Bacterial Inoculation Research Articles

The use of Lentilactobacillus buchneri PJB1 and Lactiplantibacillus plantarum MTD1 on the ensiling of whole-plant corn silage, snaplage, and high-moisture corn

Experiments were conducted over a 3-yr period to evaluate the effects of bacterial inoculants on the fermentation profile and aerobic stability of whole-plant corn silage (WPC), snaplage (SNA), and high-moisture corn (HMC). Whole-plant corn was inoculated with Lentilactobacillus buchneri PJB1 in combination with Lactiplantibacillus plantarum MTD1 or with Lpb. plantarum alone (experiments 1 and 2). Snaplage (experiment 3) and HMC (experiments 4 and 5) were inoculated with Len. buchneri in combination with Lpb. plantarum or with Len. buchneri alone. After inoculation, the feedstuffs were ensiled in 7.57-L silos and stored at 21 ± 2°C for 30 or 90 d. In experiment 5, silage was subjected to air stress for 2 h every 2 wk through 42 d and then for 2 h/wk until 90 d and had samples analyzed for their bacterial community composition by metagenomics. Overall, in all experiments, silages inoculated with Len. buchneri alone or in combination with Lpb. plantarum had more acetic acid and 1,2-propanediol and fewer yeasts than uninoculated silages. After 30 d of ensiling, inoculation with Len. buchneri alone or in combination with Lpb. plantarum did not affect the aerobic stability of SNA, but it slightly increased the stability of WPC and markedly improved the stability of HMC. After 90 d of ensiling, inoculation with Len. buchneri alone or in combination with Lpb. plantarum markedly improved the aerobic stability of WPC, SNA, and HMC. In experiment 5, inoculation increased the relative abundance (RA) of Lactobacillaceae and reduced the RA of Enterobacteriaceae and Leuconostocaceae in HMC at 30 and 90 d and the RA of Clostridiaceae in non-air-stressed HMC at 90 d. Air-stressed HMC inoculated with Len. buchneri had less lactic acid, more acetic acid and 1,2-propanediol, and markedly greater aerobic stability than uninoculated air-stressed HMC at 90 d. In conclusion, inoculation with Len. buchneri PJB1 alone or in combination with Lpb. plantarum MTD1 increased the production of acetic acid and 1,2-propanediol, inhibited yeasts development, and improved the aerobic stability of WPC, SNA, and HMC. In HMC, inoculation markedly improved aerobic stability as soon as after 30 d of ensiling, and after 90 d, inoculation improved stability even under air stress conditions.

Effect of Non-Native Endophytic Bacteria on Oat (Avena sativa L.) Growth

Endophytic bacteria are known to influence vital activities of host plants. Endophytes can promote plant growth and provide a defense response against pathogens. The use of endophytes in crop production has the potential to reduce the application of fertilizer and pesticide input and thus improve the sustainability of crop production. In this study, we investigated the effects of seed inoculation with non-native endophytic bacteria, harvested from Brassica carinata, on oat (Avena sativa L.) growth with root vigor assays and greenhouse experiments. For root vigor assay experiments, seeds of two different oat cultivars were treated with 16 endophytic bacteria previously shown to promote growth benefits on multiple crop species. For the greenhouse experiments, the effect of seed inoculation with bacterial isolates was evaluated on ten oat cultivars at two fertilization levels. The root vigor assay showed that multiple isolates, including Bacillus licheniformis, Enterobacter kobei, B. halotolerans, B. cereus, B. aryabhattai, and Lysinibacillus fusiformis, had a positive effect on seedling root growth in one of the two oat cultivars. In the other cultivar, the bacterial isolates had either no effect or a negative effect on root growth. Greenhouse studies showed that the magnitude and direction of the effect of bacterial inoculation on oat growth varied with fertilization levels, bacterial strain, and oat cultivar. However, we identified two cultivars that were more responsive to bacterial inoculation than the others and for which bacterial inoculation of seed resulted in enhanced growth in several traits under both reduced and full nitrogen levels, and this response was observed for the two isolates tested. Our results show that inoculating oat seeds with non-native bacterial endophytes can promote root and shoot growth in oats. Developing biofertilizers that are effective across crop species, crop cultivars, and environmental conditions may be possible if cultivars are selected for their responsiveness across multiple bacterial isolates and in multiple growing environments. Overall, this study indicates that non-native endophytes could be considered for the development of biofertilizers with effectiveness across crop species.

