Pseudomonas fluorescens NK4 siderophore promotes plant growth and biocontrol in cucumber

Improvement of plant growth and fruit quality by introducing a phosphoribosylpyrophosphate synthetase mutation into Methylorubrum populi

AIMS

The aim of this study was to evaluate the impact of the introduction of a phosphoribosylpyrophosphate synthetase (PRS) mutation into a plant growth-promoting strain of Methylorubrum on the enhancement of phyllosphere colonization, with the ultimate goal of improving plant growth and quality.

METHODS AND RESULTS

A strain of Methylorubrum populi (named HS04) was isolated from the groundnut leaves and found to process the plant-promoting traits, including the ability to produce indole acetic acid, siderophore, 1-aminocyclopropane-1-carboxylate deaminase, and to fix nitrogen. The application via foliar spray significantly increased the fresh weight of cucumber seedlings cultivated in a standard growth chamber, with 43.0% higher than the control group. Genomic analysis revealed that the presence of an array of genes involved in plant growth promotion, including accD, aldB, and ltaE, as well as potential nitrogen-fixation-related genes, including nifA, bchlLNB, and bchXYZ, in the HS04 strain. The introduction of the PRS mutation (an aspartic acid to an asparagine residue, D38N) in the HS04 strain (named HS04PTR) enhanced the utilization capacity of low concentrations of methanol and multi-carbon sources (C2-C5 carbon sources). The HS04PTR strain indicated a notable enhancement in the phyllosphere colonization, with the subsequent application further promoting the growth of cucumber seedlings. An agricultural solar greenhouse experiment was thus performed to assess the efficiency of the HS04PTR strain, sprayed at low abundance, in improving the growth and quality of cucumber plants, including vitamin C, reducing sugars, and total sugars.

CONCLUSIONS

Our findings provide insights into the potential of Methylorubrum/Methylobacterium strains with the PRS mutations as an efficient inoculant for advantageous agricultural applications.

Harnessing Pseudomonas spp. for sustainable plant crop protection

This review examines the role of Pseudomonas spp. bacteria as biocontrol agents against crop diseases, focusing on their mechanisms of action, efficacy, and potential applications in sustainable agriculture. Pseudomonas spp., ubiquitous in soil ecosystems and root microbiomes, have attracted attention for their ability to suppress phytopathogens and enhance plant health through various mechanisms. These include direct competition for nutrients, production of antimicrobial compounds and volatile organic compounds, competition using type VI secretion systems, and indirect induction of systemic resistance. Our review shows that Pseudomonas strains effectively control a wide range of diseases across diverse plant species, with some strains demonstrating efficacy comparable to chemical fungicides. However, the review also highlights challenges in achieving consistent performance when using Pseudomonas inoculants under field conditions due to various biotic and abiotic factors. Strategies to optimize biocontrol potential, such as formulation techniques, application methods, and integration with other management practices, are discussed. The advantages of Pseudomonas-based biocontrol for sustainable agriculture include reduced reliance on chemical pesticides, enhanced crop productivity, and improved environmental sustainability. Future research directions should focus on understanding the complex interactions within the plant microbiome, optimizing delivery systems, and addressing regulatory hurdles for commercial deployment. This review underscores the significant potential of Pseudomonas spp. in sustainable crop protection while acknowledging the need for further research to fully harness their capabilities in agricultural systems.

Rhizospheric microbiota of suppressive soil protect plants against Fusarium solani infection

BACKGROUND

Fusarium infection has caused huge economic losses in many crops. The study aimed to compare the microbial community of suppressive and conducive soils and relate to the reduction of Fusarium wilt.

RESULTS

High-throughput sequencing and microbial network analysis were used to investigate the differences in the rhizosphere microbiota of the suppressive and conducive soils and to identify the beneficial keystone taxa. Plant pathogens were enriched in the conducive soil. Potential plant-beneficial microorganisms and antagonistic microorganisms were enriched in the suppressive soil. More positive interactions and keystone taxa existed in the suppressive soil network. Thirty-nine and 16 keystone taxa were identified in the suppressive and conducive soil networks, respectively. Sixteen fungal strains and 168 bacterial strains were isolated from suppressive soil, some of which exhibited plant growth-promotion traits. Thirty-nine bacterial strains and 10 fungal strains showed antagonistic activity against F. solani. Keystone taxa Bacillus and Trichoderma exhibited high antifungal activity. Lipopeptides produced by Bacillus sp. RB150 and chitinase from Trichoderma spp. inhibited the growth of F. solani. Microbial consortium I (Bacillus sp. RB150, Pseudomonas sp. RB70 and Trichoderma asperellum RF10) and II (Bacillus sp. RB196, Bacillus sp. RB150 and T. asperellum RF10) effectively controlled root rot disease, the spore number of F. solani was reduced by 94.2% and 83.3%.

