ACC Deaminase Production Research Articles

A Study of the Different Strains of the Genus Azospirillum spp. on Increasing Productivity and Stress Resilience in Plants.

One of the most important and essential components of sustainable agricultural production is biostimulants, which are emerging as a notable alternative of chemical-based products to mitigate soil contamination and environmental hazards. The most important modes of action of bacterial plant biostimulants on different plants are increasing disease resistance; activation of genes; production of chelating agents and organic acids; boosting quality through metabolome modulation; affecting the biosynthesis of phytochemicals; coordinating the activity of antioxidants and antioxidant enzymes; synthesis and accumulation of anthocyanins, vitamin C, and polyphenols; enhancing abiotic stress through cytokinin and abscisic acid (ABA) production; upregulation of stress-related genes; and the production of exopolysaccharides, secondary metabolites, and ACC deaminase. Azospirillum is a free-living bacterial genus which can promote the yield and growth of many species, with multiple modes of action which can vary on the basis of different climate and soil conditions. Different species of Bacillus spp. can increase the growth, yield, and biomass of plants by increasing the availability of nutrients; enhancing the solubilization and subsequent uptake of nutrients; synthesizing indole-3-acetic acid; fixing nitrogen; solubilizing phosphorus; promoting the production of phytohormones; enhancing the growth, production, and quality of fruits and crops via enhancing the production of carotenoids, flavonoids, phenols, and antioxidants; and increasing the synthesis of indoleacetic acid (IAA), gibberellins, siderophores, carotenoids, nitric oxide, and different cell surface components. The aim of this manuscript is to survey the effects of Azospirillum spp. and Bacillus spp. by presenting case studies and successful paradigms in several horticultural and agricultural plants.

Influence of plant growth promoting haloalkaliphilic bacteria on mitigation salt and alkali stresses in pistachio seedlings (Pistacia vera L.)

Pistachio (Pistacia vera L.) tolerates salinity stress, but its yield decreases with increasing salinity. The present study was conducted to investigate the effect of Khorasan Razavi (Iran) native haloalkaliphile bacterial strains on the vegetative growth, biochemical parameters, and nutrient concentration of pistachio seedlings under orchard conditions. The concentration of ammonia production, tri-indole acetic acid, and ACC deaminase production were measured for Virgibacillus marismortui (61.89, 17.59 mg l-1, and 203.59 µM l-1), and Alkalibacillus haloalkaliphilus (61.55, 36.04 mg l-1 and 512.97 µM l-1), respectively. Most of the vegetative traits decreased up to 12 dS m-1 salinity and then they increased with increasing salinity to 16 dS m-1. The Akbari cultivar was superior in all studied traits except the root-to-shoot ratio. The inoculation with AlkaliBacillus Haloalkalophilus had a stronger impact on nutrient concentrations, while the mixed bacteria treatment had a greater effect on vegetative and biochemical parameters. The effect of bacteria inoculation on a sensitive cultivar (Daneshmandi) was higher in 16 dS m-1. The AlkaliBacillus Haloalkalophilus increased phosphorus, potassium, and boron to 5, 10, and 12.1 mg kg-1 while decreasing sodium to 69 mg kg-1 and Na+/K+ ratio to 0.0028 compared to the mixed bacteria treatment. The highest correlation was found between root volume and stem length (r=0.639) and diameter (r=0.629), indicating the impact of bacteria inoculation on root growth and water relations in saline and sodic conditions. Stem length and diameter growth in young pistachio seedlings are crucial for grafting and economic productivity, so two bacterial treatment mixtures are recommended. 16 dS m-1), two pistachio cultivars (Daneshmandi and se production were measured for Virgibacillus marismortui (61.89, 17.59 mg l-1 and 203.59 µM l-1), and Alkalibacillus haloalkaliphilus (61.55, 36.04 mg l-1 and 512.97 µM l-1), respectively. Results showed that most of the vegetative traits decreased up to 12 dS m-1 salinity and then they increased with increasing salinity to 16 dS m-1. The Akbari cultivar was superior in all studied traits except the root-to-shoot ratio. The inoculation with AlkaliBacillus Haloalkalophilus had a stronger impact on nutrient concentrations, while the mixed bacteria treatment had a greater effect on vegetative and biochemical parameters. The effect of bacteria inoculation on a sensitive cultivar (Daneshmandi) was higher in 16 dS m-1. The AlkaliBacillus Haloalkalophilus increased phosphorous (5 mg kg-1), potassium (10 mg kg-1), and boron (12.1 mg kg-1) concentration and decreased sodium (69 mg kg-1) and Na+/K+ ratio (0.0028) than the mixed bacteria treatment. Inoculation with AlkaliBacillus Haloalkalophilus, two mixed of strain and VirgiBacillus Marismorti treatments caused a 15.1%, 13.8%, and 7.6% reduction in Na+/K+ ratio compared to the control. AlkaliBacillus Haloalkalophilus had a greater effect on reducing the concentration of toxic elements (Na+ and Cl-) and the ratio of sodium to potassium. The highest correlation coefficient was observed between root volume and stem length (r = 0.639) and diameter (r = 0.629), indicating the impact of bacteria inoculation on root growth and water relations in saline and sodic conditions. Due to the importance of the stem length and diameter increase in the early stages of the pistachio seedlings’ growth to grafting and achieve economic productivity, the two mixtures of bacteria treatment were recommended as the maximum stem length, diameter, and leaf area with 55.2, 10.8 and 18.5 cm2, respectively.

