National Botanical Research Institute Phosphate Research Articles

Isolation And Characterization Of Phosphate Solving Bacteria From Swamp Soil With High Levels Of Acidity

Phosphate solubilizing bacteria (PSB) are one of the microbes that play an important role in soil and plant cycles. Phosphate (P) is a very important macronutrient for plants. In soil, most of the P element is found to be unavailable to plants because it is fixed by Ca, Al or Fe. This research aims to identify BPF in acid soil which has the potential to dissolve phosphate elements. The method used in this research is the isolation of BPF from acid soil using the National Botanical Research Institute's Phosphate (NBRIP) medium, phosphate dissolution index test and UV Visual. Soils from overflow type C (TLC) swamps have higher diversity compared to TLB soils. The abundance of BPF in TLC soil was higher (5,4 107 CFU per gram) compared to soil from overflow zone B (TLB) (2,9 107 CFU per gram) because TLC soil had a lower acidity level than TLB. There were 55 BPF isolates obtained from these two types of soil. Two isolates (TLB1 and TLB2) had a better phosphate solubilization index and all potential isolates that were extracted and subjected to gDNA amplification showed a DNA band at 1330-1500 bp.

Phosphate Solubilizing Bacteria Isolation Medium: Rock Phosphate or Tricalcium Phosphate?

Phosphorus is one of the essential elements limiting vegetative production in the world. Although phosphorus is abundant in soils, a tiny part is available for plants. With phosphate solubilizing bacteria (PSB), phosphorus, insoluble in soils, is transformed into a suitable form for plants. This study aimed to determine tricalcium phosphate (TCP) activities and rock phosphate (RP) used to isolate PSMs. 118 bacterial isolates, which can phosphate solubilizing, were incubated for 72 h in National Botanical Research Institute phosphate (NBRIP) medium using TCP and RP as phosphate sources. At the end of the incubation, the amount of inorganic phosphorus (Pi) in the medium and the pH of the medium was determined. As a result of bacterial incubation, an average of 57.87 mg L−1 Pi was detected in rock phosphate medium, while this rate was found to be 421 mg L−1 in TCP medium. After 72 h of incubation, it was determined that the pH of the NBRIP media varied between 3.60 and 5.05, and TCP dissolved seven times more to rock phosphate. This study has shown that TCP alone in determining the isolation and effectiveness of PSMs is not indigenous.

Molecular Characterization and Mineralizing Potential of Phosphorus Solubilizing Bacteria Colonizing Common Bean (Phaseolus vulgaris L.) Rhizosphere in Western Kenya.

Phosphorus solubilizing bacteria (PSB) are a category of microbes that transform insoluble phosphates in soil into soluble forms that crops can utilize. Phosphorus in natural soils is abundant but poorly soluble. Hence, introducing PSB is a safer way of improving its solubility. The aim of this study was to genetically characterize and determine the mineralization capability of selected PSB colonizing rhizospheres of common beans in Western Kenya. Seven potential phosphorus solubilizing bacteria (PSB) were isolated from various subregions of Western Kenya. 16S ribosomal RNA gene sequencing and National Center for Biotechnology Information (NCBI), Basic Local Alignment Search Tool (BLAST) identified the isolates. The phosphate solubilization potential of the isolates was evaluated under agar and broth medium of National Botanical Research Institute's phosphate (NBRIP) supplemented with tricalcium calcium phosphate (TCP). Identified isolates were as follows: KK3 as Enterobacter mori, B5 (KB5) as Pseudomonas kribbensis, KV1 as Enterobacter asburiae, KB3 as Enterobacter mori, KK1 as Enterobacter cloacae, KBU as Enterobacter tabaci, and KB2 as Enterobacter bugandensis. The strains B5 and KV1 were the most effective phosphorus solubilizers with 4.16 and 3.64 indices, respectively. The microbes converted total soluble phosphate concentration in broth medium which was 1395 and 1471 P μg/mL, respectively. The least performing isolate was KBU with a 2.34 solubility index. Significant (p ≤ 0.05) differences in plant biomass for Rose coco and Mwitemania bean varieties were observed under inoculation with isolates B5 and KV1. PSB isolates found in common bean rhizospheres exhibited molecular variations and isolates B5 and KV1 are the potential in solving the insufficiency of phosphorus for sustainable crop production.

