Pikovskaya Agar Medium Research Articles

Biochemical and Molecular Identification of Azospirillum brasilense Bacteria and Evaluation of Their Efficiency in Producing Hormones, Dissolving Phosphorus, and Fixing Nitrogen

The study aimed to isolate A.brasilense bacteria from the soil of the rhizosphere of different plants and different locations in Al-Diwaniyah Governorate. They were identified in two ways. The first was the routine method, which included studying the microscopic and cultural characteristics and biochemical tests of the isolates. The second method was molecular, using polymerase chain reaction (PCR) technology and using primers. It also included testing the efficiency of these isolates in dissolving tricalcium phosphate (TCP) on Pikovskaya agar medium, fixing nitrogen in the liquid nutrient medium (N.B), and measuring the amount of hormone production using an HPLC device. The results of isolation and regular and molecular identification the presence of ten isolates of bacteria bearing the characteristics of A. brasilense bacteria, out of fifteen local bacterial isolates, took the following symbols and sequences (Az2, Az3, Az5, Az6, Az7, Az9, Az11, Az12, Az13, Az14), as the results showed confirmation of the identification of the bacterial isolates identified by biochemical tests. Using a specialized primer to amplify the 462bp fragment of the 16S ribosomal RNA gene, the results of testing the efficiency of the bacteria in dissolving phosphate (TCP) showed that the isolate (Az13) outperformed the highest value in its effectiveness in dissolving metallic phosphorus through the diameter of the clear zone around the colony, which was effective in dissolving phosphate of up to 3.89 mm. As for the nitrogen fixation efficiency test, the isolate (Az3) excelled in the amount of fixed nitrogen reaching 12.44 mg.L-1. As for the amount of its production of growth regulators for Auxins, Gibberellins, and Cytokinins, the isolate (Az3) recorded the highest value in the amount of Auxins production ( Indol-3-acetic acid) its concentration reached 34.4 µg.ml-1, and as for the production of the hormone Gibberellins (GA3), the isolate (Az3) recorded the highest value amounting to 34.7 µg.ml-1, as for the production of the hormone Cytokinins (CK), The isolate (Az11) recorded the highest value, amounting to 28.8 µg.ml-1.

Analisis bakteri rhizosfer pelarut fosfat pada tanaman jagung dari wilayah Empang Sumbawa, NTB

Phosphate solubilizing bacteria are components of the soil ecosystem. They are play a pivotal role in supplying phosphate for plants. Exploration of phosphate solubilizing bacteria continues to be carried out to obtain potential isolates. This research aims to analyze phosphate solubilizing bacteria of maize rhizosphere plants in the Empang Sumbawa region, West Nusa Tenggara. The bacteria were isolated from the soil of maize plants rhizosphere in the vegetative and generative growth phases. The ability of solubilize phosphate of the isolates were tested using the spot inoculation technique on Pikovskaya Agar medium. The clear zone formed around the bacterial colony indicates the phosphate solubilization. A total of 18 isolates were successfully isolated. Eleven of them showed the ability to dissolving phosphate. The isolates V6 and V7 have the best performance, as indicated by phosphate dissolution index values of 1,3 and 1,54.

Phytoremediation of Arsenic (As) in rice plants, mediated by Bacillus subtilis strain IU31 through antioxidant responses and phytohormones synthesis

Bacteria-assisted phytoremediation uses bacteria to promote plant health and improve its ability to remediate toxic heavy metals like Arsenic (As). Here, we isolated rhizobacteria and identified them as Bacillus subtilis strain IU31 using 16S rDNA sequencing. IU31 showed phosphate solubilization potential on Pikovskaya agar medium and produced siderophores, which were detected on Chromium Azurol-S (CAS) agar medium. Indole-3-acetic acid (IAA) and gibberellins (GAs), namely GA1, GA3, GA4, GA7, GA9, GA12, GA15, and GA24, were quantified by GC/MS-SIM analysis. The expression levels of genes involved in GA and IAA biosynthesis, such as cyp112, cyp114, trpA, and trpB, were assessed using semi-quantitative RT-PCR. Plant bioassays showed that As at a 15 mg/kg concentration reduced plant growth, chlorophyll content, and biomass. However, IU31 inoculation significantly improved plant growth dynamics, enhancing As accumulation by up to 50% compared with uninoculated plants. IU31 inoculation induced the bioconcentration factor (BCF) and bioaccumulation factor (BAF) of As in plants compared to uninoculated plants, but the translocation factor (TF) of As was unaffected by IU31 inoculation. IU31 inoculation effectively restored glutathione-S-transferase (GST) and catalase (CAT) enzyme activities, as well as glutathione (GSH) and hydrogen peroxide concentrations to nearly normal levels, which were significantly elevated in plants exposed to As stress. These results show that IU31 improves plant health and growth by producing IAA and GAs, which might contribute to the uptake and detoxification of As.

