Indole Acetic Acid Production Research Articles

Fructo-oligosaccharides Alleviated Ulcerative Colitis via Gut Microbiota-Dependent Tryptophan Metabolism in Association with Aromatic Hydrocarbon Receptor Activation in Mice.

Fructo-oligosaccharide (FOS) is a typical prebiotic with intestinal health-promoting effects. Here, we explored the anticolitis activity of FOS and clarified the underlying mechanisms. Dextran sulfate sodium (DSS)-induced mice were gavaged with FOS (400 mg/kg) for 37 days, and administration of FOS alleviated DSS-induced colitis symptoms. Besides, FOS improved gut microbiota dysbiosis and modulated the intestinal microbiota-controlled tryptophan metabolic pathways. Targeted metabolomic results showed that FOS significantly increased the colonic levels of indole-3-acetic acid (IAA) and indole-3-propionic acid (IPA) and subsequently increased the expressions of aromatic hydrocarbon receptors (AhR) in the colon and further promoted the expressions of interleukin-22 (IL-22) and intestinal tight junction proteins in the colitis mice. These findings for the first time highlight a novel anticolitis mechanism of FOS by alleviating intestinal microbiota dysbiosis and modulating microbial tryptophan metabolism to promote IAA and IPA production for triggering AhR/IL-22 axis activation.

Elucidating metabolic pathways through genomic analysis in highly heavy metal-resistant Halobacterium salinarum strains

The annotated and predicted genomes of five archaeal strains (AS1, AS2, AS8, AS11 and AS19), isolated from Sfax solar saltern sediments (Tunisia) and affiliated with Halobacterium salinarum, were performed by RAST webserver (Rapid Annotation using Subsystem Technology) and NCBI prokaryotic genome annotation pipeline (PGAP). The results showed the ability of strains to use a reduced semi-phosphorylative Entner-Doudoroff pathway for glucose degradation and an Embden-Meyerhof one for gluconeogenesis. They could use glucose, fructose, glycerol, and acetate as sole source of carbon and energy. ATP synthase, various cytochromes and aerobic respiration proteins were encoded. All strains showed fermentation capability through the arginine deiminase pathway and facultative anaerobic respiration using electron acceptors (Dimethyl sulfoxide and trimethylamine N-oxide). Several biosynthesis pathways for many amino acids were identified. Comparative and pangenome analyses between the strains and the well-studied halophilic archaea Halobacterium NRC-1 highlighted a notable dissimilarity. Besides, the strains shared a core genome of 1973 genes and an accessory genome of 767 genes. 129, 94, 67, 15 and 29 unique genes were detected in the AS1, AS2, AS8, AS11 and AS19 genomes, respectively. Most of these unique genes code for hypothetical proteins. The strains displayed plant-growth promoting characteristics under heavy metal stress (Ammonium assimilation, phosphate solubilization, chemotaxis, cell motility and production of indole acetic acid, siderophore and phenazine). Therefore, they could be used as a biofertilizer to promote plant growth. The genomes encoded numerous biotechnologically relevant genes responsible for vitamin biosynthesis, including cobalamin, folate, biotin, pantothenate, riboflavin, thiamine, menaquinone, nicotinate, and nicotinamide. The carotenogenetic pathway of the studied strains was also predicted. Consequently, the findings of this study contribute to a better understanding of the halophilic archaea metabolism providing valuable insights into their ecophysiology as well as relevant biotechnological applications.

Bacillus velezensis SS-20 as a potential and efficient multifunctional agent in biocontrol, saline-alkaline tolerance, and plant-growth promotion

