Thermotolerant phosphate solubilizing microorganisms and their interaction with mung bean

Several phosphate solubilizing microorganisms (PSM) were tested for their efficiency at 35°, 40° and 45°C. There was a marked variation in their ability to solubilise tricalcium phosphate and the effect was more pronounced at 45°C. Two bacterial and one fungal strain were found to be thermotolerant as they solubilised a large amount of tricalcium phosphate at the three tested temperatures. These thermotolerant strains were identified as Bacillus subtilis (TT₀), Bacillus circulans (TT₈) and Aspergillus niger (TT₁₀). Seed inoculation of mung bean showed a better establishment of temperature tolerant strains as revealed by the rhizosphere population. The inoculation improved nodulation, the available P₂O₅ content of the alluvial soil, root and shoot biomass, straw and grain yield and phosphorus and nitrogen uptake of the crop. Among the bacterial strains, the best effect on yield was obtained with B. subtilis. However, statistically it was equivalent to streptomycin resistant mutant (M-20) and Pseudomonas striata (27). A. niger was less effective than bacteria. Though superphosphate was found to be a better source of phosphate fertiliser, the use of rock phosphate (RP₄₀), coupled with phosphate solubilising bacteria (PSB), gave results comparable to superphosphate (SP₂₀) + PSB inoculants.     

Rhizosphere mediated nutrient management in Allium hookeri Thwaites by using phosphate solubilizing rhizobacteria and tricalcium phosphate amended soil

This work describes integrated nutrient management for cultivation of Allium hookeri by using phosphate solubilizing bacteria (PSB) applied in rhizosphere, along with tricalcium phosphate (TCP). Arthrobacter luteolus S4C7, Enterobacter asburiae S5C7, Klebsiella pneumoniae S4C9, S4C10 and S6C1, and K. quasipneumoniae S6C2, were isolated from rhizosphere of Allium hookeri Thwaites, and were found to release substantial amount of soluble phosphate (124.8–266.4?μg/mL) from TCP in vitro conditions. These isolates were experimented for plant growth promoting attributes, including IAA, siderophore, and nitrogen-fixation. Treatment with PSB resulted in enhanced growth of A. hookeri Th., which was even better with TCP amendment with PSB. K.quasipneumoniae  S6C2 resulted in 39.1% and 533.3% increase (p?≤?0.05) of root length and weight respectively. The treatment with these isolates, in TCP amended soil also resulted in 200–250% increase in available P in soil, which was maximum for K. quasipneumoniae (1.866?mg/g).     

Effect of salt on survival and P-solubilization potential of phosphate solubilizing microorganisms from salt affected soils

A total of 23 phosphate solubilizing bacteria (PSB) and 35 phosphate solubilizing fungi (PSF) were isolated from 19 samples of salt affected soils. The ability of 12 selected PSB and PSF to grow and solubilize tricalcium phosphate in the presence of different concentrations of NaCl was examined. Among 12 PSB, Aerococcus sp. strain PSBCRG₁-1 recorded the highest (12.15) log viable cell count at 0.4 M NaCl concentration after 7 days after incubation (DAI) and the lowest log cell count (1.39) was recorded by Pseudomonas aeruginosa strain PSBI₃-1 at 2.0 M NaCl concentration after 24 h of incubation. Highest mycelial dry weight irrespective of NaCl concentrations was recorded by the Aspergillus terreus strain PSFCRG₂-1 (0.567 g). The percent P_i release, in general, was found to increase with increase in NaCl concentration up to 0.8 M for bacterial solubilization and declined thereafter. At 15 DAI, strain Aerococcus sp. strain PSBCRG₁-1 irrespective of NaCl concentrations showed the maximum P-solubilization (12.12%) which was significantly superior over all other isolates. The amount of P_i released in general among PSF was found to decrease with increase in NaCl concentration at all the incubation periods. Aspergillus sp. strain PSFNRH-2 (20.81%) recorded the maximum P_i release irrespective of the NaCl concentrations and was significantly superior over all other PSF at 7 DAI.     