Isolation and Characterization of Phosphorus Solubilizing Bacteria from Millet Rhizosphere in Lafia metropolis

Phosphorus is an essential, but often unavailable nutrient for plant growth in the soil due to its low solubility. Phosphorus solubilizing bacteria (PSB) convert insoluble forms of phosphorus into soluble forms that can be taken up by plants. The study aimed to isolate and characterize PSB from the rhizosphere of millet plants in Lafia, and to evaluate their potential for improving soil fertility and crop productivity. Soil samples were collected from four different locations and plated on Pikovskaya's agar medium. PSB colonies were identified based on their ability to produce clear zones around them. The PSB isolates were further characterized by morphological, biochemical, and molecular methods. The phosphate solubilizing activity and plant growth-promoting traits of the PSB isolates were also assessed. The PSB isolates were tested for their effect on the growth of millet seedlings in pots. The results showed that 16 PSB isolates belonging to four genera (Bacillus, Pseudomonas, Enterobacter, and Klebsiella) were obtained from the soil samples. The PSB isolates exhibited varying degrees of phosphate solubilizing activity, ranging from 11.2 to 81.6 mg/L. The PSB isolates also showed positive results for the production of indole acetic acid, ammonia, hydrogen-cyanide, and siderophore. The PSB inoculation significantly increased the shoot and root lengths, and fresh and dry weight of the millet seedlings. The study concluded that the PSB isolates from the millet rhizosphere in Lafia could enhance soil phosphorus availability and millet growth. The study recommended further research on the field application and optimization of the PSB inoculation.

Isolation of Phosphate Solubilizing Fungi from Soil and Their Application in Plant Growth Promotion

Phosphorus plays a significant role in numerous physiological and metabolic processes in plants. Soil phosphorus is immobilized due to the formation of insoluble complexes. The use of efficient phosphate-solubilizing microorganisms opens up a new prospect for better crop productivity and for greater yield performance without affecting the soil health. Phosphate-solubilizing fungi (PSF) enhance available phosphorus released from soil, which contributes to P requirement of plants. Hence, the present study was designed to evaluate the utilization of PSF as a biofertilizer. Pikovskaya's Agar medium was used to isolate fungal species from compost and open dumpsite soil. Isolated fungi were labelled as PSF-X, PSF-Y, and PSF-Z. A pot experiment was carried out to determine the effect of isolated fungal strains. The isolated fungal strain was introduced to the developed potting media which contained compost and soil at 1:1 ratio. Soya bean was selected as the experimental plant. Plant growth parameters (shoot length and root length) were measured to determine the effect of isolated fungal strains. Plant growth parameters were recorded after 21days. Fungi inoculated pots showed a significant increase in both shoot and root lengths in comparison to the control (n=9, p<0.05). Potting media consisting of PSF-X showed the best result. The highest root length (4.7±0.1 cm) and shoot length (35.8±1.2 cm) were recorded in pots inoculated with PSF-
 
 Hence, isolated PSF-X, PSF-Y, and PSF-Z are recommended as suitable biofertilizer strains for potting medium.
 
