ACC Deaminase Research Articles

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

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.

Assessment of Plant-Growth Promoting Potential of Bacteria Isolated from Amazonian Black Pepper Roots

Purpose: In the Amazon, farmers use chemical fertilizers on a large scale to meet the nutritional requirements of some crops. Plant-growth promoting bacteria (PGPB) offer a sustainable alternative to enhance crop productivity. This study aimed to prospect novel PGPB from Amazonian black pepper (Piper nigrum L.) roots. Methods: Bacterial isolates were obtained from plant roots, evaluated for their biofertilizing potential, and the most promising strain was selected for genome sequencing. Taxonomic classification was based on 16 S rRNA gene sequencing. ACC deaminase activity, phosphate solubilization, and nitrogen fixation were assessed. Genome sequencing was performed using the Ion GeneStudio S5 platform. Results: The 20 isolates were affiliated to Enterobacter (7 isolates), Klebsiella (4 isolates), Kosakonia (5 isolates), Bacillus (2 isolates), and two unclassified bacteria. Seven isolates were positive for ACC deaminase activity, while four were positive for the presence of the nifH gene. Nitrogenase gene was found only in Kosakonia isolates. Ninety isolates were able to solubilize phosphate. The isolate Pn16 was the most promising and presented a genome of 6,432,985 bp, GC content of 55%, 6,465 Coding Sequences, 10 Symbiotic Islands, 28 biosynthetic gene clusters, and several genes involved in plant-growth promotion such as phoU-pstSCAB-phoBR, oqxAB, ipdC, speADEGF, nifHDK. Conclusions: We were able to isolate a bacterium with potential for biofertilization. Based on phylogeny and Average Nucleotide Identity, we propose the classification of the Pn16 isolate as Kosakonia pseudosacchari Pn16.

Enhancing Pisum sativum growth and symbiosis under heat stress: the synergistic impact of co-inoculated bacterial consortia and ACC deaminase-lacking Rhizobium

The 1-aminocyclopropane-1-carboxylate (ACC) deaminase is a crucial bacterial trait, yet it is not widely distributed among rhizobia. Hence, employing a co-inoculation approach that combines selected plant growth-promoting bacteria with compatible rhizobial strains, especially those lacking ACC deaminase, presents a practical solution to alleviate the negative effects of diverse abiotic stresses on legume nodulation. Our objective was to explore the efficacy of three non-rhizobial endophytes, Phyllobacterium salinisoli (PH), Starkeya sp. (ST) and Pseudomonas turukhanskensis (PS), isolated from native legumes grown in Tunisian arid regions, in improving the growth of cool-season legume and fostering symbiosis with an ACC deaminase-lacking rhizobial strain under heat stress. Various combinations of these endophytes (ST + PS, ST + PH, PS + PH, and ST + PS + PH) were co-inoculated with Rhizobium leguminosarum 128C53 or its ΔacdS mutant derivative on Pisum sativum plants exposed to a two-week heat stress period.Our findings revealed that the absence of ACC deaminase activity negatively impacted both pea growth and symbiosis under heat stress. Nevertheless, these detrimental effects were successfully mitigated in plants co-inoculated with ΔacdS mutant strain and specific non-rhizobial endophytes consortia. Our results indicated that heat stress significantly altered the phenolic content of pea root exudates. Despite this, there was no impact on IAA production. Interestingly, these changes positively influenced biofilm formation in consortia containing the mutant strain, indicating synergistic bacteria-bacteria interactions. Additionally, no positive effects were observed when these endophytic consortia were combined with the wild-type strain. This study highlights the potential of non-rhizobial endophytes to improve symbiotic performance of rhizobial strains lacking genetic mechanisms to mitigate stress effects on their legume host, holding promising potential to enhance the growth and yield of targeted legumes by boosting symbiosis.

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.

