Phosphate-solubilizing Strains Research Articles

Assessing the role of field isolated Pseudomonas and Bacillus as growth‐promoting rizobacteria on avocado (Persea americana) seedlings

AbstractIntroductionThis research aims to assess the efficacy of two genera of rhizobacteria from avocado field isolated: Pseudomonas and Bacillus, as plant growth‐promoting microorganisms in Hass avocado trees grafted onto Zutano rootstock.Materials and MethodsThe siderophore‐producing and phosphate‐solubilizing capacity of each isolated strain was determined and plant growth‐promoting activity, nutrient accumulation, and nutrient use efficiency in Zutano variety avocado seedlings were evaluated. Molecular identification was carried out by amplification of the 16S rDNA gene of the isolated strains.ResultsPseudomonas putida, Lysinibacillus macroides, Lysinibacillus xylanilyticus, Lysinibacillus fusiformis, Bacillus subtilis and Pseudomonas plecoglossicida, were identified as the PGPR of the Bacillus and Pseudomonas genera, predominant in the avocado rhizosphere. There was found 11 phosphate solubilizing strains and 2 siderophore‐producing strains. The phosphate‐solubilizing strains, B. subtilis and P. plecoglossicida, stimulated the growth of Zutano seedlings, increasing their root dry weight (g), stem dry weight (g), leaf dry weight (g) and leaf area (cm2). Significant differences were found in nutrient uptake efficiency between inoculated plants and noninoculated plants. The increase in root biomass responded to greater phosphorus and potassium absorption in plants inoculated with P. plecoglossicida, due to this strain's high phosphate solubilization efficiency (266%).ConclusionsThe highest plant growth promotion strains were Bac F (B. subtilis), Bac M (P. plecoglossicida) and P1 (P. putida), which achieved the highest increase in root and leaf dry weight, as well as the highest nutrient extractions and nutrient uptake efficiency.

Crenobacter oryzisoli sp. nov., a novel phosphate-solubilizing bacterium isolated from the paddy soil.

Two Gram-staining-negative, facultative anaerobic, rod-shaped and phosphate-solubilizing strains designated SG2303T and SG2305, were isolated from paddy soil in China. Phylogenetic analysis based on 16S rRNA gene sequences indicated that SG2303T and SG2305 represented a member of the genus Crenobacter within the family Neisseriaceae of the phylum Pseudomonadota. Strain SG2303T displayed higher 16S rRNA gene sequence similarities with members of the genus Crenobacter ranging from 93.5 to 94.0%. Strains C. luteus YIM 78141T and C. cavernae K1W11S-77T were closest related to the isolated strains and were considered as type strains. Growth of strain SG2303T occurred at 10-55°C (optimum 37°C), pH 5.0-9.0 (optimum pH 6.0-7.0) and 0-1% (w/v) NaCl (optimum 0%). The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between strain SG2303T and its closely related taxa were 76.1-78.2% and 20.5-22.1%, respectively. The genomic DNA G + C content was 62.2%. The quinone of strain SG2303T was Q-8. The major fatty acids (> 10%) of strain SG2303T were C16:0 (30.6%), summed feature 3 (C16:1ω7c and/or C16:1ω6c) (26.0%) and C12:0 3OH (12.1%). The polar lipids were phosphatidylglycerol (PG), diphosphatidylglycerol (DPG), phosphatidylethanolamine (PE), phospholipids (PL), glycolipid (GL) and unidentified lipids (UL). Based on the results of the phylogenetic, physiological, biochemical, and morphological analysis, strain SG2303T is recognized as a novel species of the genus Crenobacter, for which the name Crenobacter oryzisoli sp. nov. is proposed. The type strain is SG2303T (= GDMCC 1.3970T = JCM 36468T). In addition, SG2303T was also able of phosphorus solubilization and promoting the growth of rice seeds. Strain SG2303T exhibited a relatively high dissolvable phosphorus content of 2.52µg·mL- 1.

Selection and Characterization of Phosphate-Solubilizing Fungi and Their Effects on Coffee Plantations.

