Siderophore Production Research Articles

Bioinoculation with Pseudomonas aeruginosa P4 enhances the peanut root nodulation and nutrient status while enriching the plant-beneficial bacteria in rhizosphere

Fluorescent Pseudomonas species are well-known as effective plant growth promoting rhizobacteria (PGPR), yet are relatively less explored for their multitrophic benefits. This study demonstrates the impact of P. aeruginosa P4 (P4) on peanut growth, nutrient status of plant and soil as well as the rhizobacterial community. Enhanced root length (53%), root weight (74%) and shoot weight (48%) in P4-treated plants, with increased potash and phosphorus levels of rhizospheric soil, correlated with indole-3-acetic acid and organic acid producing abilities of P4. Remarkably, increased nodule (87%) and pod (47%) numbers in P4-treated plants could be attributed to ∼16.3 % higher accumulation of iron, which in turn could be due to siderophore producing ability of P4. Amplified Ribosomal DNA Restriction Analysis (ARDRA)-based analysis at the approximate onset of nodulation and subsequent 16S rDNA-based metagenomic analysis estimated a significant distinction in the rhizomicrobial community diversity and abundance across control and P4-treated rhizospheres, plausibly due to P4-induced alterations in root exudate composition. Enrichment of plant-beneficial genera like Planctomyces, Mesorhizobium, Ensifer, Azospirillum, Bacillus, Nitrospira and Candidatus Nitrososphaera in P4-treated rhizosphere, could be driven by both altered root exudation and enhanced mineral nutrient availability in soil. In contrast, reduced abundance of Pseudomonas genus in P4-treated peanut rhizosphere could be attributed to direct or indirect competition between the inoculant and the resident Pseudomonas species. Collectively, a non-nitrogen-fixer P4 benefited nitrogen fixation in peanut, apparently indirectly by improving the iron nutrition and mobilization of plant-beneficial rhizobacterial species; an aspect that could be useful in determining PGPR efficacy and strategizing PGPR-mediated rhizosphere engineering.

Selection of Potential Bacteria in Termite Nest and Gut for Sustainable Agriculture

In this study, bacteria with the best abilities in cellulose degradation, siderophore production, phosphate solubility, and Pythium parasitica inhibition were selected from termite nests and guts. The isolate BTNASP 5-2, BTPK 5-3 and BTNA 5-1 from termite guts exhibited highest in siderophore production index (SPI) (4.16 ± 0.21), phosphate solubilizing index (PSI) (2.10 ± 0.14) and percentage inhibition of radial growth (PIRG) (67.07 ± 4.02 %), respectively. The BGNACMC 4-3 isolated from termite nest gave the highest cellulolytic index (CI) of 5.17 ± 0.24. Bacterial classification was performed using 16s rRNA gene sequencing. The isolates BTPK 5-3, BGNACMC 4-3 and BTNA 5-1 were found closely related to Bacillus cereus, whereas the bacterial isolate BTNASP 5-2 was closely related to Bacillus subtilis. It is also suggested that the Bacillus cereus exhibited a variety of biological activities, denoting the highest cellulase, phosphate-solubilizing and antifungal activities, while Bacillus subtilis produced only a siderophore. The results obtained suggest that the bacteria selected will be used to develop bio-compost to promote plant growth, leading to sustainable farming. HIGHLIGHTS Bacillus cereus exhibited a variety of biological activities, denoting the highest cellulase, phosphate-solubilizing, and antifungal activities Bacillus subtilis produced a siderophore The highest cellulose-degrading bacteria ( cereus BGNACMC4-3) found in termite mound nest GRAPHICAL ABSTRACT

Unlocking the Potential of Plant Growth-Promoting Rhizobacteria to Enhance Drought Tolerance in Egyptian Wheat (Triticum aestivum)