Amplicon Sequencing Analysis of Submerged Plant Microbiome Diversity and Screening for ACC Deaminase Production by Microbes

Amplicon Sequencing Analysis of Submerged Plant Microbiome Diversity and Screening for ACC Deaminase Production by Microbes

The synergy of ACC deaminase producing plant growth-promoting microbes provide drought tolerance in Ocimum basilicum L. cv. “Saumya”

The use of plant growth-promoting microorganisms is an effective agricultural practice to improve plant growth, especially under abiotic stress. In this study, the combined impact of three plant growth-promoting bacteria (PGPB) namely Brevibacterium halotolerans (Sd-6), Burkholderia cepacia (Art-7), Bacillus subtilis (Ldr-2) were tested with Trichoderma harzianum (Th) (possessing ACC deaminase producing activity) in Ocimum basilicum L. cv. “Saumya” to reduce drought-induced damages to the plants under different level of drought stress [i.e. well-watered (100 %), moderate (60 %), severe (40 %)]. These PGPB strains, along with Th, were found to be tolerant against osmotic stress when tested in growth media containing different concentrations of polyethylene glycol (PEG 8000), and all were found to endure -0.99 MPa water potential. Compared to non-inoculated control, Th+Ldr-2 treatment improved fresh herb weight (62.45 %) and oil content (61.54 %) and higher photosynthetic rate under severe drought. Besides, in relation to control, the above treatment enhanced nutrient uptake, reduced ABA, ACC as well as ethylene levels and increased IAA content in addition to an increase in important constituents of essential oil, indicating better performance in terms of plant growth under drought. Higher RWC, decreased MDA, and reduced antioxidant activities in Th+Ldr-2 treated plants compared to non-inoculated control under drought support the mechanism of the microbes providing tolerance against drought. Colony forming unit of microbes and scanning electron microscopy (SEM) study support the effective colonisation behaviour of Th+Ldr-2, which protects plants against drought stress. A consortium of diverse microbes, found to improve plant growth under drought through increased nutrient uptake, reducing the levels of ACC and ABA, improving the content of IAA, antioxidant enzymes probably reducing the effect of drought stress and improving plant biomass could be a useful tool to reduce drought-induced losses in crop plants.

Exploring the Plant Growth-Promotion Properties of Rhizospheric and Endophytic Bacteria Associated with Robinia pseudoacacia L. in Serpentine Soil.

Serpentine soils are characterized as a unique environment with low nutrient availability and high heavy metal concentrations, often hostile to many plant species. Even though these unfavorable conditions hinder the growth of various plants, particular vegetation with different adaptive mechanisms thrives undisturbed. One of the main contributors to serpentine adaptation represents serpentine bacteria with plant growth-promoting properties that assemble delicate interactions with serpentine plants. Robinia pseudoacacia L. is an invasive but adaptive species with phytoremediation potential and demonstrates extraordinary success in this environment. To explore more in-depth the role of plant growth-promoting serpentine bacteria, we isolated them and tested their various plant growth-promoting traits both from the rhizosphere and roots of R. pseudoacacia. Based on the demonstrated plant growth-promoting traits such as siderophore production, phosphate solubilization, nitrogen fixation, indole-3-acetic acid production, and ACC deaminase production, we sequenced overall 25 isolates, 14 from the rhizosphere and 11 from the roots. Although more efficient in exhibiting plant growthpromoting traits, rhizospheric bacteria showed a low rate of diversity in comparison to endophytic bacteria. The majority of the isolates from the rhizosphere belong to Pseudomonas, while isolates from the roots exhibited higher diversity with genera Pseudomonas, Bacillus, Staphylococcus, Lysinibacillus and Brevibacterium/Peribacillus/Bacillus. The capacity of the described bacteria to produce siderophores, solubilize phosphate, and fix nitrogen highlights their central role in enhancing nutrient availability and facilitating R. pseudoacacia adaptation to serpentine soils. The findings highlight the potential significance of serpentine bacteria, particularly Pseudomonas, in contributing to the resilience and growth of R. pseudoacacia in serpentine environments.