Selection and validation of reference genes for quantitative real-time polymerase chain reaction analyses of Serratia ureilytica DW2

Background: Serratia ureilytica DW2 is a highly efficient phosphate-solubilizing bacteria isolated from Codonopsis pilosula rhizosphere soil that can promote the growth of C. pilosula; nonetheless, until now, no validated reference genes from the genus Serratia have been reported that can be used for the normalization of quantitative real-time polymerase chain reaction (RT–qPCR) data. Methods: To screen stable reference genes of S. ureilytica DW2, the expression of its eight candidate reference genes (16S rRNA, ftsZ, ftsA, mreB, recA, slyD, thiC, and zipA) under different treatment conditions (pH, temperature, culture time, and salt content) was assayed by RT–qPCR. The expression stability of these genes was analyzed using different algorithms (geNorm, NormFinder, and BestKeeper). To verify the reliability of the data, the expression of the glucose dehydrogenase (gdh) gene under different soluble phosphate levels was quantified using the most stably expressed reference gene. Results: The results showed that the zipA and 16S rRNA genes were the most stable reference genes, and the least stable genes were thiC and recA. The expression of gdh was consistent with the phosphate solubilization ability on plates containing the National Botanical Research Institute phosphate growth medium. Conclusion: Therefore, this study provides a stable and reliable reference gene of Serratia for the accurate quantification of functional gene expression in future studies.

Harnessing the phosphate-solubilizing ability of Trichoderma strains to improve plant growth, phosphorus uptake and photosynthetic pigment contents in common bean (Phaseolus vulgaris)

A promising strategy for dissolving, mobilizing and enhancing the utilization of the complexed form of phosphorus (P) in soil-plant systems is the use of effective phosphate solubilizing microorganisms. In the present study, six strains of Trichoderma spp. previously obtained from the common bean rhizosphere were investigated for their ability to solubilize tricalcium phosphate (TCP) in NBRIP (National Botanical Research Institute Phosphate) broth medium. All six strains were able to solubilize TCP to various extents, with solubilization ranging from 66.9 μg/ml to 328.4 μg/ml. A significant negative linear correlation (r = - 0.94; p < 0.01) was found between solubilized P and the pH of the culture medium. The highest solubilization activity (328.4 μg/ml), fungal growth (87.21 mg/100 ml) and pH fluctuation (7.0–4.06) were achieved by Trichoderma gamsii It-62. Under pot conditions, inoculation with Trichoderma gamsii It-62 remarkably improved plant height, shoot and root weight, P uptake, photosynthetic pigments and total protein content compared with untreated common bean seedlings. These increases were significantly higher upon combined inoculation of the bioagent with TCP addition. The obtained results indicate that Trichoderma gamsii It-62 might be a promising alternative for the release of fixed forms of phosphates present in the soil, thereby increasing soil fertility.

Screening and evaluation of phosphate-solubilizing bacteria isolated from aquaculture ponds in a step-by-step strategy as potential biofertilizer.