Plant growth-promoting rhizobacteria (PGPRs) represent a promising strategy for enhancing plant resilience and yields under drought-stress conditions. This study isolated and characterized PGPR from wheat rhizosphere soil in Egypt. Four PGPR strains were evaluated for an array of plant growth-promoting traits, including IAA production, biofilm formation, siderophore production, nitrogen fixation, ACC deaminase activity, phosphate solubilization, and antagonistic potential. Molecular identification via 16S rRNA sequencing classified three isolates (MMH101, MMH102, and MMH103) within the Bacillus genus and one isolate (MMH104) as Myroides sp. Greenhouse experiments examined the effects of PGPR inoculation on the drought-stressed Egyptian wheat cultivar, Gimmeza-9. Wheat plants inoculated with PGPR isolates showed dramatic improvements in growth parameters and stress tolerance indicators compared to non-inoculated controls when subjected to a 10-day drought period, with Bacillus rugosus (MMH101) inoculation resulting in increases of 61.8% in fresh biomass, 77.2% in dry biomass, 108.5% shoot length, and 134.9% root length. PGPR treatments also elevated the chlorophyll and proline content while reducing malondialdehyde levels. The findings demonstrate the effectiveness of PGPR inoculation in enhancing the morphology, physiology, and drought stress resilience of wheat. Isolated PGPR strains hold promise as biofertilizers for improving cereal productivity under water-deficit conditions.

Exploring the dynamics of ISR signaling in maize upon seed priming with plant growth promoting actinobacteria isolated from tea rhizosphere of Darjeeling.

Plant growth-promoting rhizobacteria (PGPR) offer an eco-friendly alternative to agrochemicals for better plant growth and development. Here, we evaluated the plant growth promotion abilities of actinobacteria isolated from the tea (Camellia sinensis) rhizosphere of Darjeeling, India. 16S rRNA gene ribotyping of 28 isolates demonstrated the presence of nine different culturable actinobacterial genera. Assessment of the in vitro PGP traits revealed that Micrococcus sp. AB420 exhibited the highest level of phosphate solubilization (i.e., 445 ± 2.1µg/ml), whereas Kocuria sp. AB429 and Brachybacterium sp. AB440 showed the highest level of siderophore (25.8 ± 0.1%) and IAA production (101.4 ± 0.5µg/ml), respectively. Biopriming of maize seeds with the individual actinobacterial isolate revealed statistically significant growth in the treated plants compared to controls. Among them, treatment with Paenarthrobacter sp. AB416 and Brachybacterium sp. AB439 exhibited the highest shoot and root length. Biopriming has also triggered significant enzymatic and non-enzymatic antioxidative defense reactions in maize seedlings both locally and systematically, providing a critical insight into their possible role in the reduction of reactive oxygen species (ROS) burden. To better understand the role of actinobacterial isolates in the modulation of plant defense, three selected actinobacterial isolates, AB426 (Brevibacterium sp.), AB427 (Streptomyces sp.), and AB440 (Brachybacterium sp.) were employed to evaluate the dynamics of induced systemic resistance (ISR) in maize. The expression profile of five key genes involved in SA and JA pathways revealed that bio-priming with actinobacteria (Brevibacterium sp. AB426 and Brachybacterium sp. AB440) preferably modulates the JA pathway rather than the SA pathway. The infection studies in bio-primed maize plants resulted in a delay in disease progression by the biotrophic pathogen Ustilago maydis in infected maize plants, suggesting the positive efficacy of bio-priming in aiding plants to cope with biotic stress. Conclusively, this study unravels the intrinsic mechanisms of PGPR-mediated ISR dynamics in bio-primed plants, offering a futuristic application of these microorganisms in the agricultural fields as an eco-friendly alternative.

Exploring the potential of Bacillus for crop productivity and sustainable solution for combating rice false smut disease.

Rice false smut, which is caused by the soil-borne fungal pathogen Ustilaginoidea virens (U. virens), is one of the most threatening diseases in most of the rice-growing countries including India that causes 0.5-75% yield loss, low seed germination, and a reduction in seed quality. The assessment of yield loss helps to understand the relevance of disease severity and facilitates the implementation of appropriate management strategies. This study aimed to mitigate biotic stress in rice by employing a rhizobacterial-based bioformulation, which possesses diverse capabilities as both a plant growth promoter and a biocontrol agent against U. virens. Rhizobacteria were isolated from the soil of the rice rhizospheres from the healthy plant of the false smut affected zone. Furthermore, they were identified as Bacillus strains: B. subtilis (BR_4), B. licheniformis (BU_7), B. licheniformis (BU_8), and B. vallismortis (KU_7) via sequencing. Isolates were screened for their biocontrol potential against U. virens under in vitro conditions. The antagonistic study revealed that B. vallismortis (KU_7) inhibited U. virens the most (44.6%), followed by B. subtilis BR_4 (41.4%), B. licheniformis BU_7 (39.8%), and B. licheniformis BU_8 (43.5%). Various biochemical and plant growth promoting attributes, such as phosphate and Zn solubilization, IAA, ammonium, siderophore, and chitinase production, were also investigated for all the selected isolates. Furthermore, the potential of the isolates was tested in both in vitro and field conditions by employing talc-based bioformulation through bio-priming and root treatment. The application of bioformulation revealed a 20% decrease in disease incidence in plants treated with B. vallismortis (KU_7), a 60.5% increase in the biological yield, and a 45% increase in the grain yield. This eco-friendly approach not only controlled the disease but also improved the grain quality and reduced the chaffiness.

