NBRIP Medium Research Articles

Screening and biodiversity analysis of cultivable inorganic phosphate-solubilizing bacteria in the rhizosphere of Hydrilla verticillata.

The inorganic phosphate-solubilizing bacteria (IPB) in the rhizosphere of Hydrilla verticillata can convert insoluble inorganic phosphorus in the environment into soluble phosphorus that can be directly absorbed and utilized by Hydrilla verticillata. In this research, the roots and rhizosphere sediments of Hydrilla verticillata were collected from high-organic matter urban landscape water. The National Botanical Research Institute's Phosphate growth medium (NBRIP medium) was used to screen for efficient cultivable IPB. The 16S rRNA gene sequence analysis was used to determine the taxonomic affiliation of the strains, and ammonium molybdate spectrophotometry was used to detect the phosphate-solubilizing ability of the strains. The results show that a total of 28 IPB strains with good phosphate-solubilizing effect are obtained from the roots and rhizosphere sediments of Hydrilla verticillata. These IPB strains belong to two phyla, four orders, seven classes, nine families, and nine genera. Among these, Bacillus and Acinetobacter are the dominant genera, and the strains SWIH-7, SWIP-6, SWIP-7, SWIP-13, SWIP-15 and SWIP-16 are potential new species. The IPB strains isolated and screened in this research are rich in diversity, with potential new species and stable phosphate-solubilizing characteristic. These IPB strains are suitable for further development as microbial bacterial agents, which can be applied to promote the recovery of submerged plants in polluted water with high-organic matter, treatment of polluted water and ecological restoration of water.

Plant growth promotion characterization of endophytic bacteria from Sesbania sesban (L.) Merr. collected in Tan Hung district, Long An province, Vietnam

The study aimed to isolate and characterize endophytic bacteria associated with Sesbania sesban (L.) Merr. collected in Tan Hung district, Long An province, Vietnam. Bacterial endophytes were isolated and screened capacity of plant growth promotion by using LGI, Burks’ nitrogen free, NBRIP medium. Quantifying bacterial strain’s probability of nitrogen fixation, phosphate solubilization and IAA production was based on colorimetric methods. Isolates with the most potential of nitrogen fixation, phosphate solubilization were identified by using MALDI-TOF Mass Spectrometry. The results were that eighteen bacterial endophytes were isolated from Sesbania sesban (L.) Merr. roots. They had characteristics of promoting plant growth by nitrogen fixation, phosphate solubilization and IAA biosynthesis. DD2 and DD18 with the best capacity of nitrogen fixation and phosphate solubilization were identified as Klesiella pneumonia and Priestia megaterium, respectively. Both were previously reported as plant growth promotion bacteria.

Beneficial effects of selected rhizospheric and endophytic bacteria, inoculated individually or in combination, on non-native host plant development

Plant beneficial bacteria have been traditionally inoculated as unique strains, although combining bacteria with complementary traits could maximize their positive effect on plant growth and development. Our objective was to elaborate consortia from selected rhizospheric and endophytic bacteria with antifungal and plant growth promoting properties, and evaluate their beneficial effects on the growth of Physalis ixocarpa, an annual native Mexican species of horticultural importance. Bacterial strains were selected based on their antifungal activity against Fusarium spp. through in vitro antagonism assays. Characterization of the profile of volatile organic compounds (VOC) of newly-identified endophytic strains able to significantly inhibit Fusarium spp. evidenced the presence of sulfur compounds and ketones, reported for their antifungal activity. Seven bacterial strains were able to solubilize phosphate on NBRIP medium. Their capacity to promote the growth of A. thaliana in vitro was further tested. All stains stimulated the formation of lateral roots and root hairs, and enhanced A. thaliana biomass, most likely through auxin production. Twelve consortia were elaborated from rhizospheric and root endophytic bacteria, and the effects of consortia and individual strain inoculation on the growth and development of P. ixocarpa were evaluated in a greenhouse trial. Rhizobacterial strains A8a and 5911, and consortia formed by A8a + B3R7 and SO + B3R7 (all belonging to the Bacillus genus) showed the best results in terms of growth promotion and floral onset, with increases in plant height by up to 45% and flowering beginning 30 days before than in the Control. Our results confirm the potential of combining rhizospheric and endophytic bacteria with multiple beneficial traits for enhancing plant development and suggest that the most promising bacterial treatments could be applied to avocado trees, their natural host, to foster their productivity.

Isolation, Identification, and Characterization of Phosphate-Solubilizing Bacteria from Tunisian Soils

