Plant Growth-promoting Bacteria Strains Research Articles

The Prostrate Spurge-isolated PGPB Endophytes, EP1-AS, and EP1-BM That Can Tolerate High Levels of Salinity and Heavy Metals and Allow Wheat Growth Under These Stressors

This research investigates the potential of two Plant Growth-Promoting Bacteria (PGPB) strains, EP1-AS and EP1-BM, isolated from the halophyte Euphorbia prostrata, to enhance plant growth and provide abiotic stress resilience. The study addresses the urgent need for sustainable agricultural practices in the face of challenges like soil salinization and heavy metal contamination. The investigation comprehensively analyzes the heavy metal and salt tolerance of the PGPB strains, revealing their potential applications in promoting plant growth under adverse environmental conditions. The research further explores the impact of these PGPB strains on wheat plants subjected to varying concentrations of heavy metals and salts. Results indicate that both PGPB strains, especially EP1-BM, exhibit significant tolerance to heavy metals and salt stress. EP1-BM demonstrates remarkable resilience even under high concentrations of these stressors. The study extends its findings to in vitro testing on wheat plants, revealing the positive influence of PGPB strains on germination, shoot length, and root length in the presence of salt and heavy metals. This research underscores the significance of understanding plant-microbe interactions, particularly in the context of promoting sustainable agriculture in challenging environments. The identified resilience of PGPB strains, especially EP1-BM, suggests their potential application as bio-remediators and plant growth promoters in soils affected by salinity and heavy metal stress. The promising results observed will be followed-up field trials. They will highlight the translational potential of these PGPB strains, offering a novel avenue for developing biofertilizer formulations with a cautious approach to safety concerns. Overall, this study contributes valuable insights into harnessing the untapped potential of resilient plants and their associated microbial communities for sustainable agriculture. It addresses key global challenges outlined by the United Nations Sustainable Development Goals.

Bio-priming Treatment with PGPB Strains in Cowpea Production Increases Grain Yield and Net Income

In the 21st century, the use of beneficial microorganisms as biological fertilizers has become a notable phenomenon, driven by the ongoing search for sustainable solutions due to environmental issues associated with synthetic fertilizer use. This study aimed to investigate the effect of bio-priming with plant growth-promoting bacteria (PGPB) strains comparing them with synthetic fertilizer and rhizobium inoculation in Siirt ecological conditions. The field experiment was laid out according to a completely randomized design with four replications in the arable land of Siirt University (Siirt, Türkiye) during the 2019 summer season. Three synthetic fertilizer doses as diammonium phosphate (SF1: 100 kg ha-1, SF2: 200 kg ha-1, SF3: 300 kg ha-1) and seven biological fertilizer treatments (B1: TV61C, B2: TV62C, B3: TV126C, B4: TV24C, B5: TV53D, BMIX: TV119E+TV126C, RZB: Bradyrhizobium sp.) were compared with control (no fertilization+hydro-priming) in the study. The research results indicated that 300 kg ha-1 DAP and PGPB consortia showed the best results on agronomic characteristics. However, particularly when applied in the form of a consortium, PGPB strains exhibited performance very close to synthetic fertilization. Moreover, it was determined that 300 kg ha-1 DAP and PGPB consortia increased grain yield over hydro-primed plants by 54.6% and 42.4%, while they provided a net income of $654 and $721.6, respectively. Thus, bio-priming with PGPB increased higher net income compared with synthetic fertilizer due to lower treatment costs. In conclusion, bio-priming with PGPB strains has the potential of useful, sustainable and cost-effective strategy in cowpea production.

