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Interaction mechanism between fungi and bacteria in biochemical cycles
发布日期:2018-12-23  作者:邵晨  浏览量:102

Interaction mechanism between fungi and bacteria in biochemical cycles
Fungiand bacteria are found living together in a wide variety of environments. Theirinteractions are significant drivers of many ecosystem functions and areimportant for the health of plants and animals. A large number of fungal andbacterial families engage in complex interactions that lead to criticalbehavioural shifts of the microorganisms ranging from mutualism to antagonism.The importance of bacterial–fungal interactions (BFI) in environmental science,medicine and biotechnology has led to the emergence of a dynamic andmultidisciplinary research field that combines highly diverse approachesincluding molecular biology, genomics, geochemistry, chemical and microbialecology, biophysics and ecological modelling. In this review, we discuss recentadvances that underscore the roles of BFI across relevant habitats andecosystems. A particular focus is placed on the understanding of BFI withincomplex microbial communities and in regard of the metaorganism concept. Wealso discuss recent discoveries that clarify the (molecular) mechanismsinvolved in bacterial–fungal relationships, and the contribution of newtechnologies to decipher generic principles of BFI in terms of physicalassociations and molecular dialogues. Finally, we discuss future directions forresearch in order to stimulate synergy within the BFI research area and toresolve outstanding questions.

Fig.1 Microbial logistics in BFI. Fungalhyphae can efficiently colonise heterogeneous environmental habitats, createnew microhabitats and thereby enable a variety of emerging ecosystem processesand services that can be beneficial or detrimental to bacteria. The mycospherefunctions depend on the environment and the microorganisms involved and arehighly susceptible to disturbance.

Title:Bacterial–fungalinteractions: ecology, mechanisms and challenges

Downloadwebsite: https://academic.oup.com/femsre/article/42/3/335/4875924




Article 1:

Title: Hyphosphere interactions between an arbuscularmycorrhizal fungus and a phosphate solubilizing bacterium promote phytatemineralization in soil

Downloadwebsite:https://www.sciencedirect.com/science/article/pii/S0038071714000935?via%3Dihub

Maincontents:

Botharbuscular mycorrhizal (AM) fungi and phosphate solubilizing bacteria (PSB) areinvolved in phosphorus (P) mobilization and turnover but the influence of theirinteraction on organic P mineralization in the root free soil (hyphosphere)have been little studied. We investigated the interactive effects of an AMfungus (Rhizophagus irregularis, RI)and/or PSB (Pseudomonas alcaligenes,PA) on phytate mineralization and subsequent transfer to the host plant (Medicago sativa) using a two-compartmentmicrocosm with a central 30 μm nylon mesh barrier. The root growth compartmentcontaining 5 mg inorganic P (Pi, KH2PO4) kg−1soil was inoculated with RI or uninoculated and the AM fungal hyphal soilcontaining 75 mg organic P (Po, Na-phytate) plus 0 or 5 mg Pi kg−1soil was inoculated with PA or uninoculated.

Fig. 1 Schematicdiagram of an experimental microcosm.

Results:

1.Significantlyhigher shoot biomass production and P content among treatments were rankedRI/PA≈RI>PA≈ control irrespective of whether the plants were grown under 0or 5mg Pi kg−1soil application (Fig. 2). Comparedwith the control, 10 to 20 times significant increases (P<0.001) inshoot biomass or P content were found under both RI and RI/PA regardless of KH2PO4applicationrate, with the sole exception of shoot biomass under RI/PA (Fig.2).


Fig. 2 Differences in (a)shoot biomass production and (b) P content of 8-week-old Medicago sativaseedlings in soil inoculated with Rhizophagus irregularis (RI) and/or Pseudomonasalcaligenes (PA).