The use of phosphate-solubilizing fungi in coffee cultivation is an alternative to the use of traditional fertilizers. The objective of this study was to analyze the mechanisms involved in the phosphorus solubilization of fungal strains and to evaluate the effect of a phosphate-solubilizing strain on coffee plants. For this, phosphorus-solubilizing fungal strains were selected for evaluation of their solubilization potential and phosphatase activity. Coffee plants were inoculated in the field with a phosphate-solubilizing strain, and the soil and foliar soluble phosphorus contents, as well as coffee bean yield, were quantified. Of the 151 strains analyzed, Sagenomella diversispora, Penicillium waksmanii, and Penicillium brevicompactum showed the highest solubilization. Aspergillus niger and P. waksmanii presented the highest soluble phosphorus values; however, P. brevicompactum showed the highest phosphatase activity. The P. brevicompactum strain inoculated on the coffee plants did not favor the foliar phosphorus content but increased the soil soluble phosphorus content in two of the coffee plantations. The plants inoculated with the phosphate-solubilizing strain showed an increase in coffee bean weight on all plantations, although this increase was only significant in two of the three selected coffee plantations.

Isolation and Identification of a Phosphate-Solubilizing Pantoea dispersa with a Saline-Alkali Tolerance and Analysis of Its Growth-Promoting Effects on Silage Maize Under Saline-Alkali Field Conditions.

Phosphate-solubilizing bacteria (PSB) are microorganisms that can dissolve insoluble phosphorus (P) to accessible forms. This study aimed to screen saline-alkali-tolerant PSB and analyze its growth promoting properties, and evaluate its effects on the growth, quality, soil nutrient balance, and enzyme activities of silage maize in the field. We isolated six phosphate-solubilizing strains from rhizosphere soil of silage maize planted in saline-alkali land, and FC-1 with the best P-solubilizing effect was used for further study. The morphological, physiological and biochemical analysis, and 16S rDNA and housekeeping gene atpD sequencing were performed for identification. FC-1 was identified as Pantoea dispersa and had high P solubility. The phosphate solubility of FC-1 using four P sources ranged from 160.79 to 270.22 mg l-1. FC-1 produced indole-3-acetic acid (IAA)and decreased the pH of the growth media by secreting organic acids, including citric acid, malic acid, succinic acid, and acetic acid. The results of a field experiment indicated that FC-1 treatment increased the height, stem diameter, fresh weight, dry weight, starch content, crude protein content, and total P content of silage maize by 9.8, 9.2, 12.6, 11.7, 12.6, 18.3, and 17.4%, respectively. The nitrogen, potassium, phosphorus, and organic matter contents in the rhizosphere soil of silage maize increased by 29.8, 17.1, 17.9, and 25.3%, respectively; urease, catalase, sucrase, and alkaline phosphatase levels also increased by 24.7, 26.7, 24.0, and 19.5%, respectively. FC-1 promoted the growth of silage maize by improving nutrient metabolism and enzyme activities in saline-alkali soil and may be an effective alternative to fertilizers.

Screening of phosphorus solubilizing microorganisms in cold environment and their effects on the growth of Brassica napus.

To screen out phosphorus solubilizing strains that can adapt to cold climate in Qinghai Province, Bacillus mucilaginosus, B. megaterium, B. cereus, Streptomyces violovariabilis, S. cinnamofuscus, and S. flavoagglomeratus were screened with solid plate medium as the primary and liquid medium as the secondary screening, with calcium phosphate, lecithin, and phytic acid as the single source of phosphorus. By comprehensively comparing the size of phosphate solubilizing circle in the solid plate medium and the soluble phosphorus content in the liquid medium, three strains of phosphate solubilizing bacteria with good phosphate solubilizing effects were screened, S. violovariabilis, S. cinnamofuscus, and B. mucilaginosus. The three phosphate solubilizing bacteria were made into liquid ino-culants, and the small rapeseed pot experiment was carried out with two soils with different fertilities in a cold climate in September. Compared with the control, plant height, fresh weight, root length, and root weight of rapes in high-fertility cultivated soil increased by 35.5%, 191.0%, 26.2%, and 282.7%, while plant phosphorus absorption, total phosphorus and available phosphorus contents in the rhizosphere soil increased by 968.9%, 5.1%, and 2.1%, respectively. In low-fertility soil, plant height and fresh weight was increased by 45.8% and 61.3%, root length and weight was decreased by 2.6% and 4.4%, while plant phosphorus absorption and the contents of total P and available P in rhizosphere soil were increased by 91.5 %, 29.1%, and 213.7%, respectively. The effect of the other two inoculants treatments was less significant than S. violovariabilis. Therefore, S. violovariabilis was the phosphate solubilizing strain suitable for the cold climate in Qinghai.