Potensi Bakteri Rizosfer Tanah Salin Sebagai Rizobakteri Pemacu Pertumbuhan Tanaman Ditanah Salin

The potential of rhizobacteria as plant growth promoters in increasing crop production in saline soils continues to be carried out by exploring the types of isolates from the rhizosphere of saline soils. The purpose of this study was to obtain the types of isolates that have the potential to be developed as biofertilizers in saline soils. The research was conducted by isolating rhizosphere soil from saline soil and then testing the ability of the resulting isolates to produce phytohormones in the form of IAA, the ability to dissolve phosphate, the ability to fix nitrogen and the ability to produce the enzyme ACC deaminase. The results showed that isolates KNW 2.1, KNW 2.2, KNW 2.3 and KNW 3.2 have potential as rhizobacteria that promote plant growth in saline soils as indicated by their ability to produce the hormone IAA, the ability to dissolve phosphate, the ability to fix nitrogen, and the ability to produce the enzyme ACC deaminase which is higher than the other isolates.
 

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).

Serratia spp. as plant growth-promoting bacteria alleviating salinity, drought, and nutrient imbalance stresses.

In agricultural environments, plants are often exposed to abiotic stresses including temperature extremes, salt stress, drought, and heavy metal soil contamination, which leads to significant economic losses worldwide. Especially salt stress and drought pose serious challenges since they induce ionic toxicity, osmotic stress, and oxidative stress in plants. A potential solution can be the application of bacteria of the Serratia spp. known to promote plant growth under normal conditions Thus the mini-review aims to summarize the current knowledge on plant growth promotion by Serratia spp. (under the conditions of salinity stress, drought, and nutrient deficit) and highlight areas for development in the field. So far, it has been proven that Serratia spp. strains exhibit a variety of traits contributing to enhanced plant growth and stress tolerance, such as phytohormone production, ACC deaminase activity, nitrogen fixation, P and Zn solubilization, antioxidant properties improvement, and modulation of gene expression. Nevertheless, further research on Serratia spp. is needed, especially on two subjects: elucidating its mechanisms of action on plants at the molecular level and the effects of Serratia spp. on the indigenous soil and plant microbiota and, particularly, the rhizosphere. In both cases, it is advisable to use omics techniques to gain in-depth insights into the issues. Additionally, some strains of Serratia spp. may be phytopathogens, therefore studies to rule out this possibility are recommended prior to field trials. It is believed that by improving said knowledge the potential of Serratia spp. to stimulate plant growth will increase and strains from the genus will serve as an eco-friendly biofertilizer in sustainable agriculture more often.

D genome acquisition and breeding have had a significant impact on interaction of wheat with ACC deaminase producers in soil or ACC deaminase potential activity in the rhizosphere

Rhizosphere functioning depends on plant traits, but the underlying genotypic properties are poorly understood. Wheat has undergone several domestication events combined with genomic hybridization, including the acquisition by Triticum dicoccon (AABB genome) of the D genome from Aegilops tauschii, resulting into bread wheat Triticum aestivum (AABBDD genome). The D genome is likely to modulate the functioning of beneficial wheat-microbe interactions, but data are needed to substantiate this. Here, we tested the hypothesis that genome D is important for soil interactions of wheat with 1-aminocyclopropane-1-carboxylate (ACC) deaminase producers, a key microbial functional group that enhances plant performance by fine-tuning ethylene metabolism in roots. A range of wheat lines from T. aestivum (AABBDD), T. diccocon (AABB) and Ae. tauschii (DD) were compared based on abundance (qPCR on acdS gene marker), diversity (Illumina MiSeq) and potential ACC deaminase activity (colorimetric assays) of ACC deaminase producers in the rhizosphere. Results showed that the abundance of ACC deaminase producers was lower for D-genome wheats than D-negative T. dicoccon at 40 days, but ACC deaminase potential activity in the rhizosphere was lower for D-genome Ae. tauschii and T. aestivum landraces than T. aestivum cultivars (recent and old), while D-negative T. dicoccon was in between. Rhizosphere community structure of Ae. tauschii and T. dicoccon differed from that of T. aestivum, and differences occurred also between various genotype categories of T. aestivum. Overall, the acquisition of the D genome has had a negative impact on the ability of wheat to recruit ACC deaminase producers in soil, but bread wheats resulting from recent breeding displayed improved ACC deaminase activity in the rhizosphere.

