Pikovskaya Agar Medium Research Articles

Organic Acid Secretion and Phosphate Solubilizing Efficiency of Pseudomonas sp. PSB12: Effects of Phosphorus Forms and Carbon Sources

ABSTRACTSecretion of organic acids is an important mechanism for phosphate solubilizing bacteria (PSB) to dissolve insoluble phosphorus in soil. However, the composition of organic acids produced by PSB in the presence of different phosphorus compounds is poorly known, and little is known about the ability of PSB to degrade pollutants in sediment. In this study, we isolated a strain Pseudomonas sp. PSB12 from the sediment of the Qihe River. PSB12 had maximum phosphate solubilization index (SI) of 3.86 on Pikovskaya's agar medium. The phosphate solubilizing activity was associated with the release of organic acids produced from glucose, while the composition of organic acids produced by PSB12 was dependent on the phosphorus forms. When initial soluble phosphorus was insufficient (in MP1 and MP2 media), gluconic acid was the predominant organic acid. In contrast, formic acid, butyrate, and propanedioic acid were the main organic acids produced when only soluble phosphorus (MP3) was supplied. RT-PCR indicated that the expression of glucose dehydrogenase gene (gcd) of PSB12 was two- to four-fold higher in MP1 than in MP3. PSB12 also possessed the phenol hydroxylase gene (phe) suggesting that phenol could be used as the carbon source to dissolve insoluble phosphorus. PSB12 is a potential candidate for in situ bioremediation and for promoting plant growth in soil contaminated by phenol with low levels of soluble phosphorus.

Assessment of Penicillium bilaii inoculation in wheat (Triticum aestivum L.) for improving growth, yield and phosphorus availability in Mollisols of India

A field experiment was carried out with an aim to study the influence of two strains of Penicillium bilaii (PB -201 and PB-208) inoculation along with superphosphate application on growth, yield and P uptake of wheat (cv. PBW-343) and, also to examine the inoculation effect on P availability, forms of P and soil properties in Mollisols of Uttarakhand, India. The results showed that both strains of P. bilaii effectively solubilized tri-calcium phosphate in Pikovskaya agar medium, which was much higher over native fungal isolates. Wheat seed inoculation with P. bilaii strains along with superphosphate levels significantly influenced shoot height, shoot dry weight, number of total and effective tillers, yield attributes, yield components, tissue content and uptake of P. The treatment T7 (P. bilaii, strain PB-208 + 50% P) has resulted into the highest amount of shoot height (87.9 cm at 90 DAS), shoot dry weight (1.5 and 3.8 g at 60 and 90 DAS, respectively), grain (66.8 q ha-1) and straw yield (42.7 q ha-1) and P uptake (26.5 kg ha-1). The Olsen-P, organic carbon, dehydrogenase activity and fungal populations also increased in soil inoculated with P. bilaii strains combined with superphosphate application compared to the control soil. The conjoint use of the fungal strains with or, without P fertilization has developed an antagonistic interaction that has caused decline in yield, tissue content and uptake of P and its availability in soil. In conclusion, it is possible to reduce the rate of soluble P-fertilizer added by 50% without reducing yield, if wheat is inoculated with P-solubilizing fungi like P. bilaii.

Induced Inorganic Phosphate Solubilization Through N-Methyl-N´-Nitro-N-Nitrosoguanidine Treated Mutants of Pseudomonas koreensis Strain AK-1 (MTCC Number 12058) Under Polyethylene Glycol