CONCLUSION

Rhizospheric microbiota of suppressive soil protects plants against F. solani infection. Antagonistic microorganisms in suppressive soil inhibit pathogen growth and infection. Microbial consortia consisted of keystone taxa well control root rot disease. These findings help control Fusarium wilt. © 2024 Society of Chemical Industry.

Purification and Characterization of Desferrioxamine B of Pseudomonas fluorescens and Its Application to Improve Oil Content, Nutrient Uptake, and Plant Growth in Peanuts

Microorganisms produce siderophores, which are low-molecular-weight iron chelators when iron availability is limited. The present analyzed the role of LNPF1 as multifarious PGPR for improving growth parameters and nutrient content in peanut and soil nutrients. Such multifarious PGPR strains can be used as effective bioinoculants for peanut farming. In this work, rhizosphere bacteria from Zea mays and Arachis hypogaea plants in the Salem area of Tamil Nadu, India, were isolated and tested for biochemical attributes and characteristics that stimulate plant growth, such as the production of hydrogen cyanide, ammonia (6 µg/mL), indole acetic acid (76.35 µg/mL), and solubilizing phosphate (520 µg/mL). The 16S rRNA gene sequences identified the isolate LNPF1 as Pseudomonas fluorescens with a similarity percentage of 99% with Pseudomonas sp. Isolate LNPF1 was evaluated for the production of siderophore. Siderophore-rich supernatant using a Sep Pack C18 column and Amberlite-400 Resin Column (λmax 264) produced 298 mg/L and 50 mg/L of siderophore, respectively. The characterization of purified siderophore by TLC, HPLC, FTIR, and 2D-NMR analysis identified the compound as desferrioxamine, a hydroxamate siderophore. A pot culture experiment determined the potential of LNPF1 to improve iron and oil content and photosynthetic pigments in Arachis hypogaea L. and improve soil nutrient content. Inoculation of A. hypogea seeds with LNPF1 improved plant growth parameters such as leaf length (60%), shoot length (22%), root length (54.68%), fresh weight (47.28%), dry weight (37%), and number of nuts (66.66) compared to the control (untreated seeds). This inoculation also improved leaf iron content (43.42), short iron content (38.38%), seed iron (46.72%), seed oil (31.68%), carotenoid (64.40%), and total chlorophyll content (98.%) compared to control (untreated seeds). Bacterized seeds showed a substantial increase in nodulation (61.65%) and weight of individual nodules (95.97) vis-à-vis control. The results of the present study indicated that P. fluorescens might be utilized as a potential bioinoculant to improve growth, iron content, oil content, number of nuts and nodules of Arachishypogaea L., and enrich soil nutrients.

The role of the type VI secretion system in the stress resistance of plant-associated bacteria

The type VI secretion system (T6SS) is a powerful bacterial molecular weapon that can inject effector proteins into prokaryotic or eukaryotic cells, thereby participating in the competition between bacteria and improving bacterial environmental adaptability. Although most current studies of the T6SS have focused on animal bacteria, this system is also significant for the adaptation of plant-associated bacteria. This paper briefly introduces the structure and biological functions of the T6SS. We summarize the role of plant-associated bacterial T6SS in adaptability to host plants and the external environment, including resistance to biotic stresses such as host defenses and competition from other bacteria. We review the role of the T6SS in response to abiotic factors such as acid stress, oxidation stress, and osmotic stress. This review provides an important reference for exploring the functions of the T6SS in plant-associated bacteria. In addition, characterizing these anti-stress functions of the T6SS may provide new pathways toward eliminating plant pathogens and controlling agricultural losses.

T6SS: A Key to Pseudomonas's Success in Biocontrol?

Bacteria from the genus Pseudomonas have been extensively studied for their capacity to act as biological control agents of disease and pests and for their ability to enhance and promote crop production in agricultural systems. While initial research primarily focused on the human pathogenic bacteria Pseudomonas aeruginosa, recent studies indicate the significance of type VI secretion (T6SS) in other Pseudomonas strains for biocontrol purposes. This system possibly plays a pivotal role in restricting the biological activity of target microorganisms and may also contribute to the bolstering of the survival capabilities of the bacteria within their applied environment. The type VI secretion system is a phage-like structure used to translocate effectors into both prokaryotic and eukaryotic target cells. T6SSs are involved in a myriad of interactions, some of which have direct implications in the success of Pseudomonas as biocontrol agents. The prevalence of T6SSs in the genomes of Pseudomonas species is notably greater than the estimated 25% occurrence rate found in Gram-negative bacteria. This observation implies that T6SS likely plays a pivotal role in the survival and fitness of Pseudomonas. This review provides a brief overview of T6SS, its role in Pseudomonas with biocontrol applications, and future avenues of research within this subject matter.