The application of phosphate-solubilizing bacteria (PSB) has received little attention in aquaculture. In addition, the low efficiency of PSB as a biofertilizer in farm conditions is a major concern. Therefore, this study aims to isolate the PSB from sediment of earthen fishponds and evaluate with a more appropriate approach to ensure their effectiveness in increasing the bioavailability of phosphorus (P) in farm conditions. PSB was first isolated and selected using the National Botanical Research Institute's Phosphate (NBRIP) medium-containing tri-calcium phosphate (TCP) in solid and liquid media. Among 96 strains that were isolated, 11 strains identified by 16 s rRNA, belonging to the genera Pseudomonas and Acinetobacter, showed a higher ability to release P from TCP (48-170 mg L-1 ). Then, the efficiency of 11 strains was evaluated by combining different criteria. Among 11 selected strains, based on the ability to dissolve TCP and Ca-Phytate in culture medium, release P in sediment microcosm, and growth in a wide range of environmental conditions in fishponds, especially optimum growth at 4°C and pH above 8, Ps. deceptionensis strain Persian10 was selected as the most efficient strain for testing in aquarium conditions. In the last step, incubation of Persian10 in aquarium sediment (sterilized under gamma-ray) increased soluble P and had an impact on calcium phosphate, organic P and alkaline phosphatase activity; however, Persian10 had no impact on the concentration of iron phosphate and aluminium phosphate. Persian 10 strain can be considered a bio-fertilizer candidate in earthen fishponds as it expressed the ability to solubilize P in different conditions. It is very important to evaluate PSB in an appropriate process using a combination of different criteria to ensure optimal performance of PSB in farm conditions.

Isolation and selection of salt-tolerant bacterial strains capable of solubilizing phosphorus and synthesizing phosphatase enzyme from rice-shrimp soil in Mekong River Delta, Vietnam

The aim of this study was to isolate and select salt tolerant bacteria having both functions in phosphorus solubilization and phosphatase synthesis from rice-shrimp farming soil in saline areas in Mekong River Delta of Vietnam. Phosphorus solubilizing bacteria were isolated on National Botanical Research Institute's Phosphate (NBRIP) agar medium containing 1% NaCl and the activity of phosphatase enzyme was determined by disodium p-nitrophenyl phosphate reagent method at a wavelength of 420 nm. The result showed that from 15 saline soil samples, a total of 95 strains of phosphorus solubilizing bacteria were isolated and 19 of them showed their good phosphorus solubilization. The results about phosphatase activities of these 19 strains illustrated that TBT5-3 bacterial strain was the highest phosphatase producing strain with an amount of 0.377 U/mL after 10 days of incubation. This strain showed its best phosphatase producing capacity when cultured in the liquid culture medium containing pH 5, 1% NaCl, glucose and urea under the shaking speed of 120 rpm. Based on 16S rRNA gene sequence analysis this phosphatase synthesizing bacterial strain was genetically identified as species of Bacillus sp. TBT5-3 since 100% of this train sequence is affiliated with Bacillus megaterium.

Seed bio-priming with tri-species consortia of phosphate solubilizing rhizobacteria (PSR) and its effect on plant growth promotion

Three potential rhizobacteria namely Burkholderia gladioli (MTCC 10216), Pseudomonas sp. (MTCC 9002) and Bacillus subtilis (MTCC 8528) procured from IMTECH, Chandigarh (India) were evaluated individually and as consortia for its phosphate (P) solubilizing ability and effect of growth of fenugreek (Trigonella foenum-graecum L.) and tomato (Lycopersicon esculentum L.). Phosphate solubilizing ability of these strains individually and as consortia was tested on Pikovskayas agar medium, Phosphate solubilizing agar medium and National Botanical Research Institute phosphate agar medium containing six different sources of insoluble inorganic phosphate such as tri-calcium phosphate (TCP), di-calcium phosphate (DCP), zinc phosphate (ZP), ferric phosphate (FP), sodium di-hydrogen phosphate (SP), and aluminum phosphate (AP), and two organic P such as calcium and sodium phytate. The maximum P solubilizing ability was recorded in consortium-4 having all three potential bacterial strains. Phosphate solubilization after 7th day of incubation was 37.9 mg/100 ml of TCP, 40.01 mg/100 ml of DCP, 15.79 mg/100 ml of FP, 43.02 mg/100 ml of SP, no solubilization of ZP and AP, 39.75 mg/100 ml of calcium phytate and 24.01mg/100 ml of sodium phytate. Seed germination and the other plant parameters such as plant height and weight significantly increased in fenugreek and tomato seeds, bio-primed with consortium-4 followed by consortium-3. After bio-priming of seeds in pot assay, the level of phosphorus in soil got increased by 54% in consortium-4 treated soil followed by consortium-3 (47%) over untreated control soil. Based on these findings, consoritium-4 could be recommended as a good bio-inoculant for fenugreek, tomato and other crops in comparison to individual strains and other consortia.

