Evaluation of antibacterial activity of Stenotrophomonas maltophilia against Ralstonia solanacearum under different application conditions

Biocontrol of Bacterial Wilt Disease Using Plant-Associated Bacterial Communities in Tomato

Host-protective or disease-suppressive microorganisms are emerging as sustainable solutions for controlling crop diseases, such as bacterial wilt. However, the efficacy of biocontrol strategies is often constrained by limited resilience under varying environmental conditions and interactions with native microbial communities in the field. One major challenge is that introduced biocontrol microbes often face suppression by indigenous microbes due to competitive interactions. Synthetic communities (SynComs) offer a promising alternative strategy. However, conventional approaches to assembling SynComs by combining different microbial isolates often result in antagonism and competition among strains, leading to ineffective and inconsistent outcomes. In this study, we assembled a bacterial wilt-suppressive SynCom for tomato, composed of bacterial isolates derived from co-cultured microbial complexes associated with healthy plants. This SynCom demonstrates significant disease-suppressive effects against Ralstonia pseudosolanacearum in tomato seedlings under both axenic and soil conditions. Additionally, our findings suggest the presence of an optimal SynCom colonization level in plants, which is crucial for effective disease suppression. The SynCom also exhibits direct antibiotic activity and modulates the plant-associated microbiome. Our results provide an effective approach to constructing SynComs with consistent and effective disease-suppressive properties within microbial community contexts. [Formula: see text] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Can we control potato fungal and bacterial diseases? - microbial regulation

The potato plant is one of the main crops in the world. However, relatively little is known about key virulence factors of major fungal and bacterial diseases in potatoes, biocontrol measures to improve activity and stability, and the core driving forces in the control process. Here, we focus on analyzing the mechanisms by which genes, proteins, or (and) metabolites of potato pathogens as key virulence factors. Then, the single strain biocontrol agents, synthetic microbial communities, microbial microcapsule strategies were introduced, and the latter two strategies can improve stability and activity in biocontrol. Meanwhile, summarized the defense mechanisms of biocontrol and their specific issues in practical applications. Furthermore, explore how potato crop management, soil management, and climate effects, as crucial driving forces affect potato biocontrol in the system. Dynamic and systematic research, excavation of biocontrol strain resources, find the causes of regional disease resistance and exploration of biocontrol mechanism will provide promising solutions for biotic stress faced by potato in the future.

Potential of algal-based products for the management of potato brown rot disease

BACKGROUND

Ralstonia solanacearum causes potato brown rot disease, resulting in lower crop's production and quality. A sustainable and eco-friendly method for controlling the disease is required. Algae's bioactive chemicals have shown the potential to enhance plant defenses. For the first time, the efficacy of foliar application of Acanthophora spicifera and Spirulina platensis seaweed extracts, along with the utilization of dried algal biomasses (DABs) of Turbinaria ornata and a mixture of Caulerpa racemosa and Cystoseira myrica (1:1)on potato yield and brown rot suppression were investigated under field conditions. Field experiments were conducted in three locations: Location 1 (Kafr Shukr district, Kaliobeya governorate), Location 2 (Moneira district, Kaliobeya governorate), and Location 3 (Talia district, Minufyia governorate). Locations 1 and 2 were naturally infested with the pathogen, while location 3 was not. The study evaluated potato yield, plant nutritive status and antioxidants, soil available nitrogen-phosphorus-potassium (N-P-K), and organic matter percentage. Additionally, the shift in soil microbial diversity related to R. solanacearum suppression was examined for the most effective treatment.