Exploring Phosphate Solubilizing Bacterial Communities in Rhizospheres of Native and Exotic Forage Grasses in Alkaline-Sodic Soils of the Flooding Pampa.

The flooding pampa is one of the most important cattle-raising regions in Argentina. In this region, natural pastures are dominated by low-productivity native grass species, which are the main feed for livestock. In this context, previous studies in the region with the subtropical exotic grass Panicum coloratum highlight it as a promising species to improve pasture productivity. Cultivable phosphate solubilizing bacteria (PSB) communities associated to native (Sporobolus indicus) and exotic (Panicum coloratum) forage grasses adapted to alkaline-sodic soils of the flooding pampa were analyzed. PSB represented 2-14% of cultivable rhizobacteria and Box-PCR fingerprinting revealed a high genetic diversity in both rhizospheres. Taxonomic identification by MALDI-TOF showed that PSB populations of P. coloratum and S. indicus rhizospheres are dominated by the phylum Proteobacteria (92,51% and 96,60% respectively) and to a lesser extent (< 10%), by the phyla Actinobacteria and Firmicutes. At the genus level, both PSB populations were dominated by Enterobacter and Pseudomonas. Siderophore production, nitrogen fixation, and indoleacetic acid production were detected in a variety of PSB genera of both plant species. A higher proportion of siderophore and IAA producers were associated to P. coloratum than S. indicus, probably reflecting a greater dependence of the exotic species on rhizospheric microorganisms to satisfy its nutritional requirements in the soils of the flooding pampa. This work provides a novel knowledge about functional groups of bacteria associated to plants given that there are no previous reports dedicated to the characterization of PSB rhizosphere communities of S indicus and P coloratum. Finally, it should be noted that the collection obtained in this study can be useful for the development of bioinputs that allow reducing the use of chemical fertilizers, providing sustainability to pasture production systems for livestock.

Estuarine mangrove niches select cultivable heterotrophic diazotrophs with diverse metabolic potentials-a prospective cross-dialog for functional diazotrophy.

Biological nitrogen fixation (BNF), an unparalleled metabolic novelty among living microorganisms on earth, globally contributes ~88-101 Tg N year-1 to natural ecosystems, ~56% sourced from symbiotic BNF while ~22-45% derived from free-living nitrogen fixers (FLNF). The success of symbiotic BNF is largely dependent on its interaction with host-plant, however ubiquitous environmental heterotrophic FLNFs face many limitations in their immediate ecological niches to sustain unhindered BNF. The autotrophic FLNFs like cyanobacteria and oceanic heterotrophic diazotrophs have been well studied about their contrivances acclimated/adapted by these organisms to outwit the environmental constraints for functional diazotrophy. However, FLNF heterotrophs face more adversity in executing BNF under stressful estuarine/marine/aquatic habitats. In this study a large-scale cultivation-dependent investigation was accomplished with 190 NCBI accessioned and 45 non-accessioned heterotrophic FLNF cultivable bacterial isolates (total 235) from halophilic estuarine intertidal mangrove niches of Indian Sundarbans, a Ramsar site and UNESCO proclaimed World Heritage Site. Assuming ~1% culturability of the microbial community, the respective niches were also studied for representing actual bacterial diversity via cultivation-independent next-generation sequencing of V3-V4 rRNA regions. Both the studies revealed a higher abundance of culturable Gammaproteobacteria followed by Firmicutes, the majority of 235 FLNFs studied belonging to these two classes. The FLNFs displayed comparable selection potential in media for free nitrogen fixers and iron-oxidizing bacteria, linking diazotrophy with iron oxidation, siderophore production, phosphorus solubilization, phosphorus uptake and accumulation as well as denitrification. This observation validated the hypothesis that under extreme estuarine mangrove niches, diazotrophs are naturally selected as a specialized multidimensional entity, to expedite BNF and survive. Earlier metagenome data from mangrove niches demonstrated a microbial metabolic coupling among C, N, P, S, and Fe cycling in mangrove sediments, as an adaptive trait, evident with the co-abundant respective functional genes, which corroborates our findings in cultivation mode for multiple interrelated metabolic potential facilitating BNF in a challenging intertidal mangrove environment.