Screening and optimization of indole-3-acetic acid production and phosphate solubilization by rhizobacterial strains isolated from Acacia cyanophylla root nodules and their effects on its plant growth

BackgroundPlant growth-promoting rhizobacteria (PGPR) are known to improve plant growth and are used as biofertilizers, thanks to their numerous benefits to agriculture such as phosphorus solubilization and phytohormone production. In this paper, four rhizospheric bacteria (Phyllobacterium sp., Bacillus sp., Agrobacterium sp., and Rhizobium sp.) isolated from surface-sterilized root nodules of Acacia cyanophylla were tested for their ability to solubilize inorganic phosphate and to produce indole-3-acetic acid (IAA) under laboratory conditions. Then, the best IAA producer (Rhizobium sp.) was selected to test optimized conditions for IAA production. Finally, the effect of the four strains on plant growth for A. cyanophylla was evaluated in vivo. ResultsThe results showed that the totality of the tested isolates had solubilized inorganic phosphate (P) in both NBRIP (National Botanical Research Institute Phosphate) and PVK (Pikovskaya) media. Bacillus sp. was a high P-solubilizer and showed maximum solubilization in PVK (519 μg ml-1) and NBRIP (782 μg ml-1). The optimization of maximum phosphate solubilization was done using different sources of carbon (1%) and nitrogen (0.1%). Glucose and ammonium sulfate were selected to be the best carbon and nitrogen source for phosphate solubilization by all tested strains, except for Phyllobacterium sp., which recorded the highest phosphate solubilization with ammonium nitrate. The IAA production by the tested strains indicated that Rhizobium sp. produced the highest amount of IAA (90.21 μg ml-1) in culture media supplemented with L-tryptophan. The best production was observed with L-Trp concentration of 0.2% (116.42 μg ml-1) and at an initial pH of 9 (116.07 μg ml-1). The effect of NaCl on IAA production was tested at concentrations of 0 to 5% and the maximum production of 89.43 μg ml-1 was found at 2% NaCl. The extraction of crude IAA from this strain was done and purity was confirmed with Thin Layer Chromatography (TLC) analysis. A specific spot from the extracted IAA production was found to correspond with a standard spot of IAA with the same Rf value. Finally, the tested PGPR demonstrated growth stimulatory effects on Acacia cyanophylla seedlings in vivo, with a great increase of shoots’ and roots’ dry weights, and shoot length compared to control.The rhizobacterial isolates were identified by 16S rDNA sequence analysis as Agrobacterium sp. NA11001, Phyllobacterium sp. C65, Bacillus sp. CS14, and Rhizobium sp. V3E1. ConclusionThis study highlights the importance of the use of phosphate solubilizing and IAA producer microorganisms as biofertilizers to increase crop yields. The studied strains showed a significant phosphate solubilization potential and IAA production. The use of selected strains as inoculants would be interesting, in particular with a view of promoting sustainable agriculture. However, further studies to verify the efficacy of the best isolates in situ is certainly required.

Biosynthesis and characterization of hydroxyapatite and its composite (hydroxyapatite-gelatin-chitosan-fibrin-bone ash) for bone tissue engineering applications.