Microbial Consortia for Plant Protection against Diseases: More than the Sum of Its Parts

Biological plant protection presents a promising and exciting alternative to chemical methods for safeguarding plants against the increasing threats posed by plant diseases. This approach revolves around the utilization of biological control agents (BCAs) to suppress the activity of significant plant pathogens. Microbial BCAs have the potential to effectively manage crop disease development by interacting with pathogens or plant hosts, thereby increasing their resistance. However, the current efficacy of biological methods remains unsatisfactory, creating new research opportunities for sustainable plant cultivation management. In this context, microbial consortia, comprising multiple microorganisms with diverse mechanisms of action, hold promise in terms of augmenting the magnitude and stability of the overall antipathogen effect. Despite scientific efforts to identify or construct microbial consortia that can aid in safeguarding vital crops, only a limited number of microbial consortia-based biocontrol formulations are currently available. Therefore, this article aims to present a complex analysis of the microbial consortia-based biocontrol status and explore potential future directions for biological plant protection research with new technological advancements.

Metabolically versatile psychrotolerant Antarctic bacterium Pseudomonas sp. ANT_H12B is an efficient producer of siderophores and accompanying metabolites (SAM) useful for agricultural purposes

BACKGROUND

Bacterial siderophores are chelating compounds with the potential of application in agriculture, due to their plant growth-promoting (PGP) properties, however, high production and purification costs are limiting factors for their wider application. Cost-efficiency of the production could be increased by omitting purification processes, especially since siderophores accompanying metabolites (SAM) often also possess PGP traits. In this study, the metabolism versatility of Pseudomonas sp. ANT_H12B was used for the optimization of siderophores production and the potential of these metabolites and SAM was characterized in the context of PGP properties.

RESULTS

The metabolic diversity of ANT_H12B was examined through genomic analysis and phenotype microarrays. The strain was found to be able to use numerous C, N, P, and S sources, which allowed for the design of novel media suitable for efficient production of siderophores in the form of pyoverdine (223.50-512.60 μM). Moreover, depending on the culture medium, the pH of the siderophores and SAM solutions varied from acidic (pH < 5) to alkaline (pH > 8). In a germination test, siderophores and SAM were shown to have a positive effect on plants, with a significant increase in germination percentage observed in beetroot, pea, and tobacco. The PGP potential of SAM was further elucidated through GC/MS analysis, which revealed other compounds with PGP potential, such as indolic acetic acids, organic acids, fatty acids, sugars and alcohols. These compounds not only improved seed germination but could also potentially be beneficial for plant fitness and soil quality.

CONCLUSIONS

Pseudomonas sp. ANT_H12B was presented as an efficient producer of siderophores and SAM which exhibit PGP potential. It was also shown that omitting downstream processes could not only limit the costs of siderophores production but also improve their agricultural potential.

Research progress on iron uptake pathways and mechanisms of foodborne microorganisms and their application in the food sector

Iron is one of the essential nutrients for almost all microorganisms. Under iron-limited conditions, bacteria can secrete siderophores to the outside world to absorb iron for survival. This process requires the coordinated action of energy-transducing proteins, transporters, and receptors. The spoilage factors of some spoilage bacteria and the pathogenic mechanism of pathogenic bacteria are also closely related to siderophores. Meanwhile, some siderophores have also gradually evolved toward beneficial aspects. First, a variety of siderophores are classified into three aspects. In addition, representative iron uptake systems of Gram-negative and Gram-positive bacteria are described in detail to understand the common and specific pathways of iron uptake by various bacteria. In particular, the causes of siderophore-induced bacterial pathogenicity and the methods and mechanisms of inhibiting bacterial iron absorption under the involvement of siderophores are presented. Then, the application of siderophores in the food sector is mainly discussed, such as improving the food quality of dairy products and meat, inhibiting the attack of pathogenic bacteria on food, improving the plant growth environment, and promoting plant growth. Finally, this review highlights the unresolved fate of siderophores in the iron uptake system and emphasizes further development of siderophore-based substitutes for traditional drugs, new antibiotic-resistance drugs, and vaccines in the food and health sectors.