RESULTS

The results revealed that seaweed extracts significantly increased potato yield at all locations, which correlated with higher phosphorus absorption, while T. ornate DAB increased potato yield only at location 2, accompanied by noticeable increases in soil nitrogen and plant phosphorus. The mixed DABs of C. racemosa and C. myrica demonstrated greater disease suppression than foliar applications. The disease-suppressive effect of the mixed DABs was accompanied by significant increases in flavonoids and total antioxidant capacity (TAC). Moreover, the application of mixed DABs increased soil bacterial biodiversity, with a higher abundance of oligotrophic marine bacterial species such as Sphingopyxis alaskensis and growth-promoting species like Glutamicibacter arilaitensis, Promicromonospora sp., and Paenarthrobacter nitroguajacolicus in all three locations compared to the untreated control. Klebsiella sp., Pseudomonas putida, and P. brassicacearum abundances were increased by the mixed DABs in Location 1. These species were less abundant in locations 2 and 3, where Streptomyces sp., Bacillus sp., and Sphingobium vermicomposti were prevalent.

CONCLUSIONS

The results demonstrated that the used seaweed extracts improved potato yield and phosphorous absorption, while the mixed DABs potentially contributed in disease suppression and improved soil microbial diversity.

Evaluation of the Defined Bacterial Consortium Efficacy in the Biodegradation of NSAIDs

Due to the increasing pollution of wastewater with non-steroidal anti-inflammatory drugs, preparations need to be developed to decompose these drugs. This work aimed to develop a bacterial consortium with a defined composition and boundary conditions for the degradation of paracetamol and selected non-steroidal anti-inflammatory drugs (NSAIDs), including ibuprofen, naproxen, and diclofenac. The defined bacterial consortium consisted of Bacillus thuringiensis B1(2015b) and Pseudomonas moorei KB4 strains in a ratio of 1:2. During the tests, it was shown that the bacterial consortium worked in the pH range from 5.5 to 9 and temperatures of 15-35 °C, and its great advantage was its resistance to toxic compounds present in sewage, such as organic solvents, phenols, and metal ions. The degradation tests showed that, in the presence of the defined bacterial consortium in the sequencing batch reactor (SBR), drug degradation occurred at rates of 4.88, 10, 0.1, and 0.05 mg/day for ibuprofen, paracetamol, naproxen, and diclofenac, respectively. In addition, the presence of the tested strains was demonstrated during the experiment as well as after its completion. Therefore, the advantage of the described bacterial consortium is its resistance to the antagonistic effects of the activated sludge microbiome, which will enable it to be tested in real activated sludge conditions.

Reclamation of waste coal gangue activated by Stenotrophomonas maltophilia for mine soil improvement: Solubilizing behavior of bacteria on nutrient elements

The coal gangue has occupied the farmland and caused severe pollution to the surrounding environment, which was discharged with vast amount as a by-product of coal mining and washing. A sustainable and ecological microorganism activation method was proposed to disposal coal gangue as mineral fertilizer. A Stenotrophomonas maltophilia YZ1 bacteria was separated and found to be useful in solubilizing nutrient elements in coal gangue. The contents of available P, available K and available Si in the treated coal gangue reached 278.4 mg/kg, 1305.3 mg/kg and 522.7 mg/kg, respectively. The YZ1 bacteria dissolved the minerals of monetite (CaHPO₄), muscovite and annite by the organic acids, which were the metabolism product of YZ1 bacteria. The solubilizing mechanisms of phosphate minerals included the release of protic and the chelation of organic acid with calcium. The microbial activation method can provide nutrient elements for soil, which may realize the reclamation of coal gangue in a harmless way.

Systemic Resistance Induction of Potato and Tobacco Plants against Potato Virus Y by Klebsiella oxytoca

Simple Summary

Klebsiella oxytoca, as a type of plant growth-promoting rhizobacteria (PGPR), was studied with regards to promoting plant growth and inducing plant systemic resistance against Potato Virus Y (PVY). The results of greenhouse experiments with tobacco and potato plants demonstrated that treatments with the Klebsiella oxytoca and biochar significantly enhanced the growth, while clearly lowering the disease severity and concentration of PVY. An RT-PCR analysis of the defense genes in the tobacco and potato treated with the Klebsiella oxytoca and biochar revealed an association with enhancing the systemic resistance of tobacco and potato to PVY. Klebsiella oxytoca and biochar may be considered valuable options to control PVY in potato and other Solanaceae crops.

