PHOSPHATSOLUBILIZING BACTERIA OF THE GENUS PSEUDOMONAS AND THE EFFICIENCY OF THEIR APPLICATION TO INCREASE THE AVAILABILITY OF PHOSPHORUS

Phosphorus is the second most important element for plants after nitrogen. Fertilizers based on it, used to stimulate productivity, are inaccessible for most crops, which leads to their accumulation in the soil and environmental pollution. The use of phosphate-solubilizing bacteria increases the amount of phosphorus absorbed by plants. In most publications describing this group of bacteria, their effectiveness is assessed only in vitro by the halo zones formed on agar media with calcium orthophosphate. The aim of this study was to compare the solubilizing properties of bacteria of the genus Pseudomonas on a solid nutrient medium, as well as in sand and soil. It was shown that all studied cultures of microorganisms are capable of solubilizing insoluble phosphate in Pikovskaya's medium. The most active strains were Pseudomonas laurentiana ANT 56 and Pseudomonas sp. IB 182, isolated from the activated sludge of biological treatment facilities and arable soil, respectively. Experiments with the introduction of strains showed that the amount of mobile phosphorus in the sand increased 2.6-3.8 times in two weeks (in the control 1.2 times), while in the experiment with soil, a significant increase in the content of mobile phosphorus compared to the control was recorded only for the strain P . laurentiana ANT 17 (by 29.1%). It is assumed that the high solubilizing activity of the P. laurentiana ANT 17 strain may be due to the complex action of mechanisms of different nature, including the synthesis of indolyl-3-acetic acid and exopolysaccharide. The studies carried out make it possible to consider this bacterial strain as a promising object for creating on its basis a biological preparation for agricultural purposes.

Potential of phosphate solubilizing fungi isolated from peat soils as inoculant biofertilizer

Elfiati D, Delvian, Hanum H, Susilowati A, Rachmat HH. 2021. Potential of phosphate solubilizing fungi isolated from peat soils as inoculant biofertilizer. Biodiversitas 22: 3042-3048. Phosphate-solubilizing fungi are the microbes that have the ability to dissolve insoluble phosphate and made it available for plants. Therefore, the purpose of this study was to obtain the phosphate-solubilizing fungi from peat soils. Peat soil samples were taken in a composite at a depth 0-20 cm from the peat ecosystem in Nagasaribu Village, Lintong Nihuta Sub-district, Humbang Hasundutan District, North Sumatra, Indonesia. Soil samples were isolated to obtain phosphate-solubilizing fungi using the Pikovskaya selective medium. The obtained isolates were tested for their ability to dissolve phosphate qualitatively by calculating the dissolution index values and quantitatively by calculating the available phosphorus on Pikovskaya medium by using four phosphate sources, namely Ca3(PO4)2, AlPO4, FePO4, and phosphate rock. Total of 12 isolates of phosphate-solubilizing fungi was obtained during the present study. Based on the results of qualitative and quantitative testing, all 12 isolates have the ability to release phosphate from the four tasted phosphate sources. The qualitative test obtains dissolution index values that vary from 2.55 to 4.25, while quantitatively, the isolates were able to dissolve phosphate in the value range from 17.77 ppm to 69.86 ppm. The top five fungal isolates with highest phosphate-solubilizing potential were FG5, FG8, FG9, FG11, and FG12. Based on molecular identification, these five isolates were identified as Aspergillus niger.

Screening and identification of novel halotolerant bacterial strains and assessment for insoluble phosphate solubilization and IAA production

Background Salinity is typical in seashore soils due to the interruption of seawater in the groundwater. Soil microbes of coastal regions play a vital role in increasing plant yields. Microbe-plant associated growth and its wide spectrum with soil environment remain one of the prime factors in agriculture for field application. Making such, in this study, very precise research work is outlined to serve microbial-based solution for solubilizing the insoluble phosphate under various harsh environmental conditions and IAA production. Salt-affected soils along the coast of Bay of Bengal, Sundarbans, India, have been collected. Results A total of five isolates effectively solubilize the considerable amount of Tri-calcium phosphate {TCP, (Ca3PO4)2} ranging from 50.67 to 116.66 P2O5 parts per million (ppm) under optimized conditions, i.e., pH 8.0, 5 to 10% saline and 30 °C temperature. Out of five, three produced Indole Acetic Acid (IAA) ranging from 0.054 to 0.183 (g l−1). Identification of isolates has been carried out by morphology, biochemical characterization and 16S rDNA sequencing. Among the sequenced isolates, 1 belonged to Firmicutes, 3 were Proteobacteria and 1 was Actinobacteria. Conclusion This is the first report which shows the presence of phosphate solubilizing activity by the member of the genus Halomonas and Halobacillus from the study site. These stress-tolerant bacteria will deliver reliable and cost-effective methods to overcome the existing scenario of saline-affected agriculture.

