The effects of allelochemicals from root exudates of Flaveria bidentis on two Bacillus species

Keystone root bacteria in Ambrosia artemisiifolia promote invasive growth by increasing the colonization rate of Funneliformis mosseae

Higher arbuscular mycorrhizal fungi (AMF) colonization rates in the roots of invasive plants than in those of native plants are associated with invasion success. Keystone plant-root bacteria (or root-associated bacteria) can influence plant growth by interacting with other members of the microbial community (eg.AMF). We aimed to investigate the effects of keystone taxa on AMF colonization and their interactions on invasive plant growth. Here, the common key root-associated species from the roots of Ambrosia artemisiifolia among four geographical populations in China were identified, and the strains were subsequently isolated. Plate and pot experiments were conducted to examine the impact of keystone species on the colonization of Funneliformis mosseae and elucidate the mechanisms that enhance plant growth. Sphingomonas was identified as a common keystone root-associated genus of A. artemisiifolia. Sphingomonas sanxanigenens was found to facilitate AMF colonization in the roots of A. artemisiifolia by promoting flavonoid biosynthesis. A synergistic effect on the growth of A. artemisiifolia was observed when the plant was co-inoculated with S. sanxanigenens and F. mosseae. This study provides new insights into the mechanisms whereby root-associated microbes facilitate AMF colonization in invasive plants. These findings confirm the pivotal role of keystone microbes in weed invasion and enhance our understanding that microbial synergistic interactions promote weed invasiveness.

The synergistic interaction effect between biochar and plant growth-promoting rhizobacteria on beneficial microbial communities in soil

Excessive use of chemical fertilizers and extensive farming can degrade soil properties so that leading to decline in crop yields. Combining plant growth-promoting rhizobacteria (PGPR) with biochar (BC) may be an alternative way to mitigate this situation. However, the proportion of PGPR and BC at which crop yield can be improved, as well as the improvement effect extent on different eco-geographic region and crops, remain unclear. This research used cabbage [Brassica pekinensis (Lour.) Rupr.] as the target crop and established as treatment conventional fertilization as a control and a 50% reduction in nitrogen fertilizer at the Yunnan-Guizhou Plateau of China, adding BC or PGPR to evaluate the effects of different treatments on cabbage yield and the soil physicochemical properties. Specifically, high-throughput sequencing probed beneficial soil microbial communities and investigated the impact of BC and PGPR on cabbage yield and soil properties. The results revealed that the soil alkaline hydrolyzable nitrogen (AH-N), available phosphorus (AP), and available potassium (AK) contents were higher in the BC application than in control. The BC application or mixed with PGPR significantly increased the soil organic matter (OM) content (P<0.05), with a maximum of 42.59 g/kg. Further, applying BC or PGPR significantly increased the abundance of beneficial soil microorganisms in the whole growth period of cabbage (P<0.05), such as Streptomyces, Lysobacter, and Bacillus. Meanwhile, the co-application of BC and PGPR increased the abundance of Pseudomonas, and also significantly enhanced the Shannon index and Simpson index of bacterial community (P<0.05). Combined or not with PGPR, the BC application significantly enhanced cabbage yield (P<0.05), with the highest yield reached 1.41 fold of the control. Our research indicated that BC is an suitable and promising carrier of PGPR for soil improvement, combining BC and PGPR can effectively ameliorate the diversity of bacterial community even in acid red soil rhizosphere, and the most direct reflection is to improve soil fertility and cabbage yield.

Claroideoglomus etunicatum and Bacillus thuringiensis Affect the Growth of the Invasive Plant Ageratina adenophora and Its Defense Against the Specialist Herbivore Procecidochares utilis

Exotic plants can selectively recruit beneficial microorganisms, such as arbuscular mycorrhizal fungi (AMFs) and Bacillus spp., during their invasion process to enhance growth and competitiveness by improving nutrient absorption and strengthening defense capabilities against herbivores. However, research in the context of invasive plants remains limited. In this study, a greenhouse pot experiment was conducted to examine the effects of different treatments on the growth and defense of Ageratina adenophora. The treatments included no inoculation, inoculation with Bacillus thuringiensis (BT), inoculation with arbuscular mycorrhizal fungus (Claroideoglomus etunicatum, CE), dual inoculation with BT and CE (BT + CE), and the presence or absence of Procecidochares utilis. The results showed that both CE and BT + CE significantly enhanced nutrient concentration and promoted the growth of A. adenophora. The aboveground biomass increased by 35.48 and 53.38% under non-parasitism and by 68.03% and 103.72% under the parasitism of P. utilis for these two treatments, respectively. In comparison to the control P. utilis-parasitized A. adenophora, the BT, CE, and BT + CE treatments significantly increased protective enzyme activity, jasmonic acid concentration, and secondary metabolites. Our study indicates that the recruitment of B. thuringiensis in the rhizosphere of A. adenophora can enhance its defense ability, while C. etunicatum improved both growth and defense ability. The interaction effects of these two microorganisms enhances the regulation of growth and defense ability of A. adenophora against P. utilis parasitism, providing insights into the feedback effects of beneficial microorganisms on the interactions between invasive plants and biological control.

Establishing aqueous two-phase flotation coupled with preparative high performance liquid chromatography and its application for the purification of astragalin from Flaveria bidentis

The strategy of aqueous two-phase flotation (ATPF) followed by preparative high performance liquid chromatography (prep-HPLC) was established and used for the separation of astragalin from Flaveria bidentis. In the ATPF, the effects of sublation solvent, solution pH, (NH4)2SO4 concentration in aqueous solution, cosolvent, N2 flow rate, flotation time and volumes of the PEG phase on the recovery of astragalin were investigated in detail, and the optimal conditions of ATPF were selected: 50 wt% PEG1000 ethanol solvent as the flotation solvent, pH 4, 350 g/L of (NH4)2SO4 concentration in 5 % ethanol aqueous phase, 40 mL/min of N2 flow rate, 30 min of flotation time, 10.0 mL of flotation solvent volume and twice. After ATPF enrichment, the flotation product was further purified by prep-HPLC. As determined by HPLC, the purity of astragalin was 98.8 %.

