. In addition, the fluctuating abiotic conditions in soils, such as changing moisture contents, influence mVOC production and activity. The biotic and abiotic complexity of the soil environment hampers the extrapolation of the production and suppressing activity of mVOCs by microbial isolates on artificial growth media. Yet, several pathogen suppressive mVOCs produced by pure cultures do also occur in soil atmospheres. Therefore, an integration of lab and field studies on the production of mVOCs is needed to understand and predict the composition and dynamics of mVOCs in soil atmospheres. This knowledge, together with the knowledge of the chemistry and physical behaviour of mVOCs in soils, forms the basis for the development of sustainable management strategies to enhance the natural control of soil-borne pathogens with mVOCs. Possibilities for the mVOC-based control of soil-borne pathogens are discussed.
The authors review literature reporting on pathogen suppressive activities of volatiles (mVOCs) produced in soils by microbial communities and indicate management strategies to enhance mVOC-mediated disease control.
Highlights • The outcome of fungal–bacterial interactions is context dependent. • No direct extrapolation of pairwise interactions to community interactions. • Suppression of fungal pathogens by ...bacteria enables integration of different levels of FBI complexity. • Pairwise interactions form the basis for finding general mechanisms operating in communities.
Plants release a wide set of secondary metabolites including volatile organic compounds (VOCs). Many of those compounds are considered to function as defense against herbivory, pests, and pathogens. ...However, little knowledge exists about the role of belowground plant VOCs for attracting beneficial soil microorganisms. We developed an olfactometer system to test the attraction of soil bacteria by VOCs emitted by Carex arenaria roots. Moreover, we tested whether infection of C. arenaria with the fungal pathogen Fusarium culmorum modifies the VOCs profile and bacterial attraction. The results revealed that migration of distant bacteria in soil towards roots can be stimulated by plant VOCs. Upon fungal infection, the blend of root VOCs changed and specific bacteria with antifungal properties were attracted. Tests with various pure VOCs indicated that those compounds can diffuse over long distance but with different diffusion abilities. Overall, this work highlights the importance of plant VOCs in belowground long-distance plant-microbe interactions.
There is increasing evidence that volatile organic compounds (VOCs) play an important role in the interactions between fungi and bacteria, two major groups of soil inhabiting microorganisms. Yet, ...most of the research has been focused on effects of bacterial volatiles on suppression of plant pathogenic fungi whereas little is known about the responses of bacteria to fungal volatiles. In the current study we performed a metabolomics analysis of volatiles emitted by several fungal and oomycetal soil strains under different nutrient conditions and growth stages. The metabolomics analysis of the tested fungal and oomycetal strains revealed different volatile profiles dependent on the age of the strains and nutrient conditions. Furthermore, we screened the phenotypic responses of soil bacterial strains to volatiles emitted by fungi. Two bacteria, Collimonas pratensis Ter291 and Serratia plymuthica PRI-2C, showed significant changes in their motility, in particular to volatiles emitted by Fusarium culmorum. This fungus produced a unique volatile blend, including several terpenes. Four of these terpenes were selected for further tests to investigate if they influence bacterial motility. Indeed, these terpenes induced or reduced swimming and swarming motility of S. plymuthica PRI-2C and swarming motility of C. pratensis Ter291, partly in a concentration-dependent manner. Overall the results of this work revealed that bacteria are able to sense and respond to fungal volatiles giving further evidence to the suggested importance of volatiles as signaling molecules in fungal-bacterial interactions.
Microorganisms associated with roots are thought to be part of the so-called extended plant phenotypes with roles in the acquisition of nutrients, production of growth hormones, and defense against ...diseases. Since the crops selectively enrich most rhizosphere microbes out of the bulk soil, we hypothesized that changes in the composition of bulk soil communities caused by agricultural management affect the extended plant phenotype. In the current study, we performed shotgun metagenome sequencing of the rhizosphere microbiome of the peanut (Arachis hypogaea) and metatranscriptome analysis of the roots of peanut plants grown in the soil with different management histories, peanut monocropping and crop rotation. We found that the past planting record had a significant effect on the assembly of the microbial community in the peanut rhizosphere, indicating a soil memory effect. Monocropping resulted in a reduction of the rhizosphere microbial diversity, an enrichment of several rare species, and a reduced representation of traits related to plant performance, such as nutrients metabolism and phytohormone biosynthesis. Furthermore, peanut plants in monocropped soil exhibited a significant reduction in growth coinciding with a down-regulation of genes related to hormone production, mainly auxin and cytokinin, and up-regulation of genes related to the abscisic acid, salicylic acid, jasmonic acid, and ethylene pathways. These findings suggest that land use history affects crop rhizosphere microbiomes and plant physiology.