Isolation and Characterization of Phosphate Solubilizing Streptomyces sp. Endemic from Sugar Beet Fields of the Beni-Mellal Region in Morocco

In the course of our research, aimed at improving sugar beets phosphorus nutrition, we isolated and characterized Streptomyces sp. strains, endemic from sugar beet fields of the Beni-Mellal region, which are able to use natural rock phosphate (RP) and tricalcium phosphate (TCP) as sole phosphate sources. Ten Streptomyces sp. isolates yielded a comparable biomass in the presence of these two insoluble phosphate sources, indicating that they were able to extract similar amount of phosphorus (P) from the latter for their own growth. Interestingly, five strains released soluble P in large excess from TCP in their culture broth whereas only two strains, BP, related to Streptomyces bellus and BYC, related to Streptomyces enissocaesilis, released a higher or similar amount of soluble P from RP than from TCP, respectively. This indicated that the rate of P released from these insoluble phosphate sources exceeded its consumption rate for bacterial growth and that most strains solubilized TCP more efficiently than RP. Preliminary results suggested that the solubilization process of BYC, the most efficient RP and TCP solubilizing strain, involves both acidification of the medium and excretion of siderophores. Actinomycete strains possessing such interesting RP solubilizing abilities may constitute a novel kind of fertilizers beneficial for plant nutrition and more environmentally friendly than chemical fertilizers in current use.

Isolation and Characterization of Phosphate Solubilizing Streptomyces Endemic From Sugar Beet Fields Of the Beni-Mellal Region In Morocco

In this research, we isolated and characterized Streptomyces strains, endemic from sugar beet fields of the Beni-Mellal region, able to use natural rock phosphate (RP) and tricalcium phosphate (TCP), as sole phosphate source. Ten Streptomyces isolates yielded a comparable biomass in the presence of these two insoluble phosphate sources, indicating that they were able to extract similar amount of phosphorus (P) from the latter for their own growth. Interestingly, five strains released soluble P in large excess from TCP in their culture broth whereas only two strains, BP, related to Streptomyces bellus and BYC, related to Streptomyces enissocaesilis, released a higher or similar amount of soluble P from RP than from TCP, respectively. This indicated that the rate of P released from these insoluble phosphate sources exceeded its consumption rate for bacterial growth and that most strains solubilized TCP more efficiently than RP. Preliminary results suggested that the solubilization process of BYC, the most efficient RP and TCP solubilizing strain, involves both acidification of the medium and excretion of siderophores. Actinomycete strains possessing such interesting RP solubilizing abilities may constitute a novel kind of intrans beneficial for plant nutrition and more environmentally friendly than chemical fertilizers in current use.

Evaluation of some biophysical characteristics of five silicate solubilizing bacteria isolated from different ecosystems

Silicate solubilizing bacteria (SSB) are key microorganisms to solubilize silicate minerals in the soil. Silicon helps to increase the growth and yield of plants and to enhance the environmental stress tolerance capability of plants. The aim of this study was to evaluate the effect of several factors like pH, salinity, and temperature on silicate solubilizing capacity of five selected SSB. Moreover, phosphorus solubilizing, nitrogen-fixing and indole-3-acetic acid (IAA) synthesizing capacity of these five bacteria were also tested. Liquid soil extract medium containing 0.25% Mg2O8Si3 was used in this study. Abilities of bacteria in phosphorous solubility, nitrogen fixation, and IAA synthesis were tested in NBRIP, Burk’s and NBRIP containing 100 mg L-1 tryptophan media, respectively. The results of the study indicated that five SSB showed their high capacity in silicate solubilization at pH 7.0, NaCl 0.0% and 35oC. However, at a concentration of NaCl 0.5%, these five SSB still solubilized well silicate mineral. Moreover, they also solubilized effectively three different insoluble phosphate sources of Ca3(PO4)2, AlPO4 and FePO4 with a range varied between 105.8 and 928.7 mg P2O5 L-1, 33.9 and 49.6 mg P2O5 L-1, and 1.94 and 34.1 mg P2O5 L-1, respectively. They also fixed biologically nitrogen with a range from 1.37 to 5.09 mg NH4+ L-1 after 2 incubation days. Finally, they also showed their ability in IAA synthesis with an amount between 4.85 and 51.5 mg IAA L-1. In short, these five SSB in this study not only had the ability in silicate solubilization but also had other functions in plant growth promotion.

Intracellular Metabolomics Switching Alters Extracellular Acid Production and Insoluble Phosphate Solubilization Behavior in Penicillium oxalicum

This research aims to understand the precise intracellular metabolic processes of how microbes solubilize insoluble phosphorus (Insol-P) to increase bio-available P. Newly isolated Penicillium oxalicum PSF-4 exhibited outstanding tricalcium phosphate (TP) and iron phosphate (IP) solubilization performance—as manifested by microbial growth and the secretion of low-molecular-weight organic acids (LMWOAs). Untargeted metabolomics approach was employed to assess the metabolic alterations of 73 intracellular metabolites induced by TP and IP compared with soluble KH2PO4 in P. oxalicum. Based on the changes of intracellular metabolites, it was concluded that (i) the enhanced intracellular glyoxylate and carbohydrate metabolisms increased the extracellular LMWOAs production; (ii) the exposure of Insol-P poses potential effects to P. oxalicum in destructing essential cellular functions, affecting microbial growth, and disrupting amino acid, lipid, and nucleotide metabolisms; and (iii) the intracellular amino acid utilization played a significant role to stimulate microbial growth and the extracellular LMWOAs biosynthesis.