Comparative Genomic and Functional Analyses for Insights into Pantoea agglomerans Strains Adaptability in Diverse Ecological Niches.

Pantoea agglomerans inhabit diverse ecological niches, ranging from epiphytes and endophytes in plants, body of animals, and occasionally in the human system. This multifaceted bacterium contributes substantially to plant growth promotion, stress resilience, and biocontrol but can also act as a pathogen to its host. The genetic determinants underlying these diverse functions remain largely unfathomed and to uncover this phenomenon, nineteen strains of Pantoea agglomerans were selected and analyzed. Genome-to-Genome Distance Calculator (GGDC) which uses the Genome Blast Distance Phylogeny (GBDP) technique to calculate digital DDH values. Phylogenetic analysis via Genome-to-Genome distance, Average Nucleotide Identity, and Amino Acid Identity calculation revealed that all strains belonged to the genus Pantoea. However, strain 33.1 had a lower value than the threshold for the same species delineation. Bacterial Pan Genome Analysis (BPGA) Pipeline and MinPath analysis revealed genetic traits associated with environmental resilience, such as oxidative stress, UV radiation, temperature extremes, and metabolism of distinct host-specific carbohydrates. Protein-protein interactome analysis illustrated osmotic stress proteins closely linked with core proteins, while heavy metal tolerance, nitrogen metabolism, and Type III and VI secretion systems proteins generally associated with pathogenicity formed a separate network, indicating strain-specific characteristics. These findings shed new light on the intricate genetic architecture of Pantoea agglomerans, revealing its adaptability to inhabit diverse niches and thrive in varied environments.

Evaluation of the benefits of plant growth-promoting rhizobacteria and mycorrhizal fungi on biochemical and morphophysiological traits of Aloe barbadensis Mill under water deficit stress.

Aloe barbadensis is a drought-tolerant perennial medicinal plant with both nutritional and cosmetic uses. Drought is one of the main abiotic stresses limiting plant growth and development. However, the use of drought-resistant plants combined with beneficial soil micro-organisms could improve the effectiveness of biological methods to mitigate drought damage. This research aims to evaluate the effects of Funneliformis mosseae (MF), plant growth-promoting rhizobacteria (PGPR) (including Pseudomonas putida and Pantoea agglomerans), and their co-inoculation on the macronutrient status, antioxidant enzyme activities, and other morphophysiological traits of A. barbadensis under four irrigation regimes [25%, 50%, 75% and 100% of water requirement (WR)]. Three harvests were conducted, revealing that inoculation enhanced the survival rate and shoot fresh weight (SFW) compared to the control plants. However, at 25% WR, the SFW was reduced by 43% more than the control. across all harvests, while the PGPR + MF treatment showed increases of more than 19%, 11%, and 17% compared to the control, MF, and PGPR treatments, respectively. The results also showed that A. barbadensis exhibited innate drought tolerance up to a 50% WR level by enhancing physiological defenses, such as antioxidant enzyme activity. Inoculation increased the macronutrient status of the plant at all levels of irrigation regimes especially under severe drought conditions. The highest levels of nitrogen (N) (16.24 mg g-1 DW) and phosphorus (P) (11.29 mg g-1 DW) were observed in the PGPR + MF treatment at 100% WR. The maximum relative water content under MF inoculation and 75% WR (98.24%) (98.24%) was reached. PGPR + MF treatment alleviated drought-induced osmotic stress, as indicated by reduced antioxidant enzyme activities and electrolyte leakage. However, P. putida and P. agglomerans strains alone or in combination with F. mosseae increased plant yield, macronutrient uptake and antioxidant enzyme activity. This study underscores the potential of these PGPR and MF strains as invaluable biological tools for the cultivation of A. barbadensis in regions with severe drought stress.

Pantoea dispersa peritoneal dialysis catheter-related infection.