Использование бактериальной инокуляции для улучшения вегетативного роста и нутрицевтических качеств китайской капусты в условиях регулируемой агроэкосистемы

Abstract. In recent years, plant inoculation with beneficial plant growth-promoting microorganisms PGPR bacteria in agriculture has been steadily increasing, and they are expected to partially replace chemical fertilizers, pesticides and other growth regulators in the future, providing an environmentally friendly solution for sustainable farming practices. Consequently, the purpose of this study was to investigate the bacterial inoculation of Bacillus cereus to improve the vegetative growth and nutraceutical qualities of Chinese cabbage pak-choi plants grown by hydroponics under regulated agroecosystem conditions. Objects of the study are the plants of Chinese cabbage pak-choy (Brassica campestris ssp. cheninsis L.). Methods. When conducting research, we measured biometric indicators, determined the indicators of crude, dry matter, dietary fiber and mass fraction of ash of pak-choy plants according to GOST. The contents of vitamins, cations, anions and amino acids in plant products were estimated by capillary electrophoresis using “Kapel’-205” device (Russia). The obtained results were processed statistically by means of analysis of variance. Scientific novelty. The efficiency of root inoculation of Bacillus cereus bacteria in the cultivation of pak-choy plants by hydroponics in closed agro-ecosystems has been determined. The dependence of the improvement of quality indicators in the biomass of bacterial inoculation of pak-choi plants has been established. Results. As a result of studies, it was found that the inoculation of B. cereus had a positive effect on the development of the assimilating apparatus of pak-choi plants. The formation of the main morpho-biometric parameters (crude, dry weight, shoot length and number of leaves) of plants was not significantly affected by bacterial inoculation. All obtained values were at the control level. Pak-choi plants inoculated with bacteria showed a significant increase in concentration of mineral elements (K, S and P), amino acids (proline, phenylalanine, valine, histidine and lysine) and vitamins (ascorbic acid and choline).

Integrative transcriptomic analysis unveils lncRNA-miRNA-mRNA interplay in tomato plants responding to Ralstonia solanacearum

Ralstonia solanacearum, a bacterial plant pathogen, poses a significant threat to tomato (Solanum lycopersicum) production through destructive wilt disease. While noncoding RNA has emerged as a crucial regulator in plant disease, its specific involvement in tomato bacterial wilt remains limited. Here, we conducted a comprehensive analysis of the transcriptional landscape, encompassing both mRNAs and noncoding RNAs, in a tomato resistant line (‘ZRS_7’) and a susceptible line (‘HTY_9’) upon R. solanacearum inoculation using high-throughput RNA sequencing. Differential expression (DE) analysis revealed significant alterations in 7506 mRNAs, 997 lncRNAs, and 69 miRNAs between ‘ZRS_7’ and ‘HTY_9’ after pathogen exposure. Notably, 4548 mRNAs, 367 lncRNAs, and 26 miRNAs exhibited genotype-specific responses to R. solanacearum inoculation. GO and KEGG pathway analyses unveiled the potential involvement of noncoding RNAs in the response to bacterial wilt disease, targeting receptor-like kinases, cell wall-related genes, glutamate decarboxylases, and other key pathways. Furthermore, we constructed a comprehensive competing endogenous RNA (ceRNA) network incorporating 13 DE-miRNAs, 30 DE-lncRNAs, and 127 DEGs, providing insights into their potential contributions to the response against bacterial inoculation. Importantly, the characterization of possible endogenous target mimics (eTMs) of Sly-miR482e-3p via VIGS technology demonstrated the significant impact of eTM482e-3p-1 silencing on tomato's sensitivity to R. solanacearum. These findings support the existence of an eTM482e-3p-1-Sly-miR482e-3p-NBS-LRRs network in regulating tomato's response to the pathogen. Collectively, our findings shed light on the intricate interactions among lncRNAs, miRNAs, and mRNAs as underlying factors in conferring resistance to R. solanacearum in tomato.

Effect of cutting height, a bacterial inoculant and a fibrolytic enzyme on corn (Zea mays L.) silage quality

This study aimed to evaluate cutting height (CH) effects on ensiled corn without additives (C), with a lactic acid bacteria inoculant (L), a fibrolytic enzyme (F), or a mixture of both (FL), considering chemical composition and both in vitro digestibility dry matter (IVDMD) and in vitro neutral detergent fiber (IVNDFD). Corn was harvested at three different cutting heights (12, 25 or 42 cm above the soil) and ensiled with or without additives (AD). Data was analyzed according to a factorial design, with a 3 x 4 arrangement of treatments and three repeats. Dry matter content was highest in C12 and lowest in F12 (P<0.05) silages. As cutting height was higher, cell wall content was lower (P<0.05). Even considering it increased after the use of additives (P<0.05), the highest values occurred with FL silages. Crude protein was equal (P˃0.05) between CH and increased (P<0.05) with AD. The highest IVDMD was observed for 42 cm CH, while IVDMD and IVNDFD were higher in C and F, but lower with FL. None of the inoculation treatments, alone or combined improved corn silage quality. In fact, FL combination decreased such quality. Highlights: The efficacy of lactic acid bacteria (LAB) and exogenous fibrolytic enzyme (EFE) is a funtion of the amount of cell walls and sugars present in the maize plant at harvest. Adding LAB and EFE to maize forage harvested at different cutting heights did not improve silage quality, in fact, the combination of both additives decreased silage quality. Further studies are needed to prove the efficacy of EFE and its combination with LAB on maize silage quality.