Abstract

Potato Virus Y (PVY) is a serious potato disease that may significantly decrease potato production. To suppress potato virus infection, several measures have been undertaken. The utilization of plant growth-promoting rhizobacteria is one of these methods. Biochar soil treatment is believed to provide plants with a number of advantages, including increased plant growth and the development of systemic resistance to a variety of plant diseases. The goal of this research was to see whether adding biochar and Klebsiella oxytoca to the soil might cause PVY resistance and enhance the involved mechanisms in PVY resistance. Potato and tobacco seedlings treated with Klebsiella oxytoca and biochar exhibited the same impact of significant symptom reduction, with complete negative ELISA findings, supporting the antiviral activity of K. oxytoca and biochar. Furthermore, owing to the connection between the ISR implicated substrates, significant amounts of polyphenol oxidase, catalase, and superoxide dismutase were observed in treated plants, with the same behavior as defense genes expression levels. It may be a step forward in the development of biochar and K. oxytoca as potential environmentally friendly disease control strategies against PVY.

Genomic Analysis of the Endophytic Stenotrophomonas Strain 169 Reveals Features Related to Plant-Growth Promotion and Stress Tolerance

Plant-associated Stenotrophomonas isolates have great potential for plant growth promotion, especially under stress conditions, due to their ability to promote tolerance to abiotic stresses such as salinity or drought. The endophytic strain Stenotrophomonas sp. 169, isolated from a field-grown poplar, increased the growth of inoculated in vitro plants, with a particular effect on root development, and was able to stimulate the rooting of poplar cuttings in the greenhouse. The strain produced high amounts of the plant growth-stimulating hormone auxin under in vitro conditions. The comparison of the 16S rRNA gene sequences and the phylogenetic analysis of the core genomes showed a close relationship to Stenotrophomonas chelatiphaga and a clear separation from Stenotrophomonas maltophilia. Whole genome sequence analysis revealed functional genes potentially associated with attachment and plant colonization, growth promotion, and stress protection. In detail, an extensive set of genes for twitching motility, chemotaxis, flagella biosynthesis, and the ability to form biofilms, which are connected with host plant colonization, could be identified in the genome of strain 169. The production of indole-3-acetic acid and the presence of genes for auxin biosynthesis pathways and the spermidine pathway could explain the ability to promote plant growth. Furthermore, the genome contained genes encoding for features related to the production of different osmoprotective molecules and enzymes mediating the regulation of stress tolerance and the ability of bacteria to quickly adapt to changing environments. Overall, the results of physiological tests and genome analysis demonstrated the capability of endophytic strain 169 to promote plant growth. In contrast to related species, strain 169 can be considered non-pathogenic and suitable for biotechnology applications.

Advances in the Microbiology of Stenotrophomonas maltophilia

Stenotrophomonas maltophilia is an opportunistic pathogen of significant concern to susceptible patient populations. This pathogen can cause nosocomial and community-acquired respiratory and bloodstream infections and various other infections in humans. Sources include water, plant rhizospheres, animals, and foods. Studies of the genetic heterogeneity of S. maltophilia strains have identified several new genogroups and suggested adaptation of this pathogen to its habitats. The mechanisms used by S. maltophilia during pathogenesis continue to be uncovered and explored. S. maltophilia virulence factors include use of motility, biofilm formation, iron acquisition mechanisms, outer membrane components, protein secretion systems, extracellular enzymes, and antimicrobial resistance mechanisms. S. maltophilia is intrinsically drug resistant to an array of different antibiotics and uses a broad arsenal to protect itself against antimicrobials. Surveillance studies have recorded increases in drug resistance for S. maltophilia, prompting new strategies to be developed against this opportunist. The interactions of this environmental bacterium with other microorganisms are being elucidated. S. maltophilia and its products have applications in biotechnology, including agriculture, biocontrol, and bioremediation.