Isolation, Solubilization of Inorganic Phosphate, and Production of Organic Acids by Individual and Co-inoculated Microorganisms

Phosphate solubilizing microorganisms (PSMs) mineralize phosphate (PO4³−) to make phosphorous available for plant uptake. This study is designed to isolate the PSMs from the subtropical environmental samples. Total 35 bacterial and 18 fungal isolates were found to be effective P solubilizers depend on their ability of P solubilization that were determined qualitatively and quantitatively using National Botanical Research Institute Phosphorus media. Efficient PSMs that were solubilizing phosphate in maximum amount were identified as Pseudomonas aeruginosa, Serratia marcescens, Pseudomonas mosselii, Bacillus licheniformis, Bacillus subtilis, Bacillus species, Aspergillus flavus, Aspergillus foetidus, Aspergillus niger, Aspergillus tubingensis, and Penicillium chrysogenum. Among them, A. tubingensis was observed as the most efficient phosphate solubilizing strain. For the first time, combined phosphate solubilization activity of A. tubingensis with other efficient phosphate solubilizers was checked and found that A. tubingensis and P. aeruginosa acted synergistically and solubilized phosphate in increased amount. High-performance liquid chromatography results revealed that A. tubingensis produced variety of organic acids including succinic, gluconic, oxalic, and citric acids. Scanning electron microscopy results confirmed the presence of firmly attached large fungal hyphae on tri-calcium phosphate (Ca3(PO4)2). Thus, the results suggest that the use of these PSMs either single or combined as bioinoculants will help to increase the availability of soluble phosphorous.

Differential Plant Growth Promotion Under Reduced Phosphate Rates in Two Genotypes of Maize by a Rhizobial Phosphate-Solubilizing Strain

The biotechnological manipulation of phosphate-solubilizing bacteria (PSB) is gaining prominence to improve the poor phosphorus (P) availability in the soil and maintain crop yields. In this study, we investigated howRhizobiumsp. B02 inoculation influences maize crop development and whether its use reduces phosphate fertilizer rates. We conducted growth promotion assays using P fertilizer doses in two maize genotypes under greenhouse conditions. Morphometric, physiological, and productivity parameters were assessed in three phenological stages: tillering (V5), tassel (VT), and maturity (R6). Maize response was significantly influenced by both inoculation and plant genotype, showing that the plant-promoting effect of inoculation is substantially more prominent in the white endosperm than in the yellow endosperm maize genotype. The development of maize in all phenological stages was promoted by inoculation withRhizobiumsp. B02. The most significant influence of inoculation was observed on shoot dry weight, relative chlorophyll content, shoot P concentration, leaf area, photosynthetic rate, 1,000-grain weight, and grain yield. A 17% gain in grain yield, representing 20 g plant−1, was obtained by inoculation with 50% diammonium phosphate (DAP) compared with the control treatment at the same dose. The complete fertilization control was phenocopied by the white endosperm inoculated at 50% DAP in all productivity parameters. Therefore, half of the P fertilization in white endosperm was replaced by inoculation withRhizobiumsp. B02. Herein, we report the potential of aRhizobiumstrain in a non-legume crop to improve P management.

Phosphate-Solubilizing Pseudomonas sp. Strain WS32 Rhizosphere Colonization-Induced Expression Changes in Wheat Roots.

