Corn Responsiveness to Azospirillum: Accessing the Effect of Root Exudates on the Bacterial Growth and Its Ability to Fix Nitrogen

Inoculation with Azospirillum brasilense Strains AbV5 and AbV6 Increases Nutrition, Chlorophyll, and Leaf Yield of Hydroponic Lettuce

Inoculation with Azospirillum brasilense has promisingly increased plant yield and nutrient acquisition. The study aimed to estimate the dose of A. brasilense that increases yield, gas exchange, nutrition, and foliar nitrate reduction. The research was carried out in a greenhouse at Ilha Solteira, in a hydroponic system in randomized blocks with four replicates. The treatments consisted of doses of inoculation with A. brasilense strains AbV5 and AbV6 via nutrient solution (0, 8, 16, 32, and 64 mL 100 L-1). Inoculation with A. brasilense at calculated doses between 20 and 44 mL provided the highest fresh and dry mass of shoots and roots, number of leaves, and leaf yield. In addition, the calculated doses of inoculation with A. brasilense increased the accumulation of N, P, K, Ca, Mg, S, B, Fe, Mn, and Zn in shoots and roots, except the accumulation of Ca in roots. It also increased cell membrane integrity index (15%), relative water content (13%), net photosynthesis rate (85%), intracellular CO2 concentration (15%), total chlorophyll (46%), stomatal conductance (56%), transpiration (15%), and water use efficiency (59%). Hence, inoculation with A. brasilense at doses between 20 and 44 mL 100 L-1 is considered the best approach for increasing the growth, yield, accumulation of nutrients, and gas exchange of hydroponically grown iceberg lettuce.

Regulatory strategies for inhibiting horizontal gene transfer of ARGs in paddy and dryland soil through computer-based methods

Antibiotic resistance genes (ARGs) have been regarded as emerging pollutants due to their potential risk of resistance. Horizontal gene transfer (HGT) is the main pathway for ARGs to lead to environmental threats. Therefore, the inhabitation of ARGs' HGT can effectively inhibit ARGs' potential drug resistance risk within a single strain. In this paper, the characteristics of ARGs' HGT in paddy and dryland soils were identified and regulated by a combination of ARGs' HGT feature identification, transfer mechanism analysis and transfer process regulation. The homology modeling algorithm was used to simulate the construction of the Tn5 plasmid transposase of Escherichia coli (E. coli) for identifying ARGs' HGT characteristics. The GCG (212.617 Å) was thus determined as the target codon. Through integrated computer-based methods, results showed that the most important environmental disturbance factors for the HGT of ARGs in the paddy and dryland soils were rough farmyard manure/sewage irrigation and mining pollution, respectively. Under the disturbance of key environmental factors, the inhibitory effect of HGT of ARGs in paddy and dryland soil was reduced by 35.01 % and 34.74 %, respectively. Results demonstrated that the proposed theoretical mechanism and control strategies could effectively inhibit the HGT of E. coli ARGs in the soil environment.

Genome Mining and Gene Expression Reveal Maytansine Biosynthetic Genes from Endophytic Communities Living inside Gymnosporia heterophylla (Eckl. and Zeyh.) Loes. and the Relationship with the Plant Biosynthetic Gene, Friedelin Synthase

Even though maytansine was first discovered from Celastraceae plants, it was later proven to be an endophytic bacterial metabolite. However, a pure bacterial culture cannot synthesize maytansine. Therefore, an exclusive interaction between plant and endophytes is required for maytansine production. Unfortunately, our understanding of plant-endophyte interaction is minimal, and critical questions remain. For example: how do endophytes synthesize maytansine inside their plant host, and what is the impact of maytansine production in plant secondary metabolites? Our study aimed to address these questions. We selected Gymnosporia heterophylla as our model and used amino-hydroxybenzoic acid (AHBA) synthase and halogenase genes as biomarkers, as these two genes respond to biosynthesize maytansine. As a result, we found a consortium of seven endophytes involved in maytansine production in G. heterophylla, based on genome mining and gene expression experiments. Subsequently, we evaluated the friedelin synthase (FRS) gene's expression level in response to biosynthesized 20-hydroxymaytenin in the plant. We found that the FRS expression level was elevated and linked with the expression of the maytansine biosynthetic genes. Thus, we achieved our goals and provided new evidence on endophyte-endophyte and plant-endophyte interactions, focusing on maytansine production and its impact on plant metabolite biosynthesis in G. heterophylla.

Optimization of Environmental Conditions for Microbial Stabilization of Uranium Tailings, and the Microbial Community Response

Uranium pollution in tailings and its decay products is a global environmental problem. It is of great significance to use economical and efficient technologies to remediate uranium-contaminated soil. In this study, the effects of pH, temperature, and inoculation volume on stabilization efficiency and microbial community response of uranium tailings were investigated by a single-factor batch experiment in the remediation process by mixed sulfate-reducing bacteria (SRB) and phosphate-solubilizing bacteria (PSB, Pantoea sp. grinm-12). The results showed that the optimal parameters of microbial stabilization by mixed SRB-PSB were pH of 5.0, temperature of 25°C, and inoculation volume of 10%. Under the optimal conditions, the uranium in uranium tailings presented a tendency to transform from the acid-soluble state to residual state. In addition, the introduction of exogenous SRB-PSB can significantly increase the richness and diversity of endogenous microorganisms, effectively maintain the reductive environment for the microbial stabilization system, and promote the growth of functional microorganisms, such as sulfate-reducing bacteria (Desulfosporosinus and Desulfovibrio) and iron-reducing bacteria (Geobacter and Sedimentibacter). Finally, PCoA and CCA analyses showed that temperature and inoculation volume had significant effects on microbial community structure, and the influence order of the three environmental factors is as follows: inoculation volume > temperature > pH. The outcomes of this study provide theoretical support for the control of uranium in uranium-contaminated sites.

Special Issue Editorial: Plant Nitrogen Assimilation and Metabolism

Nitrogen is an important macronutrient for plant growth and development. Research has long been carried out to elucidate the mechanisms involved in nitrogen uptake, assimilation, and utilization in plants. However, despite recent advances, many of these mechanisms still are not fully understood. In this special issue, several research articles and two reviews, all of them aiming to elucidate some specific aspects of nitrogen (N) metabolism, are presented. Together, the articles in this issue provide a state-of-the-art perspective on important questions related to nitrogen metabolism in photosynthetic organisms, highlighting the fundamental importance of research in this field.