Unleaded agriculture: Myth to reality by wetland microbial flora

AbstractWetlands, refer to the confluence with regards to land and water having a rich biological diversity with multiple purpose. As per the Ramsar Convention, framed in August 2002, East Kolkata Wetlands have been considered to be of global significance. Although inappropriate supervision of these wetlands, has led to the gradual deterioration of this wetland. In this present study, the soil sample was collected from these reclaimed agricultural wetlands of Chowbaga area, of East Kolkata areas with coordinates of 22.5296°N, 88.4207°E. The predominant or lingering bacterial flora was isolated from the soil surrounding the rhizospheric region of Cucurbita sp. and Zea mays and their plant growth promotion properties of the lingering bacterial flora were analyzed. These plant growth promoting rhizobacteria (PGPR) included some species of Bacillus sp. that could augment plant growth by different methodologies like nitrogen fixation, phosphate solubilization, phytohormone synthesis, and siderophore production. One of the bacterial isolates DPP(C) showed highest ability of siderophore production of 37.89% at 48 hours, whereas DCP(A) showed better capability in IAA production of 56.785 μg/mL than rest of the bacterial isolates. These reclaimed agricultural lands were found to have very high quantities of heavy metals, especially lead. All the bacterial isolates, were found to have great potential in lead mitigation, whereby they could adsorb up to 8.28% of lead. Some studies have shown the capability of microbial degradation for bioremediation of organic forms of lead and thereby can be removed from agricultural field for longer period of time. The prospective potential use of PGPR has gradually escalated, since it is one of the best substitutes against the constant usage of chemical fertilizers as well as pesticides. The use of these PGPR is one of the most reliable methods for ensuring sustainable agriculture. Furthermore, in future, the PGPR population will be correlated with the nutrient availability and productivity of the plants.

Plant–Entomopathogenic Fungi Interaction: Recent Progress and Future Prospects on Endophytism-Mediated Growth Promotion and Biocontrol

Entomopathogenic fungi, often acknowledged primarily for their insecticidal properties, fulfill diverse roles within ecosystems. These roles encompass endophytism, antagonism against plant diseases, promotion of the growth of plants, and inhabitation of the rhizosphere, occurring both naturally and upon artificial inoculation, as substantiated by a growing body of contemporary research. Numerous studies have highlighted the beneficial aspects of endophytic colonization. This review aims to systematically organize information concerning the direct (nutrient acquisition and production of phytohormones) and indirect (resistance induction, antibiotic and secondary metabolite production, siderophore production, and mitigation of abiotic and biotic stresses) implications of endophytic colonization. Furthermore, a thorough discussion of these mechanisms is provided. Several challenges, including isolation complexities, classification of novel strains, and the impact of terrestrial location, vegetation type, and anthropogenic reluctance to use fungal entomopathogens, have been recognized as hurdles. However, recent advancements in biotechnology within microbial research hold promising solutions to many of these challenges. Ultimately, the current constraints delineate potential future avenues for leveraging endophytic fungal entomopathogens as dual microbial control agents.

Characterization and Field Evaluation of Potential Fluorescent Pseudomonas Isolates on Growth and Yield Attributing Characters in Chickpea

The present investigation was conducted at the research and instructional farm, College of Agriculture, Indira Gandhi Krishi Vishwavidyalaya, Raipur, Chhattisgarh, India during rabi (October–December 2019) to evaluate the influence of fluorescent Pseudomonas isolates on chickpeas through characterization and field evaluation. Eighty-eight rhizosphere soil samples were derived from different locations in Bastar and Bilaspur districts of Chhattisgarh, India. Potential isolates were required for fundamental research and practical application of plant growth-promoting rhizobacterial strains on different crops. Among eighty-eight isolates, ten fluorescent Pseudomonas (visible under UV light at 360 nm) emitting strong fluorescence were selected for the course of the investigation and characterized for the production of siderophores, phosphate solubilization, indole acetic acid, 1-aminocyclopropane-1-carboxylic acid deaminase, and analysis of antagonistic potential. Of the 10 Pseudomonas isolates, 9704 was identified as the highest phosphate solubilizer, BSP-23 was identified as the highest indole acetic acid producer, and BSP-19 was the highest siderophore producer. Fluorescent Pseudomonas isolates BS-1, BS-4, 9809, BSP-14, and BSP-19 were identified to possess 1-aminocyclopropane-1-carboxylic acid deaminase-producing ability following qualitative analysis. Our present investigation indicates that beneficial effects of fluorescent Pseudomonas could be achieved through simple and cost-effective seed treatment. Three fluorescent Pseudomonas strains, 9704, BS-14, and 9829, consistently increased seed germination and improved plant growth and yield (BS-37.9% and 9704-35.7%) attributes in chickpeas. Besides, confrontation assays performed against R. bataticola expressed varying levels of inhibition. The phylogenetic affinities of 16S rRNA gene sequencing resolved the species identities of selected isolates.