Rhizosphere colonization is a pre-requisite for the favorable application of plant growth-promoting rhizobacteria (PGPR). Exchange and mutual recognition of signaling molecules occur frequently between plants and microbes. Here, the luciferase luxAB gene was electrotransformed into the phosphate-solubilizing strain Pseudomonas sp. WS32, a type of plant growth-promoting rhizobacterium with specific affinity for wheat. A labeled WS32 strain (WS32-L) was applied to determine the temporal and spatial traits of colonization within the wheat rhizosphere using rhizoboxes experimentation under natural condition. The effects of colonization on wheat root development and seedling growth were evaluated, and RNA sequencing (RNA-seq) was performed to explore the transcriptional changes that occur in wheat roots under WS32 colonization. The results showed that WS32-L could survive in the wheat rhizosphere for long periods and could expand into new zones following wheat root extension. Significant increases in seedling fresh and dry weight, root fresh and dry weight, root surface area, number of root tips, and phosphorus accumulation in the wheat leaves occurred in response to WS32 rhizosphere colonization. RNA-seq analysis showed that a total of 1485 genes in wheat roots were differentially expressed between the inoculated conditions and the uninoculated conditions. Most of the transcriptional changes occurred for genes annotated to the following functional categories: “phosphorus and other nutrient transport,” “hormone metabolism and organic acid secretion,” “flavonoid signal recognition,” “membrane transport,” and “transcription factor regulation.” These results are therefore valuable to future studies focused on the molecular mechanisms underlying the growth-promoting activities of PGPR on their host plants.

Effect of Rhizobacteria Inoculation via Soil and Seeds on Glycine max L. Plants Grown on Soils with Different Cropping History

Field experiments testing the effect of phosphate-solubilizing rhizobacteria (PSRB) should consider the cropping history and the method used to inoculate the strains. We evaluated the hypothesis that PSRB previously isolated from soybean seedlings could be effective in promoting growth in this oilseed crop in soils with different cultivation periods. We also evaluated whether this growth promotion could be influenced by cultivation histories or the inoculation method (via seeds or soil). Thus, we conducted an experiment in five fields cultivating Glycine max during two seasons (2019/2020 and 2020/2021), to test the effectiveness of PSRB (SAF9-Brevibacillus sp., SAF11-Brevibacillus sp., and SAC36-Bacillus velezensis) compared with results observed for the inoculant BiomaPhos (mix of Bacillus subtilis and Bacillus megaterium). The present study was based on the evaluation of vegetative growth, nutritional and yield parameters, and microbial biomass carbon (MBC). PSRB were more effective than, or showed similar effectiveness to, BiomaPhos for most of the evaluated vegetative, nutritional, and yield characteristics. In the fields tested in the summer 2019/2020 crop, SAC36 and SAF9 strains stood out as growth promoters, whereas in the 2020/2021 crop, SAF11, SAC36, and BiomaPhos were notable. There did not seem to be a direct relationship between long histories of soybean cultivation as a monoculture and low yield in the field. However, yield seems to be associated with soil nutritional characters such as Ca, Mg, K, P, cation exchange capacity, and organic matter levels. PSRB inoculation positively affected nodulation (NN) and nodule dry mass (NDM) in the evaluated fields in the 2019/2020 crop, and the aerial part dry mass (APDM), NN, NDM, yield, and MBC of the evaluated fields in the 2020/2021 crop. In contrast, the inoculation method was observed to have a strong effect on APDM, NN, root dry mass, and MBC, as the plants inoculated via seed showed higher mean values than those in the plants inoculated via soil. This study demonstrated the growth-promoting potential of new phosphate-solubilizing strains, which may eventually be incorporated by the biostimulants market to freely compete with BiomaPhos.

Efficiency of the Hydroponic System as an Approach to Confirm the Solubilization of CaHPO4 by Microbial Strains Using Glycine max as a Model.

The sustainable development of agriculture can be stimulated by the great market availability of bio-inputs, including phosphate-solubilizing microbial strains. However, these strains are currently selected using imprecise and questionable solubilization methodologies in solid or liquid media. We hypothesized that the hydroponic system could be a more efficient methodology for selecting phosphate-solubilizing strains as plant growth promoters. This methodology was tested using the plant Glycine max as a model. The growth-promoting potential of the strains was compared with that of the Biomaphos® commercial microbial mixture. The obtained calcium phosphate (CaHPO4) solubilization results using the hydroponic system were inconsistent with those observed in solid and liquid media. However, the tests in liquid medium demonstrated poor performances of Codinaeopsis sp. (328EF) and Hamigera insecticola (33EF) in reducing pH and solubilizing CaHPO4, which corroborates with the effects of biotic stress observed in G. max plants inoculated with these strains. Nevertheless, the hydroponic system allowed the characterization of Paenibacillus alvei (PA12), which is also efficient in solubilization in a liquid medium. The bacterium Lysinibacillus fusiformis (PA26) was the most effective in CaHPO4 solubilization owing to the higher phosphorus (P) absorption, growth promotion, and physiological performance observed in plants inoculated with this bacterium. The hydroponic method proved to be superior in selecting solubilizing strains, allowing the assessment of multiple patterns, such as nutritional level, growth, photosynthetic performance, and anatomical variation in plants, and even the detection of biotic stress responses to inoculation, obtaining strains with higher growth promotion potential than Biomaphos®. This study proposed a new approach to confirm the solubilizing activity of microorganisms previously selected in vitro and potentially intended for the bio-input market that are useful in P availability for important crops, such as soybeans.