Immunometabolic capacities of nutritional fatty acids in regulation of inflammatory bone cell interaction and systemic impact of periodontal infection.

Novel preventive strategies in periodontal disease target the bacterial-induced inflammatory host response to reduce associated tissue destruction. Strategies focus on the modulation of tissue-destroying inflammatory host response, particularly the reduction of inflammation and promotion of resolution. Thereby, nutrition is a potent immunometabolic non-pharmacological intervention. Human studies have demonstrated the benefit of olive oil-containing Mediterranean-style diets (MDs), the main component of which being mono-unsaturated fatty acid (FA) oleic acid (OA (C18:1)). Hence, nutritional OA strengthened the microarchitecture of alveolar trabecular bone and increased circulating pro-resolving lipid mediators following bacterial inoculation with periodontal pathogen Porphyromonas gingivalis, contrary to saturated FA palmitic acid (PA (C16:0)), which is abundant in Western-style diets. Additionally, the generalized distribution of inflammatory pathway mediators can occur in response to bacterial infection and compromise systemic tissue metabolism and bone homeostasis distant from the side of infection. Whether specific FA-enriched nutrition and periodontal inoculation are factors in systemic pathology that can be immune-modulatory targeted through dietary substitution is unknown and of clinical relevance. Normal-weight C57BL/6-mice received OA-or PA-enriched diets (PA-ED, OA-ED, PA/OA-ED) or a normal-standard diet (n=12/group) for 16 weeks and were orally infected with P. gingivalis/placebo to induce periodontal disease. Using histomorphometry and LC-MS/MS, systemic bone morphology, incorporated immunometabolic FA-species, serological markers of bone metabolism, and stress response were determined in addition to bone cell inflammation and interaction in vitro. In contrast to OA-ED, PA-ED reduced systemic bone microarchitecture paralleled by increased lipotoxic PA-containing metabolite accumulation in bone. Substitution with OA reversed the bone-destructive impact of PA, which was accompanied by reduced diacylglycerols (DAG) and saturated ceramide levels. Further, PA-associated reduction in mineralization activity and concomitant pro-inflammatory activation of primary osteoblasts were diminished in cultures where PA was replaced with OA, which impacted cellular interaction with osteoclasts. Additionally, PA-ED increased osteoclast numbers in femurs in response to oral P. gingivalis infection, whereas OA-ED reduced osteoclast occurrence, which was paralleled by serologically increased levels of the stress-reducing lipokine PI(18:1/18:1). OA substitution reverses the bone-destructive and pro-inflammatory effects of PA and eliminates incorporated lipotoxic PA metabolites. This supports Mediterranean-style OA-based diets as a preventive intervention to target the accumulation of PA-associated lipotoxic metabolites and thereby supports systemic bone tissue resilience after oral bacterial P. gingivalis infection.

Differential interference of copper with endophytic bacterial inoculation: Atrazine decontamination in Acorus tatarinowii and culture solution

To clarify the interference effects of inorganic ions, Acorus tatarinowii and endophytic bacterium Herbaspirillum huttiense (Hh) were combined to decontaminate atrazine pollution under different copper levels. This study verified inoculation effects and revealed the complicated processes of atrazine transformation in solutions. 35.9% leaf biomass was promoted by Hh inoculation, and the value was lowered to 7.87% by high doses of copper. The changing trend of leaf N, K, and S contents, and tiller numbers were consistent with that of leaf biomass. Hh injection improved atrazine accumulation by 43.5% in roots, and under copper interference, this value lowered to 10.6%. Hh promoted atrazine deethylation in plants, which was copper-dose dependent in different plant organs. In solutions, atrazine was conjugated with small-molecule secretions at m/z 118, detoxicated into 2-hxydroatrazine and 2-hydroxy-4-acetamido-atrazine, then the triazine ring opened. Copper interference had a more significant impact on residual atrazine conversion products than Hh inoculation treatments. Hh treatment promoted the ring-opening degradation of atrazine in water. The addition of high doses of copper ions promoted the oxidative process of atrazine while inhibiting its ring-opening transformation process in water.

