Plant Growth-promoting Strains Research Articles

Complete genome sequence of plant growth-promoting Bacillus stratosphericus AIMST-CREST02 isolated from bulk soil of a paddy field.

Here, we present the complete genome of a plant growth-promoting strain, Bacillus stratosphericus AIMST-CREST02 isolated from the bulk soil of a high-yielding paddy plot. The genome is 3,840,451 bp in size with a GC content of 41.25%. Annotation predicted the presence of 3,907 coding sequences, including genes involved in auxin biosynthesis regulation and gamma-aminobutyric acid (GABA) metabolism.

Single and co-inoculation of biofilm-forming rhizobacteria with macroalgae extract increase barley productivity in organic matter-limited soil

Context Limitation in soil organic matter interferes with plant growth and productivity. Chemical fertilisers can provide limiting nutrients to plants, especially in barren soil, but they have detrimental effects on living organisms; therefore, plant growth-promoting (PGP) rhizobacteria may be an alternative to synthetic fertilisers to improve plant tolerance to nutrient stress. Aims This study evaluated the effects of single and co-inoculation of two PGP rhizobacterial strains with macroalgae (Cladophora glomerata) extract on barley growth. We also tested the ability of the respective strains to produce biofilm and exopolysaccharide (EPS) at different pH values under in vitro conditions. Methods Plants were cultivated in an organic matter-limited alkaline soil under field conditions. Key results All treatments increased barley growth parameters to some extent. Growth parameters increased most in Bacillus + macroalgae extract (B + MA) and Bacillus + Azotobacter + macroalgae extract (B + A + MA) treatments. These two treatments significantly enhanced shoot length by 22.9–25.7%, dry weight of shoot + spike by 118.2–154.5%, total weight of grains by 76.5–78.1%, and number of grains per spike by 94.8–112.1% in comparison with the control. The respective two treatments also increased biofilm formation and EPS production in response to alkaline pH. Conclusions Barley productivity may be increased by using PGP strains with greater potential to produce biofilm and EPS, and inoculating them with macroalgae extract. The B + MA treatment could be applied singly or in combination with Azotobacter. Implications Single or co-inoculation of such PGP bacteria with macroalgae extract may be commercialised to enhance barley productivity in organic matter-limited soils.

Isolation and characterization of PGPR obtained from different arsenic-contaminated soil samples and their effect on photosynthetic characters of maize grown under arsenic stress.

Contamination of the environment due to speedup of anthropogenic activities has become a serious threat to modern humanity. Among the contaminants, the new emerging concern is the heavy metal (HM) contamination in the environment. Because the persistence and harmfulness of heavy metals affect the ecosystem and the health of plants, animals, and humans, they are the most toxic substances in the environment. Among them, Arsenic (As) emerged as major environmental constraint leading to enormous negative effects on the plant, animal, and human health. Even in minute quantity, As is known to cause various critical diseases in humans and toxicity in plants. Research was performed to observe the capability of plant growth-promoting strains of bacteria in enhancing Zea mays (L.) growth in arsenic polluted soil. Total 30 bacterial strains were isolated from the polluted soils, screened for plant growth promotion potential and arsenic tolerance. Eighteen isolates showed resistance to different levels of sodium arsenate (ranging from 0 to 50 mM) in agar plate using LB media. Of 18 isolates, 83.3% produced IAA, methyl red, and hydrogen cyanide; 55.5% exhibited catalase activity; 61.1% showed siderophore production; 88.8% showed phosphate solubilization; and 44.4% showed oxidase, Voges proskauer activity, and KOH solubility. The most efficient isolates SR3, SD5, and MD3 with significant arsenic tolerance and plant growth-promoting (PGP) activity were examined via sequencing of amplified 16S rRNA gene. Isolates of bacteria, i.e., SR3, SD5, and MD3, showing multiple PGP-traits were identified as Bacillus pumilus (NCBI accession number: OR459628), Paenibacillus faecalis (NCBI accession number: OR461560), and Pseudochrobactrum asaccharolyticum (NCBI accession number: OR458922), respectively. Maize seeds treated with these PGPR strains were grown in pots contaminated with 50 ppm and 100 ppm sodium arsenate. Compared to untreated arsenic stressed plants, bacterial inoculation P. asaccharolyticum (MD3) resulted 20.54%, 18.55%, 33.45%, 45.08%, and 48.55% improvement of photosynthetic pigments (carotenoid content, chlorophyll content, stomatal conductance (gs), substomatal CO2, and photosynthetic rate), respectively. Principal component analysis explained that first two components were more than 96% of the variability for each tested parameter. The results indicate that in comparison to other isolates, P. asaccharolyticum isolate can be used as efficient agent for improving maize growth under arsenic polluted soil.