Enteric gram-negative bacteria-associated peritoneal dialysis (PD) peritonitis is common. These organisms are such as Escherichia coli, Klebsiella and Enterobacter species. Pantoea dispersa belongs to the order Enterobacterales, it has known benefits and a role in agricultural and environmental biotechnology. Pantoea dispersa, although still relatively rare, is being increasingly recognised to cause human infections. We are reporting a case of PD peritonitis caused by Pantoea dispersa in a kidney failure patient on continuous ambulatory peritoneal dialysis (CAPD). His peritonitis was treated well with intraperitoneal antibiotics and the patient can resume his CAPD therapy. The increasing reports of Pantoea dispersa-related human infections warrant concerns, both in immunocompromised and immunocompetent patients.

Interference of AHL signal production in the phytophatogen Pantoea agglomerans as a sustainable biological strategy to reduce its virulence.

Pantoea agglomerans is considered one of the most ubiquitous and versatile organisms that include strains that induce diseases in various crops and occasionally cause opportunistic infections in humans. To develop effective strategies to mitigate its impact on plant health and agricultural productivity, a comprehensive investigation is crucial for better understanding its pathogenicity. One proposed eco-friendly approach involves the enzymatic degradation of quorum sensing (QS) signal molecules like N-acylhomoserine lactones (AHLs), known as quorum quenching (QQ), offering potential treatment for such bacterial diseases. In this study the production of C4 and 3-oxo-C6HSL was identified in the plant pathogenic P. agglomerans CFBP 11141 and correlated to enzymatic activities such as amylase and acid phosphatase. Moreover, the heterologous expression of a QQ enzyme in the pathogen resulted in lack of AHLs production and the attenuation of the virulence by mean of drastically reduction of soft rot disease in carrots and cherry tomatoes. Additionally, the interference with the QS systems of P. agglomerans CFBP 11141 by two the plant growth-promoting and AHL-degrading bacteria (PGP-QQ) Pseudomonas segetis P6 and Bacillus toyonensis AA1EC1 was evaluated as a potential biocontrol approach for the first time. P. segetis P6 and B. toyonensis AA1EC1 demonstrated effectiveness in diminishing soft rot symptoms induced by P. agglomerans CFBP 11141 in both carrots and cherry tomatoes. Furthermore, the virulence of pathogen notably decreased when co-cultured with strain AA1EC1 on tomato plants.

PIX is an N-terminal delivery domain that defines a class of polymorphic T6SS effectors in Enterobacterales.

The type VI secretion system (T6SS), a widespread protein delivery apparatus, plays a role in bacterial competition by delivering toxic effectors into neighboring cells. Identifying new T6SS effectors and deciphering the mechanism that governs their secretion remain major challenges. Here, we report two orphan antibacterial T6SS effectors in the pathogen Pantoea agglomerans (Pa). These effectors share an N-terminal domain, Pantoea type six (PIX), that defines a widespread class of polymorphic T6SS effectors in Enterobacterales. We show that the PIX domain is necessary and sufficient for T6SS-mediated effector secretion and that PIX binds to a specialized Pa VgrG protein outside its C-terminal toxic domain. Our findings underline the importance of identifying and characterizing delivery domains in polymorphic toxin classes as a tool to reveal effectors and shed light on effector delivery mechanisms.

Cereal leaf beetle-associated bacteria enhance the survival of their host upon insecticide treatments and respond differently to insecticides with different modes of action.

The cereal leaf beetle (CLB, Oulema melanopus) is one of the major cereal pests. The effect of insecticides belonging to different chemical classes, with different mechanisms of action and the active substances' concentrations on the CLB bacterial microbiome, was investigated. Targeted metagenomic analysis of the V3-V4 regions of the 16S ribosomal gene was used to determine the composition of the CLB bacterial microbiome. Each of the insecticides caused a decrease in the abundance of bacteria of the genus Pantoea, and an increase in the abundance of bacteria of the genus Stenotrophomonas, Acinetobacter, compared to untreated insects. After cypermethrin application, a decrease in the relative abundance of bacteria of the genus Pseudomonas was noted. The dominant bacterial genera in cypermethrin-treated larvae were Lactococcus, Pantoea, while in insects exposed to chlorpyrifos or flonicamid it was Pseudomonas. Insecticide-treated larvae were characterized, on average, by higher biodiversity and richness of bacterial genera, compared to untreated insects. The depletion of CLB-associated bacteria resulted in a decrease in larval survival, especially after cypermethrin and chlorpyrifos treatments. The use of a metagenome-based functional prediction approach revealed a higher predicted function of bacterial acetyl-CoA C-acetyltransferase in flonicamid and chlorpyrifos-treated larvae and tRNA dimethyltransferase in cypermethrin-treated insects than in untreated insects.

