Characterization Of Plant Growth Promoting Rhizobacteria Research Articles

Isolation and characterization of plant growth-promoting rhizobacteria (PGPR) from eelgrass Zostera marina rhizosphere: implications for bioremediation

Plant growth-promoting rhizobacteria (PGPR) play a crucial role in enhancing plant growth. However, investigations into the presence and function of PGPR in seagrass rhizospheres remain relatively limited. In this study, we isolated 45 strains of PGPR from Zostera marina rhizospheres and assessed their functional attributes. Additionally, we evaluated the performance of these candidate strains under varying environmental conditions, such as temperature, salinity, and pH. Out of the 45 analyzed strains, 6 were found to possess the nifH gene; some strains also exhibited the ability to solubilize inorganic phosphorus, with dissolved phosphorus content ranging widely from 14.6 to 393.9 mg l-1. Eleven strains demonstrated indole-3-acetic acid production, with yields spanning from 16.3 to 42.8 mg l-1. Siderophores and ammoniated proteins were produced by 32 and 20 strains, respectively. Notably, 5 PGPR strains (F65, G84, G85, G86, and I109) displayed multiple growth-promoting properties along with strong adaptability to a wide range of physicochemical conditions. This study highlights the potential reservoir of PGPR in the eelgrass rhizosphere and provides significant implications for utilizing these bacteria to enhance the success rate of restoring degraded seagrass meadows.

Plant growth promoting rhizobacteria exploration on butterfly pea (Clitoria ternatea l) from North Maluku Indonesia

The Plant Growth Promoting Rhizobacteria (PGPR) is associated with the roots and nodules of butterfly peas (Clitoria ternatea L.). This study aims to explore the PGPR in the rhizosphere of butterfly peas and to study their potential for biofertilizer. Characterization of PGPR was based on their ability to phosphate dissolution, auxin production, and nitrogen fixation as well as synergistic and antagonistic tests, and molecular identification. A total of 11 phosphate solubilizing bacteria isolates were isolated from the rhizosphere of butterfly peas while two isolates were taken from nodules. The RTF2 isolate from the rhizosphere had the highest phosphate solubility index. Meanwhile, the RTDH5-1, F1.1, and F2.1 showed strong inhibition ability against the growth of the pathogenic Rhizoctonia solani. The nitrogenase activity of isolates F2.1 and F1.1 from nodules were 0.975 μmol mL-1 g-1 h-1; while the IAA production was 7.87 and 7.05 mg L-1, respectively. The F1.1 had 100% similarity with Bacillus aryabhattai while F2.1 was 99.84% similar with Rhizobium sp. Both isolates can be used in biofertilizer formulation for North Maluku butterfly peas.

Genomic and Metabolic Characterization of Plant Growth-Promoting Rhizobacteria Isolated from Nodules of Clovers Grown in Non-Farmed Soil

Genomic and Metabolic Characterization of Plant Growth-Promoting Rhizobacteria Isolated from Nodules of Clovers Grown in Non-Farmed Soil

Plant-beneficial Bacillus, Pseudomonas, and Staphylococcus spp. from Kumaon Himalayas and their drought tolerance response

Plant growth-promoting rhizobacteria (PGPR) have been shown to augment plant responses against drought and other abiotic stresses. In the present study, we isolated 27 bacteria from the rhizosphere of various plants cultivated in the Kumaon Himalayas., and to measure their abiotic stress tolerance, these 27 isolates were subjected to variations in pH, temperature, and drought. All 27 isolates were also screened for various plant growth-promoting traits. Among these, the four isolates RR1, ASC1, AFS3, and NG4 demonstrated various plant growth promotion activities including the synthesis of indole-3-acetic acid (IAA), siderophores, ammonia, and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase production, and concomitantly high tolerance to abiotic stresses. Moreover, 16S rRNA sequencing of these four isolates validated their identities as Bacillus, Pseudomonas, and Staphylococcus sp. Finally, to assess the in-vivo drought tolerance potential of these four isolates, a pot-trial experiment was undertaken in wheat cultivar VL-892. The results demonstrated that inoculating wheat plants with these four PGPR isolates greatly improved plant growth under drought circumstances by increasing root and shoot length and both fresh and dry weight of root and shoot. This study endeavors to discover the biochemical and molecular diversity of cultivable PGPR in six remotely located districts of Uttarakhand. In conclusion, the drought-tolerant PGPR strains described in this study are plant-beneficial and can effectively mobilize nutrients under drought conditions. Consequently, they could be used as bioinoculants to alleviate drought stress in wheat plants, in a sustainable manner. To the best of our knowledge, this is the first report of exploring the diversity and characterization of PGPR from the Kumaon Himalayas and their drought evaluation.

