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Probiotic Bacillus colonization of plant root surfaces has been reported to improve its beneficial effect. Chemotaxis, adhesion, aggregation, and biofilm formation are the four steps of root colonization by plant growth–promoting rhizobacteria (PGPRs). Compared with the other three well-studied processes, adhesion of PGPRs is less known. In this study, using mutant strains deleted for potential adhesin genes in PGPR strain Bacillus velezensis SQR9, adherence to both cucumber root surface and abiotic surface by those strains was evaluated. Results showed that deletion mutations ΔlytB, ΔV529_10500, ΔfliD, ΔyhaN, and ΔsacB reduced the adhesion to root surfaces, while, among them, only ΔfliD had significant defects in adhesion to abiotic surfaces (glass and polystyrene). In addition, B. velevzensis SQR9 mutants defective in adhesion to root surfaces showed a deficiency in rhizosphere colonization. Among the encoded proteins, FliD and YhaN played vital roles in root adhesion. This research systematically explored the potential adhesins in a well-studied PGPR strain and also indicated that adhesion progress was required for root colonization, which will help to enhance rhizosphere colonization and beneficial function of PGPRs in agricultural production. [Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

A pineapple-banana rotation was studied as a model system to investigate the potential emergence of a fungal-mediated disease-suppression in a soil highly infested with the pathogen Fusarium oxysporum causing the banana wilt disease. By using both field and pot experiments, the pineapple-banana rotation system resulted in a significant decrease of the pathogen number and next-stubble banana disease incidence (P

Trophic interactions play a central role in driving microbial community assembly and function. In gut or soil ecosystems, successful inoculants are always facilitated by efficient colonization; however, the metabolite exchanges between inoculants and resident bacteria are rarely studied, particularly in the rhizosphere. Here, we used bioinformatic, genetic, transcriptomic, and metabonomic analyses to uncover syntrophic cooperation between inoculant (Bacillus velezensis SQR9) and plant-beneficial indigenous Pseudomonas stutzeri in the cucumber rhizosphere. We found that the synergistic interaction of these two species is highly environmental dependent, the emergence of syntrophic cooperation was only evident in a static nutrient-rich niche, such as pellicle biofilm in addition to the rhizosphere. Our results identified branched-chain amino acids (BCAAs) biosynthesis pathways are involved in syntrophic cooperation. Genome-scale metabolic modeling and metabolic profiling also demonstrated metabolic facilitation among the bacterial strains. In addition, biofilm matrix components from Bacillus were essential for the interaction. Importantly, the two-species consortium promoted plant growth and helped plants alleviate salt stress. In summary, we propose a mechanism in which synergic interactions between a biocontrol bacterium and a partner species promote plant health.

Conidia of Trichoderma guizhouense (Hypocreales, Ascomycota) are frequently applied to the production of biofertilizers and biocontrol agents. Conidiation of some Trichoderma species depends on blue light and the action of different blue light receptors. However, the interplay between different blue-light receptors in light signalling remained elusive. Here, we studied the functions of the blue light receptors BLR1 and ENV1, and the MAP kinase HOG1 in blue light signalling in T. guizhouense. We found that the BLR1 dominates light responses and ENV1 is responsible for photoadaptation. Genome-wide gene expression analyses revealed that 1615 genes, accounting for ~13.4% of the genes annotated in the genome, are blue-light regulated in T. guizhouense, and remarkably, these differentially expressed genes (DEGs) including 61 transcription factors. BLR1 and HOG1 are the core components of the light signalling network, which control 79.9% and 73.9% of the DEGs respectively. In addition, the strict regulation of hydrophobin production by the blue light signalling network is impressive. Our study unravels the regulatory network based on the blue light receptors and the MAPK HOG pathway for conidiation, hydrophobin production and other processes in T. guizhouense.

Hypocrealean Trichoderma are the most extensively studied facultative mycoparasites against phytopathogenic fungi. Aerial hyphae of Trichoderma guizhouense can rapidly proliferate over Fusarium oxysporum hyphae, cause sporadic cell death and arrest the growth of the host. The results of the present study demonstrated that a unique short-chain dehydrogenase/reductase (SDR), designated as TgSDR1, was expressed at a high level in T. guizhouense challenged by the hosts. Similar to other SDRs family members, the TgSDR1 protein contains a cofactor-binding motif and a catalytic site. The subcellular localization assay revealed that the TgSDR1::GFP fusion protein translocated to lipid droplets in mycelia and conidia. The data obtained using reverse genetic approach indicated that TgSDR1 is associated with antifungal ability, plays an important role in providing reducing equivalents in the form of NADPH and regulates the amino sugar and nucleotide sugar metabolism in T. guizhouense upon encountering a host. Moreover, the TgSDR1 deletion mutant was defective in conidiation. Thus, TgSDR1 functions as a key metabolic enzyme in T. guizhouense to regulate mycotrophic interactions, defence against other fungi, such as F. oxysporum, and conidiation.

Fusarium wilt is one of the major biotic factors limiting cucumber (Cucumis sativus L.) growth and yield. The outcomes of cucumber-Fusarium interactions can be influenced by the form of nitrogen nutrition (nitrate [NO3 - ] or ammonium [NH4 + ]); however, the physiological mechanisms of N-regulated cucumber disease resistance are still largely unclear. Here, we investigated the relationship between nitrogen forms and cucumber resistance to Fusarium infection. Our results showed that on Fusarium infection, NO3 - feeding decreased the levels of the fungal toxin, fusaric acid, leaf membrane oxidative, organelle damage and disease-associated loss in photosynthesis. Metabolomic analysis and gas-exchange measurements linked NO3 - mediated plant defence with enhanced leaf photorespiration rates. Cucumber plants sprayed with the photorespiration inhibitor isoniazid were more susceptible to Fusarium and there was a negative correlation between photorespiration rate and leaf membrane injury. However, there were positive correlations between photorespiration rate, NO3 - assimilation and the tricarboxylic acid (TCA) cycle. This provides a potential electron sink or the peroxisomal H2 O2 catalysed by glycolate oxidase. We suggest that the NO3 - nutrition enhanced cucumber resistance against Fusarium infection was associated with photorespiration. Our findings provide a novel insight into a mechanism involving the interaction of photorespiration with nitrogen forms to drive wider defence.

Trichoderma is a genus of filamentous fungi that play notable roles in stimulating plant growth after colonizing the root surface. However, the key proteins and molecular mechanisms governing this stimulation have not been completely elucidated. In this study, Trichoderma guizhouense NJAU 4742 was investigated in a hydroponic culture system after interacting with cucumber roots. The total proteins of the fungus were characterized, and the key metabolic pathways along with related genes were analyzed through proteomic and transcriptomic analyses. The roles played by the regulated proteins during the interaction between plants and NJAU 4742 were further examined. The intracellular or extracellular proteins from NJAU 4742 and extracellular proteins from cucumber were quantified, and the high-abundance proteins were determined which were primarily involved in the shikimate pathway (tryptophan, tyrosine, and phenylalanine metabolism, auxin biosynthesis, and secondary metabolite synthesis). Moreover, 15N-KNO3 labeling analysis indicated that NJAU 4742 had a strong ability to convert nitrogenous amino acids, nitrate, nitrile, and amines into ammonia. The auxin synthesis and ammonification metabolism pathways of NJAU 4742 significantly contributed to plant growth. The results of this study demonstrated the crucial metabolic pathways involved in the interactions between Trichoderma spp. and plants. [Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Fusarium wilt is a devastating disease which impacts watermelon production. Soil fumigation using dazomet followed by biological organic fertilizer was applied to suppress the Fusarium wilt disease. We propose that fumigation suppresses the soil indigenous community, especially the soil-borne pathogens, while the utilization of bio-organic fertilizer facilitates the recovery of the soil microbiome to a beneficial, suppressive state through the introduction of plant growth-promoting microorganisms. Greenhouse experiment showed that applied biological organic fertilizer after dazomet fumigation effective restrain the disease incidence with a 93.6% disease control. Fumigation strongly decreased soil microbial diversity and altered relative taxa abundances, suggesting the possibility of niche release by the resident soil microbial community. Fumigation followed by bio-fertilizer transformed the soil microbial community composition and resulted in higher relative abundances of beneficial microbial groups such as Bacillus (8.5%) and Trichoderma (13.5%), coupled with lower Fusarium abundance compared to other treatments. Network analysis illustrated that soil fumigation decreased interactions within the soil microbial community with less nodes and links while bio-fertilizer addition promoted node interactions. In addition, bio-fertilizer addition after fumigation resulted in the beneficial species becoming the key network connectors. Collectively, fumigation appears to release the resident soil niche resulting in lower diversity while the beneficial microbes introduced by bio-fertilizer addition colonize these niches, leading to a more complex community with fewer pathogens that suppresses Fusarium wilt disease incidence.