Hitching a Ride in the Phyllosphere: Surfactant Production of Pseudomonas spp. Causes Co-swarming of Pantoea eucalypti 299R.

Here, we demonstrate the beneficial effect of surfactant-producing pseudomonads on Pantoea eucalypti 299R. We conducted a series of experiments in environments of increasing complexity. P. eucalypti 299R (Pe299R), and Pseudomonas sp. FF1 (Pff1) or Pe299R and surfactant-production deficient Pseudomonas sp. FF1::ΔviscB (Pff1ΔviscB) were co-inoculated in broth, on swarming agar plates, and on plants. In broth, there were no differences in the growth dynamics of Pe299R when growing in the presence of Pff1 or Pff1ΔviscB. By contrast, on swarming agar plates, Pe299R was able to co-swarm with Pff1 which led to a significant increase in Pe299R biomass compared to Pe299R growing with Pff1ΔviscB or in monoculture. Finally in planta, and using the single-cell bioreporter for reproductive success (CUSPER), we found a temporally distinct beneficial effect of Pff1 on co-inoculated Pe299R subpopulations that did not occur in the presence of Pff1ΔviscB. We tested three additional surfactant-producing pseudomonads and their respective surfactant knockout mutants on PE299R on swarming agar showing similar results. This led us to propose a model for the positive effect of surfactant production during leaf colonization. Our results indicate that co-motility might be common during leaf colonization and adds yet another facet to the already manyfold roles of surfactants.

Efficient production of isomaltulose using engineered Yarrowia lipolytica strain facilitated by non-yeast signal peptide-mediated cell surface display.

BACKGROUND: Isomaltulose is a 'generally recognized as safe' ingredient and is widely used in the food, pharmaceutical and chemical industries. The exploration and development of efficient technologies is essential for enhancing isomaltulose yield. RESULTS: In the present study, a simple and efficient surface display platform mediated by a non-yeast signal peptide was developed in Yarrowia lipolytica and utilized to efficiently produce isomaltulose from sucrose. We discovered that the signal peptide SP1 of sucrose isomerase from Pantoea dispersa UQ68J (PdSI) could guide SIs anchoring to the cell surface of Y. lipolytica, demonstrating a novel and simple cell surface display strategy. Furthermore, the PdSI expression level was significantly increased through optimizing the promoters and multi-site integrating genes into chromosome. The final strain gained 451.7 g L-1 isomaltulose with a conversion rate of 90.3% and a space-time yield of 50.2 g L-1 h-1. CONCLUSION: The present study provides an efficient way for manufacturing isomaltulose with a high space-time yield. This heterogenous signal peptide-mediated cell surface display strategy featured with small fusion tag (approximately 2.2 kDa of SP1), absence of enzyme leakage in fermentation broth and ample room for optimization, providing a convenient way to construct whole-cell biocatalysts to synthesize other products and broadening the array of molecular toolboxes accessible for engineering Y. lipolytica. © 2024 Society of Chemical Industry.

A type VI secretion system effector TseG of Pantoea ananatis is involved in virulence and antibacterial activity.