Effects of root-dip treatment with certain phosphate solubilizing microorganisms on the fusarial wilt of tomato

Root-dip application of Bacillus subtilis, Pseudomonas fluorescens, Aspergillus awamori, Aspergillus niger and Penicillium digitatum resulted in significant decline in the rhizosphere population of Fusarium oxysporum f. sp. lycopersici. A significant decrease in the severity of wilt occurred with A. awamori (37.1%) and P. digitatum (21.3%) compared to the control. Root-dip treatment with the phosphate solubilizing microorganisms tested resulted in significant increase in the yield of tomato, being greatest with A. awamori and P. digitatum in pathogen inoculated (36% and 33%) and uninoculated plants (19% and 23%). A chemical fungicide gave 24% better yield.     

Growth stimulation of Treponema denticola by periodontal microorganisms

Previous experiments have indicated that enrichment of subgingival plaque in human serum can lead to the accumulation of Treponema denticola. T. denticola depends on bacterial interactions for its growth in serum. Aim of the present study was to identify specific microorganisms involved in the growth stimulation of T. denticola. To this end, strains isolated from previous plaque enrichment cultures were tested for growth stimulation in co-cultures with T. denticola. In addition, growth of T. denticola was tested in culture filtrates of the same strains, Bacteroides intermedius, Eubacterium nodatum, Veillonella parvula and Fusobacterium nucleatum were found to enhance growth of T. denticola in co-cultures. A continuous co-culture of T. denticola, F. nucleatum and B. intermedius in human serum gave very high levels of T. denticola, up to 3.10(9).ml-1. Mechanisms involved in growth stimulation may include the ability of B. intermedius and E. nodatum to cleave the protein-core of serum (glyco-)proteins, making these molecules accessible for degradation by T. denticola. In addition, E. nodatum was found to produce a low-molecular weight growth-factor for T. denticola, that was heat-stable and acid as well as alkaline resistant. V. parvula may provide peptidase activities complementary to those of T. denticola. The nature of the growth enhancing activity of F. nucleatum is yet unknown. The data support the dependency of T. denticola on other bacterial species for growth in the periodontal pocket.     

Phosphorus and phosphate solubilizing bacteria: Keys for sustainable agriculture

Abstract

Phosphorus (P) is one of the most important minerals required for plant growth occupying a strong position among soil macro nutrients. Soil P deficiency is often fulfilled by phosphate fertilizers. P deficiency in soils is due to less total P contents in the soil and fixation of added P from chemical fertilizers as well as other organic sources like manures. The response of plant under P stress or even when it is present in adequate amount is very mild. The basic constraint in the availability of P is its solubilization as it gets fixed both in acidic and alkaline soil. Soil fixed P can only be solubilized by phosphate solubilizing microorganisms (PSMs).These bacteria released different types of organic acids in the soil which make P soluble and available to plants. The potential of these PSMs to solubilize P varies and mainly depends upon mechanism adopted for solubilization, their molecular genetics as well as their ability to release P in soil. The PSMs, having all the characteristics of phytohormone production, nitrogen fixation, as well as, heavy metal decontamination and creating salt stress tolerance in plants, are quite rare for sustainable agriculture. Application of this environment friendly approach for increasing crop productivity as well as its impact on soil and plant health is discussed in this review which will not only open new avenues of research but also provide fruitful information about phosphate solubilizing microbes for sustainable agriculture development.     

