PGP Traits Research Articles

Exploring the efficacy of drought tolerant, IAA-producing plant growth-promoting rhizobacteria for sustainable agriculture

ABSTRACT The growing human population and abiotic stresses pose significant threats to food security, with PGPR favorable as biofertilizers for plant growth and stress relief. In one study, soil samples from both cultivated and uncultivated plants in various cities were used to isolate rhizobacterial populations. Using 50 soil samples from both cultivated and uncultivated plants, isolated rhizobacterial populations were screened for various biochemical changes, PGP activities and morphological characteristics. A total of 199 rhizobacteria were isolated and screened for IAA production. The strain M28 produced maximum IAA 378.44 ± 2.5 µg ml−1, M9 formed only 34.72 ± 0.15 µg ml−1. About 19% of IAA producers were isolated from Multan, 18% Lahore, 15% from soils of Faisalabad and Sheikhupura, while 7% from Gujrat. The 21 isolates were drought tolerant to −0.14Mpa, 14 of those were PSB and 15 were N fixers. In PGP traits, maximum zinc solubility was expressed by M4 as 2 ± 0.5 cm of zone. The strain M22 produced amount of HCN, 40.12 ± 0.052 ppm. All isolates showed diverse behavior in biocompatibility, motility patterns and hydrophobicity. Selected drought tolerant strains were genetically identified by ribotyping. Multitrait PGPR could be effective biofertilizers rather than with single trait. The strain M28 having highest production of IAA, was gelatinase, methyl red positive and was also capable of nitrogen fixation. Moreover, it had maximum swimming (8.9 mm) and swarming (8.7 mm) activities after 24 h, indicating its best PGP traits for future use.

Cu-tolerant Klebsiella variicola SRB-4 increased the nanoparticle (NP) stress resilience in garden peas (Pisum sativum L.) raised in soil polluted with varying doses of copper oxide (CuO)-NP.

Utilizing metal/nanoparticle (NP)- tolerant plant growth-promoting rhizobacteria (PGPR) is a sustainable and eco-friendly approach for remediation of NP-induced phytotoxicity. Here, Pisum sativum (L.) plants co-cultivated with different CuO-NP concentrations exhibited reduced growth, leaf pigments, yield attributes, and increased oxidative stress levels. Cu-tolerant (800µM) Klebsiella variicola strain SRB-4 (Accession no. OR715781.1) recovered from metal-contaminated soils produced various PGP traits, including IAA, EPS, siderophore, HCN, ammonia, and solubilized insoluble P. The PGP substances were marginally increased with increasing CuO-NP concentrations. When applied, Cu-tolerant SRB-4 strain increased root length (18%), root biomass (15.3%), total chlorophyll (29%), carotenoids (30%), root N (21%), root P (23%), total soluble protein (20%) nodule number (32%), nodule biomass (39%) and leghaemoglobin content (18%) in 50µM CuO-NP-exposed peas. Furthermore, proline, malondialdehyde (MDA), superoxide radical, hydrogen peroxide (H2O2) content, and membrane injury in K. variicola-inoculated and 50µM CuO-NP-treated plants were maximally and significantly (p ≤ 0.05) reduced by 70.6, 26.8, 60.8, and 71.6%, respectively, over uninoculated but treated with similar NP doses. Moreover, K. variicola inoculation caused a significant (p ≤ 0.05) decline in Cu uptake in roots (71%), shoots (65.5%), and grains (76.4%) of peas grown in soil contaminated with 50µM CuO-NP. The multivariate i.e. heat map and pearson correlation analyses between the NP-treated and PGPR inoculated parameters revealed a significant and strong positive corelation. The NP-tolerant indigenous beneficial K. variicola could be applied as an alternative to enhance the production of P. sativum cultivated in nano-polluted soil systems. Additionally, more investigation is required to ascertain the seed/soil inoculation effect of K. variicola SRB-4 on soil biological activities and different crops under various experimental setups.

Phenotypic and Genomic Analysis of Enterobacter ludwigii Strains: Insights into Mechanisms Enhancing Plant Growth Both Under Normal Conditions and in Response to Supplementation with Mineral Fertilizers and Exposure to Stress Factors.