Seed bio-priming with ACC deaminase-producing bacterial strains alleviates impact of drought stress in Soybean (Glycine max (L.) Merr.)

This study investigated the efficacy of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase-producing rhizobacterial strains isolated from soybean rhizosphere to alleviate the negative impact of drought stress in soybean. Twenty rhizobacterial strains were isolated from disease-resistant soybeans, and only four isolates displayed ACC deaminase activity (more than 500 nmol of ketobutyrate mg protein−1 h−1). These strains also exhibited a variety of plant growth-promoting (PGP) traits, such as ammonia production, indole acetic acid concentration (>35 g mL−1), hydrogen cyanide (HCN) production, and solubilization of inorganic calcium orthophosphate (>70 μg mL−1). Based on 16S rDNA gene sequencing, the bacterial isolates (AKAD 1-2, AKAD 1-3, AKAD 3-1, and AKAD 3-7) were identified as Pantoea agglomerans (MH304295), Bacillus subtilis (MH304311), Bacillus cereus (MH333217), and Bacillus licheniformis (MH304284), respectively. .Seed bio-priming with these rhizobacteria improvedin vivodrought tolerance, mitigated drought stress and increased shoot length (16–68.6%), root length (40–108%), proline content (14.87–42.69%), sugar content (11.36–67.3%), and protein content (11.77–45%). The potential enzymatic activities of catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD) also increased by 35.87%, 26.63%, and 15.15%, respectively, in drought-stressed plants. The results support the efficacy of these isolates as effective bio-stimulants for improving crop performance in drought-affected agricultural fields. Thus, the present work opens new avenues for harnessing the potential of rhizobacterial bio-stimulants to address the challenges posed by drought stress in soybean cultivation, thereby advancing sustainable agricultural strategies for future food security.

Diversity, Characterization, and Potential Applications of Bacterial Endophytes Isolated from the Halophyte Limonium axillare

Recently, there has been a worldwide call to explore nature-friendly compounds, which could enhance plant growth and substitute for chemically synthesized products. Endophytes are a group of microorganisms that lives in the plants and algae symbiotically. In this research, endophytes were isolated from leaves of the halophyte, Limonium axillare. A total of 280 bacterial isolates were obtained from the leaves of L. axillare. Strains displaying similarities in terms of morphology and biochemical reactions were categorized into 48 groups. One representative from each group was identified and subjected to enzymatic and plant growth-promoting tests. Forty-eight isolates were identified using a sequence similarity-based method based on the 16S rDNA gene. The identified strains were categorized into two genera: Bacillus and Staphylococcus. Our investigation uncovered 44 isolates from the Bacillus genus, representing 10 different species, including Bacillus sp., B. pseudomycoides, B. cereus, B. paramycoides, B. velezensis, B. subtilis, B. thuringiensis, B. wiedmannii, B. anthracis, and B. bacterium. Furthermore, we observed that only 4 isolates belonged to the Staphylococcus genus, encompassing 3 distinct species: S. bacterium, S. succinus, and S. saprophyticus. The isolated bacteria were screened for extracellular enzymes, plant growth promoting traits, antifungal activity, and salinity tolerance. From the previous screening, diverse responses were obtained. Most of the isolates were secreted at least one of the hydrolysis enzymes (protease, lipase and amylase). (93.8%) of the strains showed phosphate solubilization activity. (33.3%) produce (IAA). Siderophore production potential was present in 91.7% of isolates, while ACC deaminase and HCN production activities were identified in 52.1 and 41.7% of strains, respectively. Additionally, DNase activity was evident in 27.1%, and ammonia production was observed in 31.3% of the isolates. The isolates Bacillus velezensis (AL4QUA) strain showed positive effect in the greenhouse experiment in terms of plant growth promoter agent and biocontrol agent against Fusarium oxysporum pathogen of tomato seedling. Thus, endophytes have the potential to reduce chemical inputs in conventional agricultural practices, increase nutrient uptake and improve plant stress resilience.