The Population and Isolates of Potential ACC Deaminase-Producing Rhizobacteria from Rhizospheric Soil of Peanut under Different Moisture Levels

ACC deaminase-producing rhizobacteria play an important role in enhancing plant growth and health, particularly under environmental stress conditions. This study focused on isolating and determining the population of potential ACC deaminase-producing rhizobacteria from the rhizosphere of peanut plants (Arachis hypogea L.) grown under varying moisture levels. Bacterial populations were measured using the Standard Plate Count (SPC) method on Dworkin-Foster (DF) medium supplemented with ACC as the sole nitrogen source. The isolated bacteria were screened based on their ability to grow after 24 hours of incubation on the selective medium. Results showed that bacterial colonies on nutrient agar (NA) medium varied in color, while colonies on the selective medium were uniformly white. The total population of rhizobacteria generally declined as soil moisture decreased, nevertheless, the sample from 80% available water had fewer bacteria than those of the sample from 50%. In an additional experiment, 9 out of 11 selected isolates were found to potentially produce ACC deaminase, with 5 of these being diazotrophic bacteria. This study contributes valuable information for designing irrigation systems in sustainable land management, particularly concerning plant-beneficial microbes that produce ACC deaminase and help plants tolerate environmental stressors.

Exploring plant-microbe interactions in adapting to abiotic stress under climate change: a review.

Climatic change and extreme weather events have become a major threat to global agricultural productivity. Plants coexist with microorganisms, which play a significant role in influencing their growth and functional traits. The rhizosphere serves as an ecological niche encompassing plant roots and is a chemically complex environment that supports the growth and development of diverse plant-interactive microbes. Although plant-microbe interactions have been extensively investigated however, limited exploration have been made how abiotic stresses affect the structure and assembly of microbial communities in the rhizosphere. This review highlights climate change influence on plant growth, functional traits, and microbial communities. It explores plant mechanisms for mitigating abiotic stress, such as removing reactive oxygen species (ROS), regulating antioxidant activity and indole-3-acetic acid (IAA) production, and controlling growth-inhibitory ethylene levels through colonization by bacteria producing ACC deaminase. Additionally, we elaborated the systematic communicatory network steered by hormonal crosstalk and root exudation, which can modulate and initiate the dialogues between plants and surrounding microbes. This network ultimately promotes the chemotactic movement of microbes towards the rhizosphere, facilitating their early colonization. Finally, we reviewed the recent advancements for understanding how plant-microbe interactions foster resilience under climate stress.

Synergistic interaction between Azotobacter and Pseudomonas bacteria in a growth-stimulating consortium

Intensifying agricultural production involves an active use of agrochemicals, which results in disrupted ecological balance and poor product quality. To address this issue, we need to introduce biologized science-intensive technologies. Bacteria belonging to the genera Azotobacter and Pseudomonas have complex growth-stimulating properties and therefore can be used as a bioproduct to increase plant productivity. We aimed to create a growth-stimulating consortium based on the strains of the genera Azotobacter and Pseudomonas, as well as to select optimal cultivation parameters that provide the best synergistic effect. We studied strains Azotobacter chroococcum B-4148, Azotobacter vinelandii B-932, and Pseudomonas chlororaphis subsp. aurantiaca B-548, which were obtained from the National Bioresource Center “All-Russian Collection of Industrial Microorganisms” of Kurchatov Institute. All the test strains solubilized phosphates and produced ACC deaminase. They synthesized 0.98–1.33 mg/mL of gibberellic acid and produced 37.95–49.55% of siderophores. Their nitrogen-fixing capacity ranged from 49.23 to 151.22 μg/mL. The strain had high antagonistic activity against phytopathogens. In particular, A. chroococcum B-4148 and A. vinelandii B-932 inhibited the growth of Fusarium graminearum, Bipolaris sorokiniana, and Erwinia rhapontici, while P. chlororaphis subsp. aurantiaca B-548 exhibited antagonism against F. graminearum and B. sorokiniana. Since all the test strains were biologically compatible, they were used to create several consortia. The greatest synergistic effect was achieved by Consortium No. 6 that contained the strains B-4148, B-932, and B-548 in a ratio of 1:3:1. The optimal nutrient medium for this consortium contained 25.0 g/L of Luria-Bertani medium, 8.0 g/L molasses, 0.1 g/L magnesium sulfate heptahydrate, and 0.01 g/L of aqueous manganese sulfate. The optimal cultivation temperature was 28°C. The microbial consortium created in our study has high potential for application in agricultural practice. Further research will focus on its effect on the growth and development of plants, in particular cereal crops, under in vitro conditions and in field experiments.

