Abstract
In this study, the mycosphere isolate Burkholderia terrae BS001 was confronted with the soil fungus Lyophyllum sp. strain Karsten on soil extract agar plates in order to examine its transcriptional responses over time. At the initial stages of the experiment (T1—day 3; T2—day 5), contact between both partner organisms was absent, whereas in the final stage (T3—day 8), the two populations made intimate physical contact. Overall, a strong modulation of the strain BS001 gene expression patterns was found. First, the stationary-phase sigma factor RpoS, and numerous genes under its control, were strongly expressed as a response to the soil extract agar, and this extended over the whole temporal regime. In the system, B. terrae BS001 apparently perceived the presence of the fungal hyphae already at the early experimental stages (T1, T2), by strongly upregulating a suite of chemotaxis and flagellar motility genes. With respect to specific metabolism and energy generation, a picture of differential involvement in different metabolic routes was obtained. Initial (T1, T2) up- or downregulation of ethanolamine and mandelate uptake and utilization pathways was substituted by a strong investment, in the presence of the fungus, in the expression of putative metabolic gene clusters (T3). Specifically at T3, five clustered genes that are potentially involved in energy generation coupled to an oxidative stress response, and two genes encoding short-chain dehydrogenases/oxidoreductases (SDR), were highly upregulated. In contrast, the dnaE2 gene (related to general stress response; encoding error-prone DNA polymerase) was transcriptionally downregulated at this stage. This study revealed that B. terrae BS001, from a stress-induced state, resulting from the soil extract agar milieu, responds positively to fungal hyphae that encroach upon it, in a temporally dynamic manner. The response is characterized by phases in which the modulation of (1) chemotaxis, (2) metabolic activity, and (3) oxidative stress responses are key mechanisms.
Highlights
The soil bacterium Burkholderia terrae BS001 was originally isolated on the basis of its capacity to interact with the basidiomycetous soil fungus Lyophyllum sp. strain Karsten [1]
This study revealed that B. terrae BS001, from a stress-induced state, resulting from the soil extract agar milieu, responds positively to fungal hyphae that encroach upon it, in a temporally dynamic manner
Given its presumed importance as an accelerator of metabolism, we examined the expression of the glycerol uptake (GUP) gene AKAUv1_1930108 [3] across all treatments
Summary
The soil bacterium Burkholderia terrae BS001 was originally isolated on the basis of its capacity to interact with the basidiomycetous soil fungus Lyophyllum sp. strain Karsten [1]. The soil bacterium Burkholderia terrae BS001 was originally isolated on the basis of its capacity to interact with the basidiomycetous soil fungus Lyophyllum sp. There is mounting evidence for the contention that this interacting pair forms an ecologically relevant mutualism, which we previously have coined the B. terrae BS001Lyophyllum sp. Strain Karsten interactome [2]. This bacterium has the capacity to induce the release of glycerol by the fungus and efficiently utilize it as a carbon and energy source [5]. Strain Karsten and several other fungi—established agglomerates of cells, i.e., Bprimitive^ biofilms, around the mycelia of these fungi [1] Strain BS001—upon confrontation with Lyophyllum sp. strain Karsten and several other fungi—established agglomerates of cells, i.e., Bprimitive^ biofilms, around the mycelia of these fungi [1]
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