Pathogenic microbes are known to manipulate the defences of their hosts through the production of secreted effector proteins. More recently, mutualistic mycorrhizal fungi have also been described as ...using these secreted effectors to promote host colonization. Here we characterize a mycorrhiza-induced small secreted effector protein of 10 kDa produced by the ectomycorrhizal fungus Pisolithus albus, PaMiSSP10b.
We demonstrate that PaMiSSP10b is secreted from fungal hyphae, enters the cells of its host, Eucalyptus grandis, and interacts with an S-adenosyl methionine decarboxylase (AdoMetDC) in the polyamine pathway. Plant polyamines are regulatory molecules integral to the plant immune system during microbial challenge.
Using biochemical and transgenic approaches we show that expression of PaMiSSP10b influences levels of polyamines in the plant roots as it enhances the enzymatic activity of AdoMetDC and increases the biosynthesis of higher polyamines. This ultimately favours the colonization success of P. albus.
These results identify a new mechanism by which mutualistic microbes are able to manipulate the host's enzymatic pathways to favour colonization.
•Oxalic acid extracts 100% of P from rock phosphates.•Compared to sulfuric acid, lower amount of oxalic acid is required to solubilize P.•Oxalic acid is a biotechnological alternative to produce P ...fertilizer.
Organic acids produced by microorganisms have been proposed as a biotechnological tool to release phosphorus (P) from sparingly soluble rock phosphates (RPs). In this work, organic acids commonly associated with microbial P solubilization (citric, gluconic, itaconic, malic, and oxalic) were applied at increasing doses to solubilize RPs with distinct reactivity grades. P solubilization by organic acids was compared to sulfuric acid, the traditional reagent applied in RP solubilization for fertilizer production. The acid type and its concentration had more influence on solubilized P than RP reactivity. In general, the efficiency of organic acids was oxalic > citric ≥ malic > itaconic > gluconic. Oxalic and sulfuric acids solubilized 100% of the P contained in all RPs composed by apatite Ca5(PO4)3(OH,F,Cl). However, oxalic acid was superior to sulfuric acid, releasing more P per mmol of acid applied. In average, each mmol of oxalic acid released 21 mg P, while sulfuric acid solubilized 14 mg P mmol−1. Thus, microorganisms producing oxalic acid appear as a promising alternative to process RP via a biotechnological route.
Aims
Despite the importance of the soil microbiota to plant growth, the role of soil microorganisms in crop-weed competition remains largely unexplored. Here, we investigated the influence of soil ...microbial communities and weed species on the outcome of maize-weed interactions.
Methods
The relationships between soil bacterial and fungal communities and plant growth under different cultivation managements (plant monocultures and coexistence between
Bidens pilosa
L. and
Amaranthus viridis
L. and maize) and soil conditions (sterilized soil and sterilized soil with microbiota reconstitution) were studied. Plant dry matter and soil microbial diversity were analyzed after 43 days of cultivation.
Results
Maize grew better in the presence of the weeds, indicating the occurrence of facilitation under the cultivation conditions tested. Plant cultivation led to different soil microbial communities after soil sterilization and microbiota reconstitution. In sterilized soil, the colonizing microbiota led to higher maize growth in the presence of
B. pilosa
. The opposite was observed in the soils with microbiota reconstitution, where maize grew better with
A. viridis
.
Conclusions
Soil microbial communities are involved in the facilitation of maize growth by
B. pilosa
and
A. viridis
. Facilitation intensity depends on the weed species and the way coexisting plants shape the soil microbial communities.
During fungal rock phosphate (RP) solubilization, a significant quantity of fluoride (F(-)) is released together with phosphorus (P), strongly inhibiting the process. In the present study, the effect ...of two F(-) adsorbents activated alumina (Al2O3) and biochar on RP solubilization by Aspergillus niger was examined. Al2O3 adsorbed part of the F(-) released but also adsorbed soluble P, which makes it inappropriate for microbial RP solubilization systems. In contrast, biochar adsorbed only F(-) while enhancing phosphate solubilization 3-fold, leading to the accumulation of up to 160 mg of P per liter. By comparing the values of F(-) measured in solution at the end of incubation and those from a predictive model, it was estimated that up to 19 mg of F(-) per liter can be removed from solution by biochar when added at 3 g liter(-1) to the culture medium. Thus, biochar acted as an F(-) sink during RP solubilization and led to an F(-) concentration in solution that was less inhibitory to the process. In the presence of biochar, A. niger produced larger amounts of citric, gluconic, and oxalic acids, whether RP was present or not. Our results show that biochar enhances RP solubilization through two interrelated processes: partial removal of the released F(-) and increased organic acid production. Given the importance of organic acids for P solubilization and that most of the RPs contain high concentrations of F(-), the proposed solubilization system offers an important technological improvement for the microbial production of soluble P fertilizers from RP.