Summary The secretomes of filamentous fungi contain a diversity of small secreted cysteine‐rich proteins (SSCPs) that have a variety of properties ranging from toxicity to surface activity. Some SSCPs are recognized by other organisms as indicators of fungal presence, but their function in fungi is not fully understood. We detected a new family of fungal surface‐active SSCPs (saSSCPs), here named hyphosphere proteins (HFSs). An evolutionary analysis of the HFSs in Pezizomycotina revealed a unique pattern of eight single cysteine residues (C‐CXXXC‐C‐C‐C‐C‐C) and a long evolutionary history of multiple gene duplications and ancient interfungal lateral gene transfers, suggesting their functional significance for fungi with different lifestyles. Interestingly, recombinantly produced saSSCPs from three families (HFSs, hydrophobins and cerato‐platanins) showed convergent surface‐modulating activity on glass and on poly(ethylene‐terephthalate), transforming their surfaces to a moderately hydrophilic state, which significantly favoured subsequent hyphal attachment. The addition of purified saSSCPs to the tomato rhizosphere had mixed effects on hyphal attachment to roots, while all tested saSSCPs had an adverse effect on plant growth in vitro. We propose that the exceptionally high diversity of saSSCPs in Trichoderma and other fungi evolved to efficiently condition various surfaces in the hyphosphere to a fungal‐beneficial state.

Trichoderma is an important and widely used plant growth-promoting fungus (PGPF). In this study, stevia residue amended with amino acids hydrolyzed from animal carcasses was used for the production of Trichoderma guizhouense NJAU 4742 by solid-state fermentation, and then its potential to promote corn plant growth was evaluated in combination with chemical fertilizer (CF) or organic fertilizer (OF). The highest spore number of 7×109 CFU g−1 fresh weight was obtained under the following optimal parameters: material ratio of 50% (stevia residue:rice bran=1:1), pH value of 3.0 (amended with 6.67% amino acids), initial moisture content of 60%, inoculum size of 10%, material thickness of 3 cm and an incubation time of 4 days. The aboveground corn plant biomass obtained with T. guizhouense applied alone and with CF treatments were slightly higher than those of no fertilizer control and CF treatments, respectively. However, T. guizhouense applied with OF significantly (P

Soil microbiome manipulation can potentially reduce the use of pesticides by improving the ability of soils to resist or recover from pathogen infestation, thus generating natural suppressiveness. We simulated disturbance through soil fumigation and investigated how the subsequent application of bio-organic and organic amendments reshapes the taxonomic and functional potential of the soil microbiome to suppress the pathogens Ralstonia solanacearum and Fusarium oxysporum in tomato monocultures. The use of organic amendment alone generated smaller shifts in bacterial and fungal community composition and no suppressiveness. Fumigation directly decreased F. oxysporum and induced drastic changes in the soil microbiome. This was further converted from a disease conducive to a suppressive soil microbiome due to the application of organic amendment, which affected the way the bacterial and fungal communities were reassembled. These direct and possibly indirect effects resulted in a highly efficient disease control rate, providing a promising strategy for the control of the diseases caused by multiple pathogens.

Soil-borne plant diseases cause major economic losses globally. This is partly because their epidemiology is difficult to predict in agricultural fields, where multiple environmental factors could determine disease outcomes. Here we used a combination of field sampling and direct experimentation to identify key abiotic and biotic soil properties that can predict the occurrence of bacterial wilt caused by pathogenic Ralstonia solanacearum. By analyzing 139 tomato rhizosphere soils samples isolated from six provinces in China, we first show a clear link between soil properties, pathogen density and plant health. Specifically, disease outcomes were positively associated with soil moisture, bacterial abundance and bacterial community composition. Based on soil properties alone, random forest machine learning algorithm could predict disease outcomes correctly in 75% of cases with soil moisture being the most significant predictor. The importance of soil moisture was validated causally in a controlled greenhouse experiment, where the highest disease incidence was observed at 60% of maximum water holding capacity. Together, our results show that local soil properties can predict disease occurrence across a wider agricultural landscape, and that management of soil moisture could potentially offer a straightforward method for reducing crop losses to R. solanacearum.

Filamentous fungi are known as producers of a large array of diverse secondary metabolites (SMs) that aid in securing their environmental niche. Here, we demonstrated that the SMs have an additional role in fungal defence against other fungi: Trichoderma guizhouense, a mycoparasite, is able to antagonize Fusarium oxysporum f. sp. cubense race 4 (Foc4) by forming aerial hyphae that kill the host with hydrogen peroxide. At the same time, a gene cluster comprising two polyketide synthases is strongly expressed. Using functional genetics, we characterized this cluster and identified its products as azaphilones (termed as trigazaphilones). The trigazaphilones were found lacking of antifungal toxicity but exhibited high radical scavenging activities. The antioxidant property of trigazaphilones was in vivo functional under various tested conditions of oxidative stress. Thus, we conclude that the biosynthesis of trigazaphilones serves as a complementary antioxidant mechanism and defends T. guizhouense against the hydrogen peroxide that it produces to combat other fungi like Foc4.

The form of nitrogen (N) supply influences photorespiration in C3 plants, but whether nitrate (NO3−) regulates photorespiration and, if so, the underlying mechanisms for such regulation are still unclear. Three hydroponic experiments were conducted in a greenhouse to investigate the relationships between leaf NO3− concentrations and photorespiration rates in rice (Oryza sativa L.) genotypes cv. ‘Shanyou 63’ hybrid indica and ‘Zhendao 11’ hybrid japonica or using mutants that overexpress NRT2.1 (in cv. ‘Nipponbare’ inbred japonica). We estimated photorespiratory rate from the CO2 compensation point in the absence of daytime respiration (Γ*) using the biochemical model of photosynthesis. Higher Γ* values under high N level or NO3− were significantly and positively correlated with leaf NO3− concentrations. Further elevating leaf NO3− concentrations by either resuming NO3− nutrition supply after N depletion (in cv. ‘Shanyou 63’ hybrid indica and ‘Zhendao 11’ hybrid japonica) or using mutants that overexpress NRT2.1 (in cv. ‘Nipponbare’ inbred japonica) increased Γ* values. Additionally, the activities of leaf nitrate reductase (Nr) and concentrations of organic acids involving in the tricarboxylic acid (TCA) cycle synchronously changed as environmental conditions were varied. Photorespiration rate is related to the leaf NO3− concentration, and the correlation may links to the photorespiration-TCA derived reductants required for NO3− assimilation.