 
 Keywords: Fertilizer, Fungi strain, Phosphorus, Plant growth

Identification of Potential Isolate Phosphate Solubilizing Bacteria Used 16S rRNA Gene

Plants always interact with microorganisms either negatively or positively during their life cycle. The Phosphate Solubilizing Bacteria (PSB) group is one example that has some beneficial effects on the plant. PSB can transform insoluble soil inorganic phosphates into soluble phosphorous so plants can absorb them. This research aimed to test the isolate's ability to solubilize phosphorous and use the 16S rRNA marker gene to identify it. Testing the ability of bacteria to solubilize phosphorous on Pikovskaya's agar medium used a qualitative method by observing the halo zone in the colony around it. Then the bacterial isolate was identified by analyzing the result of sequencing the 16S rRNA gene. The RZ02 bacterial isolate showed the highest performance in solubilizing phosphorous, with a 9.1 mm solubilization index. The gene of 16S rRNA was carried out by using primers 27F and 1492R with an amplicon size of 1500 base pairs. Sequencing analysis and construction of a phylogeny tree were conducted by the Mega X neighbor-joining method and showed 100% similarity with Pseudomonas aeruginosa OIS 481. The solubilization index indicated that the bacteria had a potential candidate to be one of the inoculant components for biofertilizer.

Isolation and Characterization of Phosphate-solubilizing Bacteria from Rice Field of Odisha and Their Growth Promoting Effect on Agricultural-Sectors

Organic farming will be a significant approach for farmers in the coming decades due to improved production and the preservation of soil natural properties. Phosphorus is the second most macronutrient required for plants to survive. The primary goal of this research was to know the paddy field soil nutritional status and isolate potential PSB bacteria from soil samples, which may aid in the development of a potent biofertilizer for organic farming. 12 soil samples were collected from three districts of Odisha (Kendrapara, Cuttack, Khordha). A laboratory study was conducted to isolate, identify, and characterise phosphate solubilizing bacteria from rice field soil. The morphological and biochemical traits of the PSB strains were evaluated. Four potential PSB strains PR, PA, PD, PS were chosen based on solubilization zone production and abundance in sampling site. The isolates PR had maximum phosphate solubilization index of 2.72 in pikovskaya agar medium and were strongly predominant in all regions. Phosphate solubilization and enhanced germination potential were evident in all four species. When compared to controls, good plant height, dry weight, and fresh weight were confirmed in seed germination assays with all bacterial isolates. The PR strain had the highest rate of germination 96.03%.

Minjingu phosphate rock solubilization and potential for use of Klebsiella variicola-MdE4 and Klebsiella variicola-MdG1 as biofertilizer for maize production

Limited solubility of the Tanzania’s Minjingu phosphate rock (MPR) in non-acidic soil conditions has held back its potential for widespread use in agricultural production. This study was designed to isolate, characterize and test phosphate-solubilizing bacteria for their potential to increase solubility of MPR and enhance maize plant growth under field conditions. Ten out of 19 isolates showing greatest phosphate solubilization indices on a Pikovskaya agar medium were further characterized for other plant-growth promoting traits including production of IAA, siderophores and ammonia. Two of them, namely isolates-MdE4 and MdG1 substantially outperformed other isolates in phosphate solubilization and production of IAA, ammonia and siderophores. The two isolates molecularly identified as Klebsiella variicola-MdE4 and K. variicola-MdG1 produced up 701, 699 and 750, 680 μg/ml of soluble phosphate from tricalcium phosphate and hard Minjungu rock phosphate, respectively. Additionally, Biorock P- a biofertilizer formulation containing MdE4 and MdG1 co-cultured in a molasses-based modified broth medium retained most of the phosphate solubilizing potential and other plant-growth promoting traits of MdE4 and MdG1. Co-application of MdE1 and MdG1-containing “bio-rock P” and inorganic phosphate at 20 kg P/ha resulted in higher maize grain yield than that of positive control (40 kg P/ha) under field conditions. The two isolates- Klebsiella variicola-MdE4 and K. variicola-MdG1 have the potential for use in a biofertilizer formulation for commercial field applications.

