Mycorrhizosphere Bacteria Research Articles

Mycorrhizosphere bacteria inhibit greenhouse gas emissions from microplastics contaminated soil by regulating soil enzyme activities and microbial community structure

Microplastics (MPs) accumulation in terrestrial ecosystems can affect greenhouse gases (GHGs) production by altering microbial and soil structure. Presently, research on the MPs effect on plants is not consistent, and underlying molecular mechanisms associated with GHGs are yet unknown. For the first time, we conducted a microcosm study to explore the impact of MPs addition (Raw vs. aged) and Trichoderma longibrachiatum and Bacillus subtilis inoculation (Sole vs. combination) on GHGs emission, soil community structure, physiochemical properties, and enzyme activities. Our results indicated that the addition of aged MPs considerably enhanced the GHGs emissions (N2O (+16%) and CO2 (+21%), respectively), C and N cycling gene expression, microbial biomass carbon, and soil physiochemical properties than raw MPs. However, the soil microbial community structure and enzyme activities were enhanced in raw MPs added treatments, irrespective of the MPs type added to soil. However, microbial inoculation significantly reduced GHGs emission by altering the expression of C and N cycling genes in both types of MPs added treatments. The soil microbial community structure, enzymes activities, physiochemical properties and microbial biomass carbon were enhanced in the presence of microbial inoculation in both type of MPs. Among sole and combined inoculation of Trichoderma and Bacillus subtilis, the co-applied Trichoderma and Bacillus subtilis considerably reduced the GHGs emission (N2O (−64%) and CO2 (−61%), respectively) by altering the expression of C and N cycling genes regardless of MPs type used. The combined inoculation also enhanced soil enzyme activities, microbial community structure, physiochemical properties and microbial biomass carbon in both types of MPs treatment. Our findings provide evidence that polyethylene MPs likely pose a high risk of GHGs emission while combined application of Trichoderma and Bacillus subtilis significantly reduced GHGs emission by altering C and N cycling gene expression, soil microbial community structure, and enzyme activities under MPs pollution in a terrestrial ecosystem.

Mycorrhizosphere bacteria inhibit chromium uptake and phytotoxicity by regulating proline metabolism, antioxidant defense system, and aquaporin gene expression in tomato.

Chromium (Cr) contamination in soil-plant systems poses a pressing environmental challenge due to its detrimental impacts on plant growth and human health. Results exhibited that Cr stress decreased shoot biomass, root biomass, leaf relative water content, and plant height. However, single and co-application of Bacillus subtilis (BS) and arbuscular mycorrhizal fungi (AMF) considerably enhanced shoot biomass (+ 21%), root biomass (+ 2%), leaf relative water content (+ 26%), and plant height (+ 13) under Cr stress. The frequency of mycorrhizal (F) association (+ 5%), mycorrhizal colonization (+ 13%), and abundance of arbuscules (+ 5%) in the non-stressed soil was enhanced when inoculated with combined BS and AMF as compared to Cr-stressed soil. The co-inoculation with BS and AMF considerably enhanced total chlorophyll, carotenoids, and proline content in Cr-stressed plants. Cr-stressed plants resulted in attenuated response in SOD, POD, CAT, and GR activities when inoculated with BS and AMF consortia by altering oxidative stress biomarkers (H2O2 and MDA). In Cr-stressed plants, the combined application of BS and AMF considerably enhanced proline metabolism, for instance, P5CR (+ 17%), P5CS (+ 28%), OAT (- 22%), and ProDH (- 113%) as compared to control. Sole inoculation with AMF downregulated the expression of SIPIP2;1, SIPIP2;5, and SIPIP2;7 in Cr-stressed plants. However, the expression of NCED1 was downregulated with the application of sole AMF. In contrast, the relative expression of Le4 was upregulated in the presence of AMF and BS combination in Cr-stressed plants. Therefore, it is concluded that co-application of BS and AMF enhanced Cr tolerance by enhancing proline metabolism, antioxidant enzymes, and aquaporin gene expression. Future study might concentrate on elucidating the molecular processes behind the synergistic benefits of BS and AMF, as well as affirming their effectiveness in field experiments under a variety of environmental situations. Long-term research on the effect of microbial inoculation on soil health and plant production might also help to design sustainable chromium remediation solutions.

Mycorrhizosphere Bacteria, Rahnella sp. HPDA25, Promotes the Growth of Armillaria gallica and Its Parasitic Host Gastrodia elata.