The versatile strain Bacillus velezensis SS-20 was studied to determine its agricultural benefits, including its ability to antagonize fungi, promote plant growth, and tolerate saline-alkaline conditions. Firstly, strain SS-20 was found to be an antagonist of plant pathogenic fungi such as Magnaporthe oryzae, Rhizoctonia solani, and Fusarium oxysporum, with control effects up to 82.07 %, 46.57 %, and 23.09 %, respectively. The hyphae of pathogenic fungi treated with SS-20 and its fermentation product were abnormal, swollen, deformed, and distorted. Meanwhile, strain SS-20 dissolved inorganic phosphorus (phosphate solubilization efficiency, 45.95 %), and produced siderophore (siderophore units, 54.18 ± 4.19 %), and poly-γ-glutamic acid (γ-PGA) (13.35 ± 2.61 g/L). Strain SS-20 significantly increased plant height, aboveground fresh weight, and root dehydrogenase activity compared to the control treatment under non-saline conditions (p < 0.05). In addition, strain SS-20 showed significant saline-alkaline tolerance, surviving in 10 % NaCl and pH 9.5, and enhanced plant growth under simulated saline-alkali conditions. Whole-genome sequencing analysis revealed that the chromosome of B. velezensis SS-20 consists of 3,929,792-bp with 46.5 % guanine-cytosine content and 4015 coding sequences. The antiSMASH analysis identified 12 gene clusters within strain SS-20 that encode antimicrobial compounds such as surfactin, fengycin, butirosin A/butirosin B, macrolactin H, bacillibactin, difficidin, and bacilysin, thereby corroborating the strain's biocontrol capabilities. Genes related to plant growth promotion, including siderophores, γ-PGA, indole acetic acid production, phosphate solubilization, glycine-betaine production, and Na+/H+ antiporters, were also annotated. In conclusion, B. velezensis SS-20 represents a promising biotic resource for enhancing plant growth and protecting against environmental stresses.

Rhizosphere bacteria from the Bolivian highlands improve drought tolerance in quinoa (Chenopodium quinoa Willd.).

Drought is one of the most destructive abiotic factors for agricultural production, causing considerable yield losses. Quinoa (Chenopodium quinoa Willd.) is cultivated worldwide in different environmental conditions due to its nutritional characteristics and ability to grow in harsh environments. This study aims to select drought stress tolerant rhizosphere bacteria from the Bolivian altiplano to evaluate their quinoa growth-promoting capacity, including in vitro germination, seedling growth under drought stress in greenhouse conditions and field studies. Rhizosphere soil from the southern highlands of Bolivia was collected to isolate 164 drought-stress tolerant bacteria. From these, 28 strains were shown to produce indole acetic acid, and/or to possess nitrogen-fixing or phosphate solubilizing capacity under in vitro conditions. Furthermore, all strains were evaluated for improvement of in vitro quinoa seed germination. Based on these properties, nine bacterial strains were formulated in three different matrixes and evaluated for quinoa seedling growth promotion during drought stress in a three-month greenhouse experiment. Three strains were shown to significantly (P < 0.05) increase root length of the quinoa seedlings. One strain was selected and shown to significantly (P < 0.05) increase leaf number in a field trial under semi-arid conditions in the southern altiplano in Bolivia. DNA sequencing and phylogenetic analyses of the 16S locus putatively identified the three strains with growth-promoting potential under drought stress as members of the genera Bacillus, Pseudomonas and Serratia. Microorganisms from the arid Bolivian altiplano constitute a potential biological source of bioinoculants to improve quinoa productivity and provide sustainable mitigation of climate change effects.

INOCULATION OF MULTI-TRAIT PLANT GROWTHPROMOTING RHIZOBACTERIA FOR WHEAT GROWTH PROMOTION IN POTHOUSE CONDITIONS

Plant growth-promoting rhizobacteria (PGPR) are commonly used as inoculants to improve the growth and yield of wheat crops. Thus, the present study focused on the isolating and screening of effective isolates with multi-traits PGPR activities related to plant growth and development. Bacterial strains RA4, RA11 and RA26 were showing plant growth promoting activities like potassium solubilization, phosphate solubilization, indole acetic acid production (IAA), hydrogen cyanide production (HCN), ammonium production, zinc solubilization, anti-fungal activity. The antibiotic pattern showed that bacterial isolates RA11 and RA26 were resistant against azithromycin, ampicillin and gentamicin. Identification of multi trait PGPR was carried out by 16s rRNA sequencing. Bacterial strains RA4, RA11 and RA26 were showing 99.93 %, 100 % and 99.97 % similarity and identified as Pseudomonas paraeruginosa, Bacillus cereus and Pseudomonas aeruginosa respectively. A pot house experiment was conducted in order to check the efficacy of multi-trait PGPR as inoculants for wheat growth. In our study, bacterial strain Bacillus cereus (RA11) was showing maximum plant growth promotion in the presence of the RDK of NPK in pot house conditions. Generally, results of this study revealed that use of bio fertilizers had an effective and significant role in the growth of plants.