Genetic and Transcriptomic Dissection of Host Defense to Goss's Bacterial Wilt and Leaf Blight of Maize.

Goss's wilt, caused by the Gram-positive actinobacterium Clavibacter nebraskensis, is an important bacterial disease of maize. The molecular and genetic mechanisms of resistance to the bacterium, or, in general, Gram-positive bacteria causing plant diseases, remain poorly understood. Here, we examined the genetic basis of Goss's wilt through differential gene expression, standard genome-wide association mapping (GWAS), extreme phenotype (XP) GWAS using highly resistant (R) and highly susceptible (S) lines, and quantitative trait locus (QTL) mapping using three bi-parental populations, identifying eleven disease association loci. Three loci were validated using near-isogenic lines or recombinant inbred lines. Our analysis indicates that Goss's wilt resistance is highly complex and major resistance genes are not commonly present. RNA sequencing of samples separately pooled from R and S lines with or without bacterial inoculation was performed, enabling identification of common and differential gene responses in R and S lines. Based on expression, in both R and S lines, the photosynthesis pathway was silenced upon infection, while stress-responsive pathways and phytohormone pathways, namely, abscisic acid, auxin, ethylene, jasmonate, and gibberellin, were markedly activated. In addition, sixty-five genes showed differential responses (up- or down-regulated) to infection in R and S lines. Combining genetic mapping and transcriptional data, individual candidate genes conferring Goss's wilt resistance were identified. Collectively, aspects of the genetic architecture of Goss's wilt resistance were revealed, providing foundational data for mechanistic studies.

Cadmium-tolerant Bacillus cereus 2–7 alleviates the phytotoxicity of cadmium exposure in banana plantlets

Bananas are the world's important fruit and staple crop in the developing countries. Cadmium (Cd) contamination in soils results in the decrease of crop yield and food safety. Bioremediation is an environmental-friendly and effective measure using Cd-tolerant plant growth promoting rhizobacteria (PGPR). In our study, a Cd-resistant PGPR Bacillus cereus 2–7 was isolated and identified from a discarded gold mine. It could produce multiple plant growth promoting biomolecules such as siderophores, indole-3-acetic acid (IAA), 1-aminocyclopropane-1-carboxylate (ACC)-deaminase and phosphatase. The extracellular accumulation was a main manner of Cd removal. Surplus Cd induced the expression of Cd resistance/transport genes of B. cereus 2–7 to maintain the intracellular Cd homeostasis. The pot experiment showed that Cd contents decreased by 50.31 % in soil, 45.43 % in roots, 56.42 % in stems and 79.69 % in leaves after the strain 2–7 inoculation for 40 d. Bacterial inoculation alleviated the Cd-induced oxidative stress to banana plantlets, supporting by the increase of chlorophyll contents, plant height and total protein contents. The Cd remediation mechanism revealed that B. cereus 2–7 could remodel the rhizosphere bacterial community structure and improve soil enzyme activities to enhance the immobilization of Cd. Our study provides a Cd-bioremediation strategy using Cd-resistant PGPR in tropical and subtropical area.

Appropriate handling and storage reduce the risk of bacterial growth in enteral feeding systems reused within 24 hours.

Enteral tube feeding can require considerable amounts of plastic equipment including delivery sets and containers, often disposed of after a single feeding session because of bacterial contamination concerns. The aim of this research was to assess whether reuse of delivery sets and containers for up to 24 h is safe from a microbiological perspective. Four enteral tube feeding systems (FS) were tested under hygienic controlled or repeated inoculation challenge conditions using key foodborne pathogens, to assess bacterial growth over time (FS1: ready-to-hang, closed 1-L system with delivery set reused, stored at room temperature [RT]; FS2: a prepared, powdered, open 1-L system with delivery set and container reused, stored at RT; FS3 and FS4: prepared, powdered, open 200-ml bolus systems with delivery set and container reused, stored at RT [FS3] and refrigeration [FS4]). Feed samples were cultured at 0.5, 6.5, 12.5, 18.5, and 24.5 h with >2 Δlog considered significant bacterial growth. Under hygienic control, FS1, FS3, and FS4 were below the level of enumeration (<5 CFU/g) for all bacteria tested, at all time points. In FS2, significant bacterial growth was observed from 18.5 h. Under repeated bacterial inoculation challenge, no significant growth was observed in FS1 and FS4 over 24.5 h; however, significant growth was observed in FS2 after 6.5 h and in FS3 after 10-12 h. With hygienic handling technique, there is limited bacterial growth with reuse of delivery sets and containers over 24 h. Refrigeration between feeding sessions and using boluses of reconstituted powdered feed reduce bacterial growth risk.