Antioxidative Response of Duckweed (Lemna minor L.) to Rhizosphere-Associated Pseudomonas Strains and Exogenous Indole-3-Acetic Acid

Aquatic plants, just like terrestrial plants, are exposed to oxidative stress. However, their responses are still under-researched. In this study, we examined the physiological and antioxidative responses of an aquatic plant, duckweed (Lemna minor L.), to four indole-3-acetic acid (IAA)-degrading and -producing Pseudomonas bacteria (Pseudomonas oryzihabitans D1-104/3, P. putida A3-104/5, P. gessardii C31-106/3 and P. yamanorum C44-104/1) and/or a supraphysiological level of IAA (10 mg L−1). Growth characteristics, total photosynthetic pigment content, histochemical localization of reactive oxygen species and antioxidant enzyme activity (SOD, CAT and POX) were evaluated at two time points, after 3 and 7 days of co-cultivation. Superoxide anion and hydrogen peroxide were produced and accumulated mainly in the roots, daughter fronds and veins of duckweeds. Duckweeds’ responses depended on the strain of Pseudomonas, time and exogenous IAA. Co-cultivation of duckweed with bacteria has positive or neutral effects. Exogenous application of IAA had a negative or neutral effect on enzyme activity and other parameters. Co-cultivation with P. gessardii C31-106/3 showed plant-growth-promoting effects on duckweed: increased biomass production, modulation of duckweeds’ antioxidant enzymatic activity and reduction in hydrogen peroxide content. This study widens our knowledge of aquatic plants and their response to oxidative stress, supports the hypothesis that plant growth-promoting bacteria (PGPB) induce tolerable levels of oxidative stress in plants and introduces a new PGPB strain, P. gessardii C31-106/3.

Identification of antimicrobial compounds from the plant growth promoting bacteria (PGPR) tested against Fusarium wilt of tomato caused by Fusarium oxysporum f.sp. Lycopersici

Infections and pests affecting plants pose significant threats to global food security. Over the top utilize of chemical pesticides is frequently utilized to diminish the impacts of plant illnesses caused by bacterial and parasitic pathogens. The greatest concern as we work towards more feasible horticulture is expanding agrarian efficiency for a developing populace. Microbial biocontrol operators (MBCAs) have illustrated their viability as a green procedure to oversee plant illnesses, invigorate edit development and execution, and increment yields. Other than their growth-promoting part, plant growth-promoting bacteria/fungi (PGPR/PGPF) can stifle plant illnesses by creating inhibitory chemicals and actuating a plant resistant reaction against plant pathogens. As biofertilizers and biopesticides, PGPR and PGPF are considered financially practical and appealing strategies for economical horticulture; This leads to a “win–win” circumstance. A few strains of PGPR and PGPF have been distinguished as compelling BCAs beneath controlled natural conditions. In common, any MBCA must overcome certain challenges some time recently it can be enrolled or broadly utilized for disease/pest control. Viable MBCA gives a down to earth arrangement to progress nursery edit execution with decreased fertilizer inputs and chemical pesticide utilization. This current audit points to fill the current crevice in information on plant growth-promoting microorganisms (PGPM), drawing consideration to the logical premise for arrangement, improvement proposals and extra investigate related to commercial utilize of PGPM.

A novel Biochar-PGPB strategy for simultaneous soil remediation and safe vegetable production

There is currently increasing pressure on agriculture to simultaneously remediate soil and ensure safe agricultural production. In this study, we investigate the potential of a novel combination of biochar and plant growth-promoting bacteria (PGPB) as a promising approach. Two types of biochar, corn stover and rice husk-derived, were used in combination with a PGPB strain, Bacillus sp. PGP5, to remediate Cd and Pb co-contaminated soil and enhance lettuce performance. The contaminated soil was pre-incubated with biochar prior to PGP5 inoculation. The combined application of biochar and PGPB reduced the diethylenetriaminepentaacetic acid (DTPA) -extractable Cd and Pb concentrations in the soil by 46.45%–55.96% and 42.08%–44.83%, respectively. Additionally, this combined application increased lettuce yield by 23.37%–65.39% and decreased Cd and Pb concentrations in the edible parts of the lettuce by 57.39%–68.04% and 13.57%–32.50%. The combined application showed a better promotion on lettuce growth by facilitating chlorophyll synthesis and reducing oxidative stress. These demonstrated a synergistic effect between biochar and PGPB. Furthermore, our study elucidated the specific role of the biochar-PGPB combination in soil microbial communities. Biochar application promoted the survival of PGP5 in the soil. The impact of biochar or PGPB on microbial communities was found to be most significant in the early stage, while the development of plants had a greater influence on rhizosphere microbial communities in later stage. Plants showed a tendency to recruit plant-associated microbes, such as Cyanobacteria, to facilitate growth processes. Notably, the combined application of biochar and PGPB expedited the assembly of microbial communities, enabling them more closely with the rhizosphere microbial communities in late stage of plant development and thus enhancing their effects on promoting plant growth. This study highlights the “accelerating” advantage of the biochar-PGPB combination in the assembly of rhizosphere microbiomes and offers a new strategy for simultaneous soil remediation and safe agricultural production.