Heavy metal ATPase genes (HMAs) expression induced by endophytic bacteria, “AI001, and AI002” mediate cadmium translocation and phytoremediation

Contamination of heavy metals is a serious threat, which causes threats to the environment. Our study aimed to determine the role of endophytic bacteria in Cd phytoremediation and heavy metal ATPase gene expression. Cadmium (Cd) resistant endophytic bacteria were isolated from Solanum nigrum on LB agar plates, contaminated with 0–30 mg/L Cd. The phosphate solubilization and indole-3-acetic acid (IAA) production of endophytes were estimated by growing them on Pikovskaya agar medium and GC-MS analysis, respectively. An experiment in a pot was performed to evaluate the effects of bacteria on rice plants contaminated with 5–25 mg/L of Cd. Expression of Cd response genes was quantified through qRT–PCR and Cd translocation from one part to another part of the plant was measured through the ICP. BLAST alignment of 16 S-rDNA gene sequences confirmed the bacterial isolates as Serratia sp. AI001 and Klebsiella sp. Strain AI002. Both strains tolerated Cd up to 25 mg/L and produced 27–30 μg/mL of IAA. Inoculation of AI001 and AI002 improved plant growth dynamics (i.e., plant length, biomass, chlorophyll contents), relieved electrolyte leakage, and improved reduced glutathione significantly (P < 0.05). The inoculation of AI001 and AI002 significantly (P < 0.05) induced the expression of heavy metal ATPase genes ie., “HMA2, HMA3, and HMA4” and Cd translocation compared to uninoculated plants. Both AI001 and AI002 exhibited very prominent plant-growth-promoting and Cd phytoremediation properties. The results revealed that isolates also contributed a lot to the expression of rice plant heavy metal ATPase genes and in the Cd translocation in the plant.

Isolation, Identification and Characterization of Phosphate Solubilizing Bacteria from Jhum Field of Mizoram, India

Phosphorus (P) is one of the most important nutrients and its low availability in soil is a limiting factor for the growth and development of plants. In jhum cultivation, there is considerable loss of soil nutrients especially phosphorous (P). Since soil P are an important soil nutrient, the use of native phosphate solubilizing bacteria (PSB) capable of converting the insoluble P to soluble form can serve as biofertilizers to increase the amount of plant-available P. PSB native to jhum and jhum fallow soil were isolated and screened for their phosphatase enzyme and indole compound production. These bacteria are being explored for development as biofertilizers to increase crop production in jhum cultivation as well as faster eco-restoration of jhum fallow. Base on their ability of solubilizing tri-calcium phosphate in Pikovskaya agar medium, a total of 44 PSBs were isolated from the current jhum field and different age fallow. Molecular characterization of 44 bacterial showing phosphate solubilization potential was carried out and a phylogenetic tree was constructed. All isolates showed production of acid phosphatase enzyme and indole-like compounds. Bacterial isolates MZUR22 and MZUR37 were evaluated for their efficacy to alleviate the early growth performance of rice in vitro conditions. The in vitro assessment showed that rice plants treated with PSB isolates showed a positively significant growth performance against other treatments.

Bacillus subtilis Strains Isolated from Cocoa Trees (Theobroma cacao L.) Rhizosphere for their use as Potential Plant Growth Promoting Rhizobacteria in Côte d'Ivoire.

Plant growth promoting rhizobacteria (PGPR) are important for agriculture through their activity in stimulating and facilitating plant growth. The rhizobacteria were screened for molecular characterization and followed by their indole acetic acid (IAA) production, phosphate solubility, antibiosis activity. In this study, 162 soil samples were collected from the cocoa rhizosphere to isolate Bacillus subtilis strains using Mössel agar medium with an additional egg yolk and identified by sequencing the ytcP gene. The ability of each strain to form biofilms was obtained in a tube. Indole-3-acetic acid (IAA) production was estimated in Yeast Peptone Dextrose (YPB) broth. Phosphates were solubilized by each strain on Pikovskaya agar medium. The detection of lipopeptide genes using the molecular method has established the possession of isolates by antimicrobial genes. Fifty (50) B. subtilis strains were isolated and identified using the ytcP gene. Ninety percent (90%) of the strains were able to form a biofilm. All isolates produced an IAA. Forty (40 (80%)) of B. subtilis were solubilized phosphate with phosphate solubilizing index (PSI) of 0 to 97.33 ± 0.70%. Of all B. subtilis strains, 45 (90%) have the srfAA gene, 19 (38%) have the fenD gene and 12 (24%) have the ituC gene. B. subtilis strains from cocoa rhizosphere would be beneficial for agricultural production by their PGPR activities.