Microorganisms experience intra- and inter-species interactions in the soil, and how these interactions affect the production of microbial volatile organic compounds (VOCs) is still not well-known. Here we evaluated the production and activity of microbial VOCs as driven by bacterial intra-species community interactions. We set up bacterial communities of increasing biodiversity out of 1–4 strains each of the Gram-positive Bacillus and Gram-negative Pseudomonas genera. We evaluated the ability of each community to provide two VOC-mediated services, pathogen suppression and plant-growth promotion and then correlated these services to the production of VOCs by each community. The results showed that an increase in community richness from 1 to 4 strains of both genera increased VOC-mediated pathogen suppression and plant-growth promotion on agar medium and in the soil, which was positively correlated with the production of pathogen suppressing and plant growth-promoting VOCs. Pseudomonas strains maintained while Bacillus strains reduced community productivity with an increase in community richness and produced eight novel VOCs compared with the monocultures. These results revealed that intra-species interactions may vary between Gram-negative and Gram-positive species but improved VOC-mediated functioning with respect to pathogen suppression and plant-growth promotion by affecting the amount and diversity of produced VOCs potentially affecting plant disease outcomes.

Global warming is an increasingly serious ecological problem, we examined how the active autotrophic microbes in paddy soils respond to the elevated CO2 and temperature. Here we employed stable isotope probing (SIP) to label the active bacteria using the soil samples from a fully factorial Simulated Climate Change (SCC) field experiment where soils were exposed to ambient CO2 and temperature, elevated temperature, elevated CO2, and both elevated CO2 and temperature. Around 28.9% of active OTUs belonged to ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB). Nitrosospira taxa was dominant in all soils and 80.4% of carbon-fixing bacteria under elevated temperature were classified as Nitrosomonas nitrosa. While no labeled NOBs were detected when temperature or CO2 were elevated independently, diverse NOBs were detected in the ambient conditions. We found that elevated CO2 and temperature had contrasting effects on microbial community composition, while relatively small changes were observed when CO2 and temperature were elevated simultaneously. Summarily these results suggest that carbon-fixing bacteria can respond positively to elevated CO2 concentrations, but when it’s accompanied with increase in the temperature this positive response could be weakened. Multiple abiotic factors thus need to be considered when predicting how microbial communities will respond to multiple climatic factors.

Grafting is a basic technique which is widely used to increase yield and enhance biotic and abiotic stress tolerance in plant production. The diversity and interactions of rhizobacterial assemblages shaped by grafting are important for the growth of their hosts but remain poorly understood. To test the hypothesis that plant grafting shapes complexity and co-occurrence of rhizobacterial assemblage, four types of plants, including ungrafted bottle gourd (B), ungrafted watermelon (W), grafted watermelon with bottle gourd rootstock (W/B), and grafted bottle gourd with watermelon rootstock (B/W), were cultivated in two soil types in a greenhouse, and the rhizosphere bacterial communities were analyzed by 16S rRNA gene high-throughput sequencing. Both the soil type and grafting significantly influenced the bacterial community composition. Grafting increased bacterial within-sample diversity in both soils. Core enriched operational taxonomic units (OTUs) in the W/B rhizosphere compared with the other three treatments (B, W, and B/W) were mainly affiliated with Alphaproteobacteria, Deltaproteobacteria, and Bacteroidetes, which are likely related to methanol oxidation, methylotrophy, fermentation, and ureolysis. Co-occurrence network analysis proved that grafting increased network complexity, including the number of nodes, edges, and modules. Moreover, grafting strengthened the structural robustness of the network in the rhizosphere, while ungrafted watermelon had the lowest network robustness. Homogeneous selection played a predominant role in bacterial community assembly, and the contribution of dispersal limitation was increased in grafted watermelon with bottle gourd rootstock. Grafting increased the diversity and transformed the network topology of the bacterial community, which indicated that grafting could improve species coexistence in the watermelon rhizosphere.

NJAU 4742 (Tgui) can serve as a promising strain for the development of novel biofertilizers and biofungicides. Plants primed with Tgui via inoculation were investigated to clarify the underlying mechanisms that promote root growth and development and activate the plant innate immune response. The relative expression of defence-related genes and of genes involved in the auxin signalling pathway in Zea mays and Arabidopsis thaliana was quantified. Scanning electron microscopy (SEM) was performed to visualize the colonization of Tgui in maize roots, and a proteomic approach was used to identify Tgui-derived elicitors. The establishment of Tgui in the rhizosphere of maize leads to the stimulation of the auxin synthesis pathway in maize and subsequently leads to increased plant growth. And the extracellular proteins of Tgui induced systemic resistance (ISR) of maize plants to Fusarium verticillioides (Fv) (Hypocreales, Ascomycota); the ISR of maize plants may be linked to the accumulation of reactive oxygen species (ROS) and increased deposition of callose in maize tissue. Activation of the maize immune response was triggered by the mixture of extracellular proteins secreted by Tgui into the rhizosphere. Our study thereby contributes to a better understanding of the interaction between T. guizhouense and plant roots.

Background Filamentous fungi have the ability to efficiently decompose plant biomass, and thus are widely used in the biofuel and bioprocess industries. In process, ambient pH has been reported to strongly affect the performance of the applied functional filamentous fungi. In this study, Trichoderma guizhouense NJAU4742 was investigated under the fermentation of rice straw at different initial pH values for a detailed study. Results The results showed that NJAU4742 strain could tolerate ambient pH values ranging from 3.0 to 9.0, but had significantly higher growth speed and extracellular enzyme activities under acidic conditions. At low ambient pH (T. guizhouense NJAU4742. Conclusions Most functional lignocellulases were found to be differently regulated by the ambient pH in T. guizhouense NJAU4742, which had the ability of speeding up biomass degradation by elevating the ambient pH through environmental alkalinization. These findings contribute to the theoretical basis for the biodegradation of plant biomass by filamentous fungi in the biofuel and bioprocess industries.

Chemotaxis towards root exudates and subsequent biofilm formation are very important for root colonization and for providing the beneficial functions of plant growth-promoting rhizobacteria (PGPRs). In this study, in comparison with other root-secreted compounds, D-galactose in the root exudates of cucumber was found to be a strong chemoattractant at the concentration of 1 μM for Bacillus velezensis SQR9. Chemotaxis assays with methyl-accepting chemotaxis proteins (MCPs) deletion strains demonstrated that McpA was solely responsible for chemotaxis towards D-galactose. Interestingly, D-galactose significantly enhanced the biofilm formation of SQR9 in an McpA-dependent manner. Further experiment showed that D-galactose also enhanced root colonization by SQR9. In addition, the secretion of D-galactose by cucumber roots could be induced by inoculation with SQR9, indicating that D-galactose may be an important signal in the interaction between plant and SQR9. These findings suggested that the root-secreted D-galactose was a signal, the secretion of which was induced by the beneficial bacteria, and which in turn induced colonization of the bacteria.

Background: MicroRNA plays an important role in multifarious biological processes by regulating their corresponding target genes. However, the biological function and regulatory mechanism of fungal microRNA-like RNAs (milRNAs) remain poorly understood. Methods: In this study, combined with deep sequencing and bioinformatics analysis, milRNAs and their targets from Trichoderma guizhouence NJAU 4742 were isolated and identified under solid-state fermentation (SSF) by using rice straw as the sole carbon source at 28 °C and 37 °C, respectively. Results: A critical milRNA, TGA1_S04_31828 (Tr-milRNA1), was highly expressed under heat stress (37 °C) and adaptively regulated lignocellulase secretion. Overexpression of Tr-milRNA1 (OE-Tr-milRNA1) did not affect vegetative growth, but significantly increased lignocellulose utilization under heat stress. Based on the bioinformatics analysis and qPCR validation, a target of Tr-milRNA1 was identified as Trvip36, a lectin-type cargo receptor. The expression of Tr-milRNA1 and Trvip36 showed a divergent trend under SSF when the temperature was increased from 28 °C to 37 °C. In addition, the expression of Trvip36 was suppressed significantly in Tr-milRNA1 overexpression strain (OE-Tr-milRNA1). Compared with the wild type, deletion of Trvip36 (ΔTrvip36) significantly improved the secretion of lignocellulases by reducing the retention of lignocellulases in the ER under heat stress. Conclusions: Tr-milRNA1 from NJAU 4742 improved lignocellulose utilization under heat stress by regulating the expression of the corresponding target gene Trvip36. These findings might open avenues for exploring the mechanism of lignocellulase secretion in filamentous fungi.