In this research study, we investigated four strains of Enterobacter ludwigii that showed promising properties for plant growth. These strains were tested for their ability to mobilize phosphorus and produce ammonium, siderophores, and phytohormones. The strains exhibited different values of PGP traits; however, the analysis of the complete genomes failed to reveal any significant differences in known genes associated with the expression of beneficial plant traits. One of the strains, GMG_278, demonstrated the best potential for promoting wheat growth in pot experiments. All morphological parameters of wheat were improved, both when GMG_278 was applied alone and when combined with mineral fertilizer. The combined effect we observed may suggest various mechanisms through which these treatments influence plants. The amount of pigments and proline suggests that bacterial introduction operates through pathways likely related to stress resilience. A study on the genetic mechanisms behind plant resilience to stress has revealed a significant upregulation of genes related to reactive oxygen species (ROS) defense after bacterial exposure. It is important to note that, in the initial experiments, the strain showed a significant production of salicylic acid, which is a potent inducer of oxidative stress. In addition, the synthesis of some phytohormones has been restructured, which may affect root growth and the architecture of root hairs. When combined with additional mineral fertilizers, these changes result in a significant increase in plant biomass.

Characterization of multi-trait plant growth-promoting rhizobacteria isolated from alfalfa rhizosphere and evaluation of their efficacy on tomato and watermelon growth

Plant growth-promoting rhizobacteria (PGPR) are free-existing soil-borne bacteria that can be used as bioinoculants in place of chemical fertilizers to directly or indirectly enhance plant growth. This study aimed to characterize PGPR native to the rhizosphere of alfalfa plants in Kayseri and evaluate their efficacy on the growth parameters of tomato and watermelon. A total of 56 potential PGPR isolates were isolated and 24 were selected based on their ability to produce multiple PGP traits. 16S rDNA and phylogenetic analysis characterized these isolates to be novel strains of Pseudomonas, Enterobacter, Acinetobacter, Stenotrophomonas, Staphylococcus, Lycinibacillus, and Bacillus. Sequence analysis revealed nucleotide variations and insertion/deletion mutations in their 16S rRNA genes (nucleotides 913–1408). All selected isolates demonstrated nitrogen fixation ability, whereas 54%, 83%, 71%, 54%, and 38% of isolates possessed genes for phosphate solubilization, indole-3-acetic acid (IAA) synthesis, phytase, ACC deaminase, and siderophore, respectively. Fifty-eight day old tomato and watermelon plants grown from PGPR-treated seeds showed significantly higher improvements in plant height, stem diameter, leaf area, shoot dry weight, and root fresh weight compared to non-inoculated control plants. Furthermore, treatment of watermelon seeds with these isolates significantly increased the fresh weight of shoots and the root dry weights in watermelon plants. Thus, these indigenous PGPR isolates can be used as effective seed inoculants and chemical fertilizer alternatives to enhance tomato and watermelon growth.

The potential role of electric field in enhancement of microbial-assisted phytoremediation of dibutyl phthalate contaminated soil

Dibutyl phthalate (DBP) continues being one of the most frequently detected plasticizers in agricultural soils. Electrokinetic-assisted bioremediation was considered as one of the eco-friendly and sustainable treatment systems for contaminated soils. Moreover, as an auxiliary factor, plant growth promoting rhizobacteria (PGPR) received increasing attention recently in improving phytoremediation efficiency, and the PGP traits might be enhanced by electric fields application. Therefore, the feasibility of the combined application of electricity and PGPR in assisting phytoremediation was innovatively verified in this research. The results showed that the DBP removal efficiency of maize inoculated with PGPR strain DCZL-2 increased from 58 % to 62 % compared to only phytoremediation process. and the electric field further enhanced the contaminated soil remediation (11 %). Interestingly, PGPR promoted the maize absorption of Na+ from DBP-contaminated soil, while the electric field could strengthen the excretion of Na+ from plant cells (19 %). Additionally, DCZL-2 was observed to increase the plants photosynthesis (10 %), and the microcurrent could further improve the photosynthetic efficiency (40 %). Furthermore, compared to the single PGPR-plant group, the increased relative abundance of DBP-degrading bacteria and denitrifying bacteria could enhance DBP biodegradation and soil nutrient cycling. Therefore, in addition to the growth-promoting properties of PGPR on maize growth, the electric fields could further alleviate the DBP stress on plants, thereby achieving higher remediation efficiency. Overall, this study confirmed that the combined use of electricity and PGPR-assisted phytoremediation could ecologically and efficiently remediate DBP-contaminated soil.