Soil microorganisms play an important role in maintaining natural ecological balance through active participation in carbon, nitrogen, sulfur, and phosphorous cycles. Phosphate-solubilizing bacteria (PSB) are of high importance in the rhizosphere, enhancing the solubilization of inorganic phosphorus complexes into soluble forms available for plant nutrition. The investigation of this species of bacteria is of major interest in agriculture, as they can be used as biofertilizers for crops. In the present study, 28 isolates of PSB were obtained after the phosphate enrichment of soil samples from five Tunisian regions. Five PSB species were identified by 16S rRNA gene sequencing including Pseudomonas fluorescens, P. putida, and P. taiwanensis, Stenotrophomonas maltophilia, and Pantoea agglomerans. Solid and liquid Pikovskaya's (PVK) and National Botanical Research Institute's (NBRIP) media containing insoluble tricalcium phosphate were used for the evaluation of the phosphate solubilization ability of the bacterial isolates by two methods: visual evaluation of the solubilization zone around colonies (halo) and determination of solubilized phosphates in liquid medium by the colorimetric method of the vanado-molybdate yellow. Based on the results of the halo method, the isolate of each species that showed the higher phosphate solubilization index was selected for evaluation of phosphate solubilization by the colorimetric method. In the liquid media, the bacterial isolates showed phosphate solubilization ranging from 535.70 to 618.57 µg mL-1 in the NBRIP medium, and 374.20 to 544.28 µg mL-1 in the PVK medium, with the highest values produced by P. fluorescens. The best phosphate solubilization ability and higher reduction in broth pH, which indicates higher organic acid production, were achieved in NBRIP broth for most of the PSB. Strong correlations were observed between the average capability of PSB to solubilize phosphates and both the pH and total phosphorous content in the soil. The production of the hormone indole acetic acid (IAA), which can promote plant growth, was observed for all five PSB species. Among them, P. fluorescens obtained from the forest soil of northern Tunisia showed the highest production of IAA (50.4 ± 0.9 µg mL-1).

Organic acid, phosphate, sulfate and ammonium co-metabolism releasing insoluble phosphate by Klebsiella aerogenes to simultaneously stabilize lead and cadmium.

Here, a novel phosphate-solubilizing bacterium (PSB), Klebsiella aerogenes Wn was applied to develop an environmental-friendly method to simultaneously stabilize Pb and Cd. The maximum dissolved phosphate was up to 701.36mg/L by the strain Wn. The high performance liquid chromatography (HPLC) and Pearson correlation analyses showed that the acetic acid produced by the strain Wn was significantly positively associated with the released phosphate. Moreover, 100% of 500mg/L of Pb and 100mg/L of Cd were simultaneously stabilized in the classical NBRIP medium and the major products were Pb5(PO4)3Cl, Ca7.7Cd0.8(PO4)8(H2O)2.4 and CdS, respectively. In addition, the bacterial genome and transcriptome analyses showed that the pentose phosphate pathway (PPP), pyruvate metabolism pathway, thiamine metabolic pathway, sulfate reduction and ammonium bio-transformation were coupled to promote releasing insoluble phosphate and stabilizing Pb and Cd. In the metabolism networks, the critical genes of gcd, aceE, thiE, thiS and cysH, etc. were significantly up-regulated. Our results are beneficial to deeper understand the molecular mechanisms of releasing insoluble inorganic phosphate by PSBs and develop a technology prototype to simultaneously stabilize Pb and Cd using the PSBs.

Exogenous Indole-3-Acetic Acid Production and Phosphate Solubilization by Chlorella vulgaris Beijerinck in Heterotrophic Conditions

The role of soil-borne microalgae in the edaphic ecosystem is barely known, especially concerning their plant-growth-promoting traits, although they are used as biofertilizers. In this study, a microalgal strain isolated from soil cultivated with maize was evaluated as an exogenous producer of indole-3-acetic acid (IAA) in potato dextrose broth—PD—and sugarcane molasses, with or without tryptophan, and phosphate solubilizer (in ‘National Botanical Research Institute’s phosphate’—NBRIP—medium with tricalcium phosphate)with plant-growth-promoting traits, under heterotrophic conditions. The species of microalga was identified, by sequencing the ITS region in the rDNA and the morphological characteristics, as Chlorella vulgaris. Its growth was significantly higher in the PD medium, with slower growth in molasses. The addition of tryptophan did not influence the growth of C. vulgaris in either medium, but it increased the production of IAA, mainly in the PD medium, to 265 µg mL−1. The microalga grew in the medium with insoluble phosphate, releasing phosphorus into the medium (30 mg L−1 after 72 h). This is the first study on the application of C. vulgaris as a phosphate solubilizer. More studies should be performed on C. vulgaris as a prospective plant-growth-promoting microorganism, besides its ability to produce exogenous IAA, and further investigations should be conducted on developing inexpensive culture media.

Properties of Microorganisms Isolated from Soils under Conventional and Organic Farming

Оbjective. The article presents the results of research aimed at determining the influence of different methods of tillage on the functional diversity of the soil microbiota. Soil samples containing plant residues from agricultural plots under conventional and organic farming in the Kyiv oblast were used for the study. Methods. Analysis of soil microbiota using differential diagnostic nutrient media by serial dilutions of soil suspension was performed. To quantify the phosphate-mobilizing properties of the isolated microorganisms, the concentration of phosphorus in the solution was measured (grown in NBRIP liquid medium) and detected by the Arenius spectrophotometric method on a Ulab 102UV Spectrophotometer. Results. Th e soil of the plots under organic agrotechnology of cultivation was marked by a greater number of microorganisms of all ecological and trophic groups, except oligonitrophilic and phosphate-solubilizing bacteria. The vast majority of phosphate-transforming bacteria were isolated from the soil of agricultural plots under convection farming. The largest number of cellulose-degrading isolates was isolated from the soil under organic farming plots. Five isolates have the widest range of agronomically useful properties, in particular, the ability to mobilize organic and inorganic phosphates and cellulosolytic activity: 6b, 13b, 18b, 19b, and 8m. After incubation of the isolates on an NBRIP medium at 28°C and 200 rpm for 72 hr, special analyzes for dissolved phosphorus content and pH level in the culture fluid were performed. Isolate 8m selected from chornozem (black soil) under convection agriculture and classified by us as Trichoderma sp. exhibited the highest phosphate-mobilizing activity. The vast majority of bacteria capable of phosphate transformation were isolated from the soil of agricultural