Characterization phosphate-solubilizing marine actinobacteria associated with Sargassum Sp from Menjangan kecil island, Indonesia

Phosphorus plays a crucial significant role in all life forms. Microbes have the ability to convert several forms of phosphorus into dissolved forms, so that they can also be used in the phosphorus cycle process. The aim of this research were to explore, screen, phenetic and molecular identify the phosphobacteria naturally colonized and associated with Sargassum sp. from the Menjangan Kecil Island, Karimunjawa. Total of 23 bacterial isolates associated with Sargassum sp. were screened. All isolates obtained were tested for their ability in phosphate dissolution activity in Pikovskaya agar medium. Three different isolates showed the largest dissolution activity around bacterial colonies selected for quantitative estimation of phosphate solubilization. The next screening was to choose one candidate isolate based on its highest ability in dissolving phosphate and then identifying its identity based on phenotypic character and 16S rRNA gene. Quantitative estimation of phosphate solubilization PSB isolates MBS3R was 149,32 μg P ml-1 was analyzed for 120 hours of incubation at room temperature. MBS3R isolate is a strain of Microbacterium sp, which is taxonomically included in the class of Actinobacteria, genus Microbacterium.

Endophytic bacteria isolated from Solanum nigrum L., alleviate cadmium (Cd) stress response by their antioxidant potentials, including SOD synthesis by sodA gene

Cadmium (Cd) is a toxic heavy metal and an abiotic stressor to plants; however, inoculation of endophytic bacteria can raise resistance in plants against Cd, as well as improve plant growth. In the present study, two endophytic bacterial strains were isolated from Solanum nigrum, identified as Serratia sp. IU01 and Enterobacter sp. IU02 by 16S DNA sequencing. Both IU01 and IU02 were tolerant up to 9.0 mM of Cd in culture broth and successive increase in Cd concentration from 0 mM to 9.0 mM, led to an increase in the SOD enzyme activity of the isolates. Both strains were capable of indole-3-acetic acid (IAA) synthesis and phosphate solubilization, detected through gas spectrometry-mass chromatography (GC-MS) and Pikovskaya agar medium respectively. Brassica juncea plants stressed with 0–25 mg/kg Cd showed retardation in all growth attributes, however, inoculation of strain IU01 and IU02 significantly promoted the plant growth attributes as compared to control. Moreover, antioxidant enzymes and metabolites against reactive oxygen species (ROS) including polyphenol oxidase (PPO), peroxidase (POD), catalase (CAT), superoxide dismutase (SOD), alcohol dehydrogenase (ADH), reduced glutathione (GSH), malondialdehyde (MDA), flavonoid and polyphenolic contents were also significantly relieved by inoculation of IU01 and IU02 in plant exposed to different concentration of Cd stress as compared to control plants. Phytohormone production, phosphate solubilization, and/or antioxidative support of IU01 and IU02 might be responsible for growth promotion and Cd resistance in the plant.

Molecular Identification of Rhizospheric Thermo-halotolerant Aspergillus terreus and its Correlation to Sustainable Agriculture

High phosphate solubility is one of the most important factors for increasing plant growth. This study focused on the zinc phosphate (ZP) solubilizing capacity of thermo-halotolerant Aspergillus terreus, where the growth showed halo zones on Pikovskaya agar medium that appeared at high NaCl concentrations (up to 10%) and a wide range of temperatures (up to 45 °C). Acidification of the broth was assumed to be the major mechanism for ZP solubilization by A. terreus, where the growth was related to the pH decrease in the medium containing ZP. Under pot conditions, A. terreus increased the biomass and phosphorus content of Hordeum vulgare plants. A. terreus showed a phosphorus solubilization ability with a NaCl concentration of up to 10%; therefore, A. terreus can be of great benefit in maintaining the available phosphate levels for crops in saline soils. Finally, it was found that A. terreus with ZP can substitute chemical fertilizer and help improve crop production.

Rhizospheric bacterial isolates of grass pea (Lathyrussativus L.) endowed with multiple plant growthpromoting traits.