Synergistic contributions of plant growth-promoting rhizobacteria and exogenous fulvic acid to enhance phytoremediation efficiency of perfluorooctanoic acid (PFOA)-contaminated soils: Boosting PFOA bioavailability and elevating pak choi tolerance

Perfluorooctanoic acid (PFOA), a synthetic perfluoroalkyl compound, has caused extensive soil contamination over several decades, posing serious health risks to humans through bioaccumulation in plants and subsequent transfer via the food chain. Due to the durability of PFOA in soil and its propensity to migrate and accumulate in plants, phytoremediation has been recognized as an effective remediation method. However, the phytotoxicity of PFOA and the adsorption of PFOA by soil hindered the efficiency of traditional phytoremediation. Therefore, this research employed plant growth-promoting rhizobacteria (PGPR)-assisted phytoremediation, augmented with the bio-stimulant fulvic acid (FA), to devise an effective soil remediation strategy tailored for PFOA contamination removal. The results indicated that Rhizobium sp. strain ZY2, endowed with PGP traits, significantly increased the root weight and shoot weight of pak choi by 194.67 % and 37.38 %, respectively, versus the non-inoculation treatment. Furthermore, inoculation with strain ZY2 enhanced soil alkaline phosphatase, protease, and cellulase activities, bolstering soil nutrient cycling and resource availability. On the other hand, compared to treatment with strain ZY2 alone, additional exogenous FA drastically reduced the residual fraction of PFOA in soil from 34.1 % to 1.9 %, likely mediated by complex electrostatic and hydrophobic interactions between FA and soil components. Ultimately, FA addition increased PFOA concentration in pak choi by 8.1-fold. Furthermore, FA could increase the relative abundance of beneficial rhizosphere bacteria (Actinobacterota and Methylotener, etc.), thereby creating a more favorable microenvironment for plant growth. In conclusion, the combined use of strain ZY2 and FA in phytoremediation notably strengthened plant resilience to PFOA, minimized soil sorption, and achieved high remediation efficacy, offering an effective system to mitigate PFOA-soil pollution's environmental and health risks.

Role of the Pseudomonas koreensis BB2.A.1 and Serratia liquefaciens BB2.1.1 Bacterial Strains in Maize Trace Metal Stress Management.

Plant-growth-promoting rhizobacteria (PGPR), in addition to their well-known direct effects on plant growth and development, have been reported to be effective in plant abiotic (trace metal, drought, etc.) and biotic (phytopathogens, insects, etc.) stress management. PGPRs are involved in shaping the fate of trace metals in the rhizosphere and plants and thus may also reduce trace metal stress in plants. The aims of our study were to isolate and select indigenous trace-metal-resistant PGP strains and investigate their effects on maize germination and early development. The roles of the two selected strains, Pseudomonas koreensis and Serratia liquefaciens isolated from trace-metal-contaminated soil were investigated to mitigate trace metal stress in 21-day-old Zea mays seedlings. In the present study, 13 bacterial strains were isolated and screened for PGP traits under normal and trace metal stress conditions. The effect of two selected strains was further studied on plant experiments. The germination process, plant growth parameters (length, weight, dry matter content), photosynthetic activity, GPOX activity, trace metal accumulation, and translocation in microbes inoculated Cd (0.5 mM), Zn (1 mM), and Cd + Zn (0.1 + 0.5 mM) treated maize plants was studied. Our results revealed that trace metal toxicity, in terms germination and growth parameters and antioxidant enzyme activity, was enhanced upon inoculation with Pseudomonas koreensis BB2.A.1. Chlorophyll content and accumulation studies showed enhanced results following inoculation with Serratia liquefaciens BB2.1.1. Therefore, both bacterial strains possessed beneficial traits that enabled them to reduce metal toxicity in maize.

The ecological hazards of profenofos revealed by soil beneficial-bacteria, plant seedlings, and plasmid nicking assays: A short-term toxicity investigation