Pseudomonas and Acinetobacter spp. capable of metabolizing aromatics displays multifarious plant growth promoting traits: Insights on strategizing consortium-based application to agro-ecosystems

The persistence and slow rate of natural attenuation of genotoxic and endocrine-disrupting aromatic pollutants has impacted the soil heath of agro-ecologies leading to various health and environmental issues. Ecotoxic-xenobiotic compounds degradation property along with plant growth promoting traits of microbes are beneficial for devising strategies for improved agricultural soil health and its clean-up. Present study assessed the multipartite plant growth promoting-, biocontrol- and niche adaptive- traits of five aromatic degrading soil bacteria viz. Pseudomonas bharatica CSV86T, Pseudomonas sp. C5pp, Pseudomonas sp. PP4, Pseudomonas sp. PPD and Acinetobacter sp. ISP4. Solubilization of rock phosphate (P) and feldspar (K), production of plant growth hormone (auxin; IAA), ammonia, siderophores and ACC deaminase by strain CSV86T, C5pp and PP4 were observed. Similarly, high fusaric acid resistance (MIC: 1–1.2 mg mL−1) and tolerance to salinity (5–7.5 %) was observed. In vitro application of CSV86T, C5pp, PP4 and ISP4 as consortium resulted in significant increase (P < 0.05) in the seedling shoot length (15–37 %), root length (65–150 %) and biomass (30–40 %) of wheat, mung bean and fenugreek. In-soil microcosm assay confirmed the plant growth promoting and phytoprotective ability of this consortium against toxicity of aromatics in contaminated soil. Antifungal activity against phytopathogenic fungi Magnaporthe oryzae and Aspergillus spp., ability to produce lytic enzymes and HCN suggests their biocontrol potential. Four aromatic degrading bacteria (as a consortium) exhibiting plant growth promotion and biocontrol activity could be used as an eco-friendly bioremediator-biofertilizer-biocontrol agent (bioformulation) for restoration of agricultural soil with improved crop productivity.

The design and development of EcoBiomes: Multi-species synthetic microbial consortia inspired by natural desert microbiome to enhance the resilience of climate-sensitive ecosystems

Synthetic microbial communities, which simplify the complexity of natural ecosystems while retaining their key features, are gaining momentum in engineering and biotechnology applications. One potential application is the development of bioinoculants, offering an eco-friendly, sustainable solution to promote plant growth and increase resilience to abiotic stresses amidst climate change. A potential source for stress-tolerant microbes is those associated with desert plants, evolved and shaped by selective pressures to promote host health under harsh environmental conditions. In our research, we aim to design and develop synthetic microbial consortia inspired by the natural microbiota of four desert plants native to the Arabian Peninsula, inferred from our previous work identifying the structure and predicting the function of these microbial communities using high throughput eDNA barcoding. To obtain culturable microbes that are manageable and traceable yet still representative of natural microbial communities, we combined multiple experimental protocols coupled with compatibility and synergy assessments, along with in planta testing. We isolated a total of 75 bacteria and conducted detailed biological evaluations, revealing that an overwhelming majority (84 %) of all isolates produced indole acetic acid (IAA), with 73 % capable of solubilizing phosphate, 60 % producing siderophores, 47 % forming biofilms, and 35 % producing ACC deaminase, all contributing to plant growth and stress tolerance. We constructed four synthetic microbial consortia, named EcoBiomes, consisting of synergistic combinations of multiple species that can co-exist without significant antagonism. Our preliminary data indicate that EcoBiomes enhance the resilience of heterologous host plants under simulated environmental stresses, including drought, heat, and salinity. EcoBiomes offer a unique, sustainable, and eco-friendly solution to mitigate the impact of climate change on sensitive ecosystems, ultimately affecting global food security.