Bioremediation of PBDEs and heavy metals co-contaminated soil in e-waste dismantling sites by Pseudomonas plecoglossicida assisted with biochar

Biochar-assisted microbial remediation has been proposed as a promising strategy to eliminate environmental pollutants. However, studies on this strategy used in the remediation of persistent organic pollutants and heavy metals co-contaminated soil are lacking, and the effect of the combined incorporation of biochar and inoculant on the assembly, functions, and microbial interactions of soil microbiomes are unclear. Here, we studied 2,2′,4,4′-tetrabrominated diphenyl ether (BDE-47) degradation and heavy metal immobilization by and biochar-based bacterial inoculant (BC/PP) in an e-waste contaminated soil, and corresponding microbial regulation mechanisms. Results showed that BC/PP addition was more effective in reducing Cu and Pb availability and degrading BDE-47 than inoculant alone. Notably, BC/PP facilitated bound-residue formation of BDE-47, reducing the ecological risk of residual BDE-47. Meanwhile, microbial carbon metabolism and enzyme activities (related to C-, N-, and P- cycles) were enhanced in soil amended with BC/PP. Importantly, biochar played a crucial role in inoculant colonization, community assembly processes, and microbiome multifunction. In the presence of biochar, positive interactions in co-occurrence networks of the bacterial community were more frequent, and higher network stability and more keystone taxa were observed (including potential degraders). These findings provide a promising strategy for decontaminating complex-polluted environments and recovering soil ecological functions.

Enhancing the Hydrophobicity and Antibacterial Properties of SiCN-Coated Surfaces with Quaternization to Address Peri-Implantitis.

Peri-implantitis is a major cause of dental implant failure. This disease is an inflammation of the tissues surrounding the implant, and, while the cause is multi-factorial, bacteria is the main culprit in initiating an inflammatory reaction. Dental implants with silicon carbonitride (SiCN) coatings have several potential advantages over traditional titanium implants, but their antibacterial efficiency has not yet been evaluated. The purpose of this study was to determine the anti-bacterial potential of SiCN by modifying the surface of SiCN-coated implants to have a positive charge on the nitrogen atoms through the quaternization of the surface atoms. The changes in surface chemistry were confirmed using contact angle measurement and XPS analysis. The modified SiCN surfaces were inoculated with Streptococcus mutans (S. mutans) and compared with a silicon control. The cultured bacterial colonies for the experimental group were 80% less than the control silicon surface. Fluorescent microscopy with live bacteria staining demonstrated significantly reduced bacterial coverage after 3 and 7 days of incubation. Scanning electron microscopy (SEM) was used to visualize the coated surfaces after bacterial inoculation, and the mechanism for the antibacterial properties of the quaternized SiCN was confirmed by observing ruptured bacteria membrane along the surface.

Sustaining soil health and tomato production through organic inputs and bacterial inoculations in alluvial soils detoxifying plant contaminants

The demand for organic tomatoes is gaining momentum globally, especially for their nutritional quality, shelf-life, and yield sustainability. Similarly, the restoration of metal-contaminated soils and maintenance of soil health is getting momentum through the application of organic inputs and microbial inoculations in soils. The present study evaluates different concentrated organic inputs and biofertilizers with a minimal dosage (14.3% of the recommended dose of fertilizers or RDF) under a field experiment conducted at the Agricultural Farm of Amity Institute of Organic Agriculture, Amity University, Noida, Uttar Pradesh, India. Organic treatments included mustard cake, goat manure, poultry manure, farmyard manure (FYM), neem cake, and biofertilizers (Azotobacter and phosphate solubilizing bacteria, or PSB). FYM (15 t ha−1) and vermicompost (VC 3.0 t ha−1) (T5), and the optimized inputs (containing the dual inoculation of Azotobacter and PSB, a mixture of organic inputs, and 14.3% RDF (T11) significantly improved plant height, number of branches/leaves/fruits, carotenoids, lycopene, fruit weight, yield, ascorbate peroxidase, total antioxidants, superoxide dismutase, total soluble solids (TSS), Vitamin C, and shelf-life in tomatoes. Organic inputs and inoculation of Azotobacter and PSB significantly reduced the concentration of Cd, Cr, and Pb from soils. The authors conclude that (a) the combined application of FYM and VC, and (b) the optimized mixture of bulky and concentrated organic inputs, 14.3% RDF, and the dual inoculation can improve the nutritional quality, minimize heavy metals (Cd, Cr, and Pb), and overall, sustain tomato production in the hot semi-arid alluvial sandy loam soils. The optimized organic inputs with dual microbial inoculations harness the climatic conditions in tropical regions to facilitate better color and ripening, and other quality parameters leading to higher lycopene contents in tomatoes.