Gastrodia elata is an entirely heterotrophic plant, the growth of which is completely reliant on Armillaria gallica, an orchid mycorrhizal fungus. To avoid damaging ecosystems, G. elata cultivation is shifting from woodland to farmland. However, whether the microbial community structure remains stable during this conversation is unknown. Here, we cultivated G. elata in woodland or farmland and found that woodland-cultivated G. elata produced a greater yield and larger tuber size. The relative abundance of Rahnella was 22.84- and 122.25-fold higher in woodland- and farmland-cultivated soil samples, respectively, than that in uncultivated soil samples. To investigate how Rahnella impacts the growth of G. elata and establishes symbiosis with Armillaria gallica, three Rahnella spp. strains (HPDA25, SBD3, and SBD11) were isolated from mycorrhizosphere soil samples. It was found that these strains, especially HPDA25, promoted the growth of A. gallica. Ultra-performance liquid chromatography coupled to a triple quadrupole mass spectrometry analysis detected the indole-3-acetic acid with 16.24 ng/ml in HPDA25 fermentation solution. Co-culturing with the strain HPDA25 or exogenous indole-3-acetic acid increased the branching and fresh weight of rhizomorphs and the growth rate and extracellular laccase activity of A. gallica, compared with A. gallica cultured alone. The results of RNA-seq and quantitative real-time polymerase chain reaction analysis showed that co-culturing A. gallica with HPDA25 increased the expression level of the genes including hydrophobin, SUR7/PalI family, and pectin methylesterase, whereas decreased the expression levels of glycolysis-related genes. Furthermore, co-culturing with the strain HPDA25, A. gallica promotes the growth of G. elata and enhances the tuber size of G. elata. These results provide new insights into an orchid mycorrhizal symbiosis and the cultivation of G. elata.

Mycorrhizosphere bacteria and plant-plant interactions facilitate maize P acquisition in an intercropping system

The intensive use of chemical fertilizer particularly phosphorus (P) to provide sufficient plant nutrients to meet the global food demand can deteriorate the quality of the ecosystem and are not affordable to farmers in low-resource environments. Additionally, low use efficiency of P in agriculture due to its low immobility in soil and rapid precipitation with soil minerals, which caused low bioavailable P content in soil. Therefore, a sustainable P use and management mode for cleaner agricultural production is an urgent issue to solve. Here we evaluated an alternative strategy to facilitate plant P nutrient availability with arbuscular mycorrhizal fungi (Rhizophagus irregularis) and their associated bacteria in cereal-legume intercropping based on a pot experiment. Plants were grown with or without Rhizophagus irregularis (AM) in pots against three different phosphorus levels and were inoculated with two bacteria strains (B). AMF root colonization and the influence of intercropping and microbial inoculation on plant growth and nutrient absorption were investigated. The findings showed that inoculated plants under the intercropping system produce the greatest plant growth responses and highest P uptake. The highest plant growth performance, soil P availability, and uptake were observed under the intercropping system with 30 kg P ha−1 (50% of the regular recommended P fertilizer rate) application. Further, we evaluated the influence of the microbial inoculation on mobilization of sparingly soluble phosphate. The results demonstrated a significant decreased in Al–P, Fe–P and Ca–P under the 30 kg P ha−1 fertilizer rate. Specifically, comparing with the control (Ctrl) there was 30.32% (AM) and 36.35% (AMB) reduction in Al–P, 44.53% (AM) and 45.11% (AMB) reduction in Fe–P, and 39.68% (AM) and 43.61% (AMB) decrease in Ca–P. These findings extend our knowledge regarding the significant role of plant-microbes symbiosis under intercropping system on sustainable crop production and nutrient (P) use efficiency.

Phytohormones and volatile organic compounds, like geosmin, in the ectomycorrhiza of Tricholoma vaccinum and Norway spruce (Picea abies)

The ectomycorrhizospheric habitat contains a diverse pool of organisms, including the host plant, mycorrhizal fungi, and other rhizospheric microorganisms. Different signaling molecules may influence the ectomycorrhizal symbiosis. Here, we investigated the potential of the basidiomycete Tricholoma vaccinum to produce communication molecules for the interaction with its coniferous host, Norway spruce (Picea abies). We focused on the production of volatile organic compounds and phytohormones in axenic T. vaccinum cultures, identified the potential biosynthesis genes, and investigated their expression by RNA-Seq analyses. T. vaccinum released volatiles not usually associated with fungi, like limonene and β-barbatene, and geosmin. Using stable isotope labeling, the biosynthesis of geosmin was elucidated. The geosmin biosynthesis gene ges1 of T. vaccinum was identified, and up-regulation was scored during mycorrhiza, while a different regulation was seen with mycorrhizosphere bacteria. The fungus also released the volatile phytohormone ethylene and excreted salicylic and abscisic acid as well as jasmonates into the medium. The tree excreted the auxin, indole-3-acetic acid, and its biosynthesis intermediate, indole-3-acetamide, as well as salicylic acid with its root exudates. These compounds could be shown for the first time in exudates as well as in soil of a natural ectomycorrhizospheric habitat. The effects of phytohormones present in the mycorrhizosphere on hyphal branching of T. vaccinum were assessed. Salicylic and abscisic acid changed hyphal branching in a concentration-dependent manner. Since extensive branching is important for mycorrhiza establishment, a well-balanced level of mycorrhizospheric phytohormones is necessary. The regulation thus can be expected to contribute to an interkingdom language.