Characterization of plant growth-promoting rhizobacteria (PGPR) in Persian walnut associated with drought stress tolerance

There is a lack of information on the rhizosphere of nut-bearing trees where microbial populations can benefit roots and tree growth. The current research aimed at discovering plant growth-promoting rhizobacteria (PGPR) in the rhizosphere of soil samples from around the root zone of six walnut trees, each of which was considered as a genotype, i.e. ‘TT1’, ‘TT2’, ‘SS2’, ‘ZM1’, ‘Chandler’ and ‘Haward’. The trees grew in different arid and semiarid regions of Iran and Turkey. The strains were isolated and identified based on different morphological and biochemical markers. Drought-stress tolerance was assessed in the case of each isolate through their transfer to culture medium, containing polyethylene glycol (PEG6000) at 0 and 373.80 g L−1. Resilient strains were analyzed for measuring their ability to produce siderophore, hydrogen cyanide (HCN), Indole-3-acetic acid (IAA) and Gibberellic acid (GA3). In sum, 211 isolates were identified, of which a large number belonged to the Bacillus genus and, specifically, 78% of the strains were able to grow under drought stress conditions. The genus Arthrobacter was only detected in the rhizosphere of ‘ZM1’, ‘Haward’ and ‘TT1’ genotypes. In 4% of the strains, IAA production exceeded 53 mg L−1, while a high level of phosphorus solubility was verified in 6% of the strains. No strain was found to have the capability of producing HCN. The strains were screened for drought-tolerance, which resulted in the discovery of two promising strains, i.e. ZM39 and Cha43. Based on molecular identification through amplification and sequencing of the 16S rDNA gene, these two strains seemed to belong to Bacillus velezensis and Bacillus amyloliquefaciens, respectively. The discovery of new PGPR strains could probably assist walnut trees in improving their mechanisms of adaptation to drought stress.

Isolation and Characterization of Plant Growth-Promoting Rhizobacteria from Coffee Plantation Soils and Its Influence on Maize Growth

Plant growth-promoting rhizobacteria (PGPR) are an important bacterial resource as biofertilizers, which can promote plant growth and increase crop yields. In this study, isolation, characterization, and its effect on plant promotion were assessed by isolating PGPR using soil samples collected from Jimma, Ethiopia. Out of 10 isolates, three of them (JEC3, JEC4, and JEC7) exhibited PSB traits in Pikovskaya media by solubilizing phosphate and producing IAA. Of the three isolates, JEC4 recorded the maximum phosphate solubilization index (4.98), soluble phosphate (283 μg/ml), and IAA production (10.21 μg/ml). The findings of the isolates' morphological and biochemical tests showed that JEC3, JEC4, and JEC7 as Bacillus sp., Pseudomonas sp., and Enterobacter sp., respectively. The optimization of phosphate solubilization was done using different incubation times and sources of carbon and nitrogen. Furthermore, the isolate (JEC4) was tested for plant growth-promoting (PGP) activities and indicated the production of ammonia, hydrogen cyanide, and siderophore. JEC4 isolate showed a significant increase in sideways (%) seed germination, root and shoot length, fresh and dry weight of root, and shoot of maize in field experiments than the untreated ones. The results indicate that the JEC4 isolate can be developed as a biological fertilizer for promoting crop productivity and ecosystem dynamics.