Exploring the Differential Impact of Salt Stress on Root Colonization Adaptation Mechanisms in Plant Growth-Promoting Rhizobacteria

Salinity inhibits plant growth by affecting physiological processes, but soil microorganisms like plant growth-promoting rhizobacteria (PGPR) can alleviate abiotic stress and enhance crop productivity. However, it should be noted that rhizobacteria employ different approaches to deal with salt stress conditions and successfully colonize roots. The objective of this study was to investigate the effect of salt stress on bacterial survival mechanisms such as mobility, biofilm formation, and the autoaggregation capacity of three plant growth-promoting strains: Pseudomonas putida SJ04, Pseudomonas simiae WCS417r, and Bacillus amyloliquefaciens GB03. These strains were grown in diluted LB medium supplemented with 0, 100, 200, or 300 mM NaCl. Swimming and swarming mobility were evaluated in media supplemented with 0.3 and 0.5% agar, respectively. Biofilm formation capacity was quantified using the crystal violet method, and the autoaggregation capacity was measured spectrophotometrically. In addition, we evaluated in vitro the capacity of the strains to ameliorate the effects of saline stress in Mentha piperita. The study found that the GB03 strain exhibited enhanced swarming mobility when the salt concentration in the medium increased, resulting in a two-fold increase in the halo diameter at 300 mM. However, high concentrations of NaCl did not affect the swimming mobility. In contrast, swimming motility was reduced in WCS417r and SJ04 under salt stress. On the other hand, exposure to 300 mM NaCl resulted in a 180% increase in biofilm formation and a 30% rise in the percentage of autoaggregation in WCS417r. Conversely, the autoaggregation percentage of the strains SJ04 and GB03 remained unaffected by saline stress. However, for GB03, biofilm formation decreased by 80% at 300 mM. Simultaneously, inoculation with the three evaluated strains alleviated the detrimental effects of salinity on plant growth. Under 150 mM salt stress, all strains showed increased fresh weight, with GB03 and WCS417r improving by 40% and SJ04 exhibiting the most remarkable effect with a 70% rise compared to non-inoculated plants. Despite their different strategies for mitigating salt stress, the application of these strains presents a promising strategy for effectively mitigating the negative consequences of salt stress on plant cultivation.

Evaluating of the Potential of Bacillus pumilus 3-19 as a Plant Growth-Promoting Strain

Evaluating of the Potential of Bacillus pumilus 3-19 as a Plant Growth-Promoting Strain

Combined application of microbial inoculant and kelp-soaking wastewater promotes wheat seedlings growth and improves structural diversity of rhizosphere microbial community

Industrial processing of kelp generates large amounts of kelp-soaking wastewater (KSW), which contains a large amount of nutrient-containing substances. The plant growth-promoting effect might be further improved by combined application of growth-promoting bacteria and the nutrient-containing KSW. Here, a greenhouse experiment was conducted to determine the effect of the mixture of KSW and Bacillus methylotrophicus M4-1 (MS) vs. KSW alone (SE) on wheat seedlings, soil properties and the microbial community structure in wheat rhizosphere soil. The available potassium, available nitrogen, organic matter content and urease activity of MS soil as well as the available potassium of the SE soil were significantly different (p < 0.05) from those of the CK with water only added, increased by 39.51%, 36.25%, 41.61%, 80.56% and 32.99%, respectively. The dry and fresh weight of wheat seedlings from MS plants increased by 166.17% and 50.62%, respectively, while plant height increased by 16.99%, compared with CK. Moreover, the abundance and diversity of fungi in the wheat rhizosphere soil were significantly increased (p < 0.05), the relative abundance of Ascomycetes and Fusarium spp. decreased, while the relative abundance of Bacillus and Mortierella increased. Collectively, the combination of KSW and the plant growth-promoting strain M4-1 can promote wheat seedlings growth and improve the microecology of rhizosphere microorganisms, thereby solving the problems of resource waste and environmental pollution, ultimately turning waste into economic gain.