Bacillus spp. strains that are beneficial to plants are widely used in commercial biofertilizers and biocontrol agents for sustainable agriculture. Generally, functional Bacillus strains are applied as single strain communities since the principles of synthetic microbial consortia constructed with Bacillus strains remain largely unclear. Here, we demonstrated that the mutual compatibility directly affects the survival and function of two-member consortia composed of B. velezensis SQR9 and FZB42 in the rhizosphere. A mutation in the global regulator Spo0A of SQR9 markedly reduced the boundary phenotype with wild-type FZB42, and the combined use of the SQR9∆spo0A mutant and FZB42 improved biofilm formation, root colonization and the production of secondary metabolites that are beneficial to plants. We further confirmed the correlation between the swarm discrimination phenotype between the two consortia members and the effects that are beneficial to plants in a greenhouse experiment. Our results provide evidence that social interactions among bacteria could be an influencing factor in achieving a desired community-level function.IMPORTANCEBacillus velezensis is one of the most widely applied bacteria in biofertilizers in China and Europe. Additionally, the molecular mechanisms of plant growth promotion and disease suppression by representative model strains are well established, such as B. velezensis SQR9 and FZB42. However, it remains extremely challenging to design efficient consortia based on these model strains. Here, we showed that swarm discrimination phenotype is one of the major determinants affects the performance of two-member Bacillus consortia in vitro and in the rhizosphere. Deletion in global regulatory gene spo0A of SQR9 reduced the strength of boundary formation with FZB42, result in the improved plant growth promotion performance of dual consortium. This knowledge provides new insights into efficient probiotics consortia design in Bacillus.

Plant growth depends on a range of functions provided by their associated rhizosphere microbiome, including nutrient mineralization, hormone co-regulation and pathogen suppression. Improving the ability of plant-associated microbiomes to deliver these functions is thus important for developing robust and sustainable crop production. However, it is yet unclear how beneficial effects of probiotic microbial inoculants can be optimized and how their effects are mediated. Here, we sought to enhance tomato plant growth by targeted introduction of probiotic bacterial consortia consisting of up to eight plant-associated Pseudomonas strains. We found that the effect of probiotic consortium inoculation was richness-dependent: consortia that contained more Pseudomonas strains reached higher densities in the tomato rhizosphere and had clearer beneficial effects on multiple plant growth characteristics. Crucially, these effects were best explained by changes in the resident community diversity, composition and increase in the relative abundance of initially rare taxa, instead of introduction of plant-beneficial traits into the existing community along with probiotic consortia. Together, our results suggest that beneficial effects of microbial introductions can be driven indirectly through effects on the diversity and composition of the resident plant rhizosphere microbiome.

Background The development of suppressive soils is a promising strategy to protect plants against soil-borne diseases in a sustainable and viable manner. The use of crop rotation and the incorporation of plant residues into the soil are known to alleviate the stress imposed by soil pathogens through dynamics changes in soil biological and physicochemical properties. However, relatively little is known about the extent to which specific soil amendments of plant residues trigger the development of plant-protective microbiomes. Here, we investigated how the incorporation of pineapple residues in soils highly infested with the banana Fusarium wilt disease alleviates the pathogen pressure via changes in soil microbiomes. Results The addition of above- and below-ground pineapple residues in highly infested soils significantly reduced the number of pathogens in the soil, thus resulting in a lower disease incidence. The development of suppressive soils was mostly related to trackable changes in specific fungal taxa affiliated with Aspergillus fumigatus and Fusarium solani, both of which displayed inhibitory effects against the pathogen. These antagonistic effects were further validated using an in vitro assay in which the pathogen control was related to growth inhibition via directly secreted antimicrobial substances and indirect interspecific competition for nutrients. The disease suppressive potential of these fungal strains was later validated using microbial inoculation in a well-controlled pot experiment. Conclusions These results mechanistically demonstrated how the incorporation of specific plant residues into the soil induces trackable changes in the soil microbiome with direct implications for disease suppression. The incorporation of pineapple residues in the soil alleviated the pathogen pressure by increasing the relative abundance of antagonistic fungal taxa causing a negative effect on pathogen growth and disease incidence. Taken together, this study provides a successful example of how specific agricultural management strategies can be used to manipulate the soil microbiome towards the development of suppressive soils against economically important soil-borne diseases.

SummaryNiche colonization is the key for bacterial adaptation to the environment, and competition for iron largely determines root colonization by rhizosphere microbes. Pathogenic and beneficial symbiotic bacteria use various unique secretion systems to support plant colonization or acquire limited resources from the environment. However, ubiquitous nonsymbiotic beneficial rhizobacteria have never been reported to use a unique secretion system to facilitate colonization. Here, we show that the type VII secretion system (T7SS) of the beneficial rhizobacterium Bacillus velezensis SQR9 contributes to root colonization. Knocking out T7SS and the major secreted protein YukE in SQR9 caused a significant decrease in root colonization. Moreover, the T7SS and YukE caused iron loss in plant roots in the early stage after inoculation, which contributed to root colonization by SQR9. Interestingly, purified YukE, but not inactivated YukE, could change the permeability of root cells. We speculated that secreted YukE might be directly inserted into the root cell membrane to cause iron leakage, indicating that the bacterial protein and root cell membrane interact directly. Moreover, a bacterial siderophore and the T7SS may be coordinately involved in iron acquisition by B. velezensis SQR9 for efficient root colonization. We showed that the beneficial rhizobacterium B. velezensis SQR9 could acquire iron from roots via the T7SS for rapid colonization. These findings provide the first insight into the function of the unique secretion system in nonsymbiotic beneficial rhizobacteria and reveal a novel mutualism in which plants and bacteria might share iron in a sequential manner.

While both bacteria and fungi are important for the degradation and humification of organic matter during composting, it is unclear to what extent their roles are associated with abiotic compost properties. This study evaluated changes in abiotic compost properties and the succession of bacterial and fungal communities during pig manure composting for 90 days. The compost rapidly reached thermophilic phase (>58 ℃), which lasted for 15 days. Both bacterial and fungal community compositions changed drastically during composting and while bacterial diversity increased, the fungal diversity decreased during the thermophilic phase of composting. Two taxa dominated both bacterial (Bacillales and Clostridiales) and fungal (Eurotiales and Glomerellales) communities and these showed alternating abundance fluctuations following different phases of composting. The abundance fluctuations of most dominant bacterial and fungal taxa could be further associated with decreases in the concentrations of fulvic acid, cellulose, hemicellulose and overall biodegradation potential in the compost. Moreover, bacterial predicted metabolic gene abundances dominated the first three phases of composting, while predicted fungal saprotrophic functional genes increased consistently, reaching highest abundances towards the end of composting. Finally, redundancy analysis (RDA) showed that changes in abiotic compost properties correlated with the bacterial community diversity and carbohydrate metabolism and fungal wood saprotrophic function. Together these results suggests that bacterial and fungal community succession was associated with temporal changes in abiotic compost properties, potentially explaining alternating taxa abundance patterns during pig manure composting.