The type VI secretion system (T6SS) of many gram-negative bacteria injects toxic effectors into adjacent cells to manipulate host cells during pathogenesis or to kill competing bacteria. However, the identification and function of the T6SS effectors remains only partly known. Pantoea ananatis, a gram-negative bacterium, is commonly found in various plants and natural environments, including water and soil. In the current study, genomic analysis of P. ananatis DZ-12 causing brown stalk rot on maize demonstrated that it carries three T6SS gene clusters, namely, T6SS-1, T6SS-2, and T6SS-3. Interestingly, only T6SS-1 secretion systems are involved in pathogenicity and bacterial competition. The study also investigated the T6SS-1 system in detail and identified an unknown T6SS-1-secreted effector TseG by using the upstream T6SS effector chaperone TecG containing a conserved domain of DUF2169. TseG can directly interact with the chaperone TecG for delivery and with a downstream immunity protein TsiG for protection from its toxicity. TseG, highly conserved in the Pantoea genus, is involved in virulence in maize, potato, and onion. Additionally, P. ananatis uses TseG to target Escherichia coli, gaining a competitive advantage. This study provides the first report on the T6SS-1-secreted effector from P. ananatis, thereby enriching our understanding of the various types and functions of type VI effector proteins.

[Effect of Tween 20 on enhancing extracellular polysaccharide synthesis by Pantoea alhagi NX-11].

Pantoea alhagi NX-11 exopolysaccharide (PAPS) is a novel microbial biostimulant that enhances crop resistance to salt and drought stress. It is biodegradable and holds promising applications in improving agricultural yield and efficiency. However, the fermentation process of PAPS exhibits a high viscosity due to low oxygen transfer efficiency, which hinders yield improvement and downstream processing. This study aimed to investigate the effects of seven oxygen carriers (Span 80, Span 20, Tween 80, Tween 20, glycerin, olive oil, and soybean oil) on fermentation yield. The results showed that the addition of 0.5% (V/V) Tween 20 significantly enhanced the production of PAPS. Moreover, the introduction of 0.5% (V/V) Tween 20 in a 7.5 L fermenter resulted in a PAPS titer of (16.85±0.50) g/L, which was 17.70% higher than that of the control group. Furthermore, the rheological characterization and the microstructure analysis of the polysaccharide products revealed that the characteristic structure of polysaccharides remained unchanged in the oxygen carrier treated group, but their viscosity increased. These findings may facilitate enhancing the biosynthesis efficiency of other polymer products.

Pantoea ananatis, a plant growth stimulating bacterium, and its metabolites isolated from Hydrocotyle umbellata (dollarweed).

A bacterium growing on infected leaves of Hydrocotyle umbellata, commonly known as dollarweed, was isolated and identified as Pantoea ananatis. An ethyl acetate extract of tryptic soy broth (TSB) liquid culture filtrate of the bacterium was subjected to silica gel chromatography to isolate bioactive molecules. Indole was isolated as the major compound that gave a distinct, foul odor to the extract, together with phenethyl alcohol, phenol, tryptophol, N-acyl-homoserine lactone, 3-(methylthio)-1-propanol, cyclo(L-pro-L-tyr), and cyclo(dehydroAla-L-Leu). This is the first report of the isolation of cyclo(dehydroAla-L-Leu) from a Pantoea species. Even though tryptophol is an intermediate in the indoleacetic acid (IAA) pathway, we were unable to detect or isolate IAA. We investigated the effect of P. ananatis inoculum on the growth of plants. Treatment of Lemna paucicostata Hegelm plants with 4 × 109 colony forming units of P. ananatis stimulated their growth by ca. five-fold after 13 days. After 13 days of treatment, some control plants were browning, but treated plants were greener and no plants were browning. The growth of both Cucumis sativus (cucumber) and Sorghum bicolor (sorghum) plants was increased by ca. 20 to 40%, depending on the growth parameter and species, when the rhizosphere was treated with the bacterium after germination at the same concentration. Plant growth promotion by Pantoea ananatis could be due to the provision of the IAA precursor indole.

Pantoea agglomerans bacteraemia after uterine artery embolisation: an unusual pathogen.

A woman in her 40s presented to the emergency department (ED) with a 3-week history of nausea, vomiting and diarrhoea. Blood cultures were positive for Serratia and Pantoea agglomerans spp. One month before her ED visit, she underwent targeted uterine artery embolisation with particles by an interventional radiologist. Uterine artery embolisation is considered a safe alternative to surgical removal of fibroids or hysterectomy. The patient was initially treated with targeted antibiotics for a large infected uterine fibroid but ultimately required a hysterectomy for source control. To our knowledge, this is the first documented case of P. agglomerans infecting a uterine fibroid.