The ability of bacteria and fungi to communicate with each other is a remarkable aspect of the microbial world. It is recognized that volatile organic compounds (VOCs) act as communication signals, ...however the molecular responses by bacteria to fungal VOCs remain unknown. Here we perform transcriptomics and proteomics analyses of Serratia plymuthica PRI-2C exposed to VOCs emitted by the fungal pathogen Fusarium culmorum. We find that the bacterium responds to fungal VOCs with changes in gene and protein expression related to motility, signal transduction, energy metabolism, cell envelope biogenesis, and secondary metabolite production. Metabolomic analysis of the bacterium exposed to the fungal VOCs, gene cluster comparison, and heterologous co-expression of a terpene synthase and a methyltransferase revealed the production of the unusual terpene sodorifen in response to fungal VOCs. These results strongly suggest that VOCs are not only a metabolic waste but important compounds in the long-distance communication between fungi and bacteria.
Intercropping has historically been employed as an efficient management strategy to prevent disease outbreaks. Our previous studies indicated that intercropping of peanut with the Chinese medicinal ...herb, Atractylodes lancea effectively suppressed soil-borne peanut diseases, resulting in increased peanut yields. However, the underlying mechanism is unknown. In this study, the below ground effects of A. lancea on both fungal and bacterial communities in the peanut rhizosphere were investigated using pyrosequencing of the internal transcribed spacer (ITS1) and16S rRNA gene amplicons, respectively. Closed cultivation systems were constructed to investigate the role of volatiles and exudates originating from rhizomes and roots of A. lancea on fungal and bacterial communities. Intercropping with A. lancea significantly altered fungal community composition in the peanut rhizosphere, coinciding with decline of Fusarium root rot and improvement of peanut growth. Volatiles originating from A. lancea rhizome material had more effects on fungal communities than on bacterial communities, and significantly suppressed F. oxysporum growth. Root exudates of A. lancea had no apparent inhibitory effect on F. oxysporum. Gas chromatography–mass spectrometry (GC-MS) analysis revealed 21 volatiles originating from A. lancea rhizome material and terpenes and aromatic hydrocarbons were the most common types. Our results suggest that A. lancea suppressed pathogenic Fusarium populations by means of volatiles from the rhizome. Our results support the idea that intercropping with A. lancea or use of its effective components has a strong potential for managing soil-borne fungal diseases.
•Reduction of peanut root rot by A. lancea coincided with a decline of Fusarium spp.•Soil fungal community composition was more affected than bacteria by A. lancea volatiles.•A. lancea volatiles suppressed in vitro growth of Fusarium spp.•A. lancea volatiles decreased Fusarium spp. propagule density in soil.•Many antifungal substances were detected among the A. lancea rhizome volatiles.
Art in Dispute de Boer, Wietse
11/2021, Letnik:
59
eBook
A re-examinination of the Catholic Church's response to Reformation-era iconoclasm by reconstructing debates about sacred images held in the fifteen years preceding the Council of Trent's image ...decree (1563). The volume contains editions and translations of the original texts.
Root-derived, labile organic compounds are thought to enter the rhizosphere food web mainly via consumption by mycorrhizal fungi and bacteria. Studies tracking the fate of root derived carbon via ...stable isotope probing (SIP), however, indicate an important role for saprotrophic fungi as consumers of root exudates. In addition, it was shown that a diverse group of rhizosphere bacteria have the ability to withdraw carbon from saprotrophic fungal hyphae. Based on the fast carbon-flow into saprotrophic rhizosphere fungi and the wide-spread occurrence of rhizosphere bacteria with mycophagous abilities, we argue that the current concept of rhizosphere carbon flow should be revised to account for more complex microbial food web interactions. We propose to split the bacteria thriving in the rhizosphere niche into “plant-feeders” and “fungus-feeders”. The latter would include rhizosphere bacteria feeding on all functional groups of fungi, i.e. including mycorrhiza. To indicate the importance of saprotrophic fungi as a food source for rhizosphere bacteria, we introduce a new niche, the “sapro-rhizosphere niche”. We want to stimulate a discussion on rhizosphere carbon flow by challenging the established division into a mere bacterial- and fungal channel consisting of primary consumers, and to point at research directions based on the sapro-rhizosphere concept.
•Many rhizosphere bacteria have the ability to feed on fungi.•Rhizosphere bacteria that feed on fungi occupy a distinct niche, the sapro-rhizosphere.•Bacterial feeding on fungi has implications for below-ground carbon flow and should be incorporated in food-web models.
Abstract
Filamentous fungi are critical to the decomposition of terrestrial organic matter and, consequently, in the global carbon cycle. In particular, their contribution to degradation of ...recalcitrant lignocellulose complexes has been widely studied. In this review, we focus on the functioning of terrestrial fungal decomposers and examine the factors that affect their activities and community dynamics. In relation to this, impacts of global warming and increased N deposition are discussed. We also address the contribution of fungal decomposer studies to the development of general community ecological concepts such as diversity–functioning relationships, succession, priority effects and home–field advantage. Finally, we indicate several research directions that will lead to a more complete understanding of the ecological roles of terrestrial decomposer fungi such as their importance in turnover of rhizodeposits, the consequences of interactions with other organisms and niche differentiation.
This review discusses the functioning of terrestrial decomposer fungi and examines the factors that affect their activities and community dynamics.
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