Facilitation of phosphorus uptake in maize plants by mycorrhizosphere bacteria

A major challenge for agriculture is to provide sufficient plant nutrients such as phosphorus (P) to meet the global food demand. The sufficiency of P is a concern because of it’s essential role in plant growth, the finite availability of P-rock for fertilizer production and the poor plant availability of soil P. This study investigated whether biofertilizers and bioenhancers, such as arbuscular mycorrhizal fungi (AMF) and their associated bacteria could enhance growth and P uptake in maize. Plants were grown with or without mycorrhizas in compartmented pots with radioactive P tracers and were inoculated with each of 10 selected bacteria isolated from AMF spores. Root colonization by AMF produced large plant growth responses, while seven bacterial strains further facilitated root growth and P uptake by promoting the development of AMF extraradical mycelium. Among the tested strains, Streptomyces sp. W94 produced the largest increases in uptake and translocation of 33P, while Streptomyces sp. W77 highly enhanced hyphal length specific uptake of 33P. The positive relationship between AMF-mediated P absorption and shoot P content was significantly influenced by the bacteria inoculants and such results emphasize the potential importance of managing both AMF and their microbiota for improving P acquisition by crops.

Growth and ectomycorrhization of banj oak plants co-inoculated with Scleroderma bovista and mycorrhizosphere bacteria

Effect of composite treatment of ectomycorrhizal fungus (EMF), Scleroderma bovista, along with mycorrhizosphere bacterial inoculants was studied for nine months on Quercus leucotrichophora plants grown in nursery glasshouse. Seven treatments comprising of one uninoculated control; two bacterial controls, Bacillus subtilis MB14 and Pseudomonas fluorescens MB 9, respectively; EMF control, S. bovista; two combinations of two bacterial treatments with EMF and one triple treatment of two bacteria with EMF, were used in the study. The ninth month of sampling showed that triple treatment of two strains of bacteria with EMF maximally enhanced root length (38.86 cm), dry weight (6.746 g), short roots (351.6), lateral roots (24.8) and EMF colonization (34.8%) of banj oak plant, which was fairly higher than uninoculated and bacterial controls. Bacteria treated plants showed no plant growth enhancement, whereas EMF treatment fairly enhanced plant growth. The co-inoculation practice can help oak plant in achieving the mycorrhization rate even with lower EMF doses. These findings will be beneficial for achieving the effective banj oak replantation in the Himalayan region.

Isolation and Identification of Mycorrhizosphere Bacteria and Their Antagonistic Effects Towards Ganoderma boninense in vitro

Basal stem rot caused by Ganoderma boninense is the most serious disease of oil palm ( Elaeis guineensis ) in Indonesia and it has caused major loss in palm oil production. Mycorrhizosphere bacteria offer possible advantages as biocontrol agents as they live and proliferate together with arbuscular mycorrhizal fungi, which have an ability to increase plant resistance against pathogens. A study was conducted to isolate mycorrhizosphere bacteria from spores of arbuscular mycorrhizal fungi and test their antagonistic effects against G. boninense in vitro . All bacterial isolates were identified based on 16S rDNA analysis and it revealed that eleven out of twenty mycorrhizosphere bacteria isolated were related to Bacillus with similarity ranging from 97 to 100%, whereas other isolates were identified as Pseudomonas, Streptomyces, Kocuria, Enterobacter, Brevundimonas , and Alcaligenes with similarities ranging from 96 to 100%. Fourteen out of twenty mycorrhizosphere bacteria showed a varying degree of inhibition towards the growth of G. boninense in vitro . Of these, isolate B10 (closely related to Bacillus subtilis ZJ06) showed the highest inhibitory effect followed by B17 (closely related to Bacillus subtilis N43). Therefore, these bacteria have a potential to be used as biocontrol agents to control basal stem rot disease caused by G. boninense in oil palm.