In the present study, a wild type and mutant strain of Pseudomonas koreensis strain AK-1 (MTCC number 12058) was used for enhanced inorganic phosphorus solubilization under drought stress. Five mutants namely AK-1a, AK-1b, AK-1c, AK-1d and AK-1e were found to solubilize inorganic phosphates more than that of wild type strain in drought stress of 0–10 % polyethylene glycol. On the basis of solubilization index on Pikovskaya agar medium the highest phosphate solubilization index was recorded by mutant strain AK-1c as compared to the wild type strain (AK-1). AK-1c gave the highest Phosphate solubilization index (7.67) at 0 % of polyethylene glycol concentration and lowest (3.6) at the 10 % of polyethylene glycol. AK-1e showed the lowest (4.85) at 0 % and 2.6 at 10 % P solubilization index among the five mutant strains while AK-1 wild type strain showed 4.12 at 0 % and 2.33 at 10 % polyethylene glycol. A highest (19.82) μg/ml at 2 % and 9.73 μg/ml at 10 % PEG inorganic phosphate was solubilized by AK-1c mutant strain which was more than that of wild type variety (17 μg/ml at 2 % and 7.5 μg/ml at 10 % PEG). In plant growth promoting experiment, mutant (AK-1c and AK-1a) bacterial treated soybean plants showed increased shoot length, root length, shoot fresh weight, root fresh weight and number of lateral roots under drought stress as compared to untreated control plants. Bacteria treated soybean plants in Murashige Scoog media showed significant increase in number of lateral roots as compared to the control.

Isolation and biochemical characterization of rhizobium from pea crop at Swabi

Microorganisms like Rhizobium are symbiotic bacteria forming nitrogen fixing nodules on legumes. Nodule inducing bacteria are capable of colonizing the roots of legumes to fix nitrogen and to produce phosphorus, phytohormones, siderophores and HCN. To study the important characters of Rhizobium was the main objective of this study which will help for growth and improvement of Pea. Nitrogen (N) and Phosphorus (P) are the foremost limiting nutrients in agricultural soils of Pakistan. Through the enhancement of these microorganisms the deficiency of these major plant nutrients can be control. From diverse areas of Swabi pea samples were collected. Rhizobium strains were isolated from nodules on Yeast-Manitol Agar medium (YMA) and were characterized bio-chemically for Nitrogenase activity, phytohormone production, phosphate solubalization, siderophores and HCN production. Nitrogenase was determined through calorimetrically. The production of ethylene by the Rhizobium strains were ranges from 20.7 µ moles C2H2/hr to 38.4 µ moles C2H2/hr. Phytohormone (IAA) was measured through Electro-Spectrophotometer. The qualitative assessment of phosphorus solubalization was made by size of halo zones around the colonies on Pikovskaya agar medium. Rhizobium strains produced IAA (ranging from 14.25-13.65 µg/ml), Phosphorus solubilized (18-24µg ml-1) and four Rhizobium strains were siderophores positive. Out of seven Rhizobium strains only five strains were able to produce hydrogen cyanide (HCN). Furthermore, biozotes (Biofertilizer) were prepared from inoculation of these Rhizobium strains and were applied in pot experiment to check their effects on pea. All the inoculants showed positive effect on growth and development of peas and significantly increased root shoot length, dry and fresh weight

Characterization of phosphate solubilizing bacteria isolated from Pb contaminated soils and their potential for dissolving tricalcium phosphate

Phosphorus solubilizing bacteria (PSB) enhances P availability in soils through dissolving inorganic P pools. The characteristics of PSB and the potential of three Pb tolerant phosphate solubilizing rhizobacteria, i.e. Pseudomonassp, Bacillus sp., and Actinomycites sp. were evaluated. PSB were isolated from soil samples contaminated with 300 and 500 mg Pb/kg after incubation for 30 days. Phosphate solubilizing bacteria were screened on for phosphate solubilisation ability in Pikovskaya agar medium (PA). In addition, two of the three indentified PSB strains (Pseudomonas sp. and Bacillus sp.) were characterized for their ability to solubilize tricalcium phosphate in Pikoskaya broth (PB) and also were examined their growth during culture medium incubation. The isolates exhibited different phosphate solubilization index, ranging from 1.87 to 2.98. Pseudomonas sp. had the highest ability to solubilize tricalcium phosphate: 9.82 mg P/ L and 12.23 mg P/ Lin Pikoskaya broth following the addition of 4 mg Pb/L and 2 mg /Pb L, respectively.Â

Isolation and characterization of phosphate-solubilizing bacterial species from different crop fields of Salem, Tamil Nadu, India

Phosphate-solubilizing bacterial strains (PSB) were isolated from maize, onion, jasmine, and tomato rhizosphere soils from four different localities of Salem (Tamil Nadu) - (i) Ammapalayam, (ii) Attayampatty, (iii) Seeragapadi, and (iv) Ariyanoor. Twelve efficient PSB isolates were selected from the colonies based on their ability to form clear zone on Pikovskaya's agar medium. The isolated PSB released high amount of phosphorus from calcium phosphate. The efficient bacterial strains isolated from rhizosphere soils released high amount of phosphorus. Oligonucleotide primers in RAPD characterization showed genetic variation among the bacterial strains. Amplified fragments showed 40% shared and 20% unique polymorphic bands. The rest 40% was monomorphic bands.