Crop rotation and bio-organic fertilizer application have historically been employed as efficient management strategies for soil-borne disease suppression through soil microbiome manipulation. However, details of how this occurs, and to what extent the combination of methods affects soil microbiota reconstruction from diseased soils lacks investigation. In this study, pineapple-banana rotation combined with biofertilizer application was used to suppress banana Fusarium wilt disease, and effects on both bacterial and fungal communities were investigated using the Miseq Illumine sequencing platform. Our results show that pineapple-banana rotation significantly reduces Fusarium wilt disease incidence, and that the application of bio-organic fertilizer causes additional suppression. Bacterial and fungal communities thrive using rotation in combination with bio-organic fertilizer application: taxonomic and phylogenetic α-diversity in both bacteria and fungi increase along with disease suppression. Between the two strategies, bio-organic fertilizer application affects both bacterial and fungal community composition most predominantly, followed by rotation. Large-scale changes in the fungal community composition and special Burkholderia-related network functions contribute to the observed soil borne-disease suppression. Our results indicate that pineapple-banana rotation combined with bio-organic fertilizer application has strong potential for the sustainable management of banana Fusarium wilt disease.

Trophic interactions play a central role in driving microbial community assembly and function. In gut or soil ecosystems, successful inoculants are always facilitated by efficient colonization, however, the metabolite exchanges between inoculants and resident bacteria are rarely studied, particularly in the rhizosphere. Here, we used bioinformatic, genetic, transcriptomic and metabonomic analyses to uncover syntrophic cooperation between inoculant (Bacillus velezensis SQR9) and plant-beneficial indigenous Pseudomonas stutzeri in the cucumber rhizosphere. We found that the synergistic interaction of these two species is highly environmental dependent, the emergence of syntrophic cooperation was only evident in a static nutrient-rich niche, such as pellicle biofilm in addition to the rhizosphere. Our results identified branched-chain amino acids (BCAAs) biosynthesis pathway involved in syntrophic cooperation when forming coculture biofilms. Assaying the metabolome further demonstrated metabolic facilitation among the bacterial strains. In addition, biofilm matrix components from Bacillus were essential for the interaction. Importantly, the two-species consortium promoted plant growth and helped plants alleviate salt stress. In summary, we propose a mechanism in which synergic interactions between a biocontrol bacterium and a partner species promote plant health.

Rhizosphere microorganisms interact with plant roots by producing chemical signals to regulate root development. However, the involved distinct bioactive compounds and the signal transduction pathways are remaining to be identified. Here, we show that sesquiterpenes (SQTs) are the main volatile compounds produced by plant beneficialTrichoderma guizhouenseNJAU 4742, inhibition of SQTs synthesis in this strain indicated their involvement in plant-fungus cross-kingdom signaling. SQTs component analysis further identified the cedrene, a high abundant SQT in strain NJAU 4742, could stimulate plant growth and root development. Genetic analysis and auxin transport inhibition showed that auxin receptor TIR1, AFB2, auxin-responsive protein IAA14, and transcription factor ARF7, ARF19 affect the response of lateral roots to cedrene. Moreover, auxin influx carrier AUX1, efflux carrier PIN2 were also indispensable for cedrene-induced lateral root formation. Confocal imaging showed that cedrene affected the expression ofpPIN2:PIN2:GFPandpPIN3:PIN3:GFP, which may be related to the effect of cedrene on root morphology. These results suggest that a novel SQT molecule from plant beneficialT. guizhouensecan regulate plant root development through auxin transport and signaling.One-sentence SummaryCedrene, a high- abundance sesquiterpenes produced by plant beneficialTrichoderma guizhouenseNJAU 4742, stimulatesArabidopsislateral root formation and primary root elongation by relying on auxin signaling pathway and auxin transporter PIN2 and AUX1.

Fusarium wilt of watermelon caused by Fusarium oxysporums f. sp. niveum (FON) is the most destructive disease impacting production. Soil fumigation using ammonium bicarbonate coupled with bioorganic fertilizer (BOF) application was conducted in the field in order to suppress Fusarium wilt disease. The composition of the soil microbiome after fumigation and at harvest was assessed using MiSeq high throughput sequencing. Soil fumigation succeeded in suppressing disease incidence, with a drop from 96% to

Soil microorganisms play an essential role in the redistribution of soil aggregate sizes due to the microenvironmental changes, but little is known about the changes in microbial communities (especially fungi) and their activities within different microenvironments due to agronomic managements. Here, we examined the influence of fertilization (inorganic and inorganic plus organic amendments) on soil aggregate distribution and the microbial communities within aggregates at the site of a long-term fertilization experiment. Significant impacts on soil aggregate distribution and distinct changes in fungal and bacterial communities in soil aggregates due to fertilization were observed, with the fungal community exhibiting more marked changes compared with the bacterial community. Soil carbon and nitrogen contents in aggregates were the most closely related to changes in microbial communities associated with soil aggregates. The changes of microbial taxa abundance in aggregates were generally accompanied by the redistributions of these taxa among all size aggregates, showing the preference for specific ecological niches for these taxa under fertilizations. Both applications of nitrogen alone (N) and inorganic plus organic amendment (NPKM) contributed to mega-aggregate formation. N treatment caused the low total fungal counts in mega-aggregates and carbon depletion, whereas it increased the abundance of N2O-producing fungi in both mega- and macro-aggregates, denitrifying bacteria in micro-aggregates and nitrifying bacteria in macro-aggregates. In contrast, NPKM treatment mitigated/prevented the sharp shifts of the abundance of these microbes mentioned above with nitrogen fertilization, and increased the ectomycorrhizal fungi abundance in all soil fractions as well as carbon accumulation in soil. Our results suggest that the responses of soil bacteria and fungi to fertilizations are modified by their ecological niches, which responses are responsible for the variation of ecosystem services.

Natural minerals in soil can inhibit the growth of bacteria that protect organic carbon from decay. However, the mechanism inhibiting the bacterial growth remains poorly understood. Here, using a series of cultivation experiments and biological, chemical and synchrotron-based spectral analyses, we showed that kaolinite, hematite, goethite and ferrihydrite had a significant inhibitory effect on the growth of the model bacteria Pseudomonas brassicacearum J12, which was more prominent with a concentration of 25 mg mL−1 than it was with either 10 or 5 mg mL−1. In contrast, montmorillonite promoted the growth of J12. Compared to Al-containing minerals, Fe(III)-containing minerals produced more hydroxyl radical (HO⚫) that has high efficiency for the inhibition of J12. Moreover, a significant positive correlation between HO⚫ radical and Fe(II) was found, suggesting that Fe(II) contributes to the generation of HO⚫. Furthermore, both micro X-ray fluorescence and X-ray photoelectron spectroscopies indicated that surface Fe(III) was reduced to Fe(II), which can produce HO⚫ through the well-known Fenton reaction series. Together, these findings indicate that the reduced surface Fe(II) derived from Fe(III)-containing minerals inhibits the growth of Pseudomonas brassicacearum J12 via a free-radical mechanism, which may serve as a ubiquitous mechanism between iron minerals and all of the heterotrophic bacteria in view of taxonomically and ecologically diverse heterotrophic bacteria from terrestrial environments as a vast source of superoxide.

Plant growth-promoting rhizobacteria (PGPR) substantially improve plant growth and health, but their effects on the succession of rhizosphere microbiota throughout the growth period triggered by pre-inoculation have not yet been considered. Pepper seedlings cultured from a bio-nursery substrate containing Bacillus velezensis NJAU-Z9 and ordinary nursery substrate were used in this study to evaluate the effects of pre-colonization of a PGPR strain at the seedling stage on yield enhancement. To elucidate the underlying mechanisms involved in the rhizosphere microbiota succession during the whole growth period and their association with yield enhancement, high-throughput sequencing combined with qPCR was conducted. The results showed that, compared to the control without inoculation, pre-inoculation led to a steady yield enhancement in two-season field trials, as well as higher rhizosphere bacterial richness (Chao1) and diversity (Shannon-Wiener). The plant growth stage as the first driving factor, followed by pre-colonization drove the variations of the rhizosphere microbial community composition according to multivariate regression tree analysis and principal coordinate analysis. Variance partitioning analysis (VPA) and Mantel test results showed that the previous plant growth period induced variations in the fungal and bacterial communities at the next stage. Compared to the seedling and flowering stages, the mature-stage microbial community showed a higher degree of explanation of yield enhancement. Additionally, pre-inoculation led to distinctive rhizosphere microbiota succession compared to the control, due to alteration of the initial community. The heat map analysis showed that the rhizosphere microbiota was related to crop yield. In addition to Bacillus velezensis NJAU-Z9, which showed stable abundance in the pepper rhizosphere, stable higher relative abundance of the bacterial genera Sphingomonas, Sphingopyxis, Bradyrhizobium, Chitinophaga, Dyadobacter, Streptomyces, Lysobacter, Pseudomonas and Rhizomicrobium, and the fungal genera Cladorrhinum, Cladosporium and Aspergillus throughout the growth period induced by pre-colonization was associated with yield enhancement. Overall, we conclude that pre-colonization with PGPR changed the initial rhizosphere microbiota and that the plant was triggered to further select distinctive microbes to form unique rhizosphere microbial consortia at the later growth stages, which resulted in plant growth promotion.