Beneficial rhizosphere bacteria provides active assistance in resisting Aphis gossypiis in Ageratina adenophora

Ageratina adenophora can enhance its invasive ability by using beneficial rhizosphere bacteria. Bacillus cereus is able to promote plant growth and provide a positive feedback effect to A. adenophora. However, the interaction between A. adenophora and B. cereus under the influence of native polyphagous insect feeding is still unclear. In this study, Eupatorium lindleyanum, a local species closely related to A. adenophora, was used as a control, aimed to compare the content of B. cereus in the roots of A. adenophora and rhizosphere soil after different densities of Aphis gossypii feeding, and then investigated the variations in the population of A. gossypii and soil characteristics after the addition of B. cereus. The result showed that B. cereus content in the rhizosphere soil and root of A. adenophora increased significantly under A. gossypii feeding compared with local plants, which also led to the change of α-diversity and β-diversity of the bacterial community, as well as the increase in nitrate nitrogen (NO3 -N) content. The addition of B.cereus in the soil could also inhibit the population growth of A. gossypii on A. adenophora and increase the content of ammonium nitrogen (NH4 +-N) in the soil. Our research demonstrated that B. cereus enhances the ability of A. adenophora to resist natural enemy by increasing soil ammonium nitrogen (NH4 +-N) and accumulating other beneficial bacteria, which means that rhizosphere microorganisms help invasive plants defend themselves against local natural enemies by regulating the soil environment.

Choreographing root architecture and rhizosphere interactions through synthetic biology

Climate change is driving extreme changes to the environment, posing substantial threats to global food security and bioenergy. Given the direct role of plant roots in mediating plant-environment interactions, engineering the form and function of root systems and their associated microbiota may mitigate these effects. Synthetic genetic circuits have enabled sophisticated control of gene expression in microbial systems for years and a surge of advances has heralded the extension of this approach to multicellular plant species. Targeting these tools to affect root structure, exudation, and microbe activity on root surfaces provide multiple strategies for the advancement of climate-ready crops.

Plant growth-promoting and heavy metal-resistant Priestia and Bacillus strains associated with pioneer plants from mine tailings

Open mine tailings dams are extreme artificial environments containing sizeable potentially toxic elements (PTEs), including heavy metals (HMs), transition metals, and metalloids. Furthermore, these tailings have nutritional deficiencies, including assimilable phosphorus sources, organic carbon, and combined nitrogen, preventing plant colonization. Bacteria, that colonize these environments, have mechanisms to tolerate the selective pressures of PTEs. In this work, several Priestia megaterium (formerly Bacillus megaterium), Bacillus mojavensis, and Bacillus subtilis strains were isolated from bulk tailings, anthills, rhizosphere, and endosphere of pioneer plants from abandoned mine tailings in Zacatecas, Mexico. Bacillus spp. tolerated moderate HMs concentrations, produced siderophores and indole-3-acetic acid (IAA), solubilized phosphates, and reduced acetylene in the presence of HMs. The strains harbored different PIB-type ATPase genes encoding for efflux pumps and Cation Diffusion Facilitator (CDF) genes. Moreover, nifH and nifD nitrogenase genes were detected in P. megaterium and B. mojavensis genomic DNA. They showed similarity with sequences of the beta-Proteobacteria species, which may represent likely horizontal transfer events. These Bacillus species precede the colonization of mine tailings by plants. Their phenotypic and genotypic features could be essential in the natural recovery of the sites by reducing the oxidative stress of HMs, fixing nitrogen, solubilizing phosphate, and accumulating organic carbon. These traits of the strains reflect the adaptations of Bacillus species to the mine tailings environment and could contribute to the success of phytoremediation efforts.

Effects of Septoglomus constrictum and Bacillus cereus on the competitive growth of Ageratina adenophora

Beneficial microorganisms play a pivotal role in the invasion process of exotic plants, including arbuscular mycorrhizal fungi (AMF) and Bacillus. However, limited research exists on the synergistic influence of AMF and Bacillus on the competition between both invasive and native plants. In this study, pot cultures of Ageratina adenophora monoculture, Rabdosia amethystoides monoculture, and A. adenophora and R. amethystoides mixture were used to investigate the effects of dominant AMF (Septoglomus constrictum, SC) and Bacillus cereus (BC), and the co-inoculation of BC and SC on the competitive growth of A. adenophora. The results showed that inoculation with BC, SC, and BC + SC significantly increased the biomass of A. adenophora by 14.77, 112.07, and 197.74%, respectively, in the competitive growth between A. adenophora and R. amethystoides. Additionally, inoculation with BC increased the biomass of R. amethystoides by 185.07%, while inoculation with SC or BC + SC decreased R. amethystoides biomass by 37.31 and 59.70% compared to the uninoculated treatment. Inoculation with BC significantly increased the nutrient contents in the rhizosphere soil of both plants and promoted their growth. Inoculation with SC or SC + BC notably increased the nitrogen and phosphorus contents of A. adenophora, therefore enhancing its competitiveness. Compared with single inoculation, dual inoculation with SC and BC increased AMF colonization rate and Bacillus density, indicating that SC and BC can form a synergistic effect to further enhance the growth and competitiveness of A. adenophora. This study reveals the distinct role of S. constrictum and B. cereus during the invasion of A. adenophora, and provide new clues to the underlying mechanisms of interaction between invasive plant, AMF and Bacillus.