The genome, pangenome, and physiological analysis of Leclercia adecarboxylata (kcgeb_e1), a plant growth-promoting bacterium

Plant growth-promoting bacteria (PGPB) as biofertilizer plays an important role in agriculture practices. In this study, we isolated and identified plant-associated bacteria Leclercia adecarboxylata (kcgeb_e1) from the root region of the halophytic plant Sesuvium verrucosum. We tested its physiological activity and the effect of inoculation, with and without salt, on photosynthesis using Cajanus cajan. Further, we sequenced the whole genome of L. adecarboxylata (kcgeb_e1) and carried out pangenome analysis with 12 other genomes of the same species, which highlights unique genes enriched for pathways involved in abiotic stress tolerance (salinity, drought and heat) and carbohydrate transport. Moreover, gene families involved in abiotic stress tolerance, host adhesion, and transport were under positive selection (e.g., Aldo/keto reductase family, Hemagglutinin, Porin, and sugar transport). We observed a loss of ACC deaminase gene in this pangenome; however, this strain can still produce 1-aminocyclopropane-1-carboxylate (ACC), an enhancer of abiotic stress, which suggests that its homologue, d-cysteine sulfatase, has a bifunctional activity. In addition, this strain has Indole acetic acid (IAA) and phosphate solubilization activity. Combining these findings with the efficiency of colonizing the root surface of Solanum lycopersicum, this strain showed remarkable enhancement of photosynthesis, comparing control to inoculated plants. This increase in photosynthesis is consistent with an increase in sucrose under salt treatment, but not in glucose and fructose, which acts as a sensor in opposing the negative effect of salinity and promoting sustainable growth. Given all this, our study suggests that this PGPB can act as a biofertilizer for sustainable agriculture.

Halotolerant and plant growth-promoting endophytic fungus Aspergillus terreus CR7 alleviates salt stress and exhibits genoprotective effect in Vigna radiata.

Soil salinity is one of the major environmental stresses that results in reduction of cultivable land and decreased productivity. In the present study, halotolerant and plant growth-promoting endophytic fungi were isolated from Catharanthus roseus, and their effect in mitigating salt stress in Vigna radiata was evaluated. An isolate CR7, identified to be Aspergillus terreus, showing plant growth promotion activities, viz. IAA production (23.43 ± 0.79 μg/ml), phosphate solubilization (133.63 ± 6.40 μg/ml), ACC deaminase activity (86.36 ± 2.70 μmol α-ketobutyrate/h/mg protein) etc. and ability to grow at 15% NaCl was selected for further in vivo studies. Colonization of CR7 was carried out in V. radiata which was subjected to different concentrations of salt (150, 200, and 250 mM NaCl). Under salt stress, A. terreus CR7 inoculated plants showed substantially improved root and shoot length, biomass, chlorophyll content, relative water content, phenolics, protein content, and DPPH scavenging activity. Endogenous IAA level was enhanced by 5.28-fold in treated plants at maximum salt stress. Inoculation of A. terreus CR7 affected oxidative stress parameters, exhibiting an increase in catalase and superoxide dismutase and reduction in proline, electrolyte leakage, and malondialdehyde content. Fluorescent microscopic analysis of roots revealed improved cell viability and decreased levels of glutathione and hydrogen peroxide under salt stress in treated plants. The isolate A. terreus CR7 also protected against DNA damage induced by salt stress which was evaluated using comet assay. A decrease in DNA tail length, tail moment, and olive tail moment to the extent of 19.87%, 19.76%, and 24.81%, respectively, was observed in A. terreus CR7-colonized plants under salt stress. It can be concluded that A. terreus CR7 can be exploited for alleviating the impact of salt stress in crop plants.