Streptomyces strains modulate dynamics of soil bacterial communities and their efficacy in disease suppression caused by Phytophthora capsici

The responses of rhizosphere bacterial communities of Streptomyces (SS14 and IT20 stains) treated-pepper plants following inoculation by Phytophthora capsici (PC) was investigated using Illumina MiSeq sequencing. Distinct modulation of the bacteriome composition was found for PC samples with the highest relative abundance (RA) of Chitinophaga (22 ± 0.03%). The RA of several bacterial operational taxonomic units (OTUs) was affected and caused changes in alpha and beta-diversity measures. In IT20, the RA of Cyanobacteria was enriched compared to SS14 (72%) and control samples (47%). Phylotypes belonging to Devosia, Promicromonospora, Kribbella, Microbacterium, Amylocolatopsis, and Pseudomonas genera in the rhizosphere were positively responding against the pathogen. Our findings show that the phosphate solubilizing strain IT20 has higher microbial community responders than the melanin-producing strain SS14. Also, positive interactions were identified by comparing bacterial community profiles between treatments that might allow designing synthetic bio-inoculants to solve agronomic problems in an eco-friendly way.

Peanut Endophytic Phosphate Solubilizing Bacteria Increase Growth and P Content of Soybean and Maize Plants.

Phosphorus (P) is a limiting factor of plant development due to its low availability in the soil. The use of endophytic phosphate solubilizing bacteria as a more sustainable alternative to the use of chemical phosphorus fertilizers is proposed in this study. The objectives were to analyze the effect of simple inoculations of native peanut endophytic phosphate solubilizing bacteria on plant growth promotion and P content of soybean and maize and to evaluate their survival and endophytic colonization capacity on these plants. In addition, bacterial plant cell wall degrading enzymes activities in presence or absence of root exudates was determined. Soybean, maize and peanut plants were grown on a microcosm scale and inoculated with Enterobacter sp. J49 or Serratia sp. S119. It was observed that phosphate solubilizing strains promoted the growth of maize and soybean plants and contributed significantly P to their tissues. A significant increase in the phosphate solubilizing capacity of the plant rhizosphere after the end of the assay was observed. The strains showed to survive in plant's growth substrate and in the case of Enterobacter sp. J49, it showed also to colonize endophytically maize and soybean. Root exudates of the three plants showed to produce changes in pectinase and cellulase activities of the strains. The bacterial strains analyzed in this study constitutes potential sources for the formulation of biofertilizers for their application for several crops in agricultural soils with low P content.

Characterization and Mechanisms of Biosolubilization of Rock Phosphate by Microbes Isolated from Mahanadi Estuary, Odisha, India

Microbial solubilization of rock phosphate (RP) considered being an alternative to chemical phosphorous (P) fertilizer, causing high costs and environmental pollution. This work aimed to isolate efficient phosphate solubilizing strains from the estuary region of the Mahanadi river to check their RP solubilizing efficiency, and the mechanisms were discussed. Two strains of bacteria (Bacillus thuringenesis P0B11 and Lysinobaccillus fusiformis P0B28) and a fungus (Aspergillus aculeatus P0F3) were the most effective strain solubilizing RP. This is the first report of RP solubilization by L. fusiformis P0B28 and the first report of in vitro stearic acid production during RP solubilization. In particular, the potent strain A. aculeatus P0F3 produced the highest soluble P (345.6 mg/l) on 5th day. The soluble P concentration showed a significant negative correlation (r = − 0.88, p ≤ 0.01) with the pH, while it is positively correlated with the growth of B. thuringenesis P0B11 (r = 0.87, p ≤ 0.01), L. fusiformis P0B28 (r = 0.55, p ≤ 0.01) and A. aculeatus P0F3 (r = 0.96, p ≤ 0.01), respectively. The P release process from rock phosphate fit the first-order kinetics model well (R2 = 0.8046–0.8401). Organic acids produced by the isolates found to be the major mechanism for RP solubilization by supplying H+ ions and organic anions. High P concentration was related to the high corroded structure formation on the RP surface, reduction in all mineral peak intensities and a large decrease in the intensity of vibrational bands of calcite and fluorapatite confirmed by SEM, XRD, and FTIR, respectively.

