The antibacterial mechanism of phenylacetic acid isolated from Bacillus megaterium L2 against Agrobacterium tumefaciens

The biosynthesis of L-phenylalanine-derived compounds by engineered microbes

L-Phenylalanine (L-Phe) is an important aromatic amino acid, which has been widely used in food, health care products, medicine and other fields. Based on the relatively mature microbial biosynthesis process, a variety of L-phenylalanine-derived compounds have attracted more and more attentions owing to their extensively potential applications in the fields of food, medicine, spices, cosmetics, and pesticides. However, the challenge of biosynthesis of L-phenylalanine-derived compounds remains the issue of low production and productivity. With the development of metabolic engineering and synthetic biology, the biosynthesis of L-phenylalanine has reached a high level. Therefore, the synthesis of L-phenylalanine-derived compounds based on high production strains of L-phenylalanine has broad prospects. In addition, some L-phenylalanine-derived compounds are more suitable for efficient synthesis by exogenous addition of precursors due to their longer metabolic pathways and the inhibitory effects of many intermediate products. This review systematically summarized the research progress of L-phenylalanine-derived compounds, including phenylpyruvate derivatives, trans-cinnamic derivatives, p-coumaric acid derivatives and other L-phenylalanine-derived compounds (such as flavonoids). Finally, the main strategies to improve the production of L-phenylalanine-derived compounds were summarized, and the development trends of the synthesis of L-phenylalanine-derived compounds by microbial method were also prospected.

Anti-Agrobacterium tumefactions sesquiterpene derivatives from the marine-derived fungus Trichoderma effusum

Agrobacterium tumefaciens can harm various fruit trees, leading to significant economic losses in agricultural production. It is urgent to develop new pesticides to effectively treat this bacterial disease. In this study, four new sesquiterpene derivatives, trichoderenes A-D (1-4), along with six known compounds (5-10), were obtained from the marine-derived fungus Trichoderma effusum. The structures of 1-4 were elucidated by extensive spectroscopic analyses, and the calculated ECD, ORD, and NMR methods. Structurally, the hydrogen bond formed between the 1-OH group and the methoxy group enabled 1 to adopt a structure resembling that of resorcylic acid lactones, thereby producing the ECD cotton effect. Compound 3 represents the first example of C12 nor-sesquiterpene skeleton. Compounds 1-10 were tested for their antimicrobial activity against A. tumefactions. Among them, compounds 1-3 and 8-10 exhibited inhibitory activity against A. tumefactions with MIC values of 3.1, 12.5, 12.5, 6.2, 25.0, and 12.5 μg/mL, respectively.

Comparative genomic analysis of strain Priestia megaterium B1 reveals conserved potential for adaptation to endophytism and plant growth promotion

In our study, we aimed to explore the genomic and phenotypic traits of Priestia megaterium strain B1, which was isolated from root material of healthy apple plants, to adapt to the endophytic lifestyle and promote plant growth. We identified putative genes encoding proteins involved in chemotaxis, flagella biosynthesis, biofilm formation, secretory systems, detoxification, transporters, and transcription regulation. Furthermore, B1 exhibited both swarming and swimming motilities, along with biofilm formation. Both genomic and physiological analyses revealed the potential of B1 to promote plant growth through the production of indole-3-acetic acid and siderophores, as well as the solubilization of phosphate and zinc. To deduce potential genomic features associated with endophytism across members of P. megaterium strains, we conducted a comparative genomic analysis involving 27 and 31 genomes of strains recovered from plant and soil habitats, respectively, in addition to our strain B1. Our results indicated a closed pan genome and comparable genome size of strains from both habitats, suggesting a facultative host association and adaptive lifestyle to both habitats. Additionally, we performed a sparse Partial Least Squares Discriminant Analysis to infer the most discriminative functional features of the two habitats based on Pfam annotation. Despite the distinctive clustering of both groups, functional enrichment analysis revealed no significant enrichment of any Pfam domain in both habitats. Furthermore, when assessing genetic elements related to adaptation to endophytism in each individual strain, we observed their widespread presence among strains from both habitats. Moreover, all members displayed potential genetic elements for promoting plant growth.IMPORTANCEBoth genomic and phenotypic analyses yielded valuable insights into the capacity of P. megaterium B1 to adapt to the plant niche and enhance its growth. The comparative genomic analysis revealed that P. megaterium members, whether derived from soil or plant sources, possess the essential genetic machinery for interacting with plants and enhancing their growth. The conservation of these traits across various strains of this species extends its potential application as a bio-stimulant in diverse environments. This significance also applies to strain B1, particularly regarding its application to enhance the growth of plants facing apple replant disease conditions.