Response strategies of slash pine (Pinus elliottii) to cadmium stress and the gain effects of inoculation with Herbaspirillum sp. YTG72 in alleviating phytotoxicity and enhancing accumulation of cadmium.

Phytoremediation using fast-growing woody plants assisted by plant growth-promoting bacteria (PGPB) on cadmium (Cd)-contaminated sites is considered a promising technique; however, its remediation efficiency is still affected by multiple factors. In this study, the mining areas' soil conditions were simulated with different Cd addition levels (0, 3, 6, 9mgkg-1) in order to investigate the response strategy to Cd stress of fast-growing economic tree species, slash pine (Pinus elliottii), and the effects of inoculation with the PGPB strain Herbaspirillum sp. YTG72 on the physiological activity and Cd accumulation of plants. The main results showed that there were significant (p < 0.05) increases in contents of chlorophyll and nutrient elements (P, K, Ca, and Mg) at low Cd addition level (3mgkg-1) compared to non-Cd addition treatment. When the additive amount of Cd increased, the growth of plants was severely inhibited and the content of proline was increased, as well as Cd in plants. Besides, the ratios of K:P, Ca:P, and Mg:P in plants were negatively correlated with the contents of Cd in plants and soils. Inoculation of P. elliottii with the PGPB strain Herbaspirillum sp. YTG72 improved the physiological functions of the plants under Cd stress and activated the antioxidant system, reduced the accumulation of proline, and decreased the ratios of K:P, Ca:P, and Mg:P in plant. More importantly, planting P. elliottii in Cd-contaminated soil could significantly (p < 0.05) reduce the Cd content in the rhizosphere soil, and furthermore, inoculation treatment could promote the reduction of soil Cd content and increased the accumulation of Cd by root. The results of the present study emphasized the Cd response mechanism of P. elliottii based on multifaceted regulation, as well as the feasibility of strain Herbaspirillum sp. YTG72 assisted P. elliottii for the remediation on Cd-contaminated sites.

The effects of plant growth-promoting bacteria on seed germination and seedling growth in Crassocephalum rubens

Crassocephalum rubens, a herb with potential anticancer properties, encounters challenges in production efficiency due to small seed size and elevated temperatures in cultivation areas. Our study investigates the effects of seed pelleting and plant growth-promoting bacteria (PGPB) on germination and seedling growth across temperature variations in Taiwan. Pelleted seeds demonstrate superior germination percentages linked to enhanced seed quality. Elevated temperature, particularly at 30/25 °C, enhanced germination performance, with the highest final germination percentage observed in pelleted seeds treated with water. Unexpectedly, PGPB strains— Klebsiella sp. KsGRB10 and Bacillus sp. BsGFB04—exhibited limited impact on germination rates, showing a marginal increase in seedling growth under 25/20 °C and 30/25 °C, respectively. Air temperature fluctuations influenced seedling vigor, leaf color, and physiological parameters. Remarkably, inoculation with BsGFB04 and KsGRB10 enhanced C. rubens’ tolerance to high-temperature stress conditions. Diurnal measurements in week 4, under 25/20 °C, reveal that PGPB inoculation decreased stomatal conductance and transpiration rate while maintaining the quantum yield of PSII, indicating potentially improved water-use efficiency. This study provides crucial insights into the interplay among PGPB, environmental stress, and the physiology of a wild species, paving the way for further research in the domestication of C. rubens for medicinal herb mass production.