Insight into the genome of an arsenic loving and plant growth-promoting strain of Micrococcus luteus isolated from arsenic contaminated groundwater.

Contamination of arsenic in drinking water and foods is a threat for human beings. To achieve the goal for the reduction of arsenic availability, besides conventional technologies, arsenic bioremediation by using some potent bacteria is one of the hot topics for researchers. In this context, bacterium, AKS4c was isolated from arsenic contaminated water of Purbasthali, West Bengal, India, and through draft genome sequence; it was identified as a strain of Micrococcus luteus thatcomprised of 2.4Mb genome with 73.1% GC content and 2256 protein coding genes. As the accessory genome, about 22 genomic islands (GIs) associated with many metal-resistant genes were identified. This strain was capable to tolerate more than 46,800mg/L arsenate and 390mg/L arsenite salts as well as found to be tolerable to multi-metals such as Fe, Pb, Mo, Mn, and Zn up to a certain limit of concentrations. StrainAKS4c was able to oxidize arsenite to less toxic arsenate, and its arsenic adsorption property was qualitatively confirmed through X-ray fluorescence (XRF) and Fourier transform infrared spectroscopy (FTIR) analysis. Quantitative estimation of plant growth-promoting attributes like Indole acetic acid (IAA), Gibberellic acid (GA), and proline production and enhancement of rice seedling growth in laboratory condition leads to its future applicability in arsenic bioremediation as a plant growth-promoting rhizobacteria (PGPR).

Genomic and metabolomic insights into the antimicrobial compounds and plant growth-promoting potential of Bacillus velezensis Q-426

BackgroundThe Q-426 strain isolated from compost samples has excellent antifungal activities against a variety of plant pathogens. However, the complete genome of Q-426 is still unclear, which limits the potential application of Q-426.ResultsGenome sequencing revealed that Q-426 contains a single circular chromosome 4,086,827 bp in length, with 4691 coding sequences and an average GC content of 46.3%. The Q-426 strain has a high degree of collinearity with B. velezensis FZB42, B. velezensis SQR9, and B. amyloliquefaciens DSM7, and the strain was reidentified as B. velezensis Q-426 based on the homology analysis results. Many genes in the Q-426 genome have plant growth-promoting activity, including the secondary metabolites of lipopeptides. Genome mining revealed 14 clusters and 732 genes encoding secondary metabolites with predicted functions, including the surfactin, iturin, and fengycin families. In addition, twelve lipopeptides (surfactin, iturin and fengycin) were successfully detected from the fermentation broth of B. velezensis Q-426 by ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC–QTOF–MS/MS), which is consistent with the genome analysis results. We found that Q-426 produced indole-3-acetic acid (IAA) at 1.56 mg/l on the third day of incubation, which might promote the growth of plants. Moreover, we identified eighteen volatile compounds (VOCs, including 2-heptanone, 6-methylheptan-2-one, 5-methylheptan-2-one, 2-nonanone, 2-decanone, 2-undecanone, 2-dodecanone, 2-tridecanone, 2-tetradecanone, 2-nonadecanone, pentadecanoic acid, oleic acid, dethyl phthalate, dibutyl phthalate, methyl (9E,12E)-octadeca-9,12-dienoate), pentadecane, (6E,10E)-1,2,3,4,4a,5,8,9,12,12a-decahydro-1,4-methanobenzo[10]annulene, and nonanal) based on gas chromatograph-mass spectrometer (GC/MS) results.ConclusionsWe mined secondary metabolite-related genes from the genome based on whole-genome sequence results. Our study laid the theoretical foundation for the development of secondary metabolites and the application of B. velezensis Q-426. Our findings provide insights into the genetic characteristics responsible for the bioactivities and potential application of B. velezensis Q-426 as a plant growth-promoting strain in ecological agriculture.

Effects of Bacterial and Fungal Inocula on Biomass, Ecophysiology, and Uptake of Metals of Alyssoides utriculata (L.) Medik.