Excessive and indiscriminate use of pesticides may adversely affect the growth and activity of both crop plants and soil microbial populations. The reported study was conducted to evaluate the toxicity of profenofos (PF; an organophosphate insecticide) using bacterial (Pseudomonas fluorescens PSB-3 and Enterobacter cloacae ZSB-8) and plant (Coriandrum sativum and Lactuca sativa L.) bioassays. PF was applied at rates of (0–100 µg mL−1) in vitro. Both bacterial strains were sensitive to PF but showed variable tolerance. Following PF exposure, cellular growth, morphology, survival, and inner membrane permeability of bacterial strains were significantly (p < 0.05) altered. Decreased population size coincided with decline in cellular respiration. The 100 µgmL−1 PF dosage imparted maximum impact on ZSB-8, inhibiting populations by 87%. PF also interfered with bacterial surface adherence (i.e., biofilm formation) in a concentration-dependent manner. Alterations in bacterial biomarker enzymatic activity and oxidative stress were also noted. PGP traits of bacterial strains were negatively and significantly (p ≤ 0.05) affected by insecticide. Under PF stress, reduction in indole-3-acetic and siderophore production followed the order: ZSB-8 > PSB-3. PF-induced phytotoxicity was confirmed via reduction in germination, seedling parameters, survival, tolerance, and vigor indices in both plant species. Additionally, PF caused distortion in morphology of root tips and root surfaces. Under CLSM, PF-exposed C. sativum and L. sativa roots exhibited increased oxidative stress. Cellular death in insecticide-treated roots was observed following staining with Evans blue dye. Insecticide concentration-dependent increase in stress markers (proline and MDA content), and antioxidant enzymatic activities in plant seedlings were observed. A dose-dependent conversion of super-coiled form of DNA to open circular in pBR-322 plasmid revealed the genotoxic potential of PF. These findings provide an understanding of toxic effects of profenofos on beneficial microbes and leafy edible vegetables, including their morphological, and cellular effects. Indeed, insecticidal applications deserve special attention due to their potential environmental hazards.

Unraveling the genomic secrets of Tritonibacter mobilis AK171: a plant growth-promoting bacterium isolated from Avicennia marina

The scarcity of freshwater resources resulting in a significant yield loss presents a pressing challenge in agriculture. To address this issue, utilizing abundantly available saline water could offer a smart solution. In this study, we demonstrate that the genome sequence rhizosphere bacterium Tritonibacter mobilis AK171, a halophilic marine bacterium recognized for its ability to thrive in saline and waterlogged environments, isolated from mangroves, has the remarkable ability to enable plant growth using saline irrigation. AK171 is characterized as rod-shaped cells, displays agile movement in free-living conditions, and adopts a rosette arrangement in static media. Moreover, The qualitative evaluation of PGP traits showed that AK171 could produce siderophores and IAA but could not solubilize phosphate nor produce hydrolytic enzymes it exhibits a remarkable tolerance to high temperatures and salinity. In this study, we conducted a comprehensive genome sequence analysis of T. mobilis AK171 to unravel the genetic mechanisms underlying its plant growth-promoting abilities in such challenging conditions. Our analysis revealed diverse genes and pathways involved in the bacterium’s adaptation to salinity and waterlogging stress. Notably, T. mobilis AK171 exhibited a high level of tolerance to salinity and waterlogging through the activation of stress-responsive genes and the production of specific enzymes and metabolites. Additionally, we identified genes associated with biofilm formation, indicating its potential role in establishing symbiotic relationships with host plants. Furthermore, our analysis unveiled the presence of genes responsible for synthesizing antimicrobial compounds, including tropodithietic acid (TDA), which can effectively control phytopathogens. This genomic insight into T. mobilis AK171 provides valuable information for understanding the molecular basis of plant-microbial interactions in saline and waterlogged environments. It offers potential applications for sustainable agriculture in challenging conditions.

Molecular Characterization Reveals Biodiversity and Biopotential of Rhizobacterial Isolates of Bacillus Spp

Bacillus species appearas the most attractive plant growth-promoting rhizobacteria (PGPR) and alternative to synthetic chemical pesticides. The present study examined the antagonistic potential of spore forming-Bacilli isolated from organic farm soil samples of Allahabad, India. Eighty-seven Bacillus strains were isolated and characterized based on their morphological, plant growth promoting traits and molecular characteristics. The diversity analysis used 16S-rDNA, BOX-element, and enterobacterial repetitive intergenic consensus. Two strains, PR30 and PR32, later identified as Bacillus sp., exhibited potent in vitro antagonistic activity against Ralstonia solanaceorum. These isolates produced copious amounts of multiple PGP traits, such as indole-3-acetic acid (40.0 and 54.5 μg/mL), phosphate solubilization index (PSI) (4.4 and 5.3), ammonia, siderophore (3 and 4 cm), and 1-aminocyclopropane-1-carboxylate deaminase (8.1and 9.2 μM/mg//h) and hydrogen cyanide. These isolates were subjected to the antibiotic sensitivity test. The two potent isolates based on the higher antagonistic and the best plant growth-promoting ability were selected for plant growth-promoting response studies in tomatoe, broccoli, and chickpea. In the pot study, Bacillus subtilis (PR30 and PR31) showed significant improvement in seed germination (27–34%), root length (20–50%), shoot length (20–40%), vigor index (50–75%), carotenoid content (0.543–1.733), and lycopene content (2.333–2.646 mg/100 g) in tomato, broccoli, and chickpea. The present study demonstrated the production of multiple plant growth-promoting traits by the isolates and their potential as effective bioinoculants for plant growth promotion and biocontrol of phytopathogens.