Sustainable improvement of rice growth under salinity stress using an endophytic fungus-based biofertilizer

Salinity stress adversely affects rice (Oryza sativa L.) growth, development and overall productivity. Multiple strategies have been implemented to enhance the resilience of rice plants, enabling them to grow better in saline environments. Use of biofertilizers, a sustainable alternative to chemical fertilizers, has gained significant attention in modern agriculture due to their potential to improve soil fertility, enhance crop productivity, and mitigate environmental concerns. Biofertilizers encompass a diverse group of microorganisms, including bacteria, fungi, and algae, which interact with plants through various mechanisms. These beneficial microbes have been reported to convert atmospheric nitrogen into plant-available forms and break down insoluble phosphates and zinc complexes in the soil. Additionally, they can also produce growth regulators, enhance nutrient availability, and protect plants against pathogens. In our previous study, a salt-tolerant endophytic fungus isolated from the halophytic wild rice, Oryza coarctata, was identified as Aspergillus welwitschiae Ocstreb1 by whole genome sequence analysis. During the in-vitro experiments, the endophyte showed several plant growth promoting activities such as, zinc and phosphate solubilization, siderophore, IAA, and ACC-deaminase production, nitrogen fixation, etc. in both normal and 900 mM salt stress. In this study, the endophyte was used to formulate a biofertilizer in combination with talcum powder to enhance the growth and yield of rice plants under salinity stress. This research investigated the effectiveness of the biofertilizer in four distinct salinity tanks under both non-saline and 6 dS/m saline conditions, each containing three different varieties of rice. Treatment of BRRI dhan28 (BD-28), BRRI dhan67 (BD-67) and BRRI dhan87 (BD-87) rice plants with the formulated biofertilizer significantly enhanced their yield in both non-saline and saline conditions. Among the three rice varieties, BD-28 showed the highest significant (p&lt;0.05) yield increase, with 104.20% under normal conditions and 3080.56% under salt stress. BD-67 exhibited a 45.15% increase in normal conditions and 153.64% under salt stress (P&lt;0.05). BD-87 showed a significant yield increase only under salt stress, at 293.63% (p&lt;0.05). From the results of the study, it can be proposed that the formulated biofertilizer is a potential eco-friendly and cost-effective solution to improve cultivation and yield of rice in the highly saline coastal regions of Bangladesh. Bioresearch Commu. 10(2): 1474-1481, 2024 (July)

Novel Bacillus and Prestia isolates from Dwarf century plant enhance crop yield and salinity tolerance

Soil salinity is a major environmental stressor impacting global food production. Staple crops like wheat experience significant yield losses in saline environments. Bioprospecting for beneficial microbes associated with stress-resistant plants offers a promising strategy for sustainable agriculture. We isolated two novel endophytic bacteria, Bacillus cereus (ADJ1) and Priestia aryabhattai (ADJ6), from Agave desmettiana Jacobi. Both strains displayed potent plant growth-promoting (PGP) traits, such as producing high amounts of indole-3-acetic acid (9.46, 10.00 µgml−1), ammonia (64.67, 108.97 µmol ml−1), zinc solubilization (Index of 3.33, 4.22, respectively), ACC deaminase production and biofilm formation. ADJ6 additionally showed inorganic phosphate solubilization (PSI of 2.77), atmospheric nitrogen fixation, and hydrogen cyanide production. Wheat seeds primed with these endophytes exhibited enhanced germination, improved growth profiles, and significantly increased yields in field trials. Notably, both ADJ1 and ADJ6 tolerated high salinity (up to 1.03 M) and significantly improved wheat germination and seedling growth under saline stress, acting both independently and synergistically. This study reveals promising stress-tolerance traits within endophytic bacteria from A. desmettiana. Exploiting such under-explored plant microbiomes offers a sustainable approach to developing salt-tolerant crops, mitigating the impact of climate change-induced salinization on global food security.

Abiotic stress tolerance and antifungal activities of rhizobacteria for the management of soil-borne pathogens

Cotton production is negatively affected by both biotic (diseases and insects) and abiotic (high temperature, salinity, water deficit, and extreme pH) factors. Soil-borne diseases, especially wilts and rots, significantly reduce cotton yield. Thus, we aimed to isolate and identify multi-stress tolerant bacterial antagonistic agents (AGAs) against two major soil-borne pathogens, Macrophomina phaseolina and Fusarium oxysporum. A total of 132 isolates with distinct morphologies were recovered from 25 different rhizospheric soil samples of cotton. A dual culture plate and broth assay confirmed the antagonistic activity of the isolates against these phytopathogens. Four selected AGAs thrived in salt stress induced by different NaCl concentrations, up to 1.71 M, except for isolate 62, which survived up to 0.85 M. Under osmotic stress, all the AGAs were tolerant of up to −1.03 MPa. Similarly, all the AGAs were able to survive over a temperature range of 20–50 °C except for isolate 62, which survived up to 45 °C and was regarded as thermotolerant. All four AGAs were able to grow at pH values ranging from 5 to 9. AGA 18 and S46-7 survived under highly acidic conditions (pH 4). These multi-stress tolerant AGAs also exhibited different plant growth-promoting activities, such as mineral solubilization, ACC-deaminase production, and IAA production. Molecular identification revealed the following AGAs: Bacillus siamensis SSVP1 (18), Bacillus halotolerans SSVP2 (34), Pseudomonas aeruginosa SSVP3 (62), and Bacillus tequilensis SSVP4 (S46-7). AGAs with multiple stress tolerance traits can serve as potential biocontrol agents in the field to reduce pesticide consumption in cotton-growing areas.