Continuous cropping of watermelon is known to result in the disruption of the rhizospheric bacteria and fungi that contribute to the occurrence of Fusarium wilt disease. However, the underlying changes in microbial composition and function as a response to mono-cropping are less studied. In this study, differences in composition and potential function of the microbiome between healthy and diseased soils were investigated using MiSeq targeted sequencing and the functional GeoChip array, respectively. Twenty years of continuous watermelon monoculture was found to significantly alter the soil microbial communities by increasing bacterial diversity but decreasing fungal diversity. Compare to bacterial network, fungal co-occurrence networks were less robust and less connected in the monoculture diseased soil. Identified keystone species, belonging to the Proteobacteria, Bacteroidetesand Acidobacteria, were present in both the diseased and healthy soils. Key fungal species from the healthy soil belonged solely within the Ascomycete, while in the diseased soil Basidiomycota were dominant. As such, overall variations in the composition of the soil microbiome are accompanied by changes in the identities of the keystone species when comparing healthy versus diseased soils, further suggesting that soil function may also be altered. Relative abundances of genes associated with the degradation of hemicelluloses and chitin, the Calvin circle, ammonification, stress responses, iron uptake, and nitrogen fixation were significantly higher under long-term monoculture. Particularly, Fusarium spp. relative abundance was positively correlated with the relative abundances of genes involved in adherence, cellular metabolism, and immune evasion which may facilitate pathogen infection of plant roots. In conclusion, these results highlight the significant compositional and functional differences in microbial communities between Fusarium wilt diseased soils and healthy soils under watermelon cultivation. This provides insight into the complex array of microorganisms in soils that suffer from Fusarium disease and illustrates potential directions towards the manipulation of the soil microbiome for suppression of this disease.

Chemoautotrophic ammonia-oxidizers and nitrite-oxidizers are responsible for a significant amount of soil nitrate production. The identity and composition of these active nitrifiers in soils under different long-term fertilization regimes remain largely under-investigated. Based on that soil nitrification potential significantly decreased in soils with chemical fertilization (CF) and increased in soils with organic fertilization (OF), a microcosm experiment with DNA stable isotope probing was further conducted to clarify the active nitrifiers. Both ammonia-oxidizing archaea (AOA) and bacteria (AOB) were found to actively respond to urea addition in soils with OF and no fertilizer (CK), whereas only AOB were detected in soils with CF. Around 98% of active AOB were Nitrosospira cluster 3a.1 in all tested soils, and more than 90% of active AOA were Nitrososphaera subcluster 1.1 in unfertilized and organically fertilized soils. Nitrite oxidation was performed only by Nitrospira-like bacteria in all soils. The relative abundances of Nitrospira lineage I and VI were 32% and 61%, respectively, in unfertilized soils, and that of Nitrospira lineage II was 97% in fertilized soils, indicating long-term fertilization shifted the composition of active Nitrospira-like bacteria in response to urea. This finding indicates that different fertilizer regimes impact the composition of active nitrifiers, thus, impacting soil nitrification potential.

Antibiosis and resource competition are major drivers shaping the assembly, diversity and functioning of microbial communities. While it is recognized that competition is sensitive to environmental conditions, it is unclear to what extent this mediated by the availability of different carbon resources. Here, we used a model laboratory system to directly test this by exploring how carbon resource richness and identity shape resource competition and antibiosis between plant probiotic Bacillus amyloliquefaciens and phytopathogenic Ralstonia solanacearum bacteria. We found that while sugars typically promoted B. amyloliquefaciens growth, organic and amino acids increased the production of both bacillaene and macrolactin antibiotics and the direct inhibition of R. solanacearum. In contrast, when multiple different carbon resources were available, B. amyloliquefaciens could efficiently grow and produce antibiotics at the same time. Together, these results suggest that high carbon resource richness allows concurrent expression of growth- and antibiosis-related traits, potentially altering bacterial competitive dynamics and plant growth promotion in microbial communities. A plain language summary is available for this article.

Nitrogen (N) application may lead to niche segregation of soil ammonia-oxidizing archaea (AOA) and bacteria (AOB), thereby reducing the competitive interactions between AOA and AOB due to higher ammonium substrate availability. However, the adaptive mechanisms of AOA and AOB under N enrichment remain poorly understood. Stable isotope probing (SIP) microcosm incubation was employed to reveal community changes of active AOA and AOB in a loess soil from a field experiment growing potatoes that received no N (control, CK), low N (LN, 75 kg N ha−1), and high N (HN, 375 kg N ha−1). The results showed that the soil potential nitrification rate (PNR) was measured by culturing of the soil samples from the field experiment. Soil PNR was significantly increased in HN by 87.5% and 67.5% compared with CK and LN, respectively. Compared with CK, the 13C-amoA genes of soil AOA and AOB in HN had 2.58 × 104 and 1.55 × 106 copies, representing 1.6- and 16.2-fold increase respectively. It was indicated that AOB dominated soil ammonia oxidation. A phylogenetic analysis of the 13C-amoA gene showed that N application significantly increased the proportion of 54d9-like AOA up to 90% in HN, while the Nitrososphaera gargensis-like and Nitrososphaera viennensis-like AOA were inhibited and completely disappeared. Nitrogen application also resulted in the community shift of active AOB-dominant group from Nitrosospira briensis-like to Nitrosospira sp. TCH711-like. Our study provides compelling evidence for the emergence and maintenance of active nitrifying communities under the intensified N input to an agricultural ecosystem.

Fusarium wilt disease of banana, caused by the fungus Fusarium oxysporum f. sp. cubense race 4, is a serious soil-borne fungal disease that currently threatens worldwide banana production. No single agricultural practice has yet been developed to effectively manage this disease. In the present study, greenhouse experiments were conducted to evaluate the effect of an integrated biofertilizer application after ammonia fumigation to enhance control of Fusarium wilt disease in severely infected banana mono-cropped soils. Quantitative PCR and high-throughput sequencing were used to characterise soil microbial community structure and the results from both two-season experimental studies showed that biofertilizer application after ammonia fumigation significantly reduced the incidence of banana Panama disease by approximately 55% and promoted the plant biomass, compared to the control application of cow manure to non-fumigated soil. Ammonia fumigation significantly reduced total fungal and F. oxysporum abundances and bacterial and fungal diversities. Biofertilizer application after fumigation further depleted the abundance of the pathogen. Biofertilizer application and fumigation altered the soil microbial community composition with the bacterial community responding first to fumigation, while the fungal community responded first to fertilization. Although Bacillus, including our inoculated strain, was not enriched after biofertilization, putative beneficial microbes such as Paenibacillus, Virgibacillus, Nitrosomonas, and Nitrobacter, were significantly enriched by ammonia fumigation and biofertilizer application, and were significantly correlated with disease suppression or increased plant biomass. Furthermore, fumigation and biofertilization significantly increased the soil pH and nutrient contents, with concomitant effects on the microbial community. Overall, the observed disease suppression and increased plant biomass resulting from both soil fumigation and biofertilization after banana cropping can be attributed to the reduced abundance of F. oxysporum and general suppression from altered soil properties that may enable the establishment of a beneficial soil microbiome.