Characterization of Plant Growth-Promoting Rhizobacteria (PGPR) From Saline Soil in Taiwan

The agricultural sector is continuously facing myriad of problems such as yield loss due to abiotic stress as well as phytopathogen infestation. There is well established evidence that the use of plant growth-promoting rhizobacteria (PGPR) would overcome those problems and in turn improve plant growth and crop yield. In this research bacteria strains were isolated from root surface and inner tissue of plants grown in highly saline soils. The characterization includes the ability to produce aminocyclopropane-1-carboxylate (ACC), siderophore, chitinase as well as their antifungal ability. Those abilities are considered the most reliable traits for promoting plant growth. A total of 32 strains were isolated and examined, with 16 surface isolates and 16 endophytes. Thirty bacteria isolates showed capability to produce ACC deaminase with a range of values around 1.8 – 29.6 µmol/mg/h. Thirty isolates were found to secrete siderophore that resulted in halo zones around 1.5 mm - 15 mm after 7 days. Moreover, the chitinase assay showed 13 isolates having the ability to degrade chitin. Interestingly, two isolates with the highest chitinase activity also showed superior ability to inhibit fungal growth. To conclude, a procedure has been demonstrated that rhizobacteria with PGPR traits can be isolated from saline soil. Furthermore, some of these PGPR candidates showed potential to not only promote plant growth but also to control fungal pathogen. This type of dual-functional stains could serve as an environmentally friendly biofertilizer and meanwhile also a biocontrol agent in sustainable agriculture.

Isolation and characterization of plant growth-promoting rhizobacteria and their effects on the growth of Medicago sativa L. under salinity conditions.

Plant growth-promoting rhizobacteria are a group of free-living bacteria that colonize plant rhizosphere and benefit plant root growth, thereby increasing host plant to cope with salinity induced stress. The aim of this study was to (1) isolate and characterize auxin-producing bacteria showing a high plant growth-promoting (PGP) potential, and (2) evaluate the PGP effects on the growth of Medicago sativa L under salinity stress (130mM NaCl). Of thirteen isolates, Bacillus megaterium NRCB001 (NRCB001), B. subtilis subsp. subtilis NRCB002 (NRCB002) and B. subtilis NRCB003 (NRCB003) had the ability to produce auxin, which ranged from 47.53 to 154.38μgml-1. The three auxin-producing bacterial strains were shown multiple PGP traits, such as producing siderophore and NH3, showing ACC deaminase activity, solubilize phosphate and potassium. Furthermore, NRCB001, NRCB002, and NRCB003 could survive in LB medium containing 1750mM NaCl. The three auxin-producing with salinity tolerance strains were selected for further analyses. In greenhouse experiments, when inoculated with NRCB001, NRCB002 and NRCB003, dry weight of alfalfa significantly (P < 0.05) increased by 24.1%, 23.1% and 38.5% respectively, compared with those of non-inoculated control seedlings under normal growth condition. When inoculated with NRCB002 and NRCB003, dry weight of alfalfa significantly (P < 0.05) increased by 96.9 and 71.6% respectively, compared with those of non-inoculated control seedlings under 130mM NaCl condition. Our results indicated that NRCB002 and NRCB003 having PGP traits are promising candidate strains to develop biofertilizers, especially used under salinity stress conditions.