Determination of Antagonistic Activities of Endophytic Bacteria Isolated from Different Wheat Genotypes Against Fusarium culmorum

This study aimed to evaluate the physiological and biochemical properties and enzyme activities of endophytic bacteria obtained from different wheat genotypes, as well as their effectiveness against Fusarium culmorum, which causes root and crown rot in wheat. The results obtained from double culture tests of isolates against F. culmorum showed that the inhibition rate varied between 80.56% and 13.90%. The inhibition rate against F. culmorum was 80.59% for Bacillus subtilis (MM11), 69.41% for Stenotrophomonas maltophilia (EY5), and 61.10% for Enterobacter sp. (MY3) under in vitro conditions, the most effective isolates. Pseudomonas putida (EM9) and Pseudomonas orientalis (MM21) isolates gave positive results in all tests in the production of amylase, cellulase, phosphatase, ACC deaminase, and siderophore. To identify six promising isolates, 16S rRNA gene-based sequence analysis was utilized. The efficacy of bacterial strains against F. culmorum, pot experiments were conducted in a growth room (in vivo). The results demonstrated that the combination of S. maltophilia, Enterobacter sp., and B. subtilis (MY3+EY5+MM11) yielded the most favorable outcomes in terms of disease severity, plant height, wet weight, dry weight, root wet weight, and root dry weight. The combination of Stenotrophomonas rhizophila, P. putida, and P. orientalis (EY1+EM9+MM21) exhibited promising results. Utilizing effective bacterial strains is anticipated to reduce the dependence on and costs associated with chemical fertilizers and pesticides while minimizing their environmental impact. Furthermore, these strains show potential for commercial applications pending further validation procedures. The findings from this study significantly contribute to the field of biological control strategies against F. culmorum by leveraging the diverse capabilities of endophytic bacteria.

Isolation and Molecular Profiling of Halotolerant Plant Growth Promoting Rhizosphere Fungi from Salt affected Agroforestry Plantation

Soil salinity is a major abiotic stress that adversely affects plant growth, and productivity. About 20% of irrigated lands are affected by salinity worldwide; In India, there are 6.74 million hectares of salt-affected lands. Salt-tolerant Plant Growth Promoting (PGP) microorganisms can enhance the growth of plants in such salt-stressed areas. Therefore, this study aimed to investigate the diversity of beneficial fungal communities, screen for their ability to support plant growth, and evaluate the production of various essential compounds in view of plant growth in salt-stressed lands. A total of 68 fungal colonies were isolated from 5 different agroforestry plantation sites in Karur, Tamil Nadu, South India at quarterly intervals. The isolates were screened for sodium chloride (NaCl) tolerance (0%, 5%, 10%, 15%, and 20% concentration). A total of 7 isolates showed considerable salt tolerance and were tested qualitatively in-vitro, for PGP traits such as phosphate, potassium, and zinc solubilization, nitrogen fixation, hydrogen cyanide production, siderophore production, and ACC deaminase production. Finally, 5 isolates with maximum values for PGP properties under 20% NaCl concentration were tested for the quantity of Indole-3-Acetic Acid (IAA) and Exo-polysaccharide (EPS) production. All 5 isolates were identified up to the species level using 18S rRNA gene sequencing. To the best of our knowledge, this is the first report on isolating saline-tolerant PGP Fungi (PGPF) from the rhizosphere region of Casuarina equisetifolia and Eucalyptus camaldulensis in Karur, Tamil Nadu, India. In the future, the bioformulation of PGPF and its application will boost the cultivation of tree saplings in this salt affected regions.