Growth of ornamental plants in two composts prepared from agroindustrial wastes

Two composts prepared from agroindustrial wastes were assayed as substrates: C1 from brewing waste (yeast and malt) plus lemon tree prunings; and C2 from the solid fraction of olive mill wastewater plus olive leaves. Sixteen substrates were prepared by combining each compost with Sphagnum peat or a commercial substrate (CS) in different proportions. The nutrients (N and K) provided by the composts, which acted as slow-release fertilisers, influenced especially the development of calendula, although the physical and physico-chemical properties such as total pore space and electrical conductivity (EC) were also relevant. On the other hand, in the salt-sensitive calceolaria hybrid, EC and chloride concentration were the main factors influencing growth. Adequate substrates for the development of calendula can be prepared by mixing C1 at up to 75% with peat or at up to 50% with CS, and C2 at up to 50% with peat or CS. For calceolaria, the substrate should have a lower proportion of compost, C1 at up to 50% and C2 at up to 25%, both mixed with peat or CS. Therefore, composts of agroindustrial origin such as these can be used as an alternative to peat and CSs for growing ornamental plants. provided the mixture contains at least 25% peat or CS.     

Growth and electric current loops in plants

A theory is presented for a relationship between ion accumulation and electric current loops in multicellular systems such as the roots and stems of higher plants. A network of electric circuits shows that the electric current transported across the cell membrane flows between an elongating region and a mature region, not only in roots but also in stems. In roots, ions constituting the extracellular electric current flow in the external aqueous medium, while in stems an electric current of comparable density flows within the epidermal cell wall. Based on this theoretical result, electric isolation between the elongating and mature regions was made in the case of both roots and stems. The speed of growth during the initial stage was greatly decreased due to a change in the distribution of protons around the surfaces of the plant by cutting off the electric current loop. Electrochemical calculation shows that ions are not always accumulated at the efflux site, since the ion distribution is strongly affected by the relation of the magnitudes between the electric field and electric current. The results calculated for the electric potential and pH distributions around the root agree with experimental data.     

Isolation and identification of phosphate solubilizing bacteria from chinese cabbage and their effect on growth and phosphorus utilization of plants

Phosphate solubilizing bacteria (PSB) were isolated from the rhizosphere of Chinese cabbage and screened on the basis of their solubilization of inorganic tricalcium phosphate in liquid cultures. Ten strains that had higher solubilization potential were selected, and they also produced indole-3-acetic acid, 1-aminocyclopropane-1-carboxylate (ACC) deaminase, and siderophores. The strains were identified to be members of Pseudomonas, by 16S rDNA sequence analysis. Seed bacterization with PSB strains increased the root elongation and biomass of Chinese cabbage in seedling culture, although they had no effect on phosphorus uptake of plants. The plant growth promotion by PSB in this study could be due to the production of phytohormones or mechanisms other than phosphate solubilization, since they had no effect on P nutrition.     

Inoculation with Pseudomonas putida PCI2, a phosphate solubilizing rhizobacterium,stimulates the growth of tomato plants

The use of phosphate solubilizing plant growth-promoting microorganisms as inoculants assists in the hydrolysis of insoluble forms of phosphorus leading to increased plant growth. Pseudomonas putida PCI2 was evaluated for phosphatase activity and solubilization of AlPO₄ and FePO₄. The effect of different incubation temperatures, concentrations of NaCl and different pH on growth of PCI2 and P solubilization was studied. PCI2 proved to be positive for phosphatase activity, solubilized AlPO₄ and hydrolyzed Ca₃(PO₄)₂ even in medium with 5 % NaCl. In addition, PCI2 produced 45 % units of siderophores. The production of IAA by PCI2 was stimulated in vitro by the addition of different concentrations of L-tryptophan to the culture medium. Assays with tomato seedlings showed that the length of the root was reduced as the concentration of IAA increased. On the other hand, inoculation with PCI2 caused a clear growth-promoting effect on shoot growth in the presence of L-tryptophan. P. putida PCI2 is adapted to different environmental conditions and has potential to be developed and used as an inoculant for increasing the growth of tomato plants.     