Enhanced reduction of lead bioavailability in phosphate mining wasteland soil by a phosphate-solubilizing strain of Pseudomonas sp., LA, coupled with ryegrass (Lolium perenne L.) and sonchus (Sonchus oleraceus L.).

Due to ecologically unsustainable mining strategies, there remain large areas of phosphate mining wasteland contaminated with accumulated lead (Pb). In this study, a Pb-resistant phosphate-solubilizing strain of Pseudomonas sp., LA, isolated from phosphate mining wasteland, was coupled with two species of native plants, ryegrass (Lolium perenne L.) and sonchus (Sonchus oleraceus L.), for use in enhancing the reduction of bioavailable Pb in soil from a phosphate mining wasteland. The effect of PbCO3 solubilization by Pseudomonas sp. strain LA was evaluated in solution culture. It was found that strain LA could attain the best solubilization effect on insoluble Pb when the PbCO3 concentration was 1% (w/v). Pot experiments were carried out to investigate the potential of remediation by ryegrass and sonchus in phosphate mining wastelands with phosphate rock application and phosphate-solubilizing bacteria inoculation. Compared to the control group without strain LA inoculation, the biomass and length of ryegrass and sonchus were markedly increased, available P and Pb in roots increased by 22.2%-325% and 23.3%-368%, respectively, and available P and Pb in above-ground parts increased by 4.44%-388% and 1.67%-303%, respectively, whereas available Pb in soil decreased by 14.1%-27.3%. These results suggest that the combination of strain LA and plants is a bioremediation strategy with considerable potential and could help solve the Pb-contamination problem in phosphate mining wastelands.

New entomopathogenic strain of Bacillus thuringiensis is able to solubilize different sources of inorganic phosphates

Phosphate-solubilizing strain INTA 293-1 from a soil sample of Corrientes province (Argentina) was identified as Bacillus thuringiensis based on its faculty to produce crystalline inclusions during sporulation and 16S rDNA sequence similarity. INTA 293-1 was found to produce bipyramidal and cuboidal crystals, containing major proteins of ca. 130 and 65 kDa respectively, resembling those present in Lepidoptera- and Diptera-active strains. Accordingly, INTA 293-1 showed insecticidal activity against lepidopteran and dipteran larvae. No insecticidal activity nor evident effects on the normal development of coleopteran larvae or nematodes were observed. Screening of cry, cyt and vip genes showed that INTA 293-1 contains cry1Ac, cry1Ia, cry2Aa, cry2Ab and vip3Aa genes. Furthermore, this new entomopathogenic strain of B. thuringiensis was able to solubilize different sources of inorganic phosphates in liquid media following similar solubilization kinetics. INTA 293-1 was effective in solubilizing hydroxyapatite, patagonic phosphate rock, and to a lesser extent the aluminium phosphate. The differential behaviour between them may be explained by differences in INTA 293-1 survival. Phosphate solubilization was associated with pH reduction. This study reveals a little-explored aspect of B. thuringiensis and paves the way for the development of new agrobiological products with multiple modes of action.