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

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

Isolation and characterization of hexavalent chromium-tolerant endophytic bacteria inhabiting Solanum virginicum L. roots: A study on potential for chromium bioremediation and plant growth promotion

Present study was performed with the aim to isolate Heavy metal Tolerant- PGPB (HMT-PGPB) from metal-contaminated site and use them for Cr bioremediation. Six different bacterial strains were obtained from the endosphere of Solanum virginicum L. roots and cultured using nutrient agar media amended with 20 mg/L of Cr(VI). The ability of these Cr(VI) tolerant bacterial isolates were assessed for PGP traits like producing siderophores, indole-3-acetic acid (IAA), and phosphate solubilization. The findings indicated that all of the isolates could produce exopolymeric substances and IAA, five of them could produce siderophores, and three could solubilize phosphate. Furthermore, the minimum inhibitory concentrations of these strains werealso determined. These strains were identified as Bacillus licheniformis SxR1, B. tequilensis SxR2, B. subtilis SxR3, B. velezensis SxR4, B. amyloliquefaciens SxR6, and B. stercoris SxR8. To validate the findings, it is crucial to comprehend how Cr(VI) affects Bacillus sp. SxR1 cells to determine the course of uptake and bacterial cell alteration, which was assessed via Fourier Transform-Infrared Spectroscopy (FT-IR) and Scanning Electron Microscopy (SEM).

Isolation, screening, identification, and characterization of arsenic resistant plant growth promoting rhizobacteria isolated from Pennisetum purpureum

Microbes that can progress plant productivity and health are recognized as PGPR. Rhizobacteria perform a main role in the phytoremediation process by increasing phytoremediation efficacy, thus the need to identify the superior rhizobacteria has been gaining serious attention. In the present study, Pennisetum purpureum were exposed to a series of As-polluted sand including control (0, 5, 20, 40, 60, and 80 mg kg−1) in plastic crates in a greenhouse environment. Four weeks after exposure, the plants could survive with toxicity of As pollution up to 40 mg kg−1. A total of 22 groups of bacterial isolates were confirmed based on the morphological characteristics, biochemical characteristics, and Gram staining. Preliminary and secondary As screening tests were also conducted. Identification was directed utilizing a molecular identification system. After As screening tests, 17 rhizobacterial isolates presented possible tolerance to As. Based on the molecular identification, 9 bacterial isolates were confirmed which were two [28N A UPM (Bacillus subtilis) and 28N U UPM (Bacillus australimaris)] gram-positive and seven [28N H UPM (Burkholderia seminalis), 28N G UPM (Enterobacter cloacae), 28N D UPM (Pseudomonas stutzeri), 28N I UPM (Sphingobacterium thalpophilum), 28N M UPM (Proteus mirabilis), 28N K UPM (Neisseria perflava) and 28N S UPM (Pseudomonas boreopolis)] gram-negative bacteria. All the nine identified rhizobacteria showed excellent results in terms of PGP characters. Among them, 28N U UPM (Bacillus australimaris) performed the highest PGP traits. The findings revealed that these highly As-resistant rhizobacteria have the potential to produce PGP traits and can help P. purpureum growth and productivity.