The inoculation of plants with plant-growth-promoting microorganisms (PGPM) (i.e., bacterial and fungal strains) is an emerging approach that helps plants cope with abiotic and biotic stresses. However, knowledge regarding their synergic effects on plants growing in metal-rich soils is limited. Consequently, the aim of this study was to investigate the biomass, ecophysiology, and metal accumulation of the facultative Ni-hyperaccumulator Alyssoides utriculata (L.) Medik. inoculated with single or mixed plant-growth-promoting (PGP) bacterial strain Pseudomonas fluorescens Migula 1895 (SERP1) and PGP fungal strain Penicillium ochrochloron Biourge (SERP03 S) on native serpentine soil (n = 20 for each treatment). Photosynthetic efficiency (Fv/Fm) and performance indicators (PI) had the same trends with no significant differences among groups, with Fv/Fms > 1 and PI up to 12. However, the aboveground biomass increased 4-5-fold for single and mixed inoculated plants. The aboveground/belowground dry biomass ratio was higher for plants inoculated with fungi (30), mixed (21), and bacteria (17). The ICP-MS highlighted that single and mixed inocula were able to double the aboveground biomass' P content. Mn metal accumulation significantly increased with both single and mixed PGP inocula, and Zn accumulation increased only with single PGP inocula, whereas Cu accumulation increased twofold only with mixed PGP inocula, but with a low content. Only Ni metal accumulation approached the hyperaccumulation level (Ni > 1000 mg/kg DW) with all treatments. This study demonstrated the ability of selected single and combined PGP strains to significantly increase plant biomass and plant tolerance of metals present in the substrate, resulting in a higher capacity for Ni accumulation in shoots.

Halophytic Plant Halostachys belangeriana (Moq.) Botsch as a Source of Plant Growth-Promoting Endophytic Bacteria

Halostachys belangeriana (Moq.) Botsch also known as Halostachys caspica C. A. Mey belongs to the Chenopodiaceae family and is distributed in deserts of Asian countries. The plant grows in severe salinity and drought conditions and its survival and growth can be associated with the activity of endophytic bacteria. The objective of our research was to isolate and screen endophytic bacteria from Halostachys belangeriana for plant growth promotion and reveal their plant-beneficial traits. Methods. Halostachys belangeriana (Moq.) Botsch plants were collected from the saline soil of the Kyzylkum desert in Uzbekistan in spring. The endophytic bacteria were isolated from the tissues of plants by cutting the outer sterilized shoots and roots and putting them into the water to let bacteria come from the tissues into the water. The suspension was transferred onto Tryptic Soy Agar to let bacteria grow and form separate colonies. The colonies different in shape and color were used to get pure cultures of bacteria. The bacteria were screened using plant growth-promoting activity in Petri plates by inoculating wheat seeds with the suspension of isolated bacteria. The best plant growth promoters were identified by analyzing their 16S rRNA gene and comparing it with sequences registered in GenBank of NCBI. The strains were tested for wheat growth promotion in a pot experiment and then examined for their plant-benefi cial traits: N2-fixation, phosphates solubilization, production of indole-3-acetic acid (IAA), 1-aminocyclopropane-1-carboxylate deaminase (ACC-deaminase), and siderophores. Results. A total of 25 isolates of endophytic bacteria were obtained from the tissues of Halostachys belangeriana (Moq.) Botsch. Due to the high efficiency of isolates SSU-4, SSU-7, SSU-16, SSU-18, and SSU-21 in the stimulation of wheat shoot and root growth, they were chosen for identification and (OK559720), Bacillus endophyticus SSU-7 (OK559721), Bacillus subtilis SSU-16 (OK559722), Isoptericola halotolerans SSU-18 (OK559723) and Pseudomonas kilonensis SSU-21 (OK559724), respectively. The single inoculation of seeds with tested strains increased the root and shoot length and plant fresh weight. The coinoculation of seeds with a mixture of five strains resulted in an even more increase in plant growth parameters. It was revealed that the tested strains had at least two plant-beneficial properties. The strains B. pumilus SSU-4 and P. kilonensis SSU-21 had the ability for nitrogen fixation. All strains produced IAA; however, the most active IAA producer was P. kilonensis SSU-21. Three of five strains had phosphates solubilization ability and produced ACC-deaminase and siderophores. The strains B. pumilus SSU-4 and P. kilonensis SSU-21 possessed four of five tested plant-beneficial properties. The strains B. endophyticus SSU-7 and I. halotolerans SSU-18 had three of five tested plant-beneficial traits, and B. subtilis SSU-16 could just produce IAA and ACC-deaminase. Conclusions. This is the first report about the isolation of plant growth-promoting endophytic bacteria from the desert halophytic plant Halostachys belangeriana (Moq.) Botsch. The most efficient plant growth-promoting strains were: B. pumilus SSU-4, B. endophyticus SSU-7, B. subtilis SSU-16, I. halotolerans SSU-18, and P. kilonensis SSU-21. After field experiments, these strains can be suggested for use as bioinoculants improving plants growth.