Priming Bean Seedlings to Boost Natural Plant Defenses Against Common Bacterial Wilt: Leaf Architecture, Leaf area, Foliage Water Content, and Plant Biomass Results (Part 3)

This greenhouse study evaluated the effects of two chemicals for priming kidney bean seedlings against bacterial wilt disease (Curtobacterium flaccumfaciens pv. Flaccumfaciens) (CFF). The premise of this study was that the oxidant properties of chlorine dioxide would mimic the signaling properties of radical oxygen species thereby initiating a cascade of molecular plant defenses. The factorial study included two levels for the foliar chlorine dioxide treatment, two levels for the bacterial wilt inoculation treatment, and two optional treatments. The biomass variables included oven dry total plant biomass, oven dry fruit biomass, and oven dry leaf biomass. Also, foliage and total plant water content data was collected, as well as total leaf area. Specific leaf area (SLA) was estimated from the leaf area and biomass data. The primers had equivalent leaf area, plant and fruit biomass as the water control for the CFF wilt inoculated plants. The EB 400 mg/l primer reduced SLA for the CFF inoculated plants. Both EB formulations increased aboveground water content in the CFF wilt inoculated plants. Multivariate tables revealed several significant correlations among leaf architecture, plant tissue water content, and biomass growth parameters for the EB primers and the water control treatment for the two CFF wilt treatments. Re-allocation of plant resources from plant growth to plant defenses due to chemical primers were estimated and discussed to determine the tradeoffs between plant yield and enhanced plant defenses. The three articles in this study show that chlorine dioxide primers can initiate a series of ROS and salicylic acid signals. This interplay of ROS signals and salicylic acid signals generated by the chlorine dioxide primers activates a long-term SAR response that protects plants against future pathogen attacks. In addition, interaction of the ROS and salicylic acid signals activates a suite of defense mechanisms that provide universal, multifaceted plant immunity that can be sustained across a crop season.

Application of halotolerant Azotobacter chroococcum W4ii isolated from technosoils to mitigate salt stress in wheat plant

Background: Technosoils in Inowrocław, central Poland, are impacted by human activities and exhibit high salinity (ECe up to 70 dS/m) due to a soda lime repository. These saline environments pose challenges to plant growth and soil health. However, they also offer an opportunity for the evolution of microorganisms adapted to such conditions, including plant growth-promoting rhizospheric (PGPR) bacteria. The hypothesis tested here was that introducing PGPR bacteria from these environments could boost degraded soil performance, leading to better plant biomass and improved pathogen defense. Methods: Azotobacter chroococcum W4ii was isolated from the rhizosphere of wheat (Triticum aestivum L.) for its plant growth properties on wheat plants under salt stress. Results: Wheat seeds co-inoculated with A. chroococcum W4ii under 200 mM salt stress showed significant improvement in various growth parameters such as seeds germination (by 130%), shoot biomass (15%), chlorophyll b content (40%) compared to un-inoculated ones. Bacterial inoculation decreased the level of malondialdehyde (MDA), whereas it elevated the antioxidative enzymatic activities of peroxidase (POD). The test isolate also enhanced the level of defense enzymes like β-1, 3-glucanase, which can protect plants from infection by pathogens. The bacterium could also successfully colonize the wheat plants. Conclusions: These results indicate that A. chroococcum isolated from the technosoils has the potential to promote wheat growth under salt stress and can be further used as a bioinoculant in the salt affected agricultural fields.

Cost-Effective Cultivation of Native PGPB Sinorhizobium Strains in a Homemade Bioreactor for Enhanced Plant Growth.