Harnessing synthetic microbial communities with nitrogen-fixing activity to promote rice growth

Abstract Improving the biological nitrogen fixation of rhizosphere bacteria in rice is expected to improve plant growth and productivity. Most studies have focused on the application of a single N2-fixing bacterium on rice plants. Little is known about the beneficial impacts of a bacterial consortium, which is known as the microbial synthetic community (SynCom) on rice growth, and the extent of the interaction with the microbial community. The study investigated the effect of a SynCom on rice growth and productivity. A SynCom consisting of three bacteria Azosprillium sp. NL1, Bradyrhizobium sp. NL2, and Azotobacter sp. NL3 was designed to increase the survival and density of root microorganisms. The microbial culture collections used for the reconstitution experiment were established using bacterium-free soil. A profound increase in bacterial root microbiota survival and density was observed in plants inoculated with either mono- or multi-synthetic microbial consortia. SynCom is essential for rice plant growth by improving shoot ramification and root development. The results showed that SynCom could increase the total root nitrogen-fixing (%Ndfa) value by 51.6%, with Azotobacter sp. NL3 being the most dominant. High levels of indole acetic acid production in the range of 0.65–0.8 ng per g root were observed in Azosprillium sp. NL1 and Azotobacter sp. NL3. This indicates Azotobacter sp. NL3 is a nitrogen-fixing rhizosphere bacterium that is dominant in rice-amended soils. These results support the early application of the designed SynCom as a feasible strategy for the induction of nitrogen fixation, suggesting a role for earlier effects on rhizosphere colonization and tillering of plants.

Engineering peroxisomal surface display for enhanced biosynthesis in the emerging yeast Kluyveromyces marxianus

The non-conventional yeast Kluyveromyces marxianus is a promising microbial host for industrial biomanufacturing. With the recent development of Cas9-based genome editing systems and other novel synthetic biology tools for K. marxianus, engineering of this yeast has become far more accessible. Enzyme colocalization is a proven approach to increase pathway flux and the synthesis of non-native products. Here, we engineer K. marxianus to enable peroxisomal surface display, an enzyme colocalization technique for displaying enzymes on the peroxisome membrane via an anchoring motif from the peroxin Pex15. The native KmPex15 anchoring motif was identified and fused to GFP, resulting in successful localization to the surface of the peroxisomes. To demonstrate the advantages for pathway localization, the Pseudomonas savastanoi IaaM and IaaH enzymes were co-displayed on the peroxisome surface; this increased production of indole-3-acetic acid 7.9-fold via substrate channeling effects. We then redirected pathway flux by displaying the violacein pathway enzymes VioE and VioD from Chromobacterium violaceum, increasing selectivity of proviolacein to prodeoxyviolacein by 2.5-fold. Finally, we improved direct access to peroxisomal acetyl-CoA and increased titers of the polyketide triacetic acid lactone (TAL) by 2-fold through concurrent display of the proteins Cat2, Acc1, and the type III PKS 2-pyrone synthase from Gerbera hybrida relative to the same three enzymes diffusing in the cytosol. We further improved TAL production by up to 2.1-fold through engineering peroxisome morphology and lifespan. Our findings demonstrate that peroxisomal surface display is an efficient enzyme colocalization strategy in K. marxianus and applicable for improving production of a wide range of non-native products.

Sustainable bioconversion of rice straw into indole-3-acetic acid by Streptomyces coelicoflavus using response surface methodology

AbstractRice straw is an abundant agricultural waste that poses environmental disposal challenges and can be utilized for biotechnological applications. This study investigates the potential of actinobacteria to enhance rice straw biodegradation and sustainable indole-3-acetic acid (IAA) production, addressing the need for sustainable agricultural practices. Certain actinobacteria strains can effectively degrade rice straw while optimizing IAA production under controlled fermentation conditions. Twenty actinobacteria isolates were screened for lignocellulolytic enzyme activity, and ten were selected for rice straw biodegradation. IAA production was further optimized using response surface methodology based on temperature, pH, and agitation speed (RPM). Isolate S16 achieved a degradation rate of 68.75%, while S18 produced the highest IAA concentration (1040.625 μg/mL) under optimized conditions (25 °C, pH 9, 160 RPM). The purified IAA significantly improved Medicago sativa L. growth. Furthermore, the 16S rRNA gene sequence of isolate S18 was identified it as Streptomyces coelicoflavus strain NSH24 with accession number PP 320383.1. These findings underscore the potential of actinobacteria to efficiently convert agricultural waste into valuable bioproducts and promote sustainable farming practices. By transforming rice straw into high-value products like IAA, this approach contributes to a circular economy, offering an environmentally friendly solution for biomass utilization and agricultural sustainability.