Boosting Capsicum annuum Growth Through Non-native Endophytic Bacterial Consortium

Abstract Organic and natural sources of bio-stimulant have a great expectancy to boost green agriculture practices for sustainable, safe, and smart cultivation of crops. In that regard, beneficial endophytic bacteria have great potential. They have unique features in promoting plant growth by colonizing and establishing well in plant roots. In this study, endophytes isolated from the roots of moringa, neem, sesbania, and chilli were screened for crop’s growth-enhancing activities, such as phosphorus (P) solubilization, 1-aminocyclopropane-1-carboxylic-acid deaminase (ACC deaminase) production, and indole-acetic acid (IAA) production. The phosphorus solubilization, indole-acetic acid production, and ACC deaminase production values fall in the range of 55–88 ppm, 20–164 ppm, and 0.317–0.375 mM, respectively. Chilli seeds’ three highest vigor index (VI) values were attained by MR10 (12,457 VI), MR3 (9450 VI), and MR13 (8730 VI). MR13 showed the highest seed germination energy (221%), followed by MR1 (178%) and MR3 (156%). The promising endophytes were tested on chilli seedlings as single and mixed inoculum treatments to study the efficiency of root colonization. Mixed cultures containing CKR8 and MR13 exhibited the highest seedling height (17.0 cm), followed by MR13, MR10, and MR13 (16.8 cm) compared to the control (12.6 cm). A single culture of MR10 (109.0 g and 13.53 cm2) and a mixed culture of MR10 and MR13 (100.0 g and 13.09 cm2) showed the maximum root length and surface area, respectively. The highest relative chlorophyll content was recorded by MR10 and MR13 (40.3 SPAD value), followed by MR13, MR3, and CKR8 (36.8 SPAD value). The non-native endophytic bacteria, MR13, Streptomyces panaciradicis (GenBank accession no. OM001090), and MR3, Bacillus subtilis (GenBank accession no. OM714810), could colonize the roots and improve the growth of chilli at the seedling growth stage. Graphical Abstract

PGPR-based biofertilizer modulates strawberry photosynthetic apparatus tolerance responses by severe drought, soil salinization and short extreme heat event

Drought, soil salinization and the extreme heat events increments associate to climate change will notably impact sensitive crop species, such as strawberry. A greenhouse experiment was arranged to evaluate the potential of a PGPR-based biofertilizer, with multiple PGP properties, including ACC deaminase production highly related to the limitation of ethylene levels under abiotic stress, in modulation of photosynthetic apparatus tolerance responses by severe drought (complete water withholding), salinity in irrigation water (340 mM NaCl) and short extreme heat event (37/28 °C maximum and minimum temperature range). Our results show that all stress factors triggered acute injury effects on strawberry carboxylation capacity and photosystem II energy assimilation efficiency ability; whose intensity varied depending on factor nature. However, bacterial inoculation diminished ∼67 %, 20 % and 18 % the deleterious impact imposed by drought, heat and salinity stress on the net photosynthetic rate (AN). This effect was primarily mediated by counterbalancing the diffusion of CO2 in the stomata and biochemical limitations in response to heat and salinity stress, while the reduction of biochemical damage was more notable in response to drought. Complementarily, inoculation was able to highly buffer the photochemical limitations imposed by all abiotic stress factors tested. Despite these positive effects, the application of PGPR-based biofertilizer was unable to completely reverse the impact of stress factors on strawberry photosynthesis metabolism. However, the signal of these ameliorative effects was significant enough to consider the implementation of PGPR-based biofertilizer application as a complementary tool in the management of strawberry cultivation in increasingly stressful agronomic contexts.

ACC deaminase producing bacteria alleviate the polyethylene glycol induced drought stress in black gram (Vigna mungo L.) by enhancing nutrient uptake and soil respiration activity

The present study aimed to exploit ACC deaminase (ACCD) producing drought-tolerant bacteria to mitigate drought stress (PEG stress) and simultaneous enhancement of the essential nutrients (N and P), relative water content (RWC), and chlorophyll pigment. In this study, 80 previously isolated ACCD-producing bacteria were screened for drought tolerance, and the results showed that 13.75 % (11isolates) were tolerant to up to -0.73 MPa. Further, screening of these drought tolerant ACCD producers revealed that the 11 isolates produced siderophore (96.82–99.67 %), indole-3-acetic acid like substances (15.15–70.55 µg/mL), and phosphate solubilization (39.33–142.67 µg/mL). Furthermore, pot studies (2000 ppm PEG stress) revealed an enhanced root (40.97–174.24 %) and shoot length (14.06–194.86 %) in inoculated plants compared to the control plants. In addition, inoculated plants also enhanced the uptake of nitrogen (35.10–42.61 mg/g) and phosphorus (2.67–3.68 mg/g), relative water content (55.26–83.33 %), chlorophyll (15.83–47.25 mg/g) and ACCD production in the soils (2.03–5.51 µmol/mL). The inoculated bacteria also enhanced the soil respiration activity such as dehydrogenase enzyme (65.31–144.48 µg/g), fluorescein diacetate hydrolysis (19.27–55.25 µg/g), and alkaline phosphatase (611.53–1011.53 µg/g). In conclusion, IPTS 7 (Rhodococcus kroppenstedtii) and CWN 5 (Bacillus altitudinis) can be used to mitigate drought stress and mobilize essential nutrients (N and P).