De novo Genome Assessment of Serratia marcescens SGT5.3, a Potential Plant Growth-Promoting Bacterium Isolated from the Surface of Capsicum annuum Fruit

Serratia marcescens SGT5.3, a potential plant growth-promoting strain with a wide range of functions, was isolated from the surface of Capsicum annuum fruit. Here, we report the whole-genome sequence of this bacterium. Gene prediction revealed various functional genes potentially involved in plant growth promotion and development.

Characterization of endophytic bacteria isolated from root nodules of lentil in intercropping with durum wheat

Legumes improve soil fertility by interacting symbiotically with nitrogen-fixing rhizobia allocated in root nodules. Some bacterial endophytes can coexist with rhizobia in nodules and might help legumes by enhancing stress tolerance, producing hormones stimulating plant growth, and increasing plant nutrient intake. Twenty-six bacterial endophytes from Lens culinaris root nodules cultivated in intercropping with Triticum durum were identified and characterized molecularly and biochemically. Potential plant growth-promoting strains have been selected according to the indole acetic acid and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase production, and for their inorganic phosphate solubilization ability. The presence of genes associated to ACC deaminase and nitrogenase was evaluated. Six selected strains were grown with varying NaCl and polyethylene glycol concentrations to test their salt and osmotic stress tolerance. Priestia megaterium 11NL3 and Priestia aryabhattai 19NL1, resulted to be tolerant to salinity and osmotic stress, were tested on four genotypes of T. durum seeds in different stress conditions. The effect of strain inoculation on seed germination, vigor, and root-to-shoot ratio varied depending on the type of stress and on the durum wheat genotypes. For future research, it will be necessary to test the selected bacterial strains at different plant phenological stages and to clarify the mechanisms involved in the different outcomes of plant-microbe interactions.

Revealing oxidative pentose metabolism in new Pseudomonas putida isolates.

The Pseudomonas putida group in the Gammaproteobacteria has been intensively studied for bioremediation and plant growth promotion. Members of this group have recently emerged as promising hosts to convert intermediates derived from plant biomass to biofuels and biochemicals. However, most strains of P. putida cannot metabolize pentose sugars derived from hemicellulose. Here, we describe three isolates that provide a broader view of the pentose sugar catabolism in the P. putida group. One of these isolates clusters with the well-characterized P. alloputida KT2440 (Strain BP6); the second isolate clustered with plant growth-promoting strain P. putida W619 (Strain M2), while the third isolate represents a new species in the group (Strain BP8). Each of these isolates possessed homologous genes for oxidative xylose catabolism (xylDXA) and a potential xylonate transporter. Strain M2 grew on arabinose and had genes for oxidative arabinose catabolism (araDXA). A CRISPR interference (CRISPRi) system was developed for strain M2 and identified conditionally essential genes for xylose growth. A glucose dehydrogenase was found to be responsible for initial oxidation of xylose and arabinose in strain M2. These isolates have illuminated inherent diversity in pentose catabolism in the P. putida group and may provide alternative hosts for biomass conversion.

Genome mining, antimicrobial and plant growth-promoting potentials of halotolerant Bacillus paralicheniformis ES-1 isolated from salt mine.