The Potential of Burkholderia sp. from Zea mays Roots as Plant Growth Promoting Rhizobacteria

Plant Growth-Promoting Rhizobacteria (PGPR) plays a crucial role in enhancing plant health, while Burkholderia sp. has been identified and has potential as a promising PGPR for maize plants. Recognizing the essential role of PGPR in plant health, this study explores how L-TRP addition might improve PGPR performance for better plant growth. Employing a completely randomized design, the study assesses the effects of Burkholderia sp. as PGPR on maize growth across three treatment groups: PGPR with L-TRP, PGPR without L-TRP, and a control group. The evaluation focuses on plant growth metrics, plant hormone production (auxin and gibberellin), and siderophore activity to gauge plant iron availability. Statistical analysis highlights that L-TRP supplementation notably increases auxin production in the PGPR + L-TRP group, surpassing the PGPR without L-TRP and control groups. Although both PGPR treatments elevate gibberellin levels compared to the control, auxin increase is the most significant outcome, indicating no substantial difference in gibberellin levels between the two PGPR groups. Enhanced siderophore production suggests improved iron assimilation for plants. The findings demonstrate that L-TRP supplementation with PGPR, particularly Burkholderia sp., effectively boosts maize growth, primarily through increased auxin and siderophore production. This combination presents a promising strategy for augmenting agricultural yields, especially for maize productivity, by leveraging the synergistic effects of soil microbes and nutrient supplementation.

Revealing the diversity of Jojoba-associated fungi using amplicon metagenome approach and assessing the in vitro biocontrol activity of its cultivable community.

Jojoba shrubs are wild plants cultivated in arid and semiarid lands and characterized by tolerance to drought, salinity, and high temperatures. Fungi associated with such plants may be attributed to the tolerance of host plants against biotic stress in addition to the promotion of plant growth. Previous studies showed the importance of jojoba as jojoba oil in the agricultural field; however, no prior study discussed the role of jojoba-associated fungi (JAF) in reflecting plant health and the possibility of using JAF in biocontrol. Here, the culture-independent and culture-dependent approaches were performed to study the diversity of the jojoba-associated fungi. Then, the cultivable fungi were evaluated for in-vitro antagonistic activity and in vitro plant growth promotion assays. The metagenome analysis revealed the existence of four fungal phyla: Ascomycota, Aphelidiomycota, Basidiomycota, and Mortierellomycota. The phylum Ascomycota was the most common and had the highest relative abundance in soil, root, branch, and fruit samples (59.7%, 50.7%, 49.8%, and 52.4%, respectively). Alternaria was the most abundant genus in aboveground tissues: branch (43.7%) and fruit (32.1%), while the genus Discosia had the highest abundance in the underground samples: soil (24%) and root (30.7%). For the culture-dependent method, a total of 14 fungi were isolated, identified, and screened for their chitinolytic and antagonist activity against three phytopathogenic fungi (Fusarium oxysporum, Alternaria alternata and Rhizoctonia solani) as well as their in vitro plant growth promotion (PGP) activity. Based on ITS sequence analysis, the selected potent isolates were identified as AspergillusstellatusEJ-JFF3, Aspergillusflavus EJ-JFF4, Stilbocreasp. EJ-JLF1, Fusariumsolani EJ-JRF3, and AmesiaatrobrunneaEJ-JSF4. The endophyte strain A. flavus EJ-JFF4 exhibited the highest chitinolytic activity (9 Enzyme Index) and antagonistic potential against Fusarium oxysporum, Alternaria alternata, and Rhizoctonia solani phytopathogens with inhibitory percentages of 72, 70, and 80 respectively. Also, A. flavus EJ-JFF4 had significant multiple PGP properties, including siderophore production (69.3%), phosphate solubilization (95.4 µg ml-1). The greatest production of Indol-3-Acetic Acid was belonged to A.atrobrunnea EJ-JSF4 (114.5 µg ml-1). The analysis of FUNGuild revealed the abundance of symbiotrophs over other trophic modes, and the guild of endophytes was commonly assigned in all samples. For the first time, this study uncovered fungal diversity associated with jojoba plants using a culture-independent approach and in-vitro assessed the roles of cultivable fungal strains in promoting plant growth and biocontrol. The present study indicated the significance of jojoba shrubs as a potential source of diverse fungi with high biocontrol and PGP activities.