Hydroxyapatite (HAp) is a bioactive and biocompatible material possessing osteoconductive properties used widely in the biomedical sector. In the present study, synthesis of hydroxyapatite (HAp) using a Klebsiella pneumoniae SM24 (phosphate solubilizing bacteria) isolated from the slaughterhouse. HAp synthesized using biological source showed efficient and positive enzymatic activity in the National Botanical Research Institute Phosphate Medium (NBRIP). Characterization of HAp using FTIR revealed the presence of phosphate group hydroxyapatite and XRD spectra showed polycrystalline nature. The morphological characterization of HAp using FESEM revealed the mesoporous structure and EDX spectrum indicated presence of Ca and P as the major components. In addition, a new bone composite was prepared using the synthesized HAp, Gelatine (G), Chitosan (C), Fibrin (F) and Bone ash (HApGCF) using Simulated Body Fluid (SBF) solution. The confirmation of chemical and structural characteristics of HApGCF bone composite was achieved using FTIR, XRD and SEM analyses. The HApGCF bone composite was tested over osteoblast MG-63 cells showing effective biocompatibility and osteoblast attachment on the composite surface. Therefore, the present report proposes the in vitro application of HApGCF bone composite as a replacement for major bone damage and injury in a biocompatible and non-toxic way.

Phosphate solubilization, indole-3-acetic acid synthesis and nitrogen fixation ability of various indigenous microorganism communities from different agriecosystem habitats

Bio-fertilizer formulation from indigenous microorganism communities (IMOCs) is great suitable methods applied widely in the eastern part of world for the extraction of minerals, enhancement of agriculture and waste management although its functionalities have been unknown. The aim of this study was to assess phosphate solubility, indole-3-acetic acid (IAA) biosynthesis and nitrogen fixation efficacy of various IMOCs from different farming systems within Soc Trang province of Vietnam. Phosphate solubilization and synthesis IAA abilities of collected IMOCs were investigated in National Botanical Research Institute's Phosphate (NBRIP) liquid media containing tricalcium phosphate (TCP) as the sole P source. This medium was supplemented with and without tryptophan (100 mg/L) for IAA synthesis capability evaluation while nitrogen fixation ability was tested in liquid N-free Burks media. Besides, nifH functional gene involving in nitrogen fixation was also detected by specific polF/polR primers. The results showed that all surveyed IMOCs were found to solubilize TCP with a various extent, and the maximum amount of P2O5 solubilized was over 2,000 mg/L. In regard to the IAA biosynthesis, all IMOCs were able to biosynthesize considerably IAA with the highest IAA amount of 56.6 mg/L. All surveyed IMOCs had potential in nitrogen fixation when the primer amplified nifH gene successfully from DNA of collected IMO, and eight out of 15 IMOCs proved their nitrogen fixation with quantity varied between 1.0 and 6.5 mg/L N. In conclusion, all collected IMOCs had beneficial functions for plants like phosphate solubility, IAA synthesis and biological nitrogen fixation which can be exploited for enhancing soil fertility and plant growth.

Enhancement of Growth and Grain Yield of Rice in Nutrient Deficient Soils by Rice Probiotic Bacteria

Plant associated bacteria are promising alternatives to chemical fertilizers for plant growth and yield improvement in an eco-friendly manner. In this study, rice associated bacteria were isolated and assessed for mineral phosphate solubilization and indole-3-acetic acid (IAA) production activity in vitro. Six promising strains, which were tentatively identified as phylotaxon Pseudochrobactrum sp. (BRRh-1), Burkholderia sp. (BRRh-2), Burkholderia sp. (BRRh-3), Burkholderia sp. (BRRh-4), Pseudomonas aeruginosa (BRRh-5 and BRRh-6) based on their 16S rRNA gene phylogeny, exhibited significant phosphate solubilizing activity in National Botanical Research Institute phosphate growth medium, and BRRh-4 displayed the highest phosphate solubilizing activity, followed by BRRh-5. The pH of the culture broth declined, resulting in increase of growth rate of bacteria at pH 7, which might be due to organic acid secretion by the strains. In presence of L-tryptophan, five isolates synthesized IAA and the maximum IAA was produced by BRRh-2, followed by BRRh-1. Application of two most efficient phosphate solubilizing isolates BRRh-4 and BRRh-5 by root dipping (colonization) of seedling and spraying at the flowering stage significantly enhanced the growth and grain yield of rice variety BRRI dhan-29. Interestingly, application of both strains with 50% of recommended nitrogen, phosphorus and potassium fertilizers produced equivalent or higher grain yield of rice compared to the control grown with full recommended fertilizer doses, which suggests that these strains may have the potential to be used as bioinoculants for sustainable rice production.