Salinity severely affects crop yield by hindering nitrogen uptake and reducing plant growth. Plant growth-promoting bacteria (PGPB) are capable of providing cross-protection against biotic/abiotic stresses and facilitating plant growth. Genome-level knowledge of PGPB is necessary to translate the knowledge into a product as efficient biofertilizers and biocontrol agents. The current study aimed to isolate and characterize indigenous plant growth-promoting strains with the potential to promote plant growth under various stress conditions. In this regard, 72 bacterial strains were isolated from various saline-sodic soil/lakes; 19 exhibited multiple in vitro plant growth-promoting traits, including indole 3 acetic acid production, phosphate solubilization, siderophore synthesis, lytic enzymes production, biofilm formation, and antibacterial activities. To get an in-depth insight into genome composition and diversity, whole-genome sequence and genome mining of one promising Bacillus paralicheniformis strain ES-1 were performed. The strain ES-1 genome carries 12 biosynthetic gene clusters, at least six genomic islands, and four prophage regions. Genome mining identified plant growth-promoting conferring genes such as phosphate solubilization, nitrogen fixation, tryptophan production, siderophore, acetoin, butanediol, chitinase, hydrogen sulfate synthesis, chemotaxis, and motility. Comparative genome analysis indicates the region of genome plasticity which shapes the structure and function of B. paralicheniformis and plays a crucial role in habitat adaptation. The strain ES-1 has a relatively large accessory genome of 649 genes (~ 19%) and 180 unique genes. Overall, these results provide valuable insight into the bioactivity and genomic insight into B. paralicheniformis strain ES-1 with its potential use in sustainable agriculture.

Potential of Rhizobia Nodulating Anthyllis vulneraria L. from Ultramafic Soil as Plant Growth Promoting Bacteria Alleviating Nickel Stress in Arabidopsis thaliana L.

Rhizobia, which enter into symbiosis with legumes, can also interact with non-legumes and promote plant growth. In this paper, we explored the effects of nickel (Ni, 200 µM) on Arabidopsis thaliana (Col-0) inoculated with plant growth-promoting (PGP) rhizobia nodulating ultramafic Anthyllis vulneraria. The isolated PGP strains tolerant to Ni were identified as Rhizobium sp. and Bradyrhizobium sp. The isolates highly differed in their PGP abilities and Ni resistance. Without Ni-stress, the plants inoculated with most isolates grew better and had higher photosynthetic efficiency than non-inoculated controls. Nickel treatment increased Ni concentration in inoculated plants. Plant growth, leaf anatomy, chloroplast ultrastructure, efficiency of photosynthesis, and antioxidant defense system activity were significantly impaired by Ni, however, the majority of these effects were diminished in plants inoculated with the most effective PGP rhizobia. Real-time PCR revealed an increased expression level of genes involved in auxin and gibberellin biosynthesis in the inoculated, Ni-treated plants, and this may have improved shoot and root growth after inoculation with effective isolates. Our results also suggest a positive correlation between Ni-stress parameters and antioxidant defense system activity, and also between the effectiveness of photosynthesis and plant growth parameters. We showed that the selected rhizobia, naturally nodulating Anthyllis on Ni-rich ultramafic soils can promote Arabidopsis growth and increase plant tolerance to Ni by improving different physiological and biochemical mechanisms.

Characterization of an Endophytic Antagonistic Bacterial Strain Bacillus halotolerans LBG-1-13 with Multiple Plant Growth-Promoting Traits, Stress Tolerance, and Its Effects on Lily Growth.

Microbial inoculants are an important tool for increasing arable land productivity and decreasing mineral fertilizer application. This study was aimed at isolating and identifying endophytic antagonistic bacteria from lily (Lilium davidii var. unicolor) roots grown in Northwestern China and at evaluating their antifungal activity and plant growth-promoting characteristics. For this purpose, endophytic bacteria were isolated from plant roots, and plant growth-promoting strains were identified. One bacterial strain, isolated from the root part, was identified as Bacillus halotolerans based on 16S rRNA gene sequence analysis and was designated as LBG-1-13. The strain showed antagonistic activities against important plant pathogens of lily including Botrytis cinerea, Botryosphaeria dothidea, and Fusarium oxysporum. The highest percentage of growth inhibition, i.e., 71.65 ± 2.39%, was observed for LBG-1-13 against Botryosphaeria dothidea followed by 68.33 ± 4.70% and 48.22 ± 4.11% against Botrytis cinerea and Fusarium oxysporum, respectively. Meanwhile, the isolated strain also showed plant growth-promoting traits such as the production of indole-3-acetic acid (IAA), siderophore, ACC deaminase, and phosphate solubilization activity. The strain showed ACC deaminase activity and was able to cleave 58.41 ± 2.62 nmol α-ketobutyrate (mg protein)-1 min-1. The strain exhibited tolerance to salt and drought stress in an in vitro experiment. The strain LBG-1-13 was able to grow in the presence of 10% NaCl and 20% polyethylene glycol (PEG) in the growth medium. Inoculation of Lilium varieties, Tresor and Bright Diamond, with LBG-1-13 enhanced plant growth under greenhouse and field conditions, respectively. All these results demonstrated that Bacillus halotolerans LBG-1-13 could be utilized as a good candidate in the biocontrol of lily disease and plant growth promotion in sustainable agriculture.