Integrated omics approach reveals the molecular pathways activated in tomato by Kocuria rhizophila, a soil plant growth-promoting bacterium

Plant microbial biostimulants application has become a promising and eco-friendly agricultural strategy to improve crop yields, reducing chemical inputs for more sustainable cropping systems. The soil dwelling bacterium Kocuria rhizophila was previously characterized as Plant Growth Promoting Bacteria (PGPB) for its multiple PGP traits, such as indole-3-acetic acid production, phosphate solubilization capability and salt and drought stress tolerance. Here, we evaluated by a multi-omics approach, the PGP activity of K. rhizophila on tomato, revealing the molecular pathways by which it promotes plant growth. Transcriptomic analysis showed several up-regulated genes mainly related to amino acid metabolism, cell wall organization, lipid and secondary metabolism, together with a modulation in the DNA methylation profile, after PGPB inoculation. In agreement, proteins involved in photosynthesis, cell division, and plant growth were highly accumulated by K. rhizophila. Furthermore, “amino acid and peptides”, “monosaccharides”, and “TCA” classes of metabolites resulted the most affected by PGPB treatment, as well as dopamine, a catecholamine neurotransmitter mediating plant growth through S-adenosylmethionine decarboxylase (SAMDC), a gene enhancing the vegetative growth, up-regulated in tomato by K. rhizophila treatment. Interestingly, eight gene modules well correlated with differentially accumulated proteins (DAPs) and metabolites (DAMs), among which two modules showed the highest correlation with nine proteins, including a nucleoside diphosphate kinase, and cytosolic ascorbate peroxidase, as well as with several amino acids and metabolites involved in TCA cycle. Overall, our findings highlighted that sugars and amino acids, energy regulators, involved in tomato plant growth, were strongly modulated by the K. rhizophila-plant interaction.

Impact of microbial consortium of Rhizobium tropici and Rhizobium mayense on the growth of Phaseolus vulgaris L.

The main objectives of the present investigation was to characterize and recognize potential indigenous Rhizobium spp. associated with red clover nodules, as well as to evaluate the influence of prospective rhizobia inoculation (individual and consortia) on common bean plant growth. Total of 8 rhizobia like bacteria were isolated and were investigated for their specific PGP traits, production of hydrolytic enzymes. Results revealed, four isolates synthesize IAA (22.3 ± 1.45 to 88.6 ± 1.45 μg mL−1), three isolates solubilized phosphate (40.69 ± 1.25 to 216.3 ± 1.31 μg mL−1), three isolates solubilized potassium, produced siderophore, and showed chitinase production, two isolates possess ACC deaminase activity, one isolate was able to solubilize zinc, 5 isolates produced β- 1, 3-glucanase (0.38 ± 0.005 to 2.82 ± 0.011 % units) and four isolates produced cellulase. Two bacterial isolates found to exhibit most of the PGP activities, were selected and identified on the basis of phenotypic, biochemical tests and 16S rRNA sequencing, as Rhizobium tropici IHTF-1 and Rhizobium mayense IHTF-2. Interaction of these potential rhizobium strains individually and consortia with common bean plants under greenhouse conditions boosted root and shoot length, fresh and dry biomass compared to un-inoculated control plants. SEM study revealed that both the strains, IHTF-1 and IHTF-2 colonized common bean roots. These results imply that Rhizobium spp., identified in this work, can be used as bio-inoculants to increase common bean plant production in a sustainable way.

Isolation and screening of stress tolerant and plant growth promoting root nodulating rhizobial bacteria from some wild legumes of Nagaland, India

Wild legumes are widely distributed and better adapted to extreme agro-climatic conditions because of their soil microbiota. In the present study, Root Nodulating Bacteria (RNB) were isolated from wild legumes and analysed for their abiotic stress tolerant and Plant Growth Promoting Traits (PGPT). Rhizobial strains were identified based on their 16S rRNA sequences. A total of 14 rhizobial species were characterized based, of which six were Rhizobium (AIS3, AIS9, AIR14, LUMCR3, LUMVRW4, LUMVRW8), four belongs to Burkholderia (AIS12, MOLKCS15, CHMP9, CHMP10) and one each of genera Cupriavidus (LUMMD12), Herbaspirillum (LUMVRW4), Paraburkholderia (CHMP1) and Ralstonia (LUMDes9). Stress tolerance analysis found most of the strains are to be tolerant to alkaline pH (9–11) where highest tolerance exhibited by Rhizobium sp. (strain AIS9) and Burkholderia territorii (strain MOKCS15). Seven Rhizobial strains were able to thrive at lower temperature stress (10 and 20 °C); while, strains AIS9, CHMP1 and LUMMD21 were able to grow at higher temperature (40 and 50 °C). Most of the isolate could tolerate salinity stress up to 1.5 %; but, only isolates AIS9, AIS12 and LUMMD12 could tolerate 2 and 2.5 % salt concentrations. The PGPT analyses found LUMCR3 having the highest IAA production potentiality (102.5 µg/ml); while, isolate MOKCS15 exhibited highest phosphate solubilizing activity (4.1 Phosphate Solubilization Index). The RNB isolates in the present study exhibited both stress tolerance and PGP traits indicating their potential use as biofertilizer under extreme agronomic conditions to improve productivity.