Exploration and Profiling of Potential Thermo-alkaliphilic Bacillus licheniformis and Burkholderia sp. from varied Soil of Delhi region, India and their Plant Growth-Promoting Traits

Soilless cultivation has emerged as a fundamental alternative for large-scale vegetable production because it generates high-quality yields and uses resources efficiently. While plant growth-promoting bacteria (PGPB) are known to enhance growth and physiological aspects in crops grown in soil, their application in soilless cultivation has been relatively less explored. This study aimed to isolate potential PGPBs from soil samples collected from five locations in and around the Delhi-National Capital Region (NCR), India, which were further screened for significant PGPB attributes. Among these, 51 isolated were selected for assessing the impact on Oryza sativa (rice) growth and yield grown on a hydroponic set. The results indicated that isolates AFSI16 and ACSI02 significantly improved the physiological parameters of the plants. For instance, treatment with AFSI16 showed a 23.27% increase in maximum fresh shoot mass, while ACSI02 resulted in a 46.8% increase in root fresh mass. Additionally, ACSI02 exhibited the highest shoot length (34.07%), whereas AFSI16 exhibited the longest root length (46.08%) in O.sativa. Treatment with AFSI16 also led to significant increases in total protein content (4.94%) and chlorophyll content (23.44%), while ACSI02 treatment showed a 13.48% increase in maximum carotenoid content in the leaves. The potential PGPBs were identified through 16S rRNA sequencing, as the two most effective strains, AFSI16 and ACSI02, belonged to thermo-alkaliphilic Bacillus licheniformis and Burkholderia sp., respectively. This study demonstrated the potential of these identified PGPB strains in enhancing crop performance, specifically in soilless cultivation systems.

Interaction of Zinc Mineral Nutrition and Plant Growth-Promoting Bacteria in Tropical Agricultural Systems: A Review.

The relationship between zinc mineral nutrition and plant growth-promoting bacteria (PGPB) is pivotal in enhancing agricultural productivity, especially in tropical regions characterized by diverse climatic conditions and soil variability. This review synthesizes and critically evaluates current knowledge regarding the synergistic interaction between zinc mineral nutrition and PGPB in tropical agricultural systems. Zinc is an essential and fundamental micronutrient for various physiological and biochemical processes in plants. Its deficiency affects plant growth and development, decreasing yields and nutritional quality. In tropical regions, where soil zinc availability is often limited or imbalanced, the PGPB, through different mechanisms such as Zn solubilization; siderophore production; and phytohormone synthesis, supports Zn uptake and assimilation, thereby facilitating the adverse effects of zinc deficiency in plants. This review outlines the impacts of Zn-PGPB interactions on plant growth, root architecture, and productivity in tropical agricultural systems. The positive relationship between PGPB and plants facilitates Zn uptake and improves nutrient use efficiency, overall crop performance, and agronomic biofortification. In addition, this review highlights the importance of considering indigenous PGPB strains for specific tropical agroecosystems, acknowledging their adaptability to local conditions and their potential in sustainable agricultural practices. It is concluded that Zn fertilizer and PGPBs have synergistic interactions and can offer promising avenues for sustainable agriculture, addressing nutritional deficiencies, improving crop resilience, and ensuring food security.

Growth performance and metabolic changes in lettuce inoculated with plant growth promoting bacteria in a hydroponic system

Crop cultivation in hydroponic systems is often exposed to both abiotic and biotic stresses, which impact growth. One possible approach to alleviating these stresses and improving plant growth is by utilizing plant growth-promoting bacteria (PGPB). Our previous study has shown the efficacy of two PGPB strains, Pseudomonas lundensis UB 53 and Pseudomonas migulae UB 54, in promoting growth and stimulating the generation of plant defense enzymes to mitigate biotic and abiotic stress in lettuce grown in a nutrient film technique (NFT) hydroponic system. Therefore, this study purposed to assess metabolic changes in lettuce in response to P. lundensis UB 53 and P. migulae UB 54 inoculation in a NFT hydroponic system. The results exhibited that these bacteria enhanced IAA accumulation and lettuce growth in a NFT hydroponic system. A total of 58 metabolites were detected in the root samples, including primary and secondary metabolites. It also influenced 12 metabolic pathways, with emphasis on five pathways, including the metabolism of alpha-linolenic acid, inositol phosphate, pyruvate, sulfur, and the phosphatidylinositol signaling system. These results highlight the significant roles of myo-inositol and acetic acid in metabolic pathways during the interaction between lettuce and PGPB.