Streptomyces strains can improve the quality properties and antifungal bioactivities of tomato fruits by impacting WRKY70 transcription factor gene and nitrate accumulation

The current study evaluated the effect of plant growth-promoting (PGP) strains of Streptomyces on yield, quality, and nitrate content of fruits, plant-microbe responses, and antifungal effect against blight disease caused by fungus pathogen Alternaria solani on tomato fruits in commercial greenhouse conditions. Greenhouse trials were done with four treatments including strains Y28, IC10, IT25, and commercial bio-fertilizer (Barvar NPK®) on tomato plants. In PGP treatments, the number of infected fruits significantly reduced (60%) compared to Barvar and control. Strain Y28 improved the quality of tomatoes more than other treatments. All three PGP treatments contained a higher level of total sugar concentration and antioxidant enzyme activities than Barvar and control. In contrast, PGP strains, especially Y28, significantly reduced nitrate accumulation (25%) compared to Barvar and control tomatoes. Streptomyces treatments induced more than a 20-fold increase in UDP and WRKY70 transcription factor gene expression relative to the control (P < 0.01). Based on the results, microbe-dependent plant defense induced by these strains is positively correlated to WRKY70 expression and nitrate reduction in commercial greenhouse conditions. These findings suggest that the commercial application of specific strains not only can illustrate an eco-friendly solution to induce resistance against fungal pathogens but also improve the quality properties of food plants with lower nitrate content.

Endophytic and rhizospheric bacteria associated with Paspalum atratum and its potential for plant growth promotion with different phosphate sources.

The genus Paspalum belongs to the family Poaceae and has several species that are native to Brazil. The Paspalum Germplasm Bank (GB) of the Brazilian Agricultural Research Corporation comprises approximately 450 accessions from 50 species. Among these accessions, Paspalum atratum (BGP 308) has economic potential for forage purposes. However, the endophytic and rhizospheric microbial communities within this accession and their ability to promote plant growth remain unknown. The present study aimed to isolate the endophytic and rhizospheric bacteria associated with P. atratum and to assess their potential for plant growth improvement, so-called plant growth-promoting bacteria (PGPB). For the in vitro tests, the ability of nitrogen-fixing bacteria (NFB), phosphate solubilization (PS) and indoleacetic acid (IAA) production were evaluated. A total of 116 endophytic and rhizosphere bacteria were obtained from the isolation. In the in vitro tests, 43 (37.00%) of these isolates showed positive NFB, PS, and IAA results. These isolates were identified by 16S rDNA sequencing. The phosphate solubilization index (PSI) ranged from 2 to 3.61, all 43 strains performed biological nitrogen fixation and the IAA production ranged from 12.85 to 431.41 μg ml−1. Eight of these 43 isolates were evaluated in vivo in a greenhouse using P. atratum caryopsis. The pots were filled with soil prepared with three different phosphate sources and one control without phosphate. After growth, the plants were submitted to morphological, bromatological and chemical determination. Data were analyzed using analysis of variance (ANOVA) and principal component analysis (PCA). In the in vivo test, treatments 105 (Pseudomonas sp.) and 458 (Pseudomonas sp.) were the most significant for the crystalline phosphate source, 109 (Bacillus sp.) for the sedimentary phosphate source and, as for the soluble phosphate source most treatments that received bacterial isolates had higher phosphorus content in the dry matter than the uninoculated soluble phosphate control. The 105FCR (crystalline phosphate + Pseudomonas sp.), 109FSE (sedimentary phosphate + Bacillus sp.), and 110 FSE (sedimentary phosphate + Enterobacter sp.) treatments showed the best results for plant growth promotion. This work made it possible to determine the bacterial community associated with P. atratum (BGP308) and to obtain new potential plant growth-promoting strains.