Optimizing tomato seedling growth with indigenous mangrove bacterial inoculants and reduced NPK fertilization.

The search for ecofriendly products to reduce crop dependence on synthetic chemical fertilizers presents a new challenge. The present study aims to isolate and select efficient native PGPB that can reduce reliance on synthetic NPK fertilizers. A total of 41 bacteria were isolated from the sediment and roots of mangrove trees (Avicennia marina) and assessed for their PGP traits under in vitro conditions. Of them, only two compatible strains of Bacillus species were selected to be used individually and in a mix to promote tomato seedling growth. The efficiency of three inoculants applied to the soil was assessed in a pot experiment at varying rates of synthetic NPK fertilization (0, 50, and 100% NPK). The experiment was set up in a completely randomized design with three replications. Results showed that the different inoculants significantly increased almost all the studied parameters. However, their effectiveness is strongly linked to the applied rate of synthetic fertilization. Applying bacterial inoculant with only 50% NPK significantly increased the plant height (44-51%), digital biomass (60-86%), leaf area (77-87%), greenness average (29-36%), normalized difference vegetation index (29%), shoot dry weight (82-92%) and root dry weight (160-205%) compared to control plants. Concerning the photosynthetic activity, this treatment showed a positive impact on the concentrations of chlorophyll a (25-31%), chlorophyll b (34-39%), and carotenoid (45-49%). Interestingly, these increases ensured the highest values significantly similar to or higher than those of control plants given 100% NPK. Furthermore, the highest accumulation of N, P, K, Cu, Fe, Zn, and Ca in tomato shoots was recorded in plants inoculated with the bacterial mix at 50% NPK. It was proven for the first time that the native PGP bacteria derived from mangrove plant species A. marina positively affects the quality of tomato seedlings while reducing 50% NPK.

Screening of heavy metal-resistant rhizobial and non-rhizobial microflora isolated from Trifolium sp. growing in mining areas.

Plant growth-promoting rhizobacteria (PGPR) can promote plant growth and development with several beneficial effects, especially in challenging environmental conditions, such as the presence of toxic contaminants. In this study, 49 isolates obtained from Trifolium sp. nodules growing on a Pb/Zn mine site were characterized for PGP traits including siderophores production, phosphate solubilization, extracellular enzymes production, and antifungal activity. The isolates were also screened for their ability to grow at increasing concentrations of NaCl and heavy metals, including lead, zinc, cobalt, copper, nickel, cadmium, and chromium. The findings of our study indicated that isolates Cupriavidus paucula RSCup01-RSCup08, Providencia rettgeri RSPro01, Pseudomonas putida RSPs01, Pseudomonas thivervalensis RSPs03-RSPs09, and Acinetobacter beijerinckii RSAci01 showed several key traits crucial for promoting plant growth, thus demonstrating the greatest potential. Most isolates displayed resistance to salt and heavy metals. Notably, Staphylococcus xylosus RSSta01, Pseudomonas sp. RSPs02, Micrococcus yunnanensis RSMicc01, and Kocuria dechangensis RSKoc01 demonstrated a significant capacity to grow at salt concentrations ranging from 10 to 20%, and isolates including Cupravidus paucula RSCup01-RSCup08 exhibited resistance to high levels of heavy metals, up to 1300 mg/L Pb++, 1200 mg/L Zn++, 1000 mg/L Ni++, 1000 mg/L Cd++, 500 mg/L Cu++, 400 mg/L Co++, and 50 mg/L CrVI+. Additionally, the analysis revealed that metal-resistant genes pbrA, czcD, and nccA were exclusively detected in the Cupriavidus paucula RSCup01 strain. The results of this study provide insights into the potential of plant growth-promoting rhizobacteria strains that might be used as inoculants to improve phytoremediation in heavy metal-contaminated soils.

Plant growth-promoting rhizobacteria: Peribacillus frigoritolerans 2RO30 and Pseudomonas sivasensis 2RO45 for their effect on canola growth under controlled as well as natural conditions.