Characterization of Pantoea Sp. Strain MK1D, and Erwinia Sp. Strain MK2Y as Tricalcium Phosphate Dissolving Bacteria Isolated from Calcareous Soil

This study aimed to isolate and characterize bacterial strains capable of solubilizing tricalcium phosphate (TCP) as the most commonly and insoluble phosphate in soils. Normal and molecular approaches were used to isolate and characterize phosphate dissolving bacteria (PDB) adapted to arid and semi-arid climate conditions. In this study, two strains were successfully isolated and taxonomically classified as Pantoea sp. strain MK1D, and Erwinia sp. strain MK2Y based on sequences of their 16S rRNA gene and were given GenBank accession numbers KU358676 and KU358677, respectively. This was confirmed by the formation of large halo zones on both Pikovskaya (PVK) and National Botanical Research Institute's Phosphate (NBRIP) culture media. The significant bacterial growth on liquid media was associated with the reduction of pH from 7.0 to 2.0 which lead to 83% solubilization of added TCP of 0.75 g/L. This study confirmed that both PVK and NBRIP media were reliable and comparable for the isolation of PDB and measuring their efficiency. Further studies are needed to confirm the effectiveness of these strains under pot and field conditions and their potential for commercial biofertilizers production.

Contribution of native phosphorous-solubilizing bacteria of acid soils on phosphorous acquisition in peanut (Arachis hypogaea L.).

The present investigation analyzes the in vitro P solubilization [Ca-P, Al-P, Fe(II)-P, and Fe(III)-P] efficiency of native PSB strains from acid soils of Odisha and exploitation of the same through biofertilization in peanut (Arachis hypogaea L.) growth and P acquisition. One hundred six numbers of soil samples with pH≤5.50 were collected from five districts of Odisha viz., Balasore, Cuttack, Khordha, Keonjhar, and Mayurbhanj. One bacterial isolate from each district were selected and analyzed for their P solubilization efficiency in National Botanical Research Institute Phosphate broths with Ca, Al, and Fe-complexed phosphates. CTC12 and KHD08 transformed more amount of soluble P from Ca-P (CTC12 393.30mg/L; KHD08 465.25mg/L), Al-P (CTC12 40.00mg/L; KHD08 34.50mg/L), Fe(III)-P (CTC12 175.50mg/L; KHD08 168.75mg/L), and Fe(II)-P (CTC12 47.40mg/L; KHD08 42.00mg/L) after 8days of incubation. The bioconversion of P by all the five strains in the broth medium followed the order Ca-P > Fe(III)-P > Fe(II)-P > Al-P. The identified five strains were Bacillus cereus BLS18 (KT582541), Bacillus amyloliquefaciens CTC12 (KT633845), Burkholderia cepacia KHD08 (KT717633), B. cepacia KJR03 (KT717634), and B. cepacia K1 (KM030037) and further studied for biofertilization effects on peanut. CTC12 and KHD08 enhanced the soil available P around 65 and 58% and reduced the amount of each Al3+ about 79 and 81%, respectively, over the uninoculated control pots in the peanut rhizosphere. Moreover, all tested PSB strains could be able to successfully mobilize P from inorganic P fractions (non-occluded Al-P and Fe-P). The strains CTC12 and KHD08 increased the pod yield (114 and 113%), shoot P (92 and 94%), and kernel P (100 and 101%), respectively, over the control. However, B. amyloliquefaciens CTC12 and B. cepacia KHD08 proved to be the potent P solubilizers in promoting peanut growth and yield.