Marine Plant Growth Promoting Bacteria (PGPB) inoculation technology: Testing the effectiveness of different application methods to improve tomato plants tolerance against acute heat wave stress

Regenerative agriculture aims to boost native biodiversity and ensure sustainable production. Plant Growth Promoting Bacteria (PGPB) enhance crop yield through improved nutrient use efficiency or stress tolerance. Utilizing synthetic bacterial communities (SynCom) tailored to specific challenges holds promise for enhancing plant resilience. However, challenges include designing microbial consortia and selecting SynCom application techniques. This study tested four PGPB SynCom application methods on tomato plants to evaluate their effectiveness in promoting plant resistance and recovery from short extreme heat waves. Non-invasive phenotyping techniques were used to assess plant responses to three delivery methods (watering, foliar spray, and alginate spheres immobilization) under heat stress. Plants treated with the marine PGPB SynCom through methods like leaf spraying or encapsulation in alginate spheres exhibited improved resilience in terms of Kautsky curve intensity and shape, indicating better photochemical apparatus function. These techniques also facilitated post-stress recovery. Deep photochemical analysis revealed SynCom-induced improvements in the plant's photochemical apparatus, particularly the PS II donor side. Moreover, it was also possible to observe that upon stress relief these two techniques, alongside the plants inoculated throughout watering were able to recover their photochemical profiles. Analysing the Fv/Fm values, plants inoculated through watering, alginate beads and leaf spray can be considered heat-tolerant, a characteristic conserved throughout the three sampling moments. Heat-wave exposure led to an increase in the energy absorbed by the non-inoculated plants as a counteractive measure to overcome the low energy use efficiency observed (low trapping and transported energy fluxes). The reduction in stress impact was attributed to SynCom's ACC-deaminase production, which lowered ethylene accumulation, promoting growth and photosynthetic efficiency. The study also noted reduced energy dissipation under stress relief, indicating efficient heat dissipation mechanisms due to SynCom application. Statistical models generated with the attained photochemical data allowed depicting specific fluorescence signatures of each thermal and inoculation treatment with a very high degree of accuracy, reinforcing that these different inoculation treatments have in fact different impacts on plant photochemistry but also provide a tool for future phenotyping assessments using the proposed inoculation techniques. Alginate bead based PGPB release emerged as an efficient, scalable technique with continuous benefits for plant growth and stress response.

Multifaceted growth promotion and biocontrol of Agroathelia rolfsii and induction of defense mechanism by Bacillus amyloliquefaciens SS-CR10 on chilli.

Plant-growth-promoting (PGP) endophytic bacteria are beneficial microorganisms that can help plants withstand biotic stress caused by fungal phytopathogens. In the present study, 78 endophytic bacterial isolates were isolated from chilli (Capsicum annuum L.). A potent isolate with several PGP attributes and better inhibition against Agroathelia rolfsii was selected and identified as Bacillus amyloliquefaciens using 16S rDNA homologies. Phosphate solubilization (65.9 μg ml-1), nitrogen fixation, production of IAA (9.77 to 24.45 μg ml-1), ammonia, ACC deaminase, siderophore, and hydrolytic enzymes were among the PGP traits shown by the strain SS_CR10. Furthermore, the strain demonstrated the ability to colonize roots. It significantly improved the plant's developmental traits, such as fresh and dry weight, photosynthetic pigments, and root and shoot length. LC-MS analysis and PCR amplification of lipopeptide genes also showed that surfactin, iturin, and bacilysin lipopeptides were present. Following treatments with lipopeptide extract and bacterial suspension, A. rolfsii mycelia showed severe deformation and cell death, as seen by live dead staining by fluorescent microscopy and scanning electron microscopy (SEM). Finally, the upregulation of defense-related genes CaPR1, CaPR2, and CaPR4 after bacterial treatment confirmed the induction of systemic resistance. In conclusion, this study shows how strain SS_CR10 might be useful for promoting plant growth in chilli and controlling A. rolfsii in an eco-friendly way, which would protect the health of the soil.