Trichoderma Inoculation Alleviates Cd and Pb-Induced Toxicity and Improves Growth and Physiology of Vigna radiata (L.).

Heavy metals (HMs) pose a serious threat to agricultural productivity. Therefore, there is a need to find sustainable approaches to combat HM stressors in agriculture. In this study, we isolated Trichoderma sp. TF-13 from metal-polluted rhizospheric soil, which has the ability to resist 1600 and 1200 μg mL-1 cadmium (Cd) and lead (Pb), respectively. Owing to its remarkable metal tolerance, this fungal strain was applied for bioremediation of HMs in Vigna radiata (L.). Strain TF-13 produced siderophore, salicylic acid (SA; 43.4 μg mL-1) and 2,3-DHBA (21.0 μg mL-1), indole-3-acetic acid, ammonia, and ACC deaminase under HM stressed conditions. Increasing concentrations of tested HM ions caused severe reduction in overall growth of plants; however, Trichoderma sp. TF-13 inoculation significantly (p ≤ 0.05) increased the growth and physiological traits of HM-treated V. radiata. Interestingly, Trichoderma sp. TF-13 improved germination rate (10%), root length (26%), root biomass (32%), and vigor index (12%) of V. radiata grown under 25 μg Cd kg-1 soil. Additionally, Trichoderma inoculation showed a significant (p ≤ 0.05) increase in total chlorophyll, chl a, chl b, carotenoid content, root nitrogen (N), and root phosphorus (P) of 100 μg Cd kg-1 soil-treated plants over uninoculated treatment. Furthermore, enzymatic and nonenzymatic antioxidant activities of Trichoderma inoculated in metal-treated plants were improved. For instance, strain TF-13 increased proline (37%), lipid peroxidation (56%), catalase (35%), peroxidase (42%), superoxide dismutase (27%), and glutathione reductase (39%) activities in 100 μg Pb kg-1 soil-treated plants. The uptake of Pb and Cd in root/shoot tissues was decreased by 34/39 and 47/38% in fungal-inoculated and 25 μg kg-1 soil-treated plants. Thus, this study demonstrates that stabilizing metal mobility in the rhizosphere through Trichoderma inoculation significantly reduced the detrimental effects of Cd and Pb toxicity in V. radiata and also enhanced development under HM stress conditions.

Interactive effects on ACC deaminase activity in salt‐tolerant plant growth‐promoting rhizobacteria and impacts on rice crop improvement

AbstractThe present study focuses on the 1‐aminocyclopropane‐1‐carboxylic acid (ACC) deaminase assay and the rhizospheric interactions affecting enzyme activity. We investigate the efficacy of ACC deaminase‐producing rhizobacterial activity in alleviating salt stress in rice. Among the five selected isolates, only two strains, KFSC2 and PK7, possessed the enzyme activity. The amplification of the acdS gene resulted in gene identification in all five isolates. The newly designed primer in this study was suitable for both Pseudomonas and Enterobacter species. The gene products of KFSC1 and KFSC2 were amplified, sequenced and subsequently submitted to GenBank with accession numbers OQ703930 and OQ798805, respectively. This marks the first‐ever submission of the acdS gene sequence from Pseudomonas aeruginosa to GenBank. The interactive effect of root exudates on ACC deaminase activity was assessed using amino acids, organic acids and sugars. The highest enzyme activity was obtained with aspartic acid and fructose, while organic acids and varying pH levels had negative influences on enzyme activity. Additionally, salt and proline had positive effects. These results indicate that there is a positive interaction occurring among these compounds from plants and root‐colonizing bacteria. The selected strain PK7 had a significant impact on growth parameters. Moreover, yield resulted in 252 kg/hec over the control suggests its future possibility of promising bioformulations.