Isolation and characterization of plant growth-promoting rhizobacteria from Opuntia ficus-indica and their effect on Wheat growth

Endophytic bacteria are found inside host plants without causing disease symptoms, and form a range of di erent bene cial rela onships. In this study, four bacterial strains were isolated from roots, cladodes and non gus- tatory fruits of Opun a cus-indicaL. collected from the Algerian semi-arid region. The bacteria were able to grow at temperatures as 45 °C. 16SrRNA sequencing revealed the iden ty of isolates as Pseudomonas pu da(E1)with 98% similarity,P. brassicacearum(E2) and Klebsiella pneumonia (E3,E4)with 99% similarity. The strains were tested in vitro for their biocontrol ac vity against phytopathogenic fungus, and found to have the ability to inhibit the Fusarium oxysporum f. sp. albedinis and Aspergillus niger growth. We noticed that the most important inhibitory effect recorded with P. pu da (69.78±3.93 and 65.15±2.8), and that the feeble antagonistic effect recorded with P. brassicacearum (20.57±6.04 and 8.52 ±2.8) against of F.oxysporum f.sp albdeinis and A.niger. The plant growth promo ng (PGP) proper es were demonstrated through wheat (Triticum aestivum L.) based bioassay under hydroponic condi ons.The inocula on of bacteria showed an increase in density, length of roots and stems, indica ng the PGP abili es of these bacteria. P. pu da showed a poten al for growth of wheat plant.We no ced respectively the length of both stems and roots (17.34 ± 0.54 mm; 11.07 ± 0.67 mm), and we found that fresh and dry weight was (0.23 ± 0.029 g; 0.0375 ±0.003 g). Overall the results showed that isolates characterized were able to improve the growth of plants, and inhibit the propaga on of phytopathogenic fungi. To our knowledge, this is the rst report describing the isola on of bacteria from O. cus-indica(L.) in Algerian semi-arid region.

Characterization of plant growth-promoting rhizobacteria from perennial ryegrass and genome mining of novel antimicrobial gene clusters

BackgroundPlant growth-promoting rhizobacteria (PGPR) are good alternatives for chemical fertilizers and pesticides, which cause severe environmental problems worldwide. Even though many studies focus on PGPR, most of them are limited in plant-microbe interaction studies and neglect the pathogens affecting ruminants that consume plants. In this study, we expand the view to the food chain of grass-ruminant-human. We aimed to find biocontrol strains that can antagonize grass pathogens and mammalian pathogens originated from grass, thus protecting this food chain. Furthermore, we deeply mined into bacterial genomes for novel biosynthetic gene clusters (BGCs) that can contribute to biocontrol.ResultsWe screened 90 bacterial strains from the rhizosphere of healthy Dutch perennial ryegrass and characterized seven strains (B. subtilis subsp. subtilis MG27, B. velezensis MG33 and MG43, B. pumilus MG52 and MG84, B. altitudinis MG75, and B. laterosporus MG64) that showed a stimulatory effect on grass growth and pathogen antagonism on both phytopathogens and mammalian pathogens. Genome-mining of the seven strains discovered abundant BGCs, with some known, but also several potential novel ones. Further analysis revealed potential intact and novel BGCs, including two NRPSs, four NRPS-PKS hybrids, and five bacteriocins.ConclusionAbundant potential novel BGCs were discovered in functional protective isolates, especially in B. pumilus, B. altitudinis and Brevibacillus strains, indicating their great potential for the production of novel secondary metabolites. Our report serves as a basis to further identify and characterize these compounds and study their antagonistic effects against plant and mammalian pathogens.

Mitsuaria sp. and Burkholderia sp. from Arabidopsis rhizosphere enhance drought tolerance in Arabidopsis thaliana and maize (Zea mays L.)