Genome analysis provides insights into the biocontrol ability of Mitsuaria sp. strain TWR114

Mitsuaria sp. TWR114 is a biocontrol agent against tomato bacterial wilt (TBW). We aimed to gain genomic insights relevant to the biocontrol mechanisms and colonization ability of this strain. The draft genome size was found to be 5,632,523 bp, with a GC content of 69.5%, assembled into 1144 scaffolds. Genome annotation predicted a total of 4675 protein coding sequences (CDSs), 914 pseudogenes, 49 transfer RNAs, 3 noncoding RNAs, and 2 ribosomal RNAs. Genome analysis identified multiple CDSs associated with various pathways for the metabolism and transport of amino acids and carbohydrates, motility and chemotactic capacities, protection against stresses (oxidative, antibiotic, and phage), production of secondary metabolites, peptidases, quorum-quenching enzymes, and indole-3-acetic acid, as well as protein secretion systems and their related appendages. The genome resource will extend our understanding of the genomic features related to TWR114's biocontrol and colonization abilities and facilitate its development as a new biopesticide against TBW.

Trifolium repens-Associated Bacteria as a Potential Tool to Facilitate Phytostabilization of Zinc and Lead Polluted Waste Heaps

Heavy metals in soil, as selective agents, can change the structure of plant-associated bacterial communities and their metabolic properties, leading to the selection of the most-adapted strains, which might be useful in phytoremediation. Trifolium repens, a heavy metal excluder, naturally occurs on metal mine waste heaps in southern Poland characterized by high total metal concentrations. The purpose of the present study was to assess the effects of toxic metals on the diversity and metabolic properties of the microbial communities in rhizospheric soil and vegetative tissues of T. repens growing on three 70–100-years old Zn–Pb mine waste heaps in comparison to Trifolium-associated bacteria from a non-polluted reference site. In total, 113 cultivable strains were isolated and used for 16S rRNA gene Sanger sequencing in order to determine their genetic affiliation and for in vitro testing of their plant growth promotion traits. Taxa richness and phenotypic diversity in communities of metalliferous origin were significantly lower (p < 0.0001) compared to those from the reference site. Two strains, Bacillus megaterium BolR EW3_A03 and Stenotrophomonas maltophilia BolN EW3_B03, isolated from a Zn–Pb mine waste heap which tested positive for all examined plant growth promoting traits and which showed co-tolerance to Zn, Cu, Cd, and Pb can be considered as potential facilitators of phytostabilization.

Potential use of soilborne lytic Podoviridae phage as a biocontrol agent against Ralstonia solanacearum

A new podovirus RsPod1EGY Ralstonia phage (GenBank accession no MG711516) with a specific action against R. solanacearum phylotype IIa, sequevar I (race 3, biovar 2) was isolated from Egyptian soil. The potential efficacy of the isolated phage to be used as biocontrol agent was evaluated in vitro and under greenhouse conditions. The podovirus phage produced a plaque size of 3.0-4.0 mm in diameter and completed its infection cycle in 180 min after infection with a burst size of ∼27 virions per infected cell. On the basis of restriction endonuclease analysis, the genome size of the phage was about 41 kb of double-stranded DNA. In vitro studies showed that RsPod1EGY is stable at higher temperatures (up to 60 °C), and at a wide pH range (5-9). SDS-PAGE analysis indicated the major structural protein to be approximately 32 kDa. Bacteriolytic activity of RsPod1EGY against R. solanacearum was detected at different multiplicity of infection (MOI). RsPod1EGY proved to be effective in reduction and prevention of formation of surface polysaccharides of R. solanacearum, during the exponential growth phase of the latter. Interestingly, RsPod1EGY was effective in suppression of R. solanacearum under greenhouse conditions. All Phage-treated tomato plants showed no wilt symptoms or any latent infection during the experimental period, whereas all untreated plants have wilted by 10 days post-infection. The lytic stability of RsPod1EGY phage at higher temperature as well as its effective suppression of wilting symptoms under greenhouse conditions would contribute to biocontrol the bacterial wilt disease in Egypt under field conditions.