The Ability of Endophytic Bacteria in Phosphate Solubilization and IAA Production on Chili Plant Growth

Biofertilizer is considered an alternative to chemical fertilizers for enhancing plant productivity while minimizing ecological damage. Endophytic bacteria have the ability to solubilize phosphate and produce IAA (indole acetic acid). The aim of this research is to assess the phosphate solubilization and IAA production abilities of bacterial isolates applied to chili plants. Seven bacterial isolates collection from the Microbiology Laboratory, Universitas Sumatera Utara, were tested. In quantitative tests conducted in vitro, isolates MB10 and MB11 demonstrated the highest phosphate solubilization capabilities, yielding solubilization indices of 16.2 mm and 9.5 mm, respectively. Additionally, the ability of bacterial isolates to produce IAA in vitro was evaluated using calorimetry, revealing that isolates MB8 and MB2 produced the highest concentrations of IAA, measuring 58.58 ppm and 54.64 ppm, respectively. Furthermore, in vivo application involved the inoculation of isolates MB10 and MB11 on chili plants for 30 days. Seed treatment with suspensions of isolates MB10 and MB11 resulted in decreased plant performance compared to the control. These findings indicate that some endophytic bacteria originating from the mangrove root Avicennia marina have potential for producing relatively high levels of secondary metabolites. However, direct application did not significantly enhance plant growth performance.

Co‐inoculation with Rhizobium, Azospirillum, and microalgae increases common bean yield and profitability

AbstractWidely used as inoculants in agriculture, nitrogen‐fixing bacteria can be associated with other plant growth‐promoting microorganisms (PGPMs) to increase crop grain yield. This study aimed to evaluate whether co‐inoculation with Rhizobium tropici and Azospirillum brasilense associated with microalgae or cyanobacteria enhances common bean (Phaseolus vulgaris) grain yield and its economic gains in contrasting sandy and clayey soils. Water‐soluble protein content and indole‐3‐acetic acid (IAA) production of two cyanobacteria (Anabaena cylindrica and Calotrix brevissima) and six Chlorophyta microalgae (Nannochloropsis oculata, Haematococcus pluvialis, Muriellopsis sphaerica, Chlorella protothecoides, Chlorella vulgaris, and Botryococcus braunii) were determined. Anabaena cylindrica and C. brevissima had the highest IAA production, 336.7 ± 44.7 and 94.1 ± 11.8 µg IAA mg−1 of protein, respectively. Two field experiments were carried out to evaluate the triple inoculation of these Chlorophyta microalgae and cyanobacteria associated with R. tropici plus A. brasilense on the agronomic efficiency and profitability of common bean. Co‐inoculation of C. vulgaris plus R. tropici and A. brasilense in common bean had grain yield of 1277.5 kg ha−1 in clayey soil and 2960.3 kg ha−1 in sandy soil, increasing by 219.7 and 656.0 kg ha−1, respectively, in relation to double inoculation of R. tropici + A. brasilense. In the sandy soil, common bean with triple co‐inoculation had the highest profit ($956 ha−1), which was 25.6% higher than the N fertilized plants. Co‐inoculation with PGPMs generated the highest economic gains, and in addition, it is an eco‐friendly agronomic practice for sustainable food production.