Perception of the Biocontrol Potential and Palmitic Acid Biosynthesis Pathway of Bacillus subtilis H2 through Merging Genome Mining with Chemical Analysis

Bacillus has been widely studied for its potential to protect plants from pathogens. Here, we report the whole genome sequence of Bacillus subtilis H2, which was isolated from the tea garden soil of Guiyang Forest Park. Strain H2 showed a broad spectrum of antagonistic activities against many plant fungal pathogens and bacteria pathogens, including the rice blast fungus Magnaporthe oryzae, and showed a good field control effect against rice blast. The complete genome of B. subtilis H2 contained a 4,160,635-bp circular chromosome, with an average G + C content of 43.78%. Through the genome mining of strain H2, we identified 7 known antimicrobial compound biosynthetic gene clusters (BGCs) including sporulation killing factor, surfactin, bacillaene, fengycin, bacillibactin, subtilosin A, and bacilysin. Palmitic acid (PA), a secondary metabolite, was detected and identified in the H2 strain through genome mining analysis and gas chromatography-mass spectrometry (GC-MS). Additionally, we propose, for the first time, that the type II fatty acid synthesis (FAS) pathway in Bacillus is responsible for PA biosynthesis. This finding was confirmed by studying the antimicrobial activity of PA and conducting reverse transcription-quantitative polymerase chain reaction (RT-qPCR) experiments. We also identified numerous genes associated with plant-bacteria interactions in the H2 genome, including more than 94 colonization-related genes, more than 34 antimicrobial genes, and more than 13 plant growth-promoting genes. These findings contribute to our understanding of the biocontrol mechanisms of B. subtilis H2 and have potential applications in crop disease control.

Chemical Composition, Antibacterial Activity and Mechanism of Action of Fermentation Products from Aspergillus Niger xj

Six compounds were isolated and purified from the crude acetone extract of Aspergillus niger xj. Characterization of all compounds was done by NMR and MS. On the basis of chemical and spectral analysis structure, six compounds were elucidated as metazachlor (1), nonacosane (2), palmitic acid (3), 5,5'-oxybis(5-methylene-2-furaldehyde) (4), dimethyl 5-nitroisophthalate (5) and cholesta-3,5-dien-7-one (6), respectively, and compounds 1, 4, 5 and 6 were isolated for the first time from A. niger. To evaluate the antibacterial activity of compounds 1-6 against three plant pathogenic bacteria (Agrobacterium tumefaciens T-37, Erwinia carotovora EC-1 and Ralstonia solanacearum RS-2), and the minimum inhibitory concentrations (MICs) were determined by broth microdilution method in 96-well microtiter plates. Results of the evaluation of the antibacterial activity showed that T-37 strain was more susceptible to metazachlor with the lowest MIC of 31.25 µg/mL. The antibacterial activity of metazachlor has rarely been reported, thus the antibacterial mechanism of metazachlor against T-37 strain were investigated. The permeability of cell membrane demonstrated that cells membranes were broken by metazachlor, which caused leakage of ions in cells. SDS-PAGE of T-37 proteins indicated that metazachlor could damage bacterial cells through the destruction of cellular proteins. Scanning electron microscopy results showed obvious morphological and ultrastructural changes in the T-37 cells, further confirming the cell membrane damages caused by metazachlor. Overall, our findings demonstrated that the ability of metazachlor to suppress the growth of T-37 pathogenic bacteria makes it potential biocontrol agents.