The retreat of glaciers in Antarctica has increased in the last decades due to global climate change, influencing vegetation expansion, and soil physico-chemical and biological attributes. However, ...little is known about soil microbiology diversity in these periglacial landscapes. This study characterized and compared bacterial and fungal diversity using metabarcoding of soil samples from the Byers Peninsula, Maritime Antarctica. We identified bacterial and fungal communities by amplification of bacterial 16 S rRNA region V3-V4 and fungal internal transcribed spacer 1 (ITS1). We also applied
C dating on soil organic matter (SOM) from six profiles. Physico-chemical analyses and attributes associated with SOM were evaluated. A total of 14,048 bacterial ASVs were obtained, and almost all samples had 50% of their sequences assigned to Actinobacteriota and Proteobacteria. Regarding the fungal community, Mortierellomycota, Ascomycota and Basidiomycota were the main phyla from 1619 ASVs. We found that soil age was more relevant than the distance from the glacier, with the oldest soil profile (late Holocene soil profile) hosting the highest bacterial and fungal diversity. The microbial indices of the fungal community were correlated with nutrient availability, soil reactivity and SOM composition, whereas the bacterial community was not correlated with any soil attribute. The bacterial diversity, richness, and evenness varied according to presence of permafrost and moisture regime. The fungal community richness in the surface horizon was not related to altitude, permafrost, or moisture regime. The soil moisture regime was crucial for the structure, high diversity and richness of the microbial community, specially to the bacterial community. Further studies should examine the relationship between microbial communities and environmental factors to better predict changes in this terrestrial ecosystem.
Phosphorus (P) can undergo adsorption and precipitation reactions in the soil. When fixed to iron and aluminum oxyhydroxides in highly weathered soils, P is covalently linked to the soil solid phase ...and becomes unavailable to crops. Plants and microorganisms produce organic acids as a strategy to acquire P for growth. These compounds have been used to extract P from sparingly soluble phosphate minerals and may play a role in reverting P adsorption and fixation in the soil. The objective of this work was to study the ability of Aspergillus niger FS1 and organic acids to desorb P after 40 d of contact of the nutrient with 75-μm fractions of a typical highly weathered Oxisol. Samples of the soil fractions from the A and B horizons were incubated for 40 d with P at concentrations corresponding to 90% of the soil maximum P adsorption capacity (MPAC). The ability of A. niger FS1 to desorb P from the soil was performed in a culture medium optimized for phosphate-solubilizing microorganisms. The desorption kinetics of the P bound to the soil fractions was evaluated for oxalic acid at 10 mmol L−1, and for a mixture of oxalic + citric acids, both at 5 mmol L−1. Water at pH 7.0 and at pH 2.0 was used as controls. The fungus released 18.0% of the P from the A and B horizon fractions after 7 days of growth. Oxalic acid was the most efficient compound at desorbing P from the soil, releasing 32.7% of the P from the A horizon fraction, and 18.5%, for the B horizon fraction. These findings contribute to a better understanding of the mechanistic basis of microbial P release from highly weathered soils, opening prospects for the development of microbial techniques allowing plant access to P fixed in the soils and the improvement of P fertilizer use efficiency.
•P can be desorbed from soil by organic acids and Aspergillus niger.•Aspergillus niger and organic acids can increase the efficiency of P fertilizers.•Aspergillus niger can potentially contribute to P nutrition of plants.•First report on the ability of a fungus to desorb P from a highly weathered Oxisol.
Pisolithus microcarpus (Cooke & Massee) G. Cunn is a gasteromycete that produces closed basidiocarps in symbiosis with eucalypts and acacias. The fungus produces a complex basidiocarp composed of ...peridioles at different developmental stages and an upper layer of basidiospores free of the hyphae and ready for wind dispersal upon the rupture of the basidiocarp pellis. During basidiosporogenesis, a process that takes place inside the basidiocarp peridioles, a conspicuous reserve of fatty acids is present throughout development. While several previous studies have described basidiosporogenesis inside peridioles, very little is known about gene expression changes that may occur during this part of the fungal life cycle. The objective of this work was to analyze gene transcription during peridiole and basidiospore development, while focusing specifically on cell cycle progression and lipid metabolism.
Throughout different developmental stages of the peridioles we analyzed, 737 genes were regulated between adjacent compartments (>5 fold, FDR-corrected p-value < 0.05) corresponding to 3.49% of the genes present in the P. microcarpus genome. We identified three clusters among the regulated genes which showed differential expression between the peridiole developmental stages and the basidiospores. During peridiole development, transcripts for proteins involved in cellular processes, signaling, and information storage were detected, notably those for coding transcription factors, DNA polymerase subunits, DNA repair proteins, and genes involved in chromatin structure. For both internal embedded basidiospores (hereto referred to as "Internal spores", IS) and external free basidiospores (hereto referred to as "Free spores", FS), upregulated transcripts were found to involve primary metabolism, particularly fatty acid metabolism (FA). High expression of transcripts related to β-oxidation and the glyoxylate shunt indicated that fatty acids served as a major carbon source for basidiosporogenesis.