Alcaligenes aquatilis GTE53: Phosphate solubilising and bioremediation bacterium isolated from new biotope “phosphate sludge enriched-compost”

The isolation and identification of beneficial bacteria from the active phase of composting is considered to be a key bio-quality parameter for the assessment of the process. The aim of this work was the selection and identification of beneficial bacteria from a co-composting experiment of vegetable waste (VW), olive oil mill waste (O2MW), and phosphate sludge (PS). Phosphate-solubilizing strains were isolated from the thermophilic phase using Pikovskaya (PVK) solid medium supplemented with tricalcium phosphate Ca3(PO4) (TCP) as the sole source of phosphorus (P). Therefore, the selected isolate Alcaligenes aquatilis GTE53 was tested to tolerate abiotic stresses (different levels of temperature, variable pH, high salinity and water stress). The isolate was also assessed for indole acetic acid (IAA) and siderophores synthesis, nitrogen fixation, phenol degradation and pathogens inactivation. The quality of the co-composting process was also investigated by monitoring the physico-chemical parameters. The obtained results showed that A. aquatilis GTE53 displayed a higher solubilization index of 2.4 and was efficiently dissolved, up to 162.8 and 247.4 mg·mL−1 of inorganic phosphate from PS and phosphate rock (PR), respectively. A. aquatilis GTE53 exhibited siderophores and IAA release, along with atmospheric nitrogen fixation. In addition to that, A. aquatilis GTE53 showed a high resistance to heat and tolerance to acidic and alkaline pH, high salinity and water stress. Moreover, A. aquatilis GTE53 could degrade 99.2% of phenol from a high-concentrated medium (1100 mg·L−1 of phenol) and can inactivate the most abundant pathogens in industrial wastes: Escherichia coli, Streptococcus sp., Salmonella sp., and Fusarium oxysporum albedinis. Analysis of temperature, pH, electrical conductivity, carbon/nitrogen (C/N) ratio, indicated successful co-composting. An efficient transformation of P to the available form and a great abatement of polyphenols, were also recorded during the process. The findings of this study will help to advance the understanding of A. aquatilis GTE53 functions and will facilitate its application to promote beneficial microbial organisms during composting, thus obtaining a high-quality product.

ИСПОЛЬЗОВАНИЕ ШТАММОВ МИКРООРГАНИЗМОВ ДЛЯ ПОВЫШЕНИЯ УРОЖАЙНОСТИ ЯРОВОЙ МЯГКОЙ ПШЕНИЦЫ (Triticum aestivum L.)

This paper presents the study results on the effect that presowing seed treatment and spraying nitrogen-fixing, phosphate-, and potassium-solubilizing bacteria on the seedlings of the Primorskaya 39 spring soft wheat (Triticum aestivum L.) cultivar have on the structural elements of productivity, yield, and the number of soil microorganisms. It was found that the total number of bacteria increases in the waxy ripeness stage when using both presowing treatment of seeds and spraying the microorganism strains on the seedlings. The maximum number of bacteria in the soil was detected in the variants when using strains of nitrogen-fixing and potassium-solubilizing microorganisms in presowing treatment (1.9 × 107 CFU/g of soil) and phosphate- and potassium-solubilizing microorganisms when spraying the seedlings (2.0 × 107 CFU/g of soil). The variant N1 + K2 + P6 after presowing treatment with nitrogen-fixing, potassium-, and phosphate-solubilizing microorganisms in the waxy ripeness stage showed the highest content of mobile phosphorus (92 mg/kg). High yield (4.3 t/ha) was shown by the variant N1 + P19 after presowing seed treatment with nitrogen-fixing and phosphate-solubilizing strains.

Rapid Detection of Phosphate-Solubilizing Bacteria from Agricultural Areas in Erzurum.

In this study, the newly designed pqq gene-specific primer sets were used for determination of phosphate-solubilizing capabilities of bacterial isolates from the agricultural regions of Erzurum. The specificity of newly designed primer sets (PqqA2F/PqqA2R, Pqq5F/Pqq5R, PqqF2/PqqF2R) were tested against ten isolates, whose phosphate-solubilizing activities were initially proved by the conventional methods. Non-phosphate-solubilizing bacteria were also chosen as negative control. According to the results, five of ten phosphate-solubilizing bacteria with PqqA2F/PqqA2R, two of ten phosphate-solubilizing bacteria with Pqq5F/Pqq5R primer set, and one of ten phosphate solubilizing with PqqF2F/PqqF2R bacteria were successfully amplificated in the PCR assay and none of the non-phosphate-solubilizing bacteria was amplificated. Then, the molecular characterization of the active phosphate-solubilizing strains was done based on the partial 16S ribosomal RNA gene region sequence analysis method. Two isolates of Enterobacter sp., 1 Rhizobium sp., 1 Enterococcus sp., 1 Bacillus cereus, 1 Bacillus atrophaeus, 1 Bacillus aryabhattai, 1 Acinetobacter sp., 1 Pseudomonas japonica, and 1 Enterobacter cloacae were identified as active phosphate-solubilizing strains. Consequently, the results showed that this specific primer sets could be used as an economic, rapid, and useful tool for the detection of phosphate-solubilizing strains in the agricultural researches.