Bacillus amyloliquefaciens WS-10 as a potential plant growth-promoter and biocontrol agent for bacterial wilt disease of flue-cured tobacco

BackgroundBacterial wilt disease caused by the soilborne bacterium Ralstonia solanacearum is a serious threat to flue-cured tobacco production. In this study, an indigenous disease suppressive Bacillus strain was isolated from the rhizosphere soil of healthy tobacco plants, and its biocontrol and plant growth promoting (PGP) potential were evaluated in in-vivo and in-vitro assays.ResultsThrough isolation and screening of 250 isolates, WS-10 was found to be the best candidate antagonistic strain against R. solanacearum (WS-001). In-vitro assays revealed that the isolated strain WS-10 (Bacillus amyloliquefaciens) showed an effective antagonistic activity against R. solanacearum WS-001 and several plant-pathogenic fungi. As promising PGP rhizobacteria, WS-10 had the ability of nitrogen fixation, solubilization of inorganic potassium and phosphate, and biosynthesis of indole-3-acetic. In a co-culture assay, it significantly inhibits the growth of WS-001. Our greenhouse experiments showed that the soil physicochemical properties and accumulation of dry matter contents in different plant parts (roots, stems, and leaves) were significantly increased in the presence of B. amyloliquefaciens WS-10. The soil treated with B. amyloliquefaciens WS-10 displayed significantly higher values of the average well color development index, the utilization ability of 6 types of carbon sources by rhizosphere microorganisms, and the diversity indices of the rhizosphere microbial communities. In planta assay, B. amyloliquefaciens WS-10 significantly reduced tobacco bacterial wilt disease incidence by up to 73.36, 43.82, and 86.82% under three different treatments by improving the functional diversity and biological activity of the soil microbial community.ConclusionsObtained findings suggested that B. amyloliquefaciens WS-10 had an excellent potential as a growth-promoting and biocontrol agent of tobacco bacterial wilt disease due to its multiple beneficial traits of nutrient solubilization and disease suppression. Thus, we conclude that B. amyloliquefaciens WS-10 was a high potential PGP and biocontrol strain for healthy production of tobacco crop.

Multifarious Indigenous Diazotrophic Rhizobacteria of Rice (Oryza sativa L.) Rhizosphere and Their Effect on Plant Growth Promotion.

A diverse group of rhizobacteria persists in the rhizospheric soil, on the surface of roots, or in association with rice plants. These bacteria colonize plant root systems, enhance plant growth and crop yield. Indigenous rhizobacteria are known to promote soil health, grain production quality and serve as sustainable bioinoculant. The present study was aimed to isolate, identify and characterize indigenous plant growth promoting (PGP) diazotrophic bacteria associated with the rhizosphere of rice fields from different areas of Jammu and Kashmir, India. A total of 15 bacteria were isolated and evaluated for various PGP traits, antagonistic activity against phytopathogens, production of hydrolytic enzymes and biofilm formation under in-vitro conditions. The majority of the isolated bacteria were Gram-negative. Out of 15 bacterial isolates, nine isolates produced IAA (12.24 ± 2.86 to 250.3 ± 1.15 μg/ml), 6 isolates exhibited phosphate solubilization activity (36.69 ± 1.63 to 312.4 ± 1.15 μg/ml), 7 isolates exhibited rock phosphate solubilization while 5 isolates solubilized zinc (10–18 mm), 7 isolates showed siderophore production, 8 isolates exhibited HCN production, 6 isolates exhibited aminocyclopropane-1-carboxylate (ACC) deaminase activity, 13 isolates exhibited cellulase activity, nine isolates exhibited amylase and lipase activity and six isolates exhibited chitinase activity. In addition, 5 isolates showed amplification with the nifH gene and showed a significant amount of nitrogenase activity in a range of 0.127–4.39 μmol C2H4/mg protein/h. Five isolates viz., IHK-1, IHK-3, IHK-13, IHK-15 and IHK-25 exhibited most PGP attributes and successfully limited the mycelial growth of Rhizoctonia solani and Fusarium oxysporum in-vitro. All the five bacterial isolates were identified based on morphological, biochemical and 16S rDNA gene sequencing study, as Stenotrophomonas maltophilia, Enterobacter sp., Bacillus sp., Ochrobactrum haematophilum and Pseudomonas aeruginosa. Rice plants developed from seeds inoculated with these PGP strains individually had considerably higher germination percentage, seed vigor index and total dry biomass when compared to control. These findings strongly imply that the PGP diazotrophic bacteria identified in this work could be employed as plant growth stimulators in rice.