Biocontrol potential of endophytic bacterium Bacillus altitudinis GS-16 against tea anthracnose caused by Colletotrichum gloeosporioides

Background

As one of the main pathogens causing tea anthracnose disease, Colletotrichum gloeosporioides has brought immeasurable impact on the sustainable development of agriculture. Given the adverse effects of chemical pesticides to the environment and human health, biological control has been a focus of the research on this pathogen. Bacillus altitudinis GS-16, which was isolated from healthy tea leaves, had exhibited strong antagonistic activity against tea anthracnose disease.

Methods

The antifungal mechanism of the endophytic bacterium GS-16 against C. gloeosporioides 1-F was determined by dual-culture assays, pot experiments, cell membrane permeability, cellular contents, cell metabolism, and the activities of the key defense enzymes.

Results

We investigated the possible mechanism of strain GS-16 inhibiting 1-F. In vitro, the dual-culture assays revealed that strain GS-16 had significant antagonistic activity (92.03%) against 1-F and broad-spectrum antifungal activity in all tested plant pathogens. In pot experiments, the disease index decreased to 6.12 after treatment with GS-16, indicating that strain GS-16 had a good biocontrol effect against tea anthracnose disease (89.06%). When the PE extract of GS-16 treated mycelial of 1-F, the mycelial appeared deformities, distortions, and swelling by SEM observations. Besides that, compared with the negative control, the contents of nucleic acids, protein, and total soluble sugar of GS-16 group were increased significantly, indicating that the PE extract of GS-16 could cause damage to integrity of 1-F. We also found that GS-16 obviously destroyed cellular metabolism and the normal synthesis of cellular contents. Additionally, treatment with GS-16 induced plant resistance by increasing the activities of the key defense enzymes PPO, SOD, CAT, PAL, and POD.

Conclusions

We concluded that GS-16 could damage cell permeability and integrity, destroy the normal synthesis of cellular contents, and induce plant resistance, which contributed to its antagonistic activity. These findings indicated that strain GS-16 could be used as an efficient microorganism for tea anthracnose disease caused by C. gloeosporioides.

Antibacterial activity mechanism of coptisine against Pasteurella multocida

Objective

Pasteurella multocida is a widespread zoonotic pathogen that causes severe damage to the poultry industry. This study focused on the antibacterial effects and mechanism of action of coptisine against P. multocida.

Methods

The minimum inhibitory concentration and half maximal inhibitory concentration of coptisine against P. multocida was measured. Additionally, the effect of coptisine on growth, cell wall, activity of respiratory enzymes, soluble protein content and DNA synthesis were also analyzed. Finally, the effect of coptisine on gene transcription was determined using RNA sequencing.

Results

We demonstrated that coptisine has a strong antibacterial effect against P. multocida, with a minimum inhibitory concentration of 0.125 mg/mL. Moreover, the measurement of the half maximal inhibitory concentration confirmed that coptisine was safe for the pathogen. The growth curve showed that coptisine inhibited bacterial growth. Measurement of alkaline phosphatase activity in the culture solution showed that coptisine affected cell wall permeability. Transmission electron microscopy revealed that coptisine chloride destroyed the cell structure. In addition, coptisine blocked the respiratory system, as measured by the levels of critical enzymes of the tricarboxylic acid cycle and glycolysis, succinate dehydrogenase and lactate dehydrogenase, respectively. Similarly, coptisine inhibited the synthesis of soluble proteins and genomic DNA. The KEGG pathway analysis of the differentially expressed genes showed that they were associated with cellular, respiratory, and amino acid metabolism, which were downregulated after coptisine treatment. Additionally, genes related to RNA degradation and the aminoacyl-tRNA pathway were upregulated.

Conclusion

In this study, we demonstrated that coptisine exerts an antibacterial effect on P. multocida. These findings suggest that coptisine has a multifaceted impact on various pathways, resulting in the inhibition of P. multocida. Thus, coptisine is a potential alternative to antibiotics for the treatment of P. multocida infections in a clinical setting.