Phosphorus Solubilization and Plant Growth Promotion Ability of Rhizobacteria of R. communis L Growing in Assam, India

Castor (Ricinus communis L) is the primary host plant of eri silkworm and its rhizosphere harbours diverse group of microbial community with biofertilizer potentiality. Phosphate solubilizing bacteria (PSB) render available phosphate (P) in agricultural soil by P mineralization process through enzyme mediated reaction. In search for PSB strains, 15 castor rhizobacteria were isolated and characterized for morphological and biochemical properties. The isolates were screened in vitro for P solubilization efficiency both qualitatively and quantitatively. Isolate MAJ PSB12 produced highest soluble P concentration (322.20 µmol/l) in National Botanical Research Institute Phosphate medium after 96 h of incubation with a maximum drop in pH to 5.4 from 7.0. Among the isolates, maximum content of IAA (24.6 mg/l) and GA3 (3.921 mg/l) was also found to be produced by the same strain. The most potential isolate was identified as Bacillus firmus MAJ PSB12 by 16S rRNA gene homology analysis and the sequence was submitted to National Centre for Biotechnology Information GenBank. Although many species belonging to the genus Bacillus are efficient P solubilizer, application of native rhizobacteria is easier for adaptation and succession during biofertilization process. B. firmus MAJ PSB12 can be utilized as potential biofertilizer to promote sustainable castor cultivation in sericulture for upliftment of rural livelihood.

Isolation and Characterization of Phosphate Solubilizing Bacteria from the Rhizosphere of Faba Bean (Vicia faba L.) in Meknes Region, Morocco

Aims: The objective of this research was to isolate phosphate solubilizing bacteria (PSB) from faba bean rhizosphere in Meknes region and evaluate in vitro their potential for P solubilization as well as their response to the effect of temperature, NaCl, pH and antibiotics. Study Design: Rhizosphere soil and root nodules from faba bean crop in different sites from Meknes region were collected for the study. Place and Duration of Study: Department of Biology (Soil & Environment Microbiology Unit) Faculty of Sciences, Moulay Ismail University, Meknes, Morocco; between February and August 2014. Methodology: Four strains, which retained their P-solubilizing ability after repeated subculturing, from a total of seventy eight isolates were purified, characterized and identified by 16S rRNA gene sequencing. Results: The isolates were closely related to Pseudomonas cedrina (PT19), Rahnella aquatilis HX2 (P24), Rhizobium nepotum (BSP30) and Rhizobium tibeticum (Rh8). P solubilization index of Original Research Article Rfaki et al.; BMRJ, 6(5): 247-254, 2015; Article no.BMRJ.2015.077 248 these isolates ranged from 1, 57-2, 88 in tricalcium phosphate amended National Botanical Research Institute's Phosphate (NBRIP) agar medium. Amount of phosphate solubilized ranged from 62.45 to 119.95 mg P L -1 and drop in pH of the medium ranged from 7 to 3.5. Besides, these strains exhibited resistance to several antibiotics. Conclusion: The ability of the PSB to solubilize insoluble P and their adaptation to environmental conditions add value to these strains, which could lead to improved inoculants to increase the available phosphorus in the soil for faba bean plant growth and to promote sustainable agriculture.

English

The objective of this work was to isolate, screen and evaluate in vitro, the phosphate solubilization activity of rhizobacteria isolated from Triticum aestivum rhizosphere soil in the Meknes region of Morocco. Five best isolates from 240 ones were selected based on the solubilization of insoluble phosphates (Ca3 (PO4)2) in both agar plate and broth assays using National Botanical Research Institute's phosphate (NBRIP) medium. The bacterial isolates were identified based on their phenotypic and 16S rRNA genes sequencing data as Variovorax paradoxus (BT1), Pseudomonas reinekei (BT4), Pseudomonas libanensis (BT10), Pseudomonas lurida (BT11) and Pantoea agglomerans (BT12). P solubilization index of these isolates ranged from 2.88 to 3.48, amount of phosphate solubilized ranged from 24.23 to 56.95 mg P L-1 and drop in pH of the medium ranged from 7 to 3.2. All the isolated PSB were efficient phosphate solubilizers and can be used as bioinoculants to increase the available phosphorus in the soil for wheat plant growth. Key words: Triticum aestivum, rhizobacteria, rhizosphere, phosphate, solubilizing capacity.