Functional Characterization and Localization of Plant-Growth Promoting Bacteria Grown Under Stressful Conditions.

Various bacterial species are associated with plant roots. However, symbiotic and free-living plant growth-promoting bacteria (PGPB) can only help plants to grow and develop under normal and stressful conditions. Several biochemical and in vitro assays were previously designed to differentiate between the PGPB and other plant-associated bacterial strains. This chapter describes and summarizes some of these assays and proposes a strategy to screen for PGPB. To determine the involvement of the PGPB in abiotic stress tolerance, assays for the ability to produce 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, ammonium, gibberellic acid (GA), indole acetic acid (IAA), and microbial volatile organic compounds (mVOCs) are described in this chapter. Additionally, assays to show the capacity to solubilize micronutrients such as potassium, phosphorus, and zinc by bacteria were also summarized in this chapter. To determine the contribution of the PGPB in biotic stress tolerance in plants, Fe-siderophore, hydrogen cyanide, and antibiotic and antifungal metabolites production assays were described. Moreover, assays to investigate the growth-promotion activities of a bacterium strain on plants, using the gnotobiotic root elongation, in vitro, and pots assays, were explained. Finally, an assay for the localization of endophytic bacterium in plant tissues was also presented in this chapter. Although the assays described in this chapter can give evidence of the nature of the mechanism behind the PGPB actions, other unknown growth-promoting means are yet to decipher, and until then, new methodologies will be developed.

Genetic architecture of the response of Arabidopsis thaliana to a native plant-growth-promoting bacterial strain.

By improving plant nutrition and alleviating abiotic and biotic stresses, plant growth-promoting bacteria (PGPB) can help to develop eco-friendly and sustainable agricultural practices. Besides climatic conditions, soil conditions, and microbe-microbe interactions, the host genotype influences the effectiveness of PGPB. Yet, most GWAS conducted to characterize the genetic architecture of response to PGPB are based on non-native interactions between a host plant and PGPB strains isolated from the belowground compartment of other plants. In this study, a GWAS was set up under in vitro conditions to describe the genetic architecture of the response of Arabidopsis thaliana to the PGPB Pseudomonas siliginis, by inoculating seeds of 162 natural accessions from the southwest of France with one strain isolated from the leaf compartment in the same geographical region. Strong genetic variation of plant growth response to this native PGPB was observed at a regional scale, with the strain having a positive effect on the vegetative growth of small plants and a negative effect on the vegetative growth of large plants. The polygenic genetic architecture underlying this negative trade-off showed suggestive signatures of local adaptation. The main eco-evolutionary relevant candidate genes are involved in seed and root development.

Evaluation of Biocontrol Potential of Bacillus spp. and Pseudomonas fluorescens UM270 against Postharvest Fungal Pathogens

Fungal pathogens are the main causal agents of postharvest diseases of fruits and vegetables. To prevent this problem and avoid the use of harmful chemical fungicides, safer and greener alternatives have been sought. One of these alternatives is the use of plant-growth-promoting bacteria (PGPB). In this study, we evaluated in vitro four well-known PGPB strains (Pseudomonas fluorescens UM270, Bacillus toyonensis COPE52, Bacillus sp. E25, and Bacillus thuringiensis CR71) for their biocontrol potential against nineteen postharvest fungal pathogens. In vivo assays were also performed, and bacterial cells were inoculated on harvested strawberries and grapes with the pathogens Botrytis cinerea, Alternaria alternata, and Fusarium brachygibbosum to evaluate loss of firmness and disease incidence. Our results show that the four strains antagonized fungi in direct and indirect confrontation assays. Stronger antagonism was observed by the action of diffusible metabolites (DMs) compared to volatile organic compound (VOC) activity. All PGPB significantly improved the fruit firmness and reduced disease incidence caused by the fungal pathogens tested. However, strain UM270 showed excellent biocontrol activity, reducing the disease incidence of Fusarium brachygibbosum, Botrytis cinerea, and Alternaria alternata on strawberry fruits by 60%, 55%, and 65%, respectively. Diffusible antifungals and VOCs such as 2,4-diacetyl phloroglucinol, siderophores, auxins, fengycins, and N, N-dimethyl-hexadecyl amine, among others, might be responsible for the beneficial activities observed. These results suggest excellent biocontrol activities to inhibit postharvest pathogenic fungi and improve harvested fruit quality.