Phosphate-Solubilizing Pseudomonas sp. Strain P34-L Promotes Wheat Growth by Colonizing the Wheat Rhizosphere and Improving the Wheat Root System and Soil Phosphorus Nutritional Status

Rhizosphere colonization is a requirement for field applications of plant growth-promoting rhizobacteria (PGPR). Complex signal exchanges and mutual recognition occur between microbes and plants. Here, the phosphate-solubilizing strain Pseudomonas sp. P34, which is a type of PGPR with affinity to wheat, was isolated from a wheat rhizosphere via wheat germ agglutinin. A pTR102 plasmid harboring the luciferase luxAB gene was transferred into P34. The labeled strain (P34-L) was then used to track the temporal and spatial characteristics of rhizosphere colonization and examine the effects of colonization on wheat development. The transcript levels of the phosphate transporter gene TaPT4, a phosphorus deficiency indicator, in wheat roots were monitored by quantitative reverse transcription PCR (qRT-PCR). The results indicated that P34-L could survive within the wheat rhizosphere for a long time and colonize new spaces in the wheat rhizosphere following the elongation of wheat roots. Compared with uninoculated wheat plants, plants inoculated with P34-L exhibited significantly increased phosphorus accumulation in the leaves; seedling and root weight; total root length; root projection area; root surface area; and number of root tips, forks, and crossings, thus demonstrating the great value of applying this strain in wheat production by promoting root growth and dry matter accumulation. The downregulation of TaPT4 transcript levels in the wheat roots also suggested that a high-phosphorus environment was established by P34-L. These results lay a foundation for further research on the relationships between PGPR and their host plants. Moreover, a potentially ideal biofertilizer-producing strain for use in sustainable agriculture was developed.

Aislamiento y selección de hongos de suelo solubilizadores de fósforo nativos del estado de Coahuila, México

Antecedentes y Objetivos: La deficiencia de fósforo en los cultivos agrícolas generalmente es atendida mediante la aplicación de fertilizantes. Sin embargo, estas prácticas resultan costosas y causan deterioro al medio ambiente. El uso de bio-productos como los hongos solubilizadores de fósforo constituyen una alternativa promisoria. El objetivo de este trabajo fue aislar y seleccionar hongos del suelo fosfato solubilizadores nativos de Coahuila, México, con potencial para ser utilizados como biofertilizantes.Métodos: El aislamiento de los hongos se llevó a cabo mediante la técnica de filtración de partículas de suelo. La selección de las cepas se realizó en el medio de cultivo de Sundara con fosfato tricálcico; la capacidad fosfato solubilizadora se detectó visualmente mediante la presencia de halos hialinos en el medio de cultivo. La evaluación cualitativa se determinó mediante el índice de eficiencia de solubilización. En la evaluación cuantitativa, los cultivos se incubaron en medio líquido por 25 días y cada cinco se midió el P soluble, pH y biomasa fúngica.Resultados clave: Se obtuvo un total de 271 aislamientos de hongos; de éstos 52.76% proyectaron resultados positivos a la prueba cualitativa de solubilización de fósforo. En cuanto a la eficiencia de solubilización, ésta fluctuó entre 2.06-6.85 unidades. Las cepas Sp. Mz54, Aspergillus sp. 4C19, Penicillium sp. Mu73, Penicillium sp. Mu77 y Penicillium sp. A56 presentaron los mayores índices de eficiencia de solubilización (t<0.005). En la medición cuantitativa, la cepa Penicillium sp. Mu73 solubilizó la mayor cantidad de fósforo (83.26 mg l-1) (t<0.005). De acuerdo con los análisis de regresión, el fósforo aumentó a medida que el pH decreció (r2=0.81).Conclusiones: La cepa Penicillium sp. Mu73 tiene un alto potencial para ser utilizada como biofertilizante ya que promueve un alto contenido de fósforo soluble en condiciones in vitro.