The implementation of bioreactor systems for the production of bacterial inoculants as biofertilizers has become very important in recent decades. However, it is essential to know the bacterial growth optimal conditions to optimize the production and efficiency of bioinoculants. The aim of this work was to identify the best nutriment and mixing conditions to improve the specific cell growth rates (µ) of two PGPB (plant growth-promoting bacteria) rhizobial strains at the bioreactor level. For this purpose, the strains Sinorhizobium mexicanum ITTG-R7T and Sinorhizobium chiapanecum ITTG-S70T were previously reactivated in a PY-Ca2+ (peptone casein, yeast extract, and calcium) culture medium. Afterward, a master cell bank (MCB) was made in order to maintain the viability and quality of the strains. The kinetic characterization of each bacterial strain was carried out in s shaken flask. Then, the effect of the carbon and nitrogen sources and mechanical agitation was evaluated through a factorial design and response surface methodology (RSM) for cell growth optimization, where µ was considered a response variable. The efficiency of biomass production was determined in a homemade bioreactor, taking into account the optimal conditions obtained during the experiment conducted at the shaken flask stage. In order to evaluate the biological quality of the product obtained in the bioreactor, the bacterial strains were inoculated in common bean (Phaseolus vulgaris var. Jamapa) plants under bioclimatic chamber conditions. The maximum cell growth rate in both PGPB strains was obtained using a Y-Ca2+ (yeast extract and calcium) medium and stirred at 200 and 300 rpm. Under these growth conditions, the Sinorhizobium strains exhibited a high nitrogen-fixing capacity, which had a significant (p < 0.05) impact on the growth of the test plants. The bioreactor system was found to be an efficient alternative for the large-scale production of PGPB rhizobial bacteria, which are intended for use as biofertilizers in agriculture.

Endophytic Bacillus strains enhance biomass and bioactive metabolites of Gloriosa superba

Gloriosa superba L. is an economically important medicinal plant and variation in its colchicine content may be due to associated endo- and ectophytic beneficial microbes. Among them, endophytic bacteria contribute to enhancing plant growth, induce biotic and abiotic stress tolerance, and play a significant role in secondary metabolite synthesis. In the present study, 76 native endophytic bacteria were isolated from high and low-colchicine and gloriosine-containing chemotypes of G. superba rhizome and characterized for vegetative growth enhancement and abiotic stress mitigation. The screening has resulted in the selection of 23 plant growth-promoting (PGP) bacterial endophytes with abiotic stress tolerance. Most of these isolates belong to the Bacillus genera identification based on the 16S rRNA gene. Based on the significant enhancement in maize (Zea mays L.; as model host plant) under greenhouse conditions ten efficient bacterial strains were selected. Further, three endophytic bacterial strains, NBRI HYL5 and NBRI HYL8 (high colchicine and gloriosine containing chemotype), and NBRI LYN9 (low colchicine and gloriosine containing chemotype) were selected based on the survivability and enhanced 1-aminocyclopropane-1- carboxylate (ACC) deaminase activity, phosphate solubilization, biofilm, Indole acidic acid (IAA), exopolysaccharide, and alginate production abilities under different abiotic stress conditions. Finally, a greenhouse experiment was conducted to evaluate the effect of selected bacterial endophyte inoculation in G. superba for growth enhancement and secondary metabolite content. The results showed that plants treated with NBRI HYL5 and NBRI HYL8 significantly enhanced the colchicine content (97–98 %) and gloriosine content (70–73 %), respectively as compared with control. However, inoculation of NBRI LYN9 has demonstrated significant enhancement only in gloriosine content (79 %). In addition, NBRI HYL5 and NBRI HYL8 have demonstrated significant improvement in overall vegetative growth parameters, photosynthetic pigments, and total soluble sugar content. Colonization and persistence of selected endophytic bacteria in G. superba rhizome and shoot clearly depicted the involvement not only in enhancing the vegetative growth but also in enhancing the colchicine and gloriosine content. Overall, this study presents the beneficial role of endophytic Bacillus strains in enhancing the growth of G. superba and secondary metabolite content may lead to contribute in sustainable cultivation of economically important medicinal plants.

Cupriavidus metallidurans bacteria enhance sodium uptake by plants

Here we report that Cupriavidus metallidurans bacteria increase sodium (Na+) accumulation in Arabidopsis thaliana and quinoa (Chenopodium quinoa). Given the metal mobilizing feature of the bacteria, we tested this hypothesis that the bacteria can increase the uptake of Na+, a metal ion, by plants. In agar plate assays under salinity conditions, the bacterial inoculation significantly decreased plant biomass by 280% and 20% in Arabidopsis and quinoa, respectively. In pot experiments under the salinity conditions, the bacterial inoculation resulted in about 60% loss of the quinoa plant biomass. We detected a significant high accumulation of Na+ in the leaf and stem tissues of the bacteria-inoculated quinoa plants, suggesting an association between increased Na+ accumulation and bacteria-mediated growth retardation in the plants. Altogether we report a novel phenomenon, in which bacteria increase Na+ uptake by plants.