The main aim of this work was to examine the plant growth promoting, biocontrol activities and stress competency of grass pea rhizobacterial strains from Ethiopia. Serial dilutions were carried out to isolate rhizobacterial strains from the rhizosphere soil samples. The isolates were characterized for their plant growth promoting, biocontrolling and stress tolerance potential. The isolates that showed better performance in the tested parameters were identified by 16S rRNA gene sequencing. Among the isolates tested on Pikovskaya agar medium, 22 isolates that showed solubilization index of >2·41cm were selected for further screening tests. Isolate AAUGPR-53 identified as Enterococcus species, Enterococcus casseliflavus strain showed the highest phosphate solubilization index and indole-3-acetic acid production efficiency of 4·81±0·02 (μgml-1 ) and 56·55±0·45 (μgml-1 ), respectively. Sixteen (72·7%) of the isolates showed invitro antifungal inhibition against Fusarium oxysporum f. sp. lentis with isolates AAUGPR-92 and AAUGPR-91 identified as Enterococcus species, E. casseliflavus strain and Enterococcus gallinarum strain exhibiting the highest inhibition of 83 and 78%, respectively. Likewise, 68·2%, 91·30%, 45·5%, 77·3% and 100% of the isolates produced chitinase, protease, cellulase, HCN and NH3 , respectively. Most of the isolates showed good tolerance to the tested stress factors. The 16S rRNA partial sequencing of the rhizobacterial isolates proved their taxonomic position in the existing bacterial isolates. The results indicated that three strains, AAUGPR-53, 91 and 92, that showed maximum sequence identity (99%) to Enterococcus species, E. casseliflavus and E. gallinarum were recommended as microbial inoculants for trials under greenhouse and field conditions. This study illustrates an effective alternative to conventional fertilizers that may contribute to crop disease reduction. Our results provide a foundation for future research that will lead to identifying potentially useful biocontrol strains found in the rhizosphere of grass pea.

An ability of endophytic bacteria from nutgrass (cyperus rotundus) from lafau beach of north nias in producing indole acetic acid and in solubilizing phosphate

Endophytic bacteria have taken much attention for their potency to promote plant growth. This study was aimed to isolate endophytic bacteria from nutgrass (Cyperus rotundus) and to examine their potency in producing indole acetic acid (IAA) and in solubilizing phosphate. Isolation of endophytic bacteria was done by slicing and sterilizing root, stem, and leaf sample surface with alcohol 70% and sodium hypochlorite 2%, followed by incubation of the sliced samples in nutrient agar medium. Morphological characterization and simple biochemical tests were performed on bacterial isolates. All bacterial isolates were examined for their ability to produce indole acetic acid and to solubilize phosphate. Three isolates (AZ5, AZ12 and AZ6) out of fifteen indicated the ability to produce indole acetic acid and to solubilize phosphate. IAA producing test using spectrophotometry method showed that AZ5, AZ12,and AZ6 produce more IAA with concentration of 49,91, 48,18, and 44,45 ppm, respectively. Phosphate solubilizing test using Pikovskaya agar medium showed that the three isolates were able to solubilize phosphate with index of 6.27, 3,31, and 3.41 respectively.

Phosphate solubilizing endophytic actinomycetes from mangrove plants Rhizophora mucronata and Sonneratia caseolaris and its effect on Seedling vigour

The aim of the present study was to isolate phosphate solubilizing endophytic actinomycetes from two mangrove plants Rhizophora mucronata and Sonneratia caseolaris, to estimate phosphate solubilization quantitatively and to check its efficiency on Seedling vigour. The plant parts were surface sterilized and were plated on Oat meal agar supplemented with 10% sea water and a total of 11 endophytic actinomycetes were isolated. The isolates were screened for Phosphate solubilization using Pikovskaya's agar medium. The potent isolates were subjected for fermentation and the broth culture was subjected for quantitative estimation of phosphate solubilization by Johnson and Koening method. The effect of extracts of endophytic actinomycetes was also evaluated by seed germination and seedling vigour test. Of the total 11 isolates, Isolate RO 4, RO 7, RO 9, RO 10 and RO 11 demonstrated Phosphate solubilizing activity in the form of halo zone around the colonies and were selected for further studies. The broth cultures showed high amount of phosphate release compared to the standard. Highest amount of phosphate was recorded for Isolate RO 11 about 1410μg/ml. Isolate RO 7 and RO 11 showed the highest effect on Seedling vigour index. The results of the present study reveal that phosphate solubilizing endophytic actinomycetes can be used as a source of biofertilizer.