Non-ribosomal peptides (NRPs) are one of the largest groups of natural microbial secondary metabolites, which include peptides such as the antibiotics vancomycin and gramicidin, as well as lipopeptides (surfactin, iturin A and bacillomycin). In this study, banana Fusarium wilt disease suppressive and conducive soils were chosen to investigate the role of microbes that harbor the NRPS gene in disease suppression based on the 454-pyrosequencing platform and real-time PCR technique. The results showed that higher abundances and diversity of microbes that harbor the NRPS gene were observed in the suppressive soil samples than in the conducive soil. According to the results of the DNA sequences blastx of NRPS, the main microbial taxa harboring the NRPS gene were identified, and Pseudomonas in Proteobacteria and Streptomyces in Actinobacteria might be remarkably related to Fusarium wilt disease suppression. Furthermore, the Mantel test showed that compared with bacteria community and chemical properties, the microbial community harboring the NRPS gene had a more significant impact on the disease incidences of Fusarium wilt. This study provided non-specific relationships between groups of microbes harboring NRPS genes and Fusarium wilt disease suppression suggesting potential interaction based on correlation evidence, and pointed out a potential mechanism of suppressive soil.

The effect of genetic markers and reference databases on analyses of fungal communities were estimated using fungal large subunit (LSU) and internal transcribed spacer (ITS) amplicon datasets in consecutive years of rhizosphere samples from three candidate biofuel crops, corn (Zea mays), switchgrass (Panicum virgatum), and miscanthus (Miscanthus × giganteus). These two marker genes were selected to contrast possible differences in biological conclusions. In addition, two ITS schemes based on two ITS reference databases were used to assess differences due to reference database composition. A taxonomy-supervised method was invoked using the Ribosomal Database Project naive Bayesian classifier that accesses all three databases. The UNITE classification scheme had the highest number of classified taxa in the raw classification result; however, it also had the highest proportion of unknown taxa (sequences that were classified to “unclassified,” “unidentified,” incertae sedis or, in the case of Warcup, to matches containing two unique names). After removal of these unknown taxa, LSU had the highest classification rate followed by Warcup and UNITE. As expected, the communities resolved using the two ITS databases, based on the same sequences, were relatively more similar than those from the lower-coverage LSU classification scheme. The choice of marker gene or even the same reads with different classification databases revealed different community patterns due to database coverage, e.g., the relative abundance of the most abundant groups changed or were only detected in one or two of the classification schemes, such as for Mortierella, Fusarium, and Phoma. No marked difference in fungal beta-diversity was identified among the three methods. Differentiation between the three biofuel crops and between the drought and normal rainfall years was apparent, regardless of method. Though classification rates, taxonomic conflicts, and coverage differences within the high-abundance fungal groups varied according to classification scheme, there was no overall impact on beta diversity among the three methods.

Bacillus amyloliquefaciens NJN-6, a plant growth promoting bacterium can act as an efficient antagonist against F. oxysporum f. sp. cubense (FOC). This study tests the response of antibiotic producing genes (ituA and bamD) and biofilm formation related genes (epsD and yqxM) in strain NJN-6 to phenolic acids in banana root exudates. Phenolic acid in banana root exudates (infected or non-infected by FOC) were identified by HPLC. Transcription analysis of genes involved in biofilm formation and antibiotic synthesis in strain NJN-6 were investigated with quantitative reverse transcription PCR (RT-qPCR). We found that the transcription levels of two antibiotic producing genes and two biofilm formation related genes in strain NJN-6 were upregulated in the banana seedling roots. Root secretion of phthalic acid, salicylic acid and cinnamic acid were enhanced in FOC infected banana seedlings. Further additional experiments demonstrated that the transcription level of ituA, bamD and epsD increased linearly to the concentration of phthalic acid. Results from antibiotic production and biofilm formation assays demonstrated a similar trend to gene transcription analysis. The results in this study indicated that the phenolic acids in root exudates of banana can potentially enhance root colonization and pathogen suppression abilities of Bacillus amyloliquefaciens NJN-6.

Although composting, a measure to dispose agricultural waste, is widely accepted and applied, specific knowledge of microbially driven effects on nitrous oxide (N2O) emissions during composting remains limited. Here, we monitored the impact of sawdust on N2O emissions during pig manure composting. The results suggested that adding sawdust to the compost improved the compost temperature and reduced N2O emissions. The addition of sawdust significantly altered the bacterial community structure and enhanced community turnover during the composting process. The addition of sawdust significantly reduced the relative abundance of denitrification and ureolysis, while increasing the relative abundance of nitrogen fixation. Specifically, adding sawdust may reduce N2O emissions by reducing the relative abundance of Salinithrix, Truepera, Azomonas, Iamia, Silanimonas, Phycisphaera, and Gp21 during the thermophilic and mature phases of the composting period.

Composting is an environmentally friendly way to turn plant and animal wastes into organic fertilizers. However, it is unclear to what extent the source of animal waste products (such as manure) affects the physicochemical and microbiological properties of compost. Here, we experimentally tested how the type of livestock manure of herbivores (sheep and cattle) and omnivores (pig and chicken) influences the bacterial and fungal communities and physicochemical properties of compost. Higher pH, NO3-N, Total carbon (TC) content and C/N were found in sheep and cattle manure composts, while higher EC, NH4-N, Total nitrogen (TN) and total phosphorus (TP) content were measured in pig and chicken manure composts. Paired clustering between herbivore and omnivore manure compost metataxonomy composition was also observed at both initial and final phases of composting. Despite this clear clustering, all communities changed drastically during the composting leading to reduced bacterial and fungal diversity and large shifts in community composition and species dominance. While Proteobacteria and Chloroflexi were the major phyla in sheep and cattle manure composts, Firmicutes dominated in pig and chicken manure composts. Together, our results indicate that feeding habits of livestock can determine the biochemical and biological properties of manures, having predictable effects on microbial community composition and assembly during composting. Manure metataxonomy profiles could thus potentially be used to steer and manage composting processes.

The phytohormone indole-3-acetic acid (IAA) has been demonstrated to contribute to the plant growth-promoting effect of rhizobacteria, but the IAA biosynthesis pathway in rhizobacteria remains unclear. The ysnE gene, encoding a putative tryptophan acetyltransferase, has been demonstrated to be involved in and strongly contribute to IAA production in Bacillus, but the mechanism is unknown. In this study, to investigate how ysnE participates in IAA biosynthesis in the plant growth-promoting rhizobacterium Bacillus amyloliquefaciens SQR9, differences in the produced IAA biosynthesis intermediates between wild-type SQR9 and ΔysnE were analyzed and compared, and the effects of different intermediate compounds on the production of IAA and the accumulation of other intermediates were also investigated. The results showed that the mutant ΔysnE produced more indole-3-lactic acid (ILA) and tryptamine (TAM) than the SQR9 wild-type strain (nearly 1.6- and 2.1-fold), while the production of tryptophol (TOL) was significantly decreased by 46%. When indole-3-pyruvic acid (IPA) served as the substrate, the concentration of ILA in the ΔysnE fermentation broth was much higher than that of the wild type, while IAA and TOL were significantly lower, and ΔysnE was lower than SQR9 in IAA and TOL with the addition of TAM. The TOL content in the ΔysnE fermentation broth was much lower than that in the wild-type SQR9 with the addition of ILA. We suggest that ysnE may be involved in the IPA and TAM pathways and play roles in indole acetaldehyde (IAAld) synthesis from IPA and TAM and in the conversion of ILA to TOL.