Characterizing indigenous plant growth promoting bacteria and their synergistic effects with organic and chemical fertilizers on wheat (Triticum aestivum).

The excessive use of chemical fertilizers is deteriorating both the environment and soil, making it a big challenge faced by sustainable agriculture. To assist the efforts for the solution of this burning issue, nine different potential native strains of plant growth-promoting bacteria (PGPB) namely, SA-1(Bacillus subtilis), SA-5 (Stenotrophomonas humi),SA-7(Azospirillum brasilense), BH-1(Azospirillum oryzae), BH-7(Azotobacter armeniacus), BH-8(Rhizobium pusense), BA-3(Azospirillum zeae), BA-6(Rhizobium pusense), and BA-7(Pseudomonas fragi) were isolated that were characterized morphologically, biochemically and molecularly on the basis of 16S rRNA sequencing. Furthermore, the capability of indigenous PGPB in wheat (Triticum aestivum, Chakwal-50) under control, DAP+FYM, SA-1,5,7, BH-1,7,8, BA-3,6,7, DAP+ FYM + SA-1,5,7, DAP+FYM+ BH-1,7,8 and DAP+FYM+ BA-3,6,7 treatments was assessed in a randomized complete block design (RCBD). The results of the study showed that there was a significant increase in plant growth, nutrients, quality parameters, crop yield, and soil nutrients at three depths under SA-1,5,7, BH-1,7,8, and BA-3,6,7 in combination with DAP+FYM. Out of all these treatments, DAP+ FYM + BA-3,6,7 was found to be the most efficient for wheat growth having the highest 1000-grain weight of 55.1 g. The highest values for plant height, no. of grains/spike, spike length, shoot length, root length, shoot dry weight, root dry weight, 1000 grain weight, biological yield, and economic yield were found to be 90.7 cm, 87.7 cm, 7.20 cm, 53.5 cm, 33.5 cm, 4.87 g, 1.32 g, 55.1 g, 8209 kg/h, and 4572 kg/h, respectively, in the DAP+FYM+BA treatment. The DAP+FYM+BA treatment had the highest values of TN (1.68 µg/mL), P (0.38%), and K (1.33%). Likewise, the value of mean protein (10.5%), carbohydrate (75%), lipid (2.5%), and available P (4.68 ppm) was also highest in the DAP+FYM+BA combination. C:P was found to be significantly highest (20.7) in BA alone but was significantly lowest (11.9) in DAP+FYM+BA. Hence, the integration of strains BA-3, BA-5, and BA-7 in fertilizers can be regarded as the most suitable choice for agricultural growth in the sub-mountainous lower region of AJK. This could serve as the best choice for sustainable wheat growth and improved soil fertility with lesser impacts on the environment.

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.

Grain quality and yield response of rice to application of plant growth-promoting bacteria and amino acids

To investigate the effects of foliar application of plant growth-promoting bacteria (PGPB) and amino acids (AAs) on grain yield, nutrient concentrations and protein content of rice grain, a field experiment was conducted as a split-plot in a randomized complete block design with three replications during 2019-2020. The experimental treatments included the PGPB at five levels (control, P. agglomerans strain O4 (PGPB1), P. putida strain P13 + P. agglomerans strain P5 (PGPB2), P. koreensis strain S14 + P. vancouverensis strain S19 (PGPB3), and PGPB1 + PGPB2 + PGPB3 (PGPB4) as main plots and AAs at four levels (control, methionine, lysine, and methionine + lysine) as sub-plots. The results indicated that PGPB significantly enhanced the grain yield, protein content and nutrient uptake in rice grains when compared with control plants. However, the plants treated with co-application of PGPB strains (PGPB4) showed higher yield, higher protein accumulation and greater nutrients uptake such as N, P, K and Fe compared with individual application of PGPB strains and untreated plants. Among the separate application of PGPB strains, rice plants treated with PGPB1 with capability to N-fixing had the potential for enhance yield and improve protein and nutrients accumulation. The combined foliar application of AAs had greatest impact in increasing yield and improving rice grain quality in terms of protein content and uptake of nutrients, especially N, Ca and Fe in grain. Overall, our results suggest that co-applications of PGPB strains (PGPB4) and using a mixture of two AAs (methionine + lysine) may find value as plant growth-promoting for increasing rice yield and quality.