Transcriptomic analysis and knockout experiments reveal the role of suhB in the biocontrol effects of Pantoea jilinensis D25 on Botrytis cinerea.

Tomato gray mold, caused by Botrytis cinerea, is an important disease in tomato. Pantoea jilinensis D25, isolated form tomato rhizosphere soil, can prevent B. cinerea infection in tomato. To determine the underlying biocontrol mechanism, the transcriptome of P. jilinensis D25 was assessed. Differential expression analysis revealed that 941 genes were upregulated and 997 genes were downregulated. Through transcriptome analysis, the suhB gene was knocked out. ΔPj-suhB exhibited lower swimming motility and colonization abilities than strain D25. After 4 days of co-cultivation, ΔPj-suhB could reduce the colony diameter, mycelial weight, and spore production of B. cinerea with the inhibitory rates of 31.72 %, 39.62 %, and 47.42 %, respectively, compared with control. However, the inhibitory rates of strain D25 were 52.91 %, 60.09 %, and 76.85 %, respectively, compared with control. Strain D25 could significantly downregulate pathogenesis-related genes in B. cinerea, whereas the expression level of these genes in B. cinerea was higher after treatment with ΔPj-suhB than after that with strain D25. In vitro experiments revealed that the lesion area and disease control efficacy were 1.520 and 0.038 cm2 and 68.7 % and 99.0 %, respectively, after ΔPj-suhB and strain D25 treatments. Pot experiments revealed that ΔPj-suhB and strain D25 could prevent tomato plants from B. cinerea infection with the disease reduction rate of 37.5 % and 75.0 %, respectively. Though the activities of defense-related enzymes and expression level of defense related genes in tomato plants were increased under ΔPj-suhB treatment, these effects were higher after strain D25 treatment. Thus, these results demonstrated that suhB was the key gene in strain D25 underlying its biocontrol effect and mobility.

Isolation, whole-genome sequencing, and annotation of two antibiotic-producing and antibiotic-resistant bacteria, Pantoea rodasii RIT 836 and Pseudomonas endophytica RIT 838, collected from the environment.

Antimicrobial resistance (AMR) is a global threat to human health since infections caused by antimicrobial-resistant bacteria are life-threatening conditions with minimal treatment options. Bacteria become resistant when they develop the ability to overcome the compounds that are meant to kill them, i.e., antibiotics. The increasing number of resistant pathogens worldwide is contrasted by the slow progress in the discovery and production of new antibiotics. About 700,000 global deaths per year are estimated as a result of drug-resistant infections, which could escalate to nearly 10 million by 2050 if we fail to address the AMR challenge. In this study, we collected and isolated bacteria from the environment to screen for antibiotic resistance. We identified several bacteria that showed resistance to multiple clinically relevant antibiotics when tested in antibiotic susceptibility disk assays. We also found that two strains, identified as Pantoea rodasii RIT 836 and Pseudomonas endophytica RIT 838 via whole genome sequencing and annotation, produce bactericidal compounds against both Gram-positive and Gram-negative bacteria in disc-diffusion inhibitory assays. We mined the two strains' whole-genome sequences to gain more information and insights into the antibiotic resistance and production by these bacteria. Subsequently, we aim to isolate, identify, and further characterize the novel antibiotic compounds detected in our assays and bioinformatics analysis.

Bacterial Strains Isolated from Stingless Bee Workers Inhibit the Growth of Apis mellifera Pathogens.