Lateral root formation is coordinated by both endogenous and external factors. As biotic factors, plant growth-promoting rhizobacteria can affect lateral root formation, while the regulation mechanism is unclear. In this study, by applying various marker lines, we found that volatile compounds (VCs) from Bacillus amyloliquefaciens SQR9 induced higher frequency of DR5 oscillation and prebranch site formation, accelerated the development and emergence of the lateral root primordia and thus promoted lateral root development in Arabidopsis. We demonstrated a critical role of auxin on B. amyloliquefaciens VCs-induced lateral root formation via respective mutants and pharmacological experiments. Our results showed that auxin biosynthesis, polar transport and signalling pathway are involved in B. amyloliquefaciens VCs-induced lateral roots formation. We further showed that acetoin, a major component of B. amyloliquefaciens VCs, is less active in promoting root development compared to VC blends from B. amyloliquefaciens, indicating the presence of yet uncharacterized/unknown VCs might contribute to B. amyloliquefaciens effect on lateral root formation. In summary, our study revealed an auxin-dependent mechanism of B. amyloliquefaciens VCs in regulating lateral root branching in a non-contact manner, and further efforts will explore useful VCs to promote plant root development.

This study aimed to isolate psychrotrophic cellulose-degrading fungi and to investigate their application potential for composting in cold climate regions in China. One out of five psychrotrophic cellulose-degrading fungal isolates was identified as a novel fungal species, Aureobasidium paleasum sp. nov., with a strong straw degradation potential. Enzyme activity assays and FITR spectroscopy revealed high cellulolytic activities of this psychrotrophic fungus at lower temperatures, with high thermal adaptability from 5 °C to 50 °C (optimum at 10 °C). A. paleasum efficiently decomposed rice straws and cellulose at 10 °C compared to the common cellulose-degrading fungus Penicillium oxalicum. In comparison to P. oxalicum, A. paleasum shortened the thermophilic stage, enhanced compost maturity and improved compost quality. Our work suggests that the psychrotrophic fungus A. paleasum is efficient for rice straw degradation and composting at low temperatures, highlighting its application potential for composting in colder regions.

Background Microbiomes play vital roles in plant health and performance, and the development of plant beneficial microbiomes can be steered by organic fertilizer inputs. Especially well-studied are fertilizer-induced changes on bacteria and fungi and how changes in these groups alter plant performance. However, impacts on protist communities, including their trophic interactions within the microbiome and consequences on plant performance remain largely unknown. Here, we tracked the entire microbiome, including bacteria, fungi, and protists, over six growing seasons of cucumber under different fertilization regimes (conventional, organic, and Trichoderma bio-organic fertilization) and linked microbial data to plant yield to identify plant growth-promoting microbes. Results Yields were higher in the (bio-)organic fertilization treatments. Soil abiotic conditions were altered by the fertilization regime, with the prominent effects coming from the (bio-)organic fertilization treatments. Those treatments also led to the pronounced shifts in protistan communities, especially microbivorous cercozoan protists. We found positive correlations of these protists with plant yield and the density of potentially plant-beneficial microorganisms. We further explored the mechanistic ramifications of these relationships via greenhouse experiments, showing that cercozoan protists can positively impact plant growth, potentially via interactions with plant-beneficial microorganisms including Trichoderma, the biological agent delivered by the bio-fertilizer. Conclusions We show that protists may play central roles in stimulating plant performance through microbiome interactions. Future agricultural practices might aim to specifically enhance plant beneficial protists or apply those protists as novel, sustainable biofertilizers.

Soil-borne pathogens cause high losses in crop yields globally. The development of environmentally friendly approaches is urgently needed, but is often constrained by complex interactions between root-associated microbes and pathogens. Here, we demonstrate that the interactions within microbial consortia mediated by iron-scavenging siderophores play an important role in reducing pathogen infection and enhancing plant health. This study provides a promising and novel research direction for dealing with a wide range of microbial infections through iron exploitation, which is important for the colonization and infection of both plant and human hosts by pathogens., Interactions between plant pathogens and root-associated microbes play an important role in determining disease outcomes. While several studies have suggested that steering these interactions may improve plant health, such approaches have remained challenging in practice. Because of low iron availability in most soils, competition for iron via secreted siderophore molecules might influence microbial interaction outcomes. Here, we tested if bacterial interactions mediated by iron-scavenging siderophores can be used to predict the disease suppressiveness of microbial consortia against soilborne Ralstonia solanacearum, a bacterial pathogen in the tomato rhizosphere. Iron availability significantly affected the interactions within inoculated consortia and between the consortia and the pathogen. We observed contrasting effects of siderophores and other nonsiderophore metabolites on the pathogen growth, while the siderophore effects were relatively much stronger. Specifically, disease incidence was reduced in vivo when the inoculated consortia produced siderophores that the pathogen could not use for its own growth. Employing siderophore-mediated interactions to engineer functionally robust microbial inoculants shows promise in protecting plants from soilborne pathogens. IMPORTANCE Soil-borne pathogens cause high losses in crop yields globally. The development of environmentally friendly approaches is urgently needed, but is often constrained by complex interactions between root-associated microbes and pathogens. Here, we demonstrate that the interactions within microbial consortia mediated by iron-scavenging siderophores play an important role in reducing pathogen infection and enhancing plant health. This study provides a promising and novel research direction for dealing with a wide range of microbial infections through iron exploitation, which is important for the colonization and infection of both plant and human hosts by pathogens.

Soil-borne plant diseases are increasingly causing devastating losses in agricultural production. The development of a more refined model for disease prediction can aid in reducing crop losses through the use of preventative control measures or soil fallowing for a planting season. The emergence of high-throughput DNA sequencing technology has provided unprecedented insight into the microbial composition of diseased versus healthy soils. However, a single independent case study rarely yields a general conclusion predictive of the disease in a particular soil. Here, we attempt to account for the differences among various studies and plant varieties using a machine-learning approach based on 24 independent bacterial data sets comprising 758 samples and 22 independent fungal data sets comprising 279 samples of healthy or Fusarium wilt-diseased soils from eight different countries. We found that soil bacterial and fungal communities were both clearly separated between diseased and healthy soil samples that originated from six crops across nine countries or regions. Alpha diversity was consistently greater in the fungal community of healthy soils. While diseased soil microbiomes harbored higher abundances of Xanthomonadaceae, Bacillaceae, Gibberella, and Fusarium oxysporum, the healthy soil microbiome contained more Streptomyces Mirabilis, Bradyrhizobiaceae, Comamonadaceae, Mortierella, and nonpathogenic fungi of Fusarium. Furthermore, a random forest method identified 45 bacterial OTUs and 40 fungal OTUs that categorized the health status of the soil with an accuracy >80%. We conclude that these models can be applied to predict the potential for occurrence of F. oxysporum wilt by revealing key biological indicators and features common to the wilt-diseased soil microbiome.

Background Rhizosphere microbiome is dynamic and influenced by environment factors surrounded including pathogen invasion. We studied the effects of Ralstonia solanacearum pathogen abundance on rhizosphere microbiome and metabolome by using high throughput sequencing and GC-MS technology. Results There is significant difference between two rhizosphere bacterial communities of higher or lower pathogen abundance, and this difference of microbiomes was significant even ignoring the existence of pathogen. Higher pathogen abundance decreased the alpha diversity of rhizosphere bacterial community as well as connections in co-occurrence networks. Several bacterial groups such as Bacillus and Chitinophaga were negatively related to the pathogen abundance. The GC-MS analysis revealed significantly different metabolomes in two groups of rhizosphere soils, i.e., the rhizosphere soil of lower harbored more sugars such as fructose, sucrose and melibiose than that in high pathogen abundance. Conclusions The dissimilar metabolomes in two rhizosphere soils likely explained the difference of bacterial communities with Mantel test. Bacillus and Chitinophaga as well as sugar compounds negatively correlated with high abundance of pathogen indicated their potential biocontrol ability.