Evaluation of brassinosteroids and plant growth-promoting bacteria on the growth and yield of Lactuca sativa L. under soilless cultivation conditions

Soilless crops have become an important alternative for large-scale vegetable production because of the quality of their products and optimization of resources. Brassinosteroids (Brs) and Plant Growth-Promoting Bacteria (PGPB), has been reported to promote growth and physiological parameters in soil crops, but there are few reports on the application of these compounds in soilless crops. The effects of Brs ((25R)-3β 5α-dihydroxy-spirostan-6-one) and three strains of PGPB (Bacillus velezensis, Pseudomona sp., and Azospirillum brasilense) on the growth and yield of lettuce under hydroponic conditions were evaluated. Two separate experiments were carried out: one using a substrate in pots under greenhouse conditions and the other using a deep-flow hydroponic system in a growth room with artificial LED lighting. Plant physiological parameters (yield, dry weight, root surface area, and leaf area) and PGPB attributes under in vitro tests (phosphate solubilization and indole-3-acetic acid (IAA) synthesis) were determined using in vitro tests. A completely randomized design was used in all experiments. The results showed that in in vitro tests Azospirillum brasilense and Pseudomonas sp. were the strains that synthesized the highest amounts of IAA (36 mg mL−1 and 34 mg mL−1, respectively). Phosphorus solubilization was significantly higher in the Pseudomonas sp. strain (110.35 µg mL−1). Regarding physiological and quality parameters, the application of Brs (0.5 ppm), Bacillus velezensis, and Azospirillum brasilense (1 × 106 CFU mL−1) caused an increase between 20% and 40% on variables such as plant yield, leaf area, root surface area, and colorimetry of lettuce for substrate or hydroponic conditions, respectively.

Comparative Functional Genome Analysis Reveals the Habitat Adaptation and Biocontrol Characteristics of Plant Growth-Promoting Bacteria in NCBI Databases.

Plant growth-promoting bacteria (PGPB) are a group of beneficial microorganisms that include 60 bacterial genera, such as Bacillus, Pseudomonas, and Burkholderia, which widely colonize plant leaves and soil, promote plant growth, and/or inhibit pathogen infection. However, the genetic factors underpinning adaptation of PGPB to plant leaves and soil remain poorly understood. In this study, we performed a comparative functional genome analysis approach to investigate the functional genes of 195 leaf-associated (LA) and 283 soil-associated (SA) PGPB strains and their roles in adapting to their environment, using 95 strains from other-associated (OA) environmental habitats with growth-promoting or antimicrobial functions as negative controls. Comparison analysis of the enrichment of nonredundant (NR) protein sequence databases showed that cytochrome P450, DNA repair, and motor chemotaxis genes were significantly enriched in LA PGPB strains related to environmental adaptation, while cell wall-degrading enzymes, TetR transcriptional regulatory factors, and sporulation-related genes were highly enriched in SA PGPB strains. Additionally, analysis of carbohydrate-active enzymes demonstrated that glycosyltransferases (GTs) and glycoside hydrolases (GHs) were abundant families in all PGPB strains, which is in favor of plant growth, and enriched in SA PGPB strains. Except for most Bacillus strains, SA PGPB genomes contained significantly more secondary metabolism clusters than LA PGPB. Most LA PGPB contained hormone biosynthesis genes, which may contribute to plant growth promotion, while SA PGPB harbored numerous carbohydrate and antibiotic metabolism genes. In summary, this study further deepens our understanding of the habitat adaptation and biocontrol characteristics of LA and SA PGPB strains. IMPORTANCE Plant growth-promoting bacteria (PGPB) are essential for the effectiveness of biocontrol agents in plant phyllosphere and rhizosphere. However, little is known about the ecological adaptation of PGPB to different habitats. In this study, comparative functional genome analysis of leaf-associated (LA), soil-associated (SA), and other-associated (OA) PGPB strains was performed. We found that genes related to the metabolism of hormones were enriched in LA PGPB. Carbohydrate and antibiotic metabolism genes were enriched in SA PGPB, which likely facilitated their adaptation to the plant growth environment. Our findings provide genetic insights on LA and SA PGPB strains' ecological adaptation and biocontrol characteristics.