Serratia marcescens AB1: A rhizosphere bacterium mitigating the acetochlor stress on the soil environment

Microbial remediation, a significant research focus in bioremediation, shows promise in addressing pollution. In this study, the optimal medium for acetochlor-degrading bacteria AB1 was determined by the response surface method as 29.94 g L−1 sucrose, 10.06 g L−1 yeast extract, and 20.32 g L−1 NaCl. The single-factor method identified optimum degradation conditions, including a temperature of 30 °C, pH of 7.0, inoculation with 3% AB1, and an initial acetochlor concentration of 10 mg L−1. The strain reached a maximum degradation rate of 79.87% within 5 days. AB1 performed nitrogen fixation, phosphorus dissolution, potassium hydrolysis, siderophore production, and biofilm formation. In the presence of acetochlor, it also induced the upregulation of genes, wza and luxS. Utilizing a green fluorescent protein and rifampicin-resistant strain LAB1-gfp, it demonstrated stable colonization in maize rhizospheres and soils, enhancing growth and degradation. This reduced the acetochlor half-life to 12.77 days and increased soil enzyme activity, providing a theoretical foundation for acetochlor bioremediation.

A comprehensive comparative genomic analysis revealed that plant growth promoting traits are ubiquitous in strains of Stenotrophomonas.

Stenotrophomonas strains, which are often described as plant growth promoting (PGP) bacteria, are ubiquitous in many environments. A total of 213 genomes of strains of Stenotrophomonas were analyzed using comparative genomics to better understand the ecological roles of these bacteria in the environment. The pan-genome of the 213 strains of Stenotrophomonas consists of 27,186 gene families, including 710 core gene families, 11,039 unique genes and 15,437 accessory genes. Nearly all strains of Stenotrophomonas harbor the genes for GH3-family cellulose degradation and GH2- and GH31-family hemicellulose hydrolase, as well as intact glycolysis and tricarboxylic acid cycle pathways. These abilities suggest that the strains of this genus can easily obtain carbon and energy from the environment. The Stenotrophomonas strains can respond to oxidative stress by synthesizing catalase, superoxide dismutase, methionine sulfoxide reductase, and disulfide isomerase, as well as managing their osmotic balance by accumulating potassium and synthesizing compatible solutes, such as betaine, trehalose, glutamate, and proline. Each Stenotrophomonas strain also contains many genes for resistance to antibiotics and heavy metals. These genes that mediate stress tolerance increase the ability of Stenotrophomonas strains to survive in extreme environments. In addition, many functional genes related to attachment and plant colonization, growth promotion and biocontrol were identified. In detail, the genes associated with flagellar assembly, motility, chemotaxis and biofilm formation enable the strains of Stenotrophomonas to effectively colonize host plants. The presence of genes for phosphate-solubilization and siderophore production and the polyamine, indole-3-acetic acid, and cytokinin biosynthetic pathways confer the ability to promote plant growth. These strains can produce antimicrobial compounds, chitinases, lipases and proteases. Each Stenotrophomonas genome contained 1-9 prophages and 17-60 genomic islands, and the genes related to antibiotic and heavy metal resistance and the biosynthesis of polyamines, indole-3-acetic acid, and cytokinin may be acquired by horizontal gene transfer. This study demonstrates that strains of Stenotrophomonas are highly adaptable for different environments and have strong potential for use as plant growth-promoting bacteria.

IAA-producing plant growth promoting rhizobacteria from Ceanothus velutinus enhance cutting propagation efficiency and Arabidopsis biomass.