Isolation and characterization of salt-stress-tolerant rhizosphere soil bacteria and their effects on plant growth-promoting properties

PGPR has a higher potential impact on agricultural crops. It enhances plant growth and development in a variety of adverse environmental conditions, including biotic and abiotic stresses. The PGPR is commercially vital since it is more efficient, safe for the environment, and beneficial to the economy. Nowadays, salt stress has an impact on the agricultural ecosystem. Salt-tolerant PGPR can directly stimulate plant growth and development by producing a variety of metabolites and phytohormones. The current study looked at the isolation of salt-tolerant bacterial species and their ability to stimulate plant development. Four bacterial species were chosen for their better salt stress tolerance (0–5%). They were identified by 16S rRNA sequencing: Solibacillus silvestris BR1, Peribacillus frigoritolerans BR2, Paenibacillus taichungensis CR1, and Solibacillus isronensis CR2. These strains were positive production of indole acetic acid with varying incubation periods (19.66 ± 1.528 to 646.111 ± 8.058 µg/mL), salt stress (ranging from 29.556 ± 1.171 to 147.8111 ± 2.086 µg/mL), phosphate solubilization (0.145 ± 0.011 to 0.921 ± 0.007 µg/mL), ammonium production (0.299 ± 0.047 to 1.202 ± 0.142 µg/mL), HCN production (0.308 ± 0.051 to 4.269 ± 0.069 µg/mL), and siderophore production (0.190 ± 0.064 to 1.543 ± 0.108 µg/mL) for control strains were used without salt stress. The production level was expressed using a standard curve containing various standards.

IAA-producing bacteria from the rhizosphere of chickpea (Cicer arietinum L.): Isolation, characterization, and their effects on plant growth performance

Indole-3-acetic acid (IAA), a crucial plant hormone, regulates diverse physiological processes. This study aimed to isolate and characterize IAA-producing bacteria from the chickpea (Cicer arietinum L.) rhizosphere and evaluate their effects on plant growth. From 54 rhizosphere samples, 118 bacteria (designated as GAC) were isolated and screened for IAA production using a Salkowski colorimetric assay, and Bergey's manual was used for biochemical identification. Isolates were grown under various conditions and in vitro screened for their growth promotion traits. A PCR investigation was performed for IAA and nitrogen-fixing genes, and evaluated for greenhouse conditions. Among them, 27 isolates produced IAA, with eight high producers selected. Morphological and biochemical identification classified the six isolates as Pseudomonas and the other two as Bacillus. Optimal conditions for IAA production were observed at 500 μg/ml tryptophan, 35 °C, and pH 7.0. A 48-h incubation was ideal for IAA production, except for GAC-34 and GAC-73, which required 72 h. All the isolates achieved optimal IAA levels with tryptone and sucrose as nitrogen and carbon sources, respectively. Moreover, all isolates showed nitrogen fixation ability, and the six isolates exhibited phosphate solubilization. PCR confirmed the amplification of nifH (300 bp), nifK (360 bp), and ipdC (1170 bp) genes. Greenhouse experiments demonstrated that eight selected isolates significantly enhanced chickpea growth parameters (p < 0.001). These findings suggest that these IAA-producing bacteria have the potential to be used as biofertilizers to improve crop productivity, although further molecular identification and field studies are required.

Antibiotics Resistance and PGPR Traits of Endophytic Bacteria Isolated in Arid Region of Morocco

This study aimed to characterize endophytic bacteria isolated from legume nodules and roots in the rhizosphere soils of Acacia trees in Morocco’s arid regions. The focus was on identifying bacterial strains with plant growth-promoting rhizobacteria (PGPR) traits and antibiotic resistance, which could enhance legume productivity under various abiotic stresses. Autochthonous legumes were used to harbor the endophytic bacteria, including chickpea (Cicer arietinum), faba bean (Vicia faba), lentil (Lens culinaris), and common bean (Phaseolus vulgaris). In a previous study, seventy-two isolates were obtained, and molecular characterization grouped them into twenty-two bacterial isolates. These twenty-two bacterial isolates were then further analyzed for their antibiotic resistance and key PGPR traits, such as phosphate solubilization, indole-3-acetic acid (IAA) production, and siderophore production. The results revealed that 86.36% of the isolates were resistant to erythromycin, 45.45% to ciprofloxacin, 22.73% to ampicillin-sulbactam, and 9.09% to tetracycline, with ciprofloxacin and tetracycline being the most effective. All isolates produced IAA, with HN51 and PN105 exhibiting the highest production at 6 µg of IAA per mg of protein. The other isolates showed varying levels of IAA production, ranging from moderate to low. Siderophore production, assessed using CAS medium, indicated that the strains PN121, LR142, LNR146, and HR26 exhibited high production, while the rest demonstrated moderate to low capacities. Additionally, 18.2% of the isolates demonstrated phosphate solubilization on YED-P medium, with PR135 and LNR135 being the most efficient, achieving solubilization indices of 2.14 and 2.13 cm, respectively. LR142 and LNR146 showed a moderate solubilization efficiency. Overall, these findings indicate that these isolated endophytic bacteria possess significant potential as biofertilizers, owing to their antibiotic resistance, IAA production, siderophore production, and phosphate solubilization abilities. These characteristics position them as promising candidates for enhancing legume growth under abiotic stress and contributing to sustainable agriculture in arid regions.