Phosphate Solubilization by &amp;lt;i&amp;gt;Bacillus subtilis&amp;lt;/i&amp;gt; and &amp;lt;i&amp;gt;Serratia marcescens&amp;lt;/i&amp;gt; Isolated from Tomato Plant Rhizosphere

Plants need phosphorus for many physiological activities in a form of phosphate anions. Three different bacterial strains (Bacillus subtilis PH, Serratia marcescens PH1, and Serratia marcescens PH2), recently isolated from tomato plant rhizosphere, have high phosphate solubilization index (SI from 2.8 to 3.2) on Pikovskaya agar medium (which contains calcium phosphate). Moreover, phosphate release from calcium in Pikovskaya broth over 5 days is increasing with cell growth for the different isolates. The most efficient phosphate solubilization case is the mixed culture of the 3 strains (OD475 is almost 1). On the other hand, pH values decreased dramatically with time due to organic acids secretion and the maximum acidification level is recoded for Serratia marcescens PH2 (pH = 1.94). Interestingly, the isolates are resistance to important pesticides (oxamyl, thiophanate methyl, and captan) that are commonly used in the sampling area. This resistance is very favorable and increases the persistence of the phosphate solubilizing bacteria in contaminated soils. The isolates are therefore plant symbionts and growth promoting agents.

Isolation and Characterization of a Pseudomonas aeruginosa Strain PGP for Plant Growth Promotion

The present study has identified a free living bacterial strain from dump garbage soil, capable of forming large halo zone in National Botanical Research Institute’s Phosphate medium and Pikovskaya agar medium with phosphate solubilization index of 4.0. The phosphate solubilization ranged from 304.08 to 2073.01 ± 0.33 µg ml−1 in 3–12 days in NBRIP broth containing tricalcium phosphate and pH decreased from 7.0 to 3.8. The strain showed growth and color change in different nitrogen free media and nitrogen fixation in the supernatant was estimated to be 3.057 ± 0.34 and 7.87 ± 0.34 mg l−1 on 30th and 45th days of incubation. Indole acetic acid, ammonia, siderophore, and hydrogen cyanide production by the strain were quantified. 16s rDNA analysis confirmed the strain as Pseudomonas aeruginosa. Pot based assay with Indian mustard showed that seed coating of the strain significantly enhanced plant wet weight (up to 140%), plant dry weight (up to 88%), root length (up to 25%) and shoot length (up to 14%) over un-inoculated controls. It also showed that seed bacterization resulted in greater enhancement of plant growth than direct inoculation in the plant rhizoplane. Nitrogen and phosphorous content of the seed treated plants were 40.61 and 100% higher than the untreated controls further confirming the nitrogen fixation and phosphate solubilization efficiency of the strain.

Soil organic carbon and phosphorus availability regulate abundance of culturable phosphate-solubilizing bacteria in paddy fields

Low availability of phosphorus (P) is a major constraint for optimal crop production, as P is mostly present in its insoluble form in soil. Therefore, phosphate-solubilizing bacteria (PSB) from paddy field soils of the Indo-Gangetic Plain, India were isolated, and their abundance was attempted to be correlated with the physicochemical characteristics of the soils. Ninety-four PSB were isolated on Pikovskaya's agar medium, and quantitative phosphate solubilization was evaluated using NBRIP medium. The isolates solubilized P up to a concentration of 1 006 μg mL−1 from tricalcium phosphate with the secretion of organic acids. These isolates were identified by 16S rRNA gene sequence comparison, and they belonged to Gammaproteobacteria (56 isolates), Firmicutes (28 isolates), Actinobacteria (8 isolates), and Alphaproteobacteria (2 isolates). Phylogenetic analysis confirmed the identification by clustering the isolates in the clade of the respective reference organisms. The correlation analysis between PSB abundance and physicochemical characteristics revealed that the PSB population increased with increasing levels of soil organic carbon, insoluble P, K+, and Mg2+. The promising PSB explored in this study can be further evaluated for their biofertilizer potential in the field and for their use as potent bio-inoculants.