Climate-induced drought impacts plant growth and development. Recurring droughts increase the demand for water for food production and landscaping. Native plants in the Intermountain West region of the US are of keen interest in low water use landscaping as they are acclimatized to dry and cold environments. These native plants do very well at their native locations but are difficult to propagate in landscape. One of the possible reasons is the lack of associated microbiome in the landscaping. Microbiome in the soil contributes to soil health and impacts plant growth and development. Here, we used the bulk soil from the native plant Ceanothus velutinus (snowbrush ceanothus) as inoculant to enhance its propagation. Snowbrush ceanothus is an ornamental plant for low-water landscaping that is hard to propagate asexually. Using 50% native bulk soil as inoculant in the potting mix significantly improved the survival rate of the cuttings compared to no-treated cuttings. Twenty-four plant growth-promoting rhizobacteria (PGPR) producing indole acetic acid (IAA) were isolated from the rhizosphere and roots of the survived snowbrush. Seventeen isolates had more than 10µg/mL of IAA were shortlisted and tested for seven different plant growth-promoting (PGP) traits; 76% showed nitrogen-fixing ability on Norris Glucose Nitrogen free media,70% showed phosphate solubilization activity, 76% showed siderophore production, 36% showed protease activity, 94% showed ACC deaminase activity on DF-ACC media, 76% produced catalase and all of isolates produced ammonia. Eight of seventeen isolates, CK-6, CK-22, CK-41, CK-44, CK-47, CK-50, CK-53, and CK-55, showed an increase in shoot biomass in Arabidopsis thaliana. Seven out of eight isolates were identified as Pseudomonas, except CK-55, identified as Sphingobium based on 16S rRNA gene sequencing. The shortlisted isolates are being tested on different grain and vegetable crops to mitigate drought stress and promote plant growth.

Characterization and exploration of an As(III)-oxidizing bacterium TMKU1 for plant growth promotion under arsenic stress

Arsenic (As) pollution has been recognized as a serious global environmental problem. Though various remediation strategies are being explored to cope up with the As-toxicity, currently microbe-assisted detoxification of As is found to be the most promising technique for restoring As-contaminated rhizosphere soil for its eco-friendly nature. As(III)-oxidizing bacteria were reported to most suitable in this regard. In this study, an As(III)-oxidizing bacterium, TMKU1 was isolated from As-contaminated rhizospheric soil that could withstand up to 20 mM As(III) and 95 mM As(V). The strain was closely related to the genus Acinetobacter, according to 16 S rDNA analysis. The strain could transform ∼70% of As(III) to As(V) under aerobic culture condition. The transformation of As(III) was found to be catalyzed by arsenite oxidase, which is constitutive nature in this strain. The As(III)-oxidase was found to be encoded by the functional gene aioA harbored on the genomic DNA. The enzyme was localized mostly in the periplasm, and the partially purified enzyme showed the Km = 95.76667 μM and Vmax = 0.356341 M min−1g−1 protein. The novelty of this strain is that it could express plant growth promoting features like phosphate solubilization, siderophore production, IAA production and N2-fixation, both under stress-free and As-stress conditions. Seed bacterization with TMKU1 not only significantly increased the germination of chickpea seeds, but also shielded the seedlings from the As toxicity and accumulation. Overall, the results suggest that this bacterial candidate would be of potential use in agricultural practices for detoxification of As in crop field.

Evaluation of commercial importance of endophytes isolated from Argemone mexicana and Papaver rhoeas.

The paper industry is a composite one constituting different types of mills, processes, and products. The paper industries consume large amounts of resources, like wood and water. These industries also create huge amounts of waste that have to be treated. In our study, 23 endophytic bacteria were isolated from Argemone mexicana, and 16 endophytic bacteria were isolated from Papaver rhoeas. Seventeen and 15 bacterial endophytes from A. mexicana and P. rhoeas, respectively, showed cellulose-degrading activity. The biochemical and molecular characterization were done for endophytic bacteria with cellulolytic activity. The consortium of cellulose-degrading endophytic bacteria from A. mexicana showed endoglucanase activity (0.462IU/ml) and FPCase enzyme activity (0.269IU/ml) and from P. rhoeas gave endoglucanase activity (0.439IU/ml) and FPCase enzyme activity (0.253IU/ml). Degraded carboxy methylcellulose and filter paper were further treated by Saccharomyces cerevisiae and bioethanol was produced. Cellulose-degrading endophytic bacteria were also tested for auxin, siderophore production, and phosphate solubilization activities. Individual cellulose-degrading endophytic bacteria with plant growth-promoting activities were used as biofertilizers, tested for plant growth-promoting activities using Basmati Pusa 1121 rice, and plant growth parameters were recorded. The degraded paper enhances the growth of rice plants. Selected bacterial endophytes and their consortia from A. mexicana and P. rhoeas were powerful cellulose degraders, which can be further employed for ethanol production and as significant biofertilizers in agriculture.