Comprehensive characterization and resistome analysis of Antarctic Pseudomonas migulae strain CAS19.

Although traditionally considered pristine, Antarctica faces an increasing threat of antibiotic resistance due to human intervention. Here, we obtained a bacterial isolate, the CAS19 strain, from a lake water sample from Ardley Island, Antarctica and characterized it comprehensively. The CAS19 was a psychrotrophic and neutrophilic/alkalitolerant bacterium thriving at temperatures from 15 to 33°C and pH levels from 6.0 to 9.0. Besides the production of siderophore and indole acetic acid, it also exhibited proteolytic and lipolytic activities. It was identified as Pseudomonas migulae by multilocus (16S rRNA, gyrB, rpoB and rpoD) sequence analysis, and its genome was 6.5 Mbps in length, had 59% GC content, and contained 5,821 coding sequences. The CAS19 was resistant to several antibiotics, including trimethoprim, penicillin, vancomycin, and erythromycin, confirmed by RT-qPCR analysis, with a notable increase in dfr (63-fold), bla (461-fold), vanW (31.7-fold) and macA (24.7-fold) expressions upon antibiotic exposure. Additionally, CAS19 exhibited resistance to heavy metals with an order of Cr(III) = Cu(II) > Ni(II) > Zn(II) > Cd(II), and showed diesel fuel (5%) degradation capacity. Cold-related genes cspA_2 and cspD were overexpressed at 4 and 15°C, consistent with the cold adaptation mechanism. In conclusion, for the first time an Antarctic P. migulae isolate has been characterized in detail, uncovering a rich resistome repertoir that might be associated with anthropogenic disturbances.

Arabinoxylan Alleviates Obesity by Regulating Gut Microbiota and Bile Acid Metabolism.

Overweight and obesity are major and increasingly global public health concern. High intake of dietary fiber is negatively correlated with obesity and obesity-related metabolic diseases. Here, we investigated the impact of arabinoxylan on obesity based on the modification of gut microecology. Arabionxylan reduced body weight and improved glucose metabolism, as well as intestinal barrier function and metabolic endotoxemia in obese mice. Supplementation with arabinoxylan increased the relative abundance of Prevotellaceae_UCG_001, Lachnospiraceae_NK4A136_group, Clostridia_UCG_014, Alistipes, Bacteroides, and Ruminococcus, which was associated with the upregulated 7α-dehydroxylation function and production of secondary bile acids (deoxycholic acid and lithocholic acid). The modification of gut microbiota by arabinoxylan also influenced the production of SCFAs, genistein, daidzein, indolelactic acid, and indoleacetic acid, contributing to the amelioration of obesity. Our study highlights the antiobesity effects of arabinoxylan through the modification of gut microbiota and the production of bioactive metabolites.

Genetic Diversity and Functional Potential of Streptomyces spp. Isolated from Pachmarhi Biosphere Reserve, India.