Some rhizosphere microbes, such as plant growth-promoting rhizobacteria (PGPR), can alleviate plant drought stress and improve water use efficiency and productivity under drought conditions. The aims of this study are: 1) isolation and characterization of PGPRs from the rhizosphere of Arabidopsis plants that could improve drought tolerance of Arabidopsis and maize; 2) studying the potential mechanisms of improved plant drought tolerance by the isolated bacteria. In this study, bacteria isolates were isolated from the rhizosphere of Arabidopsis plants subjected to water limitation. Subsequently, the isolates were cultured and screened for their ability to improve drought tolerance of Arabidopsis. Potential mechanisms of improved plant drought tolerance by these bacteria including bacterial exopolysaccharide and 1-aminocyclopropane-1-carboxylic acid deaminase production, plant root system architecture modification, and plant physiological responses were also explored. Two bacterial isolates that conferred the greatest drought tolerance to Arabidopsis were further characterized. Both bacteria exhibit 1-aminocyclopropane-1-carboxylic acid deaminase activity, which can promote drought tolerance by decreasing plant ethylene levels. In vitro study showed that both Mitsuaria sp. ADR17 and Burkholderia sp. ADR10 altered the root structure system of Arabidopsis. Moreover, inoculation of Zea mays L. with either strain reduced evapotranspiration (i.e., soil water loss), and changed the plant proline and malondialdehyde levels, antioxidant enzymes activity, and phytohormone contents under drought stress. These results indicate that both strains interact with plants in ways that allow them to alter root system architecture, plant physiological responses and phytohormone levels under drought conditions to alleviate stress and improve plant survival. The results also indicated that each individual isolate has a separate pleiotropic effect.

Caracterización y efecto de Azotobacter, Azospirillum y Pseudomonas asociadas a Ipomoea Batatas del Caribe Colombiano

El uso de Rizobacterias promotoras de crecimiento vegetal (PGPR, por sus siglas en ingles) constituye una alternativa al uso de fertilizantes químicos favoreciendo el rendimiento de los cultivos. La presente investigación tuvo como objetivo la búsqueda, selección y caracterización de PGPR de los géneros Azotobacter, Azospirillum y Pseudomonas nativas de la rizósfera de cultivos de Ipomoea batatas de zonas productoras representativas del Caribe Colombiano. Los aislados seleccionados se caracterizaron molecularmente y realizaron pruebas de solubilización de fósforo, producción de índoles y reducción de acetileno. Las cepas fueron probadas a nivel de invernadero en plántulas de Ipomoea batatas producidas in vitro en las que se evaluó la altura, longitud radicular, masa seca de la parte aérea y radicular. Asociada a la rizósfera de Ipomoea batatas se obtuvieron cepas de Azotobacter vinelandii, Azotobacter chroococcum, Azospirillum lipoferum, Azospirillum brasilense y Pseudomonas denitrificans, las cepas fueron capaces de solubilizar fósforo, producir índoles y reducir acetileno. Se obtuvo incrementos en parámetros de crecimiento como longitud radicular, altura, peso seco aéreo y radicular en plántulas de Ipomoea batatas en invernadero con la inoculación de las bacterias seleccionadas frente a plántulas sin inocular. Los resultados catalogan a los aislados obtenidos como posibles microorga-nismos con potencial como biofertilizantes en batata.

Using plant growth-promoting rhizobacteria (PGPR) to improve plant growth

The characterization of PGPR (plant growth promoting rhizobacteria) bacteria associated to Agrostis capillaris, and evaluation of plant growth promotion mechanisms, as well as correlation of them with the potential effects on the growth of the plants in unfavorable conditions, in order to improve the efficiency of phytoremediation of contaminated soils were investigated. The results indicate that in the presence of bacterial inoculation the growth of plants on heavy metal contaminated soil was higher compared to uninoculated plants, which confirms the PGPR characteristics of selected isolates. To demonstrate the effects in plant growth the different variants of plants inoculation were applied. The inoculation of rape and fescue grass with PGPR bacteria, directly during germination as well after two weeks of growth, were the most efficient methods for protecting seeds from growth inhibition on heavy metal contaminated soil. The bacteria associated with plant rhizosphere naturally occurring in contaminated areas due to the biochemical activity stimulate plant growth and thus improve the soil phytoremediation process.

Isolation and characterization of plant growth-promoting rhizobacteria from wheat rhizosphere and their effect on plant growth promotion.