Complete genome analysis of sugarcane root associated endophytic diazotroph Pseudomonas aeruginosa DJ06 revealing versatile molecular mechanism involved in sugarcane development.

Sugarcane is an important sugar and bioenergy source and a significant component of the economy in various countries in arid and semiarid. It requires more synthetic fertilizers and fungicides during growth and development. However, the excess use of synthetic fertilizers and fungicides causes environmental pollution and affects cane quality and productivity. Plant growth-promoting bacteria (PGPB) indirectly or directly promote plant growth in various ways. In this study, 22 PGPB strains were isolated from the roots of the sugarcane variety GT42. After screening of plant growth-promoting (PGP) traits, it was found that the DJ06 strain had the most potent PGP activity, which was identified as Pseudomonas aeruginosa by 16S rRNA gene sequencing. Scanning electron microscopy (SEM) and green fluorescent protein (GFP) labeling technology confirmed that the DJ06 strain successfully colonized sugarcane tissues. The complete genome sequencing of the DJ06 strain was performed using Nanopore and Illumina sequencing platforms. The results showed that the DJ06 strain genome size was 64,90,034 bp with a G+C content of 66.34%, including 5,912 protein-coding genes (CDSs) and 12 rRNA genes. A series of genes related to plant growth promotion was observed, such as nitrogen fixation, ammonia assimilation, siderophore, 1-aminocyclopropane-1-carboxylic acid (ACC), deaminase, indole-3-acetic acid (IAA) production, auxin biosynthesis, phosphate metabolism, hydrolase, biocontrol, and tolerance to abiotic stresses. In addition, the effect of the DJ06 strain was also evaluated by inoculation in two sugarcane varieties GT11 and B8. The length of the plant was increased significantly by 32.43 and 12.66% and fresh weight by 89.87 and 135.71% in sugarcane GT11 and B8 at 60 days after inoculation. The photosynthetic leaf gas exchange also increased significantly compared with the control plants. The content of indole-3-acetic acid (IAA) was enhanced and gibberellins (GA) and abscisic acid (ABA) were reduced in response to inoculation of the DJ06 strain as compared with control in two sugarcane varieties. The enzymatic activities of oxidative, nitrogen metabolism, and hydrolases were also changed dramatically in both sugarcane varieties with inoculation of the DJ06 strain. These findings provide better insights into the interactive action mechanisms of the P. aeruginosa DJ06 strain and sugarcane plant development.

Bacillus paralicheniformis RP01 Enhances the Expression of Growth-Related Genes in Cotton and Promotes Plant Growth by Altering Microbiota inside and outside the Root.

Plant growth-promoting bacteria (PGPB) can promote plant growth in various ways, allowing PGPB to replace chemical fertilizers to avoid environmental pollution. PGPB is also used for bioremediation and in plant pathogen control. The isolation and evaluation of PGPB are essential not only for practical applications, but also for basic research. Currently, the known PGPB strains are limited, and their functions are not fully understood. Therefore, the growth-promoting mechanism needs to be further explored and improved. The Bacillus paralicheniformis RP01 strain with beneficial growth-promoting activity was screened from the root surface of Brassica chinensis using a phosphate-solubilizing medium. RP01 inoculation significantly increased plant root length and brassinosteroid content and upregulated the expression of growth-related genes. Simultaneously, it increased the number of beneficial bacteria that promoted plant growth and reduced the number of detrimental bacteria. The genome annotation findings also revealed that RP01 possesses a variety of growth-promoting mechanisms and a tremendous growth-promoting potential. This study isolated a highly potential PGPB and elucidated its possible direct and indirect growth-promoting mechanisms. Our study results will help enrich the PGPB library and provide a reference for plant-microbe interactions.