Even though canola is one of the most important industrial crops worldwide, it has high nutrient requirements and is susceptible to pests and diseases. Therefore, natural methods are sought to support the development of these plants. One of those methods could be a plant growth-promoting rhizobacteria (PGPR) that have a beneficial effect on plant development. The aim of this study was a genomic comparison of two PGPR strains chosen based on their effect on canola growth: Peribacillus frigoritolerans 2RO30, which stimulated canola growth only in sterile conditions, and Pseudomonas sivasensis 2RO45, which promoted canola growth in both sterile and non-sterile conditions. First of all, six bacterial strains: RO33 (Pseudomonas sp.), RO37 (Pseudomonas poae), RO45 (Pseudomonas kairouanensis), 2RO30 (Peribacillus frigoritolerans), 2RO45 (Pseudomonas sivasensis), and 3RO30 (Pseudomonas migulae), demonstrating best PGP traits in vitro, were studied for their stimulating effect on canola growth under sterile conditions. P. frigoritolerans 2RO30 and P. sivasensis 2RO45 showed the best promoting effect, significantly improving chlorophyll content index (CCI) and roots length compared to the non-inoculated control and to other inoculated seedlings. Under non-sterile conditions, only P. sivasensis 2RO45 promoted the canola growth, significantly increasing CCI compared to the untreated control and to other inoculants. Genome comparison revealed that the genome of P. sivasensis 2RO45 was enriched with additional genes responsible for ACC deaminase (acdA), IAA (trpF, trpG), and siderophores production (fbpA, mbtH, and acrB) compared to 2RO30. Moreover, P. sivasensis 2RO45 showed antifungal effect against all the tested phytopathogens and harbored six more biosynthetic gene clusters (BGC), namely, syringomycin, pyoverdin, viscosin, arylpolyene, lankacidin C, and enterobactin, than P. frigoritolerans 2RO30. These BGCs are well known as antifungal agents; therefore, it can be assumed that these BGCs were responsible for the antifungal activity of P. sivasensis 2RO45 against all plant pathogens. This study is the first report describing P. sivasensis 2RO45 as a canola growth promoter, both under controlled and natural conditions, thus suggesting its application in improving canola yield, by improving nutrient availability, enhancing stress tolerance, and reducing environmental impact of farming practices.

Endophytic bacteria associated with critically endangered medicinal plant Trillium govanianum (Wall ex. Royle) and their potential in soil nutrition alleviation

Trillium govaniaunm is a critically endangered medicinal plant commonly known as ‘Nag Chhatri’ that grows mainly in the dry temperate zone of western Himalayas India. Here, in the present study, T. govanianum plants have been explored to isolate and identify bacterial endophytes with plant growth promoting potential and to evaluate their effects on soil biochemical property under field conditions. In total, 107 endophytic bacteria have been isolated from T. govanianum which were then tested for their in vitro plant growth promoting activity. Twenty two bacterial strains which showed all PGP traits were selected for evaluating their enzymatic and drought tolerating potential. The best P-solubilisation and IAA production 92.56 ± 2.29 μg/ml, and 62.74 ± 0.58 μg/ml were recorded by strain Ar13 respectively" in this way, the strain Ar13 demonstrated the best P-solubilisation and IAA production, whereas Ms5 produced the highest siderophore production i.e. 94.86 ± 2.02%. The maximum protease (18.00 ± 0.11 mm) was shown by strain Ms5 whereas, Ar13 showed the highest cellulase (20.00 ± 0.41 mm), chitinase (22 ± .02 mm) and ACC deaminase (48.84 ± ± 0.17 µM ά-KB mg−1h − 1). In total three bacterial isolates were further selected for further studies and identified as Pantoea spp. Ar13, Microbacterium spp. Ar17 and Pseudomonas spp. Ms5 by 16S rRNA gene sequencing. Furthermore, these three selected bacterial isolates were utilized individually and in consortia for the field application for consecutive two years. The findings unveiled a notably enhancement of micronutrients in all plants subjected to bacterial strains, when compared to the control group. The consortium of endophytes recorded significantly higher total soil organic carbon (2.58 ± 0.03%), electric conductivity (0.21 ± 0.01 dsm-1), and soil nutrients like available N (418.75 ± 1.42 kg ha-1), P (36.05 ± 0.12 kg ha-1), K (291.23 ± 0.99 kg ha-1) content and soil enzymes like dehydrogenase, phosphatase and microbial population. To our knowledge, this is the very first report of its kind of the isolation of endophytic bacterial strains from T. govanianum and microorganisms that can be utilized in future applications for agricultural sustainability.