The present study was conducted to characterize the native plant growth promoting (PGP) bacteria from wheat rhizosphere and root-endosphere in the Himalayan region of Rawalakot, Azad Jammu and Kashmir (AJK), Pakistan. Nine bacterial isolates were purified, screened in vitro for PGP characteristics and evaluated for their beneficial effects on the early growth of wheat (Triticum aestivum L.). Among nine bacterial isolates, seven were able to produce indole-3- acetic acid in tryptophan-supplemented medium; seven were nitrogen fixer, and four were able to solubilize inorganic phosphate in vitro. Four different morphotypes were genotypically identified based on IGS-RFLP fingerprinting and representative of each morphotype was identified by 16S rRNA gene sequencing analysis except Gram-positive putative Bacillus sp. Based on 16S rRNA gene sequence analysis, bacterial isolates AJK-3 and AJK-9 showing multiple PGP-traits were identified as Stenotrophomonas spp. while AJK-7 showed equal homologies to Acetobacter pasteurianus and Stenotrophomonas specie. Plant inoculation studies indicated that these Plant growth-promoting rhizobacteria (PGPR) strains provided a significant increase in shoot and root length, and shoot and root biomass. A significant increase in shoot N contents (up to 76%) and root N contents (up to 32%) was observed over the un-inoculated control. The study indicates the potential of these PGPR for inoculums production or biofertilizers for enhancing growth and nutrient content of wheat and other crops under field conditions. The study is the first report of wheat associated bacterial diversity in the Himalayan region of Rawalakot, AJK.

Isolation and characterization of plant growth-promoting rhizobacteria and their effects on phytoremediation of petroleum-contaminated saline-alkali soil

This study aimed to isolate promising halotolerant and alkalotolerant plant growth-promoting rhizobacteria and to study their effects on the growth of tall fescue and phytodegradation efficiency in a petroleum-contaminated saline–alkaline soil. A total of 115 PGPR strains were isolated from the rhizosphere of tall fescue grown in petroleum-contaminated saline–alkaline soils. Of these, 5 strains indicating 1-aminocyclopropane-l-carboxylic acid deaminase activity>1.0M α-KBmg−1h−1 were selected for further studies. The isolate D5A presented the highest plant-growth-promoting activity and was identified as Klebsiella sp. It grew well on the Luria–Bertani medium containing 9% NaCl and at a pH range of 4–10. A pot experiment was then conducted to study the effect of isolates on phytoremediation. The results showed that inoculation of D5A promoted tall fescue growth and enhanced remediation efficiency in petroleum-contaminated saline–alkaline soil.

English

Plant growth-promoting rhizobacteria (PGPR) are beneficial bacteria that colonize plant roots and enhance plant growth by a wide variety of mechanisms. The use of PGPR is steadily increasing in agriculture and offers an attractive way to replace chemical fertilizers, pesticides and supplements. In the present study, isolation and characterization of PGPR from the rhizospheric soil of wheat was done for the enhancement of wheat growth. Rhizospheric soils samples were collected from different areas of Uttar Pradesh, India. Twenty two (22) isolates of bacteria were successfully isolated, biochemically characterized and screened for their plant growth promoting traits like production of indole acetic acid (IAA), ammonia production, siderophore production and phosphate solubilization. On the basis of multiple plant growth promoting activities among 22 isolates, 17 isolates were also evaluated for their quantitative production of IAA. The isolates Ps-AB4, Ps-BK1 and Ps-JN 2 showed highest IAA production (79.67-110.12 &micro;g/L). Out of 22, 20 and 6 isolates produced ammonia and siderophore, respectively, while 10 isolates solubilized phosphate on the Pikovskaya&rsquo;s agar medium. The present study reveals that the use of Pseudomonas isolates Ps-AB4, Ps-BK1 and Ps-JN2 as inoculants biofertilizers might be beneficial for wheat cultivation. Key words: Indole acetic acid, NH3, Pseudomonas spp., phosphate solubilization, wheat.