Apis mellifera bees are an important resource for the local economy of various regions in Argentina and the maintenance of natural ecosystems. In recent years, different alternatives have been investigated to avoid the reduction or loss of colonies caused by pathogens and parasites such as Ascosphaera apis, Aspergillus flavus, and Paenibacillus larvae. We focused on bacterial strains isolated from the intestine of native stingless bees, to elucidate their antagonistic effect on diseases of A. mellifera colonies. For this purpose, worker bees of the species Tetragonisca fiebrigi, Plebeia spp., and Scaptotrigona jujuyensis were captured from the entrance to tree hives and transported to the laboratory, where their intestines were extracted. Twenty bacterial colonies were isolated from the intestines, and those capable of inhibiting enterobacteria in vitro and producing organic acids, proteases, and chitinases were selected. Four genera, Levilactobacillus, Acetobacter, Lactiplantibacillus, and Pantoea, were selected and identified by the molecular marker that codes for the 16S rRNA gene. For inhibition assays, cell suspensions and cell-free suspensions were performed. All treatments showed significant antibacterial effects, in comparison with the controls, against P. larvae and antifungal effects against A. apis and A. flavus. However, the mechanisms by which these bacteria inhibit the growth of these pathogens were not studied.

Simultaneous removal of aliphatic and aromatic crude oil hydrocarbons by Pantoea agglomerans isolated from petroleum-contaminated soil in the west of Iran.

Hydrocarbons are considered as one of the most common and harmful environmental pollutants affecting human health and the environment. Bioremediation as an environmentally friendly, highly efficient, and cost-effective method in remediating oil-contaminated environments has been interesting in recent decades. In this study, hydrocarbon degrader bacterial strains were isolated from the highly petroleum-contaminated soils in the Dehloran oil field in the west of Iran. Out of 37 isolates, 15 can grow on M9 agar medium that contains 1.5 g L-1 of crude oil as the sole carbon source. The morphological, biochemical, and 16SrRNA sequencing analyses were performed for the isolates. The choosing of the isolates as the hydrocarbon degrader was examined by evaluating the efficacy of their crude oil removal at a concentration of 10 g L-1 in an aqueous medium. The results showed that five isolates belonging to Pseudomonas sp., Pseudomonas oryzihabitans, Roseomonas aestuarii, Pantoea agglomerans, and Arthrobacter sp. had a hyper hydrocarbon-degrading activity and they could remove more than 85% of the total petroleum hydrocarbon (TPH) after 96 h. The highest TPH removal of about 95.75% and biodegradation rate of 0.0997 g L-1 h-1 was observed for P. agglomerans. The gas chromatography-mass spectroscopy (GC-MS) analysis was performed during the biodegradation process by P. agglomerans to detect the degradation intermediates and final products. The results confirmed the presence of intermediates such as alcohols and fatty acids in the terminal oxidation pathway of alkanes in this biodegradation process. A promising P. agglomerans NB391 strain can remove aliphatic and aromatic hydrocarbons simultaneously.

Improved Viability of Spray-Dried Pantoea agglomerans for Phage-Carrier Mediated Control of Fire Blight.

Fire blight, caused by Erwinia amylovora, is a devastating bacterial disease that threatens apple and pear production. It is mainly controlled by using antibiotics, such as streptomycin. Due to development of E. amylovora resistant strains and the excessive agricultural use of antibiotics, there is an increased awareness of the possibility of antibiotic resistance gene transfer to other microbes. Urgent development of biocontrol agents (BCAs) is needed that can be incorporated into integrated pest management programs as antibiotic alternatives. A novel phage-carrier system (PCS) that combines an antagonistic bacterium, Pantoea agglomerans, with its ability to act as a phage-carrier bacterium for Erwinia phages has been developed. The low viability of P. agglomerans cells following spray-drying (SD) has been a challenge for the industrial-scale production of this PCS. Here, an SD protocol was developed for P. agglomerans by modifying the growth medium and bacterial cell formulation using D(+)-trehalose and maltodextrin. The developed protocol is amenable to the industrial-scale production of the BCA/PCS. The P. agglomerans viability was greater than 90% after SD and had a shelf life at 4 °C of 4 months, and reconstituted cells showed a 3 log reduction in E. amylovora counts with a pear disc assay.

Pantoea trifolii sp. nov., a novel bacterium isolated from Trifolium rubens root nodules.