Role of Bacterial Inoculant and Organic Matter in Improving some Soil Physical Properties and Water use Efficiency of Maize under Drought Conditions in Iraq

Field experiment was carried out at the Agricultural Research Directorate Research Station, Ministry of Science and Technology in Autumn 2018 to study the role of liquid bacterial inoculant and addition of organic matter in improving physical properties, water consumption and water use efficiency of the maize crop (Zea mays L.) under drought conditions prevailing in Iraq. Bacterial inoculated was added with two levels with, without adding, adding organic fertilizer at three levels (0, 1.5 and 3%) of the soil weight. Irrigation was scheduled when depleting (50, 60 and 70%) of the available water. Water consumption were 584, 437 and 317 mm under (50, 60 and 70%) of available water depletion respectively. The addition of bacterial inoculant and 3% organic matter was significantly superior to treatments at 50 and 60% of available water depletion. Saturated hydraulic conductivity and soil aggregate stability under these two treatments were 1.81 and 1.75 cm h−1 and 0.530 and 0.524% respectively. The grain yield was 12.321 and 12.162 t ha−1 under the above-mentioned treatments respectively. The highest rate of water use efficiency was 2.98 kg m−3 under 60 % moisture depletion, with bacterial inoculant and under addition of organic matter at the level of 3%.

First report in South Korea of a bacterial leaf blight of oats caused by Pseudomonas salomonii.

In March 2020, approximately 20% of leaves in a commercial oat field growing Avena sativa (cv. Samhan) in Jeongeup, Korea (35.3859°, 126.5607°), displayed leaf blight in the seedling stage of development. The lesions observed in 2020 were of a yellow discoloration that spread from the leaf tip downward with minimal brown delineation (Fig. S1A). These symptoms differed from the haloes delineated at the edges by extensive brown necrosis caused by Pseudomonas coronofaciens (Kim 2020a; Fig. S1C). To isolate the causal agent, 3-cm-long pieces of symptomatic leaves from ten different oat plants were disinfected by submersion in 70% ethanol for 5 min followed by immersion in 1% sodium hypochlorite for 5 min and rinsing extensively with sterile distilled water. The air-dried segments were transferred intact to nutrient agar, and only one colony type (yellow-colored, wet, with a shiny convex surface) was observed. After single colony isolation, three isolates from different 2020 field-grown diseased leaves, termed 2007, 2009, and 2011, were selected at random. The isolates produced fluorescent siderophores on King's medium B and triggered a hypersensitive response (HR) when infiltrated into tobacco (cv. Xanthi) leaves (Fig. S1D). Multilocus sequence typing analysis with four housekeeping genes was used for taxonomic identification of these isolates (Maiden et al. 1998). The 16S rRNA sequences were amplified with the 27F/1492R universal primers (Weisburg et al. 1991). The primers for three housekeeping genes were designed using genome sequence of P. coronaficiens X-1 causing halo blight disease in Korea (NZ_CP050260.1, Kim, 2020b). The products obtained had sizes of 640 bp for gltA (using primers F: 5'-CCT GGT AGC CAA GAT GCC GAC-3'; R: 5'-CAA AGA TCA CGG TGA ACA TGC TGG-3'), 710 bp for gyrB (with primers F: 5'-TCG GCA GCC GAG GTC ATC ATG AC-3'; R: 5'-TTG TCT TTG GTC TGC GAG CTG AA-3'), and 870 bp for rpoD ( with primers F: 5'-GTG AAG GCG AAA TCG AAA TCG-3'; R: 5'-CCG ATG TTG CCT TCC TGG ATC AG-3'). The concatenated sequences (2,353 bp/2,376 bp) had 99% identity with the gene sequences from P. salomonii type strain (AY091528.1, NZ_FNOX01000003, LC486864.1, LC486849.1), but lesser identity (90%) with P. coronafaciens (Fig. S2). Pathogenicity of the Korean isolates was confirmed by fulfilling Koch's postulates using leaves of 2 week-old greenhouse-grown 'Samhan' seedlings. Plants (n=50) were sprayed with 108 cfu/ml bacterial suspensions in water or with sterile water as controls. The plants were incubated for a week at 23 °C in 100% relative humidity under a 10 h light/14 h dark photoperiod. Five days after bacterial inoculation, yellow discoloration appeared at the leaf tips which progressed downward with time (Fig. S1B). Three bacterial isolates extracted from yellowed, inoculated leaves had 16S rRNA gene sequences identical to that of P. salomonii Korean isolates, 2007, 2009 and 2011, and they caused the anticipated symptoms when inoculated into oat leaves. These findings indicate that P. salomonii should be added to the potential pathogens of oats grown in Korea. Understanding whether spring weather conditions (warmth and humidity) boost this oat disease will help devise disease alert systems for farmers (Anderson 2004; Chakraborty 2005).