Although metabolomics is widely used to assess the detrimental effects of antibiotics and characterize stress response, the relationships between metabolites and biological endpoints following antibiotics remain unknown. In our study, we exposed ryegrass seeds to sulfamethoxazole for five days. The results showed that sulfamethoxazole inhibited plant growth (by 12.90–85.83%). It also decreased chlorophyll content (by 35.40–93.32%), carotenoid content (by 32.76–90.18%), and root cell permeability (by 98.43–99.29%), but increased root reactive oxygen species (ROS) concentration (increasing rate: 11.32- to 137.36-times). Moreover, high sulfamethoxazole concentrations increased superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities. To elucidate the association between metabolites and biological endpoints, we conducted an orthogonal partial least squares analysis. The results showed that sulfamethoxazole significantly altered six metabolic pathways. Among the metabolites modulated by sulfamethoxazole, amino acids mainly affected root growth and ROS concentration, whereas carbohydrates were substantially associated with the effect of sulfamethoxazole on cell permeability. Many metabolites had contrasting effects. For example, some metabolites increased root fresh weight and improved cell permeability by decreasing ROS levels and SOD, POD, and CAT activities. By contrast, some metabolites negatively affected root fresh weight and cell permeability by increasing ROS levels and SOD, POD, and CAT activities. These observations bring new insights into ryegrass responses to sulfamethoxazole-induced stress.

Metabolomics is a commonly used method to study the responses of organisms to environmental changes. However, the relationships between metabolites and biological endpoints still need further discussion. In this study, we exposed wheat seeds to sulfamethoxazole (0, 1, 10, 100 mg/L) for 5 days. The results show that sulfamethoxazole (SMX) had an inhibitory effect on wheat growth. It reduced shoot length, root length, shoot fresh weight, root fresh weight, chlorophyll content, and carotenoid content. At the same time, it increased the concentration of reactive oxygen species, the activity of superoxide dismutase, the activity of peroxidase, and the activity of catalase in the root. An orthogonal partial least squares analysis and correlation analysis were performed. SMX transformed five key metabolic pathways. Notably, certain metabolic alterations exhibited negative correlations with reactive oxygen species (ROS) accumulation and antioxidant enzyme activities (including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)), while showing positive associations with root growth parameters (fresh weight and length). Conversely, other metabolic changes appeared to promote ROS generation and enhance antioxidant enzyme activities, consequently inhibiting root growth. These findings offer novel perspectives on the metabolic regulation of wheat’s stress response to SMX exposure.

Pseudoiodinine is an antimicrobial compound produced by Pseudomonas mosselii that exhibits strong inhibitory activity against bacterial and fungal pathogens of rice, highlighting its potential as a green biopesticide. However, the regulatory mechanisms underlying pseudoiodinine production remain poorly understood. In this study, genome-wide random mutagenesis identified two insertion mutants of 277-3 and 277-23 that completely abolished antagonistic activity against Xanthomonas oryzae pv. oryzicola (Xoc) RS105, with transposon insertions mapped to tolB and tolR, respectively. Further analysis showed that mutations in tolB and tolR significantly impaired bacterial growth during the exponential phase, suggesting that the Tol-Pal system is required for the optimal growth of P. mosselii. Consistently, overexpression of the tol-pal operon resulted in a 3.2-fold increase in pseudoiodinine production compared with the original strain. These findings indicate that the Tol-Pal system contributes to pseudoiodinine production primarily by maintaining efficient bacterial growth. Collectively, this study provides the first insight into the Tol-Pal system in promoting pseudoiodinine production and suggests its potential application in engineering P. mosselii strains.