Isolation, Characterization, and Screening of Endospore Forming Endophytic Bacteria from Cowpea [Vigna unguiculata (L.) Walp.] for Plant Growth Promotion and Abiotic Stress Mitigation

We performed isolation and characterization of endospore forming endophytic bacteria (EEB) from endorhizospheric region of healthy bush cowpea var. Bhagyalakshmi. All the EEB isolates were evaluated for their ability to produce plant growth promoting traits such as production of indole acetic acid (IAA), gibberellic acid, ammonia, ACC deaminase, volatile organic compounds and siderophore, and capacity for nitrogen fixation, and solubilization of phosphorus and potassium. Roll towel assay was used for assessing the seedling vigour index of cowpea after seed priming with the EEB isolates. Based on growth promotion and seedling vigour index, seven superior bacterial isolates were selected, and antagonistic activity against the fungal pathogens Fusarium oxysporum, Rhizoctonia solani, Colletotrichum sp., Phytophthora sp., and Pythium sp., was assayed. The isolates were pooled together to form a consortium and biopriming of cowpea seeds were done. Bioprimed seeds were tested for plant growth promotion and abiotic stress management in cowpea under protray condition. The seedlings of the bioprimed cowpea seeds showed better seedling vigour index and stress tolerance compared to hydro-primed seeds and the unprimed control. EEB isolated from the host plant could be developed as plant growth promoting bioagents.

Impact of two Erwinia sp. on the response of diverse Pisum sativum genotypes under salt stress

Currently, salinization is impacting more than 50% of arable land, posing a significant challenge to agriculture globally. Salt causes osmotic and ionic stress, determining cell dehydration, ion homeostasis, and metabolic process alteration, thus negatively influencing plant development. A promising sustainable approach to improve plant tolerance to salinity is the use of plant growth-promoting bacteria (PGPB). This work aimed to characterize two bacterial strains, that have been isolated from pea root nodules, initially called PG1 and PG2, and assess their impact on growth, physiological, biochemical, and molecular parameters in three pea genotypes (Merveille de Kelvedon, Lincoln, Meraviglia d’Italia) under salinity. Bacterial strains were molecularly identified, and characterized by in vitro assays to evaluate the plant growth promoting abilities. Both strains were identified as Erwinia sp., demonstrating in vitro biosynthesis of IAA, ACC deaminase activity, as well as the capacity to grow in presence of NaCl and PEG. Considering the inoculation of plants, pea biometric parameters were unaffected by the presence of the bacteria, independently by the considered genotype. Conversely, the three pea genotypes differed in the regulation of antioxidant genes coding for catalase (PsCAT) and superoxide dismutase (PsSOD). The highest proline levels (212.88 μmol g−1) were detected in salt-stressed Lincoln plants inoculated with PG1, along with the up-regulation of PsSOD and PsCAT. Conversely, PG2 inoculation resulted in the lowest proline levels that were observed in Lincoln and Meraviglia d’Italia (35.39 and 23.67 μmol g−1, respectively). Overall, this study highlights the potential of these two strains as beneficial plant growth-promoting bacteria in saline environments, showing that their inoculation modulates responses in pea plants, affecting antioxidant gene expression and proline accumulation.

Endophytic fungi from Himalayan silver birch as potential source of plant growth enhancement and secondary metabolite production.

Mountain biodiversity is under unparalleled pressure due to climate change, necessitating in-depth research on high-altitude plant's microbial associations which are crucial for plant survival under stress conditions. Realizing that high-altitude tree line species of Himalaya are completely unexplored with respect to the microbial association, the present study aimed to elucidate plant growth promoting and secondary metabolite producing potential of culturable endophytic fungi of Himalayan silver birch (Betula utilis D. Don). ITS region sequencing revealed that the fungal isolates belong to Penicillium species, Pezicula radicicola, and Paraconiothyrium archidendri. These endophytes were psychrotolerant in nature with the potential to produce extracellular lytic activities. The endophytes showed plant growth promoting (PGP) traits like phosphorus solubilization and production of siderophore, indole acetic acid (IAA), and ACC deaminase. The fungal extracts also exhibited antagonistic potential against bacterial pathogens. Furthermore, the fungal extracts were found to be a potential source of bioactive compounds including the host-specific compound-betulin. Inoculation with fungal suspension improved seed germination and biomass of soybean and maize crops under net house conditions. In vitro PGP traits of the endophytes, supported by net house experiments, indicated that fungal association may support the growth and survival of the host in extreme cold conditions.