Streptomyces is a diverse genus, well known for producing a wide array of metabolites that have significant industrial utilization. The present study investigates the genetic and functional diversity of Streptomyces spp. isolated from the Pachmarhi Biosphere Reserve (PBR), India, an unexplored site. The 16S rRNA gene sequencing and analysis revealed 96 isolates belonging to 40 different species indicating a substantial phylogenetic diversity. The strains were clustered into two groups: a major cluster with 94 strains and a small cluster with two strains. BOX- PCR analyses revealed an incredible genetic diversity existing among the strains of Streptomyces spp. in PBR. The analyses revealed the intra-species diversity and inter-species closeness within the genus Streptomyces in the study area. Qualitative screening for enzyme production has shown that 53, 42, 41, 11, and 54 strains tested positive for CMCase, xylanase, amylase, pectinase, and β-glucosidase, respectively. Additionally, 54 strains tested positive for PHB production. The strains were assayed quantitatively for the production of CMCase, xylanase, amylase, and pectinase. Streptomyces sp. MP9-2, Streptomyces sp. MP10-11, Streptomyces sp. MP10-18, and Streptomyces sp. MP10-6 recorded maximum CMCase (0.604 U/mL), xylanase (0.553 U/mL), amylase (1.714 U/mL), and pectinase (13.15 U/mL) activities, respectively. Furthermore, several strains demonstrated plant growth-promoting traits, viz. zinc and phosphate solubilization and production of ammonia, HCN (hydrogen cyanide), and IAA (Indole acetic acid), and nitrogen fixation. Fifty strains showed antifungal activity against Fusarium oxysporum f. sp. lycopersici with inhibitions ranging from 7.5 to 47.5%. Current findings underscore the ecological and biotechnological significance of Streptomyces spp. in the unexplored habitat of PBR.

The role of Ni- and Cd-resistant rhizobacteria in promoting the growth of rice seedlings and alleviating the combined phytotoxicity of Ni and Cd

The problem of potentially toxic metal pollution is increasingly acute with the development of human society. In this study, we investigated the remediation of nickel (Ni) and cadmium (Cd) co-contamination through inoculating rice with three new-isolated Ni- and Cd-resistant plant growth-promoting rhizobacteria (PGPR) Y3, Y4, and Y5. These three strains possessed growth-promoting properties, including 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity, the ability of indoleacetic acid (IAA) production, phosphate solubilization, siderophores production, and exopolysaccharide (EPS) development. According to 16S rDNA sequence homology, strains Y3, Y4, and Y5 were identified as Pseudomonas sp., Chryseobacterium sp., and Enterobacter sp., respectively. Based on the results of rice germination experiments conducted under combined toxicity, we set the contamination concentrations for Ni2+ at 20 μg mL−1 and Cd2+ at 40 μg mL−1. Then we conducted potting experiments at these concentration levels to study the effects of strains Y3, Y4, and Y5 on rice growth under synergistic Ni and Cd stress. The results indicated that the inoculated strains Y3, Y4, and Y5 were effective in promoting the growth of rice seedlings under the combined stress of Ni and Cd, and conferring tolerance to Ni and Cd by increasing the antioxidant enzyme activities of the seedlings. Among them, strain Y3 exhibited stronger ACC deaminase activity, IAA production capacity, and EPS production capacity, showing the most pronounced growth-promoting effect on rice. It was demonstrated that after inoculation with strain Y3, the germination rate of rice seeds increased by 43 %, the fresh weight of stems improved by 35 %, and the chlorophyll content enhanced by 70 % and other growth-promoting phenomena. Additionally, under Ni and Cd stress, strain Y5 performed better than strain Y4 in terms of IAA production capacity and its influence on rice root growth, suggesting that IAA production might play a specifically essential role in root growth under Ni and Cd stress.

Characterization of Sinorhizobium strains isolated from arid and semi-arid areas of Morocco promoting the growth of Vachellia gummifera

Vachellia gummifera is a nitrogen-fixing shrub endemic to Morocco, and represents a suitable candidate for reforestation programs in dry areas. In this study, we identified seven root microsymbionts of V. gummifera, and determined their phenotypic characteristics, Plant Growth-Promoting (PGP) activities and their symbiotic efficiency. The bacteria were isolated from root nodules of the plant grown in Moroccan forest soils located in arid and semi-arid regions. The 16S rRNA gene sequences analysis of seven isolates showed similarity values ranging from 99.85% to 99.92% with Sinorhizobium fredii USDA205T. The phenotypic analyses displayed that the strains use different carbohydrates, mainly mono and di-saccharides, as a sole carbon source, and 13 out of 15 amino acids tested as the sole nitrogen source. The strains have variable tolerance to heavy metals, but are sensitive to salinity and high temperature, as no one grew in the presence of 2% NaCl (w/v) or at 40 °C, respectively. On the other hand, the strains grew in a very high osmotic stress environment induced by PEG 6000 (20% w/v), and they all grow in a pH range between 6.5 and 9. The strains possess PGP activities, such as phosphate solubilization, siderophore, and indole acetic acid production. Inoculation under axenic conditions showed that the strains increased the aerial biomass of inoculated plants up to 217%, whereas the relative symbiotic efficiency percentages (74.87–140,3%) showed that most strains are very efficient. From all these results we concluded that our strains may be proposed as inoculum for large-scale applications, such as reforestation programs.