Our results show that basidiocarp formation in P. microcarpus involves a complex array of genes that are regulated throughout peridiole development. We identified waves of transcripts with coordinated regulation and identified transcription factors which may play a role in this regulation. This is the first work to describe gene expression patterns during basidiocarp formation in an ectomycorrhizal gasteromycete fungus and sheds light on genes that may play important roles in the developmental process.
The elemental ratios of plant tissues are associated with the adaptive and competitive success of a plant species in an ecosystem. So far, no study has evaluated if and how crop–weed competition ...influences the elemental ratios of competing populations, although such information is important to understand weed infestation dynamics and to improve weed management in agroecosystems. The objective of this study was to analyze weed–crop elemental ratios during interspecific competition between weeds and crops in greenhouse experiments. For this, maize (Zea mays L.) and the weeds Amaranthus viridis L, Bidens pilosa L., and Ipomoea grandifolia (Dammer) O'Donell were grown under seven treatments: maize and weed monocultures, and maize in competition with weeds. Competition between plants practically did not influence growth and nutrient contents of maize but reduced weed growth and nutrient uptake. Maize showed few changes in elemental ratios. In contrast, B. pilosa and I. grandifolia were very sensitive to competition and showed significant increases in C : N, C : P, C : K, N : P, and N : K ratios when grown with maize. A. viridis showed low flexibility of nutrient : nutrient ratios under the same competitive pressure as that faced by B. pilosa and I. grandifolia. The interspecific competition led to increases only in the C : P ratio of A. viridis shoots. Therefore, interspecific competition changes the elemental ratios, mainly of the weeds, and the magnitude of this change is dependent on the plant species involved. Interspecific competition changes plant biomass quality (higher C : nutrient ratios), mainly for B. pilosa and I. grandifolia.
Human occupation of Trindade Island caused the decline of much of its vegetation and pronounced changes of the island's landscape. The main factor behind these changes was human colonization and the ...introduction of goats by Edmond Harlley in 1700. Without natural predators on the island, these animals proliferated uncontrolled and consumed almost all plant cover. High declivities in most parts of the island led to soil erosion and loss of surface soil. The goats were finally eradicated in 2005, allowing vegetation to recover since then. This work explored the hypothesis that the recovery of the island's vegetation was accompanied by the recovery of physicochemical characteristics and soil biological functions. Soils in revegetated areas showed higher values of microbial biomass, basal respiration, microbial quotient, mineralizable nitrogen, and enzymatic activities, and lower metabolic quotient. Principal component analyzes demonstrated that the correlations between the indicators and the principal components remained practically unchanged in two sampling periods (rainy and dry season). Biological indicators are more related to the presence or absence of vegetation than to the type of vegetation, soil physicochemical properties or time of sampling. The natural recovery of the vegetation, combined with the microbiological indicators of soil, demonstrate the improvement of the insular ecosystem after goats were eradicated.
•The revegetation of Trindade Island increased the soil microbiological function.•There was no seasonal effect on microbial indicators for a same soil in the island.•The revegetation of Trindade Island provides recovery of the soil quality.
•Ammonium increases the mobilization of non-exchangeable Ca reservoirs.•The acquisition of Ca2+ from non-exchangeable fractions by E. urograndis is induced by ammonium.•The release of Ca from ...Ca-oxalate does not change as a function of soil pH.
Eucalypt plants can take up calcium (Ca) from soils with nondetectable levels of exchangeable Ca2+. This suggests the operation of unknown processes capable of rendering non-exchangeable forms of the nutrient available to eucalypts. An explanatory hypothesis for this phenomenon is that soil acidification by ammonium can release Ca from Ca-oxalate and soil minerals. Therefore, the objective of this work was to study the interactions between Ca-oxalate and ammonium on Ca and N nutrition of a Eucalyptus grandis × Eucalyptus urophylla hybrid (Eucalyptus urograndis) in a soil with nondetectable exchangeable Ca2+. For this, E. urograndis seedlings (clone AEC 144) were grown in pots with soil fertilized with the combination of five Ca doses (0, 0.10, 0.20, 0.40, and 0.80 cmolc/kg) as Ca-oxalate, and five N doses (0, 25, 50, 100, and 200 mg/kg) as NH4Cl. The experiment was conducted in a greenhouse for 60 days. Two additional experiments were conducted to verify the stability of Ca-oxalate at different doses in the soil along an incubation time of 60 days and at different soil pH. E. urograndis dry matter production and Ca and N uptake were highly dependent on ammonium applied to the soil, but only slightly influenced by Ca-oxalate. When no Ca-oxalate was added, Ca from a non-exchangeable source was transferred to E. urograndis. This transfer increased with increasing ammonium supply, stabilizing at the highest N dose applied. Ca-oxalate solubilization in the soil without E. urograndis plants ranged from 62 to 94% after 60 days of soil incubation and the release of Ca from Ca-oxalate did not change as a function of pH. In general, the release of Ca from Ca-oxalate presented two behaviors: pH-independent (trial without plants) and pH/NH4+-dependent (trial with plants). This is the first report demonstrating that ammonium lead to the mobilization of non-exchangeable Ca reservoirs by E. urograndis plants cultivated in a soil with no exchangeable Ca.
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