Growth of ornamental plants irrigated with nutrient or polyethylene glycol solutions of different osmotic potentials

Summary Six ornamental species (Petunia hybrida, Callistephus hortensis, Coleus blumei, Celosia pyramidalis, Antirrhinum majus andTagetes erecta) were grown in solutions containing high concentrations of polyethylene glycol (MW 4000) or of Nitrogen: Phosphorus: Potassium. At equal osmotic potentials, top dry weight, leaf area and leaf elongation rate were all reduced more by polyethylene glycol than by NPK. Polyethylene glycol also produced some leaf damage which did not occur with NPK solutions. Osmotic potentials of –600 kPa due to NPK reduced growth of the six species by at least 25% compared with growth of control plants (at –20 kPa). Tolerance ranking to high fertilizer in the irrigation solution increased from Snapdragon (most sensitive), Marigold Coleus, Aster, Celosia and Petunia (most tolerant).     

Phosphate-solubilizing microorganisms isolated from rhizospheric and bulk soils of colonizer plants at an abandoned rock phosphate mine

The abandoned “Monte-Fresco” rock phosphate mine in Táchira, Venezuela, was sampled to study the biodiversity of phosphate-solubilizing microorganisms (PSM). Rhizosphere and bulk soils were sampled from colonizer plant species growing at a mined site where pH and soluble P were higher than the values found at a near by unmined and shrubby soil. Counting and isolating of PSM choosing strains showing high solubilization halos in a solid minimal medium with hydroxyapatite as phosphate source were evaluated using ammonia or nitrate as nitrogen sources and dextrose, sucrose, and mannitol as carbohydrate sources. A larger number of PSM were found in the rhizospheric than in the bulk soil. Six fungal strains belonging to the genus Penicillium and with high hydroxyapatite dissolution capacities were isolated from bulk soil of colonizer plants. Five of these strains had similar phenotypes to Penicillium rugulosum IR-94MF1 but they solubilized hydroxyapatite at different degrees with both nitrogen sources. From 15 strains of Gram-negative bacteria isolated from the rhizosphere of colonizer plants, 5 were identified as diazotrophic free-living encapsulated Azotobacter species able to use ammonium and/or nitrate to dissolve hydroxyapatite with glucose, sucrose and/or mannitol. Different nitrogen and carbohydrate sources are parameters to be considered to further characterize the diversity of PSM.     

Isolation and characterization of phosphate solubilizing rhizobacteria to improve plant health of tomato

In the present study, 43 isolates of Phosphate solubilizing rhizobacteria (PSRB) were isolated from 37 rhizospheric soil samples of tomato collected from tomato growing regions of Karnataka. Among the 43 isolates, 33 were found to be positive for solubilizing both inorganic and organic forms of phosphorous. The isolates were analyzed for their ability to colonize roots of tomato and to increase the seed quality parameters under laboratory conditions. On the basis of above criteria, 16 isolates were selected for further studies. Organic acids from PSRB isolates were analyzed and phytase zymogram for two isolates viz., PSRB21 and 31 was prepared. Under greenhouse conditions, all selected isolates showed increased shoot length, root length, fresh weight, dry weight and phosphorous content of tomato seedlings to various extent with respect to control. Analysis of pH and available phosphorous in rhizosphere soil samples of 30 day-old-seedlings revealed that the available phosphorous content was high in rhizospheric soil samples of plants raised from seeds bacterized with PSRB isolates over control. Even though all selected PSRB’s were able to increase the plant growth, only few of them showed protection against fusarium wilt and none of them against early blight.     

Interactions of chromium with microorganisms and plants

Chromium is a highly toxic non-essential metal for microorganisms and plants. Due to its widespread industrial use, chromium (Cr) has become a serious pollutant in diverse environmental settings. The hexavalent form of the metal, Cr(VI), is considered a more toxic species than the relatively innocuous and less mobile Cr(III) form. The presence of Cr in the environment has selected microbial and plant variants able to tolerate high levels of Cr compounds. The diverse Cr-resistance mechanisms displayed by microorganisms, and probably by plants, include biosorption, diminished accumulation, precipitation, reduction of Cr(VI) to Cr(III), and chromate efflux. Some of these systems have been proposed as potential biotechnological tools for the bioremediation of Cr pollution. In this review we summarize the interactions of bacteria, algae, fungi and plants with Cr and its compounds.