Isolation and characterization of plant growth-promoting rhizobacteria from wheat roots by wheat germ agglutinin labeled with fluorescein isothiocyanate

Thirty-two isolates were obtained from wheat rhizosphere by wheat germ agglutinin (WGA) labeled with fluorescein isothiocyanate (FITC). Most isolates were able to produce indole acetic acid (65.6%) and siderophores (59.3%), as well as exhibited phosphate solubilization (96.8%). Fourteen isolates displayed three plant growth-promoting traits. Among these strains, two phosphate-dissolving ones, WS29 and WS31, were evaluated for their beneficial effects on the early growth of wheat (Triticum aestivum Wan33). Strain WS29 and WS31 significantly promoted the development of lateral roots by 34.9% and 27.6%, as well as increased the root dry weight by 25.0% and 25.6%, respectively, compared to those of the control. Based on 16S rRNA gene sequence comparisons and phylogenetic positions, both isolates were determined to belong to the genus Bacillus. The proportion of isolates showing the properties of plant growth-promoting rhizobacteria (PGPR) was higher than in previous reports. The efficiency of the isolation of PGPR strains was also greatly increased by WGA labeled with FITC. The present study indicated that WGA could be used as an effective tool for isolating PGPR strains with high affinity to host plants from wheat roots. The proposed approach could facilitate research on biofertilizers or biocontrol agents.

Comparison of the bacterial community and characterization of plant growth-promoting rhizobacteria from different genotypes of Chrysopogon zizanioides (L.) Roberty (Vetiver) rhizospheres

Molecular approaches [PCR-denaturing gradient gel electrophoresis (DGGE)] were used to determine whether three different vetiver (Chrysopogon zizanioides) genotypes, commercially used in Brazil and considered economically important over the world, select specific bacterial populations to coexist in their rhizospheres. DGGE profiles revealed that the predominant rhizospheric bacterial community hardly varies regarding the vetiver genotype. Moreover, using traditional cultivation methods, bacterial strains were isolated from the different rhizospheres. Colonies presenting different morphologies (83) were selected for determining their potential for plant growth promotion. More than half of the strains tested (57.8%) were amplified by PCR using nifH-based primers, specific for the enzyme nitrogenase reductase. The production of siderophores was observed in 88% of the strains, while the production of antimicrobial substances was detected in only 14.5% of the isolates when Micrococcus sp. was used as the indicator strain. Production of indole-3-acetic acid and the solubilization of phosphate were observed in 55.4% and 59% of the isolates, respectively. In total, 44 strains (53%) presented at least three characteristics of plant growth promotion and were submitted to amplified ribosomal DNA restriction analysis. Twenty-four genetic groups were formed at 100% similarity and one representative of each group was selected for their identification by partial 16S rRNA gene sequencing. They were affiliated with the genera Acinetobacter, Comamonas, Chryseobacterium, Klebsiella, Enterobacter, Pantoea, Dyella, Burkholderia, or Pseudomonas. These strains can be considered of great importance as possible biofertilizers in vetiver.

Characterization of plant growth-promoting rhizobacteria using capillary isoelectric focusing with whole column imaging detection

Capillary isoelectric focusing (cIEF) can be a useful tool for the characterization and identification of microbes. Based on the whole column imaging detection (WCID) technique and using plant growth-promoting rhizobacteria (PGPR) as test microbes, we present a two-level cIEF characterization method for the characterization and identification of bacteria. Intact bacteria were first characterized according to their apparent isoelectric points measured by cIEF-WCID and then lysed bacteria were further characterized by cIEF profiling of the intracellular proteins. Cellular clustering was found to be the main experimental barrier for the characterization of intact bacteria. The addition of sodium chloride (100 mM) to the sample mixture was found to be an effective way to reduce clustering. Due to the high efficiency and high resolution of cIEF-WCID, characterization of bacteria according to their intracellular proteins can be implemented simply and quickly without optimization of the experimental conditions. To improve the detection sensitivity with laser induced fluorescence (LIF)-WCID, the possibility to label bacteria with a non-covalent fluorescent dye, NanoOrange, was explored.