2.Significantly higher soil MBP among treatments ranked RI/PA>PA>RI≈controlwhen no Pi was supplied and PA>RI/PA>RI≈control under 5mgPikg−1soilapplication (Fig.3). Compared to the control, MBP in the hyphal soil under PA increasedsignificantly under both 0 (from 1.2 to 2.3mgPkg−1soil) and 5mgPikg−1soil(from 1.6 to 6.2mgkg−1soil) applications (Fig.3;P<0.001).In contrast, inoculation with RI had no effect on MBP (P=0.65). Compared withRI treatment dual RI/PA inoculation soil significantly increased MBP in thehyphal soil irrespective of the KH2PO4 application.


Fig.3Differences in microbial biomass P (MBP) concentration in soil inoculated with Rhizophagusirregularis (RI) and/or Pseudomonas alcaligenes M20 (PA).

3.The control treatment had the lowest while the dual RI/PA inoculation had thehighest acid phosphatase activity in the hyphal soil (Fig.4).Significantly higher soil acid phosphatase activity among treatments generallyfollowed the sequence RI/PA≥PA≥RI>control under both the 0 and 5mgPikg−1soilapplications. Significantly higher soil phytate-P concentrations amongtreatments generally followed the trend control ≥RI≥PA≥RI/PA under both the 0and 5mg Pi kg−1 soil applications.


Fig.4Differences in (a) acid phosphatase activity and (b) phytate-P concentration insoil inoculated with Rhizophagus irregularis (RI) and/or Pseudomonasalcaligenes M20 (PA).

Conclusion:

The study has demonstratedfor the first time that the PSB associated with AM fungal hyphae may play amajor role in phytate P mineralization and the AMfungus exerts priming effects on the mineralization and turnover of phytate inthe hyphosphere. This finding improves our understanding of the mechanismof organic P turnover by direct interactions between AM fungi and theirassociated bacteria.



Article 2:

Title: Mycelium-mediatedtransfer of water and nutrients stimulates bacterial activity in dry and oligotrophicenvironments

Downloadwebsite:https://www.nature.com/articles/ncomms15472

Maincontents:

Fungal–bacterialinteractions are highly diverse and contribute to many ecosystem processes.Their emergence under common environmental stress scenarios however, remainselusive. Here we use a synthetic microbial ecosystem based on the germinationof Bacillus subtilis spores toexamine whether fungal and fungal-like (oomycete) mycelia reduce bacterialwater and nutrient stress in an otherwise dry and nutrient-poor microhabitat.We find that the presence of mycelia enables the germination and subsequentgrowth of bacterial spores near the hyphae. Using a combination of time offlight- and nanoscale secondary ion mass spectrometry (ToF- and nanoSIMS)coupled with stable isotope labelling, we link spore germination to hyphaltransfer of water, carbon and nitrogen. Our study provides direct experimentalevidence for the stimulation of bacterial activity by mycelial supply of scarceresources in dry and nutrient-free environments. We propose that mycelia maystimulate bacterial activity and thus contribute to sustaining ecosystemfunctioning in stressed habitats.

(a)Scheme and photographs of the setup employed to carry out the germination, growthand labelling experiments. The synthetic ecosystem is comprised of two agarplugs serving as water and nutrient sources (‘with’) for the fungi or theoomycete inoculated on top of one of the agar plugs. A silicon wafer free ofwater and nutrients (‘without’) placed in the middle between the two ‘with’zones served as carrier for spores of B.subtilis. An air gap between the ‘with’ and ‘without’ zone prevented thediffusion of water or substrates to the spore region. (b) Gradual enlargementof bright-field micrographs of the silicon wafer overgrown by mycelium of P. ultimum. In close vicinity to thehyphae (black arrow) rod-shaped, vegetative bacterial cells (magenta arrows)were found, whereas smaller, round-shaped spores (yellow arrows) were located moredistantly. (c) Fluorescence micrograph of the 4′,6-diamidine-2-phenylindol(DAPI)-stained wafer showing P. ultimumhyphae containing nuclei (white arrows) and vegetative cells as well as sporesof B. subtilis.



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