Diversity and functional traits of seed endophytes of Dysphania ambrosioides from heavy metal contaminated and non-contaminated areas.

Seed endophytes played a crucial role on host plants stress tolerance and heavy metal (HM) accumulation. Dysphania ambrosioides is a hyperaccumulator and showed strong tolerance and extraordinary accumulation capacities of multiple HMs. However, little is known about its seed endophytes response to field HM-contamination, and its role on host plants HM tolerance and accumulation. In this study, the seed endophytic community of D. ambrosioides from HM-contaminated area (H) and non-contaminated area (N) were investigated by both culture-dependent and independent methods. Moreover, Cd tolerance and the plant growth promoting (PGP) traits of dominant endophytes from site H and N were evaluated. The results showed that in both studies, HM-contamination reduced the diversity and richness of endophytic community and changed the most dominant endophyte, but increased resistant species abundance. By functional trait assessments, a great number of dominant endophytes displayed multiple PGP traits and Cd tolerance. Interestingly, soil HM-contamination significantly increased the percentage of Cd tolerance isolates of Agrobacterium and Epicoccum, but significantly decreased the ration of Agrobacterium with the siderophore production ability. However, the other PGP traits of isolates from site H and N showed no significant difference. Therefore, it was suggested that D. ambrosioides might improve its HM tolerance and accumulation through harboring more HM-resistant endophytes rather than PGP endophytes, but to prove this, more work need to be conducted in the future.

Genomic insights into Streptomyces hygroscopicus subsp. hygroscopicus SRF1: a potential biocontrol agent against fusarium wilt with plant growth-promoting abilities in tomatoes

ABSTRACT Streptomyces sp. isolate SRF1 has previously demonstrated promising results in controlling various plant fungi under in vitro conditions. However, further exploration of its genome and its efficacy in disease control and plant growth promotion under in vivo conditions is warranted. This study aimed to utilise whole genome sequencing (WGS) to classify Streptomyces sp. isolate SRF1 at the species level and predict genes associated with antagonistic ability and plant growth promotion, thereby assessing its potential as a biocontrol agent against fusarium wilt and a promoter of plant growth. WGS was employed to elucidate the taxonomic classification of isolate SRF1 and predict genes involved in disease suppression and plant growth promotion. In vitro assays were conducted to evaluate its antagonistic activity against Fusarium oxysporum f. sp. lycopersici (Fol) and its production of cellulase, amylase, indole-3-acetic acid (IAA), and siderophores. Pot experiments were carried out using SRF1 cell suspension and culture filtrate to assess its efficacy against Fol and its impact on tomato growth. Real-time PCR analysis was performed to correlate gene expression levels with observed activities. The results showed that isolate SRF1 was classified as S. hygroscopicus subsp. hygroscopicus and demonstrated antagonism against Fol. Furthermore, WGS revealed genes or gene clusters associated with disease control, including those encoding antifungal agents such as butyrolactol A, nigericin, and hygromycin A. Additionally, genes responsible for auxin biosynthesis, siderophore production, and carbohydrate-digesting enzymes such as chitinase, cellulase, and amylase were identified, suggesting potential roles in disease suppression and plant growth promotion.

Siderophores and competition for iron govern myxobacterial predation dynamics.

Bacterial predators are decisive organisms that shape microbial ecosystems. In this study, we investigated the role of iron and siderophores during the predatory interaction between two rhizosphere bacteria: Myxococcus xanthus, an epibiotic predator, and Sinorhizobium meliloti, a bacterium that establishes nitrogen-fixing symbiosis with legumes. The results show that iron enhances the motility of the predator and facilitates its predatory capability, and that intoxication by iron is not used by the predator to prey, although oxidative stress increases in both bacteria during predation. However, competition for iron plays an important role in the outcome of predatory interactions. Using combinations of predator and prey mutants (nonproducers and overproducers of siderophores), we have investigated the importance of competition for iron in predation. The results demonstrate that the competitor that, via the production of siderophores, obtains sufficient iron for growth and depletes metal availability for the opponent will prevail in the interaction. Consequently, iron fluctuations in soils may modify the composition of microbial communities by altering the activity of myxobacterial predators. In addition, siderophore overproduction during predation can alter soil properties, affecting the productivity and sustainability of agricultural operations.