Identification of Cyclic Dipeptides from Escherichia coli as New Antimicrobial Agents against Ralstonia Solanacearum

Ralstonia solanacearum is a causative agent of bacterial wilt in many important crops throughout the world. How to control bacterial wilt caused by R. solanacearum is a major problem in agriculture. In this study, we aim to isolate the biocontrol agents that have high efficacy in the control of bacterial wilt. Three new bacterial strains with high antimicrobial activity against R. solanacearum GMI1000 were isolated and identified. Our results demonstrated that these bacteria could remarkably inhibit the disease index of host plant infected by R. solanacearum. It was indicated that strain GZ-34 (CCTCC No. M 2016353) showed an excellent protective effect to tomato under greenhouse conditions. Strain GZ-34 was characterized as Escherichia coli based on morphology, biochemistry, and 16S rRNA analysis. We identified that the main antimicrobial compounds produced by E. coli GZ-34 were cyclo(l-Pro-d-Ile) and cyclo(l-Pro-l-Phe) using electrospray ionization mass spectrometry (ESI-MS) and nuclear magnetic resonance (NMR) analysis. The two active compounds also interfered with the expression levels of some pathogenicity-contributors of R. solanacearum. Furthermore, cyclo(l-Pro-l-Phe) effectively inhibited spore formation of Magnaporthe grisea, which is a vital pathogenesis process of the fungal pathogen, suggesting cyclic dipeptides from E. coli are promising potential antimicrobial agents with broad-spectrum activity to kill pathogens or interfere with their pathogenesis.

The PGPR Stenotrophomonas maltophilia SBP-9 Augments Resistance against Biotic and Abiotic Stress in Wheat Plants

Certain plant growth promoting bacteria have ability to ameliorate abiotic and/or biotic stressors, which can be exploited to enhance plant growth and productivity of the plants under stress conditions. Therefore, the present study aimed to examine the role of a rhizospheric bacterial isolate SBP-9 isolated from Sorghum bicolor (i) in promoting the wheat plant growth under salinity stress, and (ii) in enhancing the defense response in wheat against fungal pathogen "Fusarium graminearum." The test isolate possessed plant growth promoting (PGP) traits including ACC deaminase (ACCD), gibberellic acid, indole acetic acid (IAA), siderophore, and inorganic phosphate solubilization. Under salt (NaCl) stress, inoculation of this isolate to wheat plant significantly increased plant growth in terms of various growth parameters such as shoot length/root length (20-39%), fresh weight/dry weight (28-42%), and chlorophyll content (24-56%) following inoculation of test isolate SBP-9. Bacterial inoculation decreased the level of proline, and malondialdehyde, whereas elevated the antioxidative enzymatic activities of superoxide-dismutase (SOD; 28-41%), catalase (CAT; 24-56%), and peroxidase (POX; 26-44%). Furthermore, it also significantly decreased the Na+ accumulation in both shoot and roots in the range of 25-32%, and increased the K+ uptake by 20-28%, thereby favoring the K+/Na+ ratio. On the other hand, the test isolate also enhanced the level of defense enzymes like β-1, 3 glucanase, phenylalanine ammonia lyase (PAL), peroxidae (PO), and polyphenol oxidase (PPO), which can protect plants from the infection of pathogens. The result of colonization test showed an ability of the test isolate to successfully colonize the wheat plants. These results indicate that Stenotrophomonas maltophilia SBP-9 has potential to promote the wheat growth under biotic and abiotic (salt) stressors directly or indirectly and can be further tested at field level for exploitation as bioinoculant.