Indole-3-Acetic Acid Producing Yeasts in the Phyllosphere of Legumes: Benefits for Chili Growth

Plant growth-promoting yeast (PGPY), which is associated with plants, has demonstrated the ability to enhance plant growth and crop yield and provide an effective alternative strategy for reducing the extensive use of chemical fertilizers. However, plant development and yield effects of the phyllosphere yeast have received comparatively little research. Therefore, 95 phylloplane yeast were isolated from the leaves of plants in Leguminosae, and their capability to produce indole-3-acetic acid (IAA) in yeast extract peptone dextrose (YPD) broth supplemented with L-tryptophan was evaluated in this research. Forty-two isolates were selected, due to their ability to produce IAA. Among these isolates, 7 showed high IAA production of more than 40 mg/g DW in YPD with tryptophan as the precursor. These strains were identified as Candida tropicalis, Pichia kudriavzevii and Tortispora caseinolytica based on morphological and D1/D2 domain of LSU rDNA sequence analysis. Other plant growth promotion traits, including the solubilization of phosphate, production of ammonia and siderophores and ACC deaminase activity, were also investigated. The results revealed that Candida tropicalis KPS2219 exhibited maximum IAA production of 54.10 mg/g DW, high ammonia production at 1.16 mg/mL and siderophore production. In a greenhouse experiment, the ability of C. tropicalis KPS2219 to enhance the growth of chili seedlings was investigated. The results revealed that seed priming followed by foliar spraying with C. tropicalis KPS2219 significantly increased the root length, shoot length, root dry weight and stem dry weight of the seedlings by 17.72, 29.15, 60 and 46.15 %, respectively, in comparison to those of the uninoculated control. These findings indicate the possibility of C. tropicalis KPS2219 as a bioinoculant to promote plant development and the effectiveness of foliar application. The efficacy of employing yeast consortiums to enhance growth will be investigated for further study. HIGHLIGHTS Phylloplane yeasts with remarkably high IAA production and multiple traits that promote the growth of plants were isolated from the new habitat, legumes. Spraying the yeast cells on the leaves of chili plants accelerated the growth of the plant. GRAPHICAL ABSTRACT

ACC (1-aminocyclopropane-1-carboxylic acid) deaminase producing endophytic bacteria improve hydroponically grown lettuce in the greenhouse during summer season

In the summer, cool season crops like lettuce are typically not grown in a greenhouse because evaporative coolers cannot sufficiently lower the temperature to their optimal range (12–18 °C). The objective of this study was to increase yields of two butterhead lettuce cultivars (‘Buttercrunch’ and ‘Rex’) under summer heat stress utilizing bacterial endophytes with high 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. ACC is a precursor of ethylene. ACC deaminase reduces stress in plants by cleaving ACC into α-ketobutyrate and ammonia and lowering ethylene levels. Four bacterial endophytes (IALR387, IALR1385, IALR1794 and IALR1819) having high levels of ACC deaminase activity were selected from the Plant Endophyte Research Center's bacterial endophyte collection. The endophytes were identified as either Paraburkholderia sp. (IALR387 and IALR1385) or Burkholderia contaminans (IALR1794 and IALR1819). These 4 bacterial endophytes were tested in ‘Buttercrunch’ and ‘Rex’ during summer 2022 in two greenhouse experiments. The inoculation of lettuce with these bacterial endophytes enhanced lettuce growth in greenhouse hydroponic production except for IALR1385. In both cultivars, IALR1819 improved lettuce growth the most with shoot fresh and dry weights and the chlorophyll content.