Complete Genome of Achromobacter xylosoxidans, a Nitrogen-Fixing Bacteria from the Rhizosphere of Cowpea (Vigna unguiculata [L.] Walp) Tolerant to Cucumber Mosaic Virus Infection.

Achromobacter xylosoxidans is one of the nitrogen-fixing bacteria associated with cowpea rhizosphere across Africa. Although its role in improving soil fertility and inducing systemic resistance in plants against pathogens has been documented, there is limited information on its complete genomic characteristics from cowpea roots. Here, we report the complete genome sequence of A. xylosoxidans strain DDA01 isolated from the topsoil of a field where cowpea plants tolerant to cucumber mosaic virus (CMV) were grown in Ibadan, Nigeria. The genome of DDA01 was sequenced via Illumina MiSeq and contained 6,930,067 nucleotides with 67.55% G + C content, 73 RNAs, 59 tRNAs, and 6421 protein-coding genes, including those associated with nitrogen fixation, phosphate solubilization, Indole3-acetic acid production, and siderophore activity. Eleven genetic clusters for secondary metabolites, including alcaligin, were identified. The potential of DDA01 as a plant growth-promoting bacteria with genetic capabilities to enhance soil fertility for resilience against CMV infection in cowpea is discussed. To our knowledge, this is the first complete genome of diazotrophic bacteria obtained from cowpea rhizosphere in sub-Saharan Africa, with potential implications for improved soil fertility, plant disease resistance, and food security.

Effects of Plant Growth Promoting Halotolerant Pseudomonas Aeruginosa JCM 5962 with Hydrocarbon Degradation Ability, Isolated from Sundarbans Mangrove Area in West Bengal, on Abelmoschus esculentus (Okra) Plant Growth

Plant growth promoting rhizobacteria (PGPR) play a key role in sustainable agricultural practices leading to increased crop productivity. Moreover, PGPR with ability to diminish abiotic stresses like salinity and hydrocarbon contamination in soil, can be developed into potent biofertilizers with maximum ecological benefits. Sundarbans mangrove region in West Bengal, a natural reservoir of diverse microbiota is an important source of PGPR adapted to high salinity and other abiotic stresses like hydrocarbon contamination due to oil spillage and water transport systems, rendering the soil unsuitable for farming. In the present study, a potent PGPR has been isolated from rhizospheric soil of Matla riverbed in mangrove areas of Sundarbans, with simultaneous nitrogen fixing, phosphate solubilizing and plant hormone like indole acetic acid (IAA) producing properties as well as high salt tolerance and hydrocarbon bioremediation abilities. The strain has been identified as Pseudomonas aeruginosa JCM 5962 (NCBI Accession number MK544832.1) on the basis of 16S rRNA analysis. The isolated Pseudomonas aeruginosa strain showed atmospheric nitrogen fixation (3612 ± 2 mg N/ Kg of soil), highest phosphate solubilization index of 3.0 ± 0.06 and 37.14 µg/mL of IAA production. This potent strain also showed salt tolerance upto 7% in culture broth and an uptake of 18.72% of salt. Highest hydrocarbon degradation was shown by this strain in presence of diesel as the sole carbon source. The isolated Pseudomonas aeruginosa strain showed overall improvement in growth of Abelmoschus esculentus (Okra) plants in pot experiments in different conditions like absence of any abiotic stress, presence of 5% salt stress and presence of 1% diesel contaminant. These results indicate that Pseudomonas aeruginosa JCM 5962 can be developed as a potent biofertilizer to be used in agricultural lands of Sundarbans mangrove regions and other areas which are plagued by high salinity and increasing hydrocarbons, particularly petroleum contamination.