English

The Bacillus by their intrinsic properties have several mechanisms of procuring beneficial effects to plants. They are among the most successful bacterial communities in the solubilization of phosphates. Ten Bacillus strains were isolated from the rhizosphere of wheat from three areas in arid and semi-arid regions in Algeria. These strains were tested for their ability to solubilize phosphates on liquid and solid media: LB (Luria-Bertani), NBRIP (National Botanical Research Institute Phosphate) and PVK (Pikovskaya) supplemented with Ca3(PO4)2 (5 g/l). The highest levels of soluble phosphates were obtained on PVK and NBRIP liquid (177.68 and 173.28 µg/ml for D13 and D1 strains, respectively). Phosphates solubilization is always associated with a decrease in the pH of the medium. An inverse relationship (r = -0.4224) existed between the levels of soluble phosphate and the decrease of pH in medium. To test the solubilization capacity of theBacillus strains under salt stress, concentrations of NaCl (0, 2, 4, 6 and 8%) were added to the NBRIP medium. The solubilization capacity was negatively affected by the increase of salinity. However, the response of the Bacillus to salt was strain dependent. Strains D1 and D13, which produced the best rate of solubilization were used to study the ability of osmoprotectants (glycine-betaine, proline) to restore the ability to solubilize phosphate at high salt concentrations. However, these strains do not seem to accumulate these types of osmoprotectants.   Key words: Bacillus, phosphate solubilization, NaCl, osmoprotectant.

Solubilization of inorganic phosphate and production of organic acids by bacteria isolated from a Moroccan mineral phosphate deposit

Three efficient inorganic-phosphate solubilizing bacteria (PSB) were isolated from a phosphate rock deposit of a Moroccan mine. The phosphate solubilization index of these isolates, determined in National Botanical Research Institute's phosphate (NBRIP) medium supplemented with tribasic calcium phosphate, ranging from 2.8 to 4.4. The medium pH dropped from 7.0 to 3.5 units after growth under continuous agitation for seven days. PSB6, the most efficient PSB, closely related to

Phosphate solubilization potential and phosphatase activity of rhizospheric Trichoderma spp.

Trichoderma sp., a well known biological control agent against several phytopathogens, was tested for its phosphate (P) solubilizing potential. Fourteen strains of Trichoderma sp. were isolated from the forest tree rhizospheres of pinus, deodar, bamboo, guava and oak on Trichoderma selective medium. The isolates were tested for their in-vitro P-solubilizing potential using National Botanical Research Institute Phosphate (NBRIP) broth containing tricalcium phosphate (TCP) as the sole P source, and compared with a standard culture of T. harzianum. All the cultures were found to solubilize TCP but with varying potential. The isolate DRT-1 showed maximum amount of soluble phosphate (404.07 µg.ml-1), followed by the standard culture of T. harzianum (386.42 µg.ml-1) after 96 h of incubation at 30+1(0)C. Extra-cellular acid and alkaline phosphatases of the fungus were induced only in the presence of insoluble phosphorus source (TCP). High extra-cellular alkaline phosphatase activity was recorded for the isolate DRT-1 (14.50 U.ml-1) followed by the standard culture (13.41 U.ml-1) at 72h. The cultures showed much lesser acid phosphatase activities. Under glasshouse conditions, Trichoderma sp. inoculation increased chickpea (Cicer arietinum) growth parameters including shoot length, root length, fresh and dry weight of shoot as well as roots, in P-deficient soil containing only bound phosphate (TCP). Shoot weight was increased by 23% and 33% by inoculation with the isolate DRT-1 in the soil amended with 100 and 200 mg TCP kg-1 soil, respectively, after 60 d of sowing. The study explores high P-solubilizing potential of Trichoderma sp., which can be exploited for the solubilization of fixed phosphates present in the soil, thereby enhancing soil fertility and plant growth.