Interactions between mycorrhizal fungi and mycorrhizosphere bacteria during mineral weathering: Budget analysis and bacterial quantification

The impact of ectomycorrhizal fungi or rhizosphere bacteria on tree seedling growth and nutrient uptake is well known. However, few studies have combined those microorganisms in one experiment to clarify their relative contribution and interactions in nutrient acquisition. Here, we monitored the respective contributions of pine roots, two ubiquitous forest ectomycorrhizal fungi Scleroderma citrinum and Laccaria bicolor, and two S. citrinum-mycorrhizosphere bacterial strains of Burkholderia glathei and Collimonas sp., on mineral weathering, nutrient uptake, and plant growth. Pinus sylvestris plants were grown on quartz–biotite substrate and inoculated or not with combinations of mycorrhizal fungi and/or bacterial strains. Magnesium and potassium fluxes were measured and nutrient budgets were calculated. Both ectomycorrhizal fungi significantly increased Mg plant uptake. No significant effects of the two bacterial strains were detected on the K and Mg budgets, but co-inoculating the mycorrhizal fungus S. citrinum and the efficient mineral-weathering B. glathei bacterial strain significantly improved the Mg budget. Similarly, co-inoculating S. citrinum with the Collimonas sp. bacterial strain significantly improved the pine biomass compared to non-inoculated pine plants. In order to better understand this process, we monitored the survival of the inoculated bacterial strains in the quartz–biotite substrate, the pine rhizosphere, and the mycorrhizal niche. The results showed that the two bacterial strains harboured different colonization behaviours both of which depended on the presence of the ectomycorrhizal partner. The populations of the Burkholderia strain were maintained in all these environments with a significantly higher density in the mycorrhizal niche, especially of S. citrinum. In contrast the population of the Collimonas strain reached the detection level except in the treatment inoculated with S. citrinum. These results highlight the need for taking into account the ecology of the microorganisms, and more specifically the fungal–bacterial interactions, when studying mineral weathering and plant nutrition.

Screening for Putative PGPR to Improve Establishment of the Symbiosis Lactarius deliciosus-Pinus sp.

A screening for plant growth promoting rhizobacteria (PGPR) was carried out in the mycorrhizosphere of wild populations of Pinus pinea and P. pinaster, and in the mycosphere of associated Lactarius deliciosus. A total of 720 bacteria were isolated, purified, and grouped by morphological criteria. Fifty percent of the isolates were selected and tested for aminocyclopropanecarboxylic acid (ACC) degradation, auxin and siderophore production, and phosphate solubilization. Thirty eight percent of the isolates showed at least one of the evaluated activities. Nutrient-related traits were associated with P. pinaster, whereas hormone production traits predominated in P. pinea. These activities were found mostly in Gram positive isolates. After PCR-RAPDs (random amplified polymorphic DNA) analysis, 10 groups appeared with 85% similiarity when considering all isolates, indicating the low diversity in the system. One strain of each group was identified by 16S rDNA sequencing. Our results suggest that P. pinaster selects for mycorrhizosphere bacteria that mobilize nutrients, whereas P. pinea selects for bacteria that have the capacity to increase root growth via production of plant growth regulators.

Production of B-group vitamins by bacteria isolated from soil, rhizosphere, and mycorrhizosphere of pine (Pinus sylvestris L.)

Studies on the production of B vitamins by soil, rhizosphere, and mycorrhizosphere bacteria have revealed that such ability is common among these organisms. Thiamin, nicotinic and folic acids were produced by the greatest number of bacteria. Bacteria isolated from the rhizosphere and mycorrhizosphere produced more riboflavin than those originating from the soil distant from roots. In general the soil strains produced higher amounts of vitamins (except riboflavin) than the root-zone isolates. Two and three vitamins were produced by the majority of bacteria. The synthesis of four and five vitamins was found in few strains only.

Synthesis of free amino acids by bacteria isolated from soil, rhizosphere, and mycorrhizosphere of pine (Pinns sylvestris L.)

Summary Production of free amino acids was studied in 50 strains of soil and root zone bacteria (rhizosphere and mycorrhizosphere) of pine (Pinus sylvestris L.). Most of the soil bacteria produced considerable amounts of glutamic acid and, somewhat less, of alanine and valine. Rhizosphere bacteria synthesized in general small amounts (with the exceptions of few strains) of glutamic acid, alanine lysine and unidentified ninhydrin-positive compound X2. On the other hand, the mycorrhizosphere bacteria produced considerably large amounts of alanine, leucine, and valine. Soil bacteria produced glutamic acid in amounts of 22–87μg/mg dry mass. This compound was excreted in amounts of 0.5–70 μg/mg dry mass by rhizosphere and mycorrhizosphere organisms. The quantity of other amino acids, excreted by the bacteria studied, was smaller than those mentioned above. It is suggested that the amino acids, produced by the root zone-inhabiting bacteria of pine, are essential for amino acids-requiring organisms, for mycorrhizal fungi, as well as for the plantmicrobe interrelationships.