Phosphate solubilization by Rhizobium strains.

Forty-six Rhizobium isolates from legume root and stem nodules were examined for their phosphate-solubilizing ability on Pikovskaya's agar medium. Rhizobium isolates from root nodules of Cassia absus, Vigna trilobata and three strains from Sesbania sesban showed zone of tricalcium phosphate (TCP) solubilization. The isolate from C. absus showed maximum solubilization (620 μg/ml) after 12 d of incubation, while the Rhizobium sp. strain 26 (from S. sesban) showed the least amount (150 μg/ml) of phosphate solubilization. Among the carbon sources tested for their ability to solubilize TCP, maximum solubilization (620 μg/ml) was observed in glucose by Rhizobium isolate from C. absus. Phosphate solubilization increased with increase in glucose concentration steeply up to 2% and slowly above this concentration in four isolates. Among the nitrogen sources tested, maximum solubilization (620 μg/ml) was observed in ammonium sulphate by Rhizobium isolate from C. absus.

Efficacy of rhizobacteria for growth promotion in sorghum under greenhouse conditions and selected modes of action studies

SUMMARYThe screening of rhizobacteria for growth promotion of sorghum (Sorghum bicolour(L.) Moench) was conducted under greenhouse conditions for a total of 78 bacteria isolated from the rhizosphere of sorghum in Ethiopia, and 86 isolates from the rhizosphere and rhizoplane of grasses in South Africa. Three isolates from Ethiopia, all identified asBacillus cereus, enhanced growth promotion by resulting in statistically significant increases in at least five parameters. Of these,B. cereus(KBE7-8) resulted in significant increase in shoot and root biomass. Among effective isolates from South Africa,B. cereus(NAS4-3) andStenotrophomonas maltophilia(KBS9-B) showed significant increases in all the parameters measured. The isolates which resulted in significant growth promotion colonized the roots effectively with a count up to ⩾108cfu/g. In the study conducted to elucidate the possible modes of action by these effective isolates, indole 3-acetic acid-like substances were detected in culture filtrates of the isolates ranging from 4·2 μg/ml bySerratia marcescens(KBS9-R) to 22·8 μg/ml byB. cereus(KBS5-H) in the presence of 2 mg tryptophan/g nutrient broth solution. Higher rates of solubilization of tricalcium phosphate on Pikovskaya agar medium were shown byChryseomonas luteola(KBS5-F),S. marcescens(KBS6-H) andB. cereus(KBE9-1). There is very limited knowledge of the use of rhizobacteria in agriculture in Ethiopia and South Africa. The current study therefore generates valuable information towards application of plant growth promoting rhizobacteria as alternatives to chemical fertilizers.

Searching for phosphate solubilizing fungal isolates from soil

A total of 354 fungal isolates were obtained from soil samples collected from forests, river basins and agricultural fields of North Bengal using serial dilution, direct soil plating, serial root washing and root maceration techniques. Cultural characteristics of the isolated fungi were studied and microscopic observations were made for identification of these isolates. All the isolates were screened for their phosphate solubilizing activities in vitro. A total of 70 fungal isolates showed phosphate solubilizing activities as detected in Pikovskaya's agar medium. Quantitative evaluation of phosphate solubilization in liquid medium supplemented with two phosphate sources (tricalcium phosphate and rock phosphate) was carried out for all the isolates showing phosphate solubilizing activity. Maximum phosphate solubilizing capacity was shown by three isolates of A. niger while A. clavatus showed minimum activity. Genomic DNA was extracted from sixteen isolates showing high activity and PCR amplification of DNA from nine isolates was done.