A novel bacterium, designated strain MMK2T, was isolated from a surface-sterilised root nodule of a Trifolium rubens plant growing in south-eastern Poland. Cells were Gram negative, non-spore forming and rod shaped. The strain had the highest 16S rRNA gene sequence similarity with P. endophytica (99.4%), P. leporis (99.4%) P. rwandensis (98.8%) and P. rodasii (98.45%). Phylogenomic analysis clearly showed that strain MMK2T and an additional strain, MMK3, should reside in the genus Pantoea and that they were most closely related to P. endophytica and P. leporis. Genome comparisons showed that the novel strain shared 82.96-93.50% average nucleotide identity and 26.2-53. 2% digital DNA:DNA hybridization with closely related species. Both strains produced siderophores and were able to solubilise phosphates. The MMK2T strain was also able to produce indole-3-acetic acid. The tested strains differed in their antimicrobial activity, but both were able to inhibit the growth of Sclerotinia sclerotiorum 10Ss01. Based on the results of the phenotypic, phylogenomic, genomic and chemotaxonomic analyses, strains MMK2T and MMK3 belong to a novel species in the genus Pantoea for which the name Pantoea trifolii sp. nov. is proposed with the type strain MMK2T (= DSM 115063T = LMG 33049T).

Interspecific hybridization and inoculation with Pantoea eucalypti improve forage performance of Lotus crop species under alkaline stress.

This study was designed to elucidate the physiological responses of three Lotus forage accessions to alkaline stress, and the influence of inoculating with Pantoea eucalypti endophyte strain on alkaline stress mitigation. A diploid L. corniculatus (Lc) accession, L. tenuis (Lt), and the interspecific hybrid Lt × Lc obtained from these two parental lines were exposed to alkaline stress (pH 8.2). Both Lt and the Lt × Lc hybrid are alkaline-tolerant compared to Lc, based on observations that dry mass was not reduced under stress, and there were no chlorosis symptoms on leaf blades. In all three Lotus accessions, Fe2+ concentration under stress decreased in aerial parts and simultaneously increased in roots. Inoculation with P. eucalypti considerably increased Fe2+ content in shoots of all three Lotus forage species under alkaline treatment. Photochemical efficiency of PSII was affected in Lc accession only when exposed to alkaline treatment. However, when cultivated under alkalinity with inoculation, plants recovered and had photosynthetic parameters equivalent to those in the control treatment. Together, the results highlight the importance of inoculation with P. eucalypti, which contributes significantly to mitigating alkaline stress. All results provide useful information for improving alkaline tolerance traits of Lotus forage species and their interspecific hybrids.

Pantoea jilinensis D25 enhances tomato salt tolerance via altering antioxidant responses and soil microbial community structure.

As a major challenge to global food security, soil salinity is an important abiotic stress factor that seriously affects the crop growth and yield. In this study, the mechanism of salt resistance of Pantoea jilinensis D25 and its improving effect on salt tolerance of tomato were explored with salt resistance-related genes identified in strain D25 by genomic sequencing. The results showed that in comparison with the treatment of NaCl, strain D25 significantly increased the fresh weight, shoot length, root length, and chlorophyll content of tomato under salt stress by 46.7%, 20%, 42.4%, and 44.2%, respectively, with increased absorptions of various macronutrients and micronutrients and decreased accumulation of Na+. The activities of defense enzymes (peroxidase, catalase, superoxide dismutase, phenylalanine ammonia-lyase, and polyphenol oxidase) were enhanced, while the content of malondialdehyde was decreased. The results of quantitative real-time PCR analysis showed that the expressions of genes (SlSOS1, SlNHX1, SlHKT1.1, SlSOD1, SlAPX2, SlAOS, SlPin II, Solyc08g066270.1, Solyc03g083420.2 and SlGA20ox1) related to ion transporters, antioxidant machinery, key defense, serine/threonine protein kinase synthesis, and gibberellin (GA) signal protein were up-regulated and were the highest in the treatment of both NaCl and strain D25. The activities of enzymes (dehydrogenase, urease, invertase, and catalase activities) related to soil fertility were enhanced. The results of 16S rRNA sequencing showed that soil microbial diversity and the abundance of probiotics (e.g., Acidibacter, Limnobacter, and Romboutsia) were significantly increased. Our study provided strong experimental evidence to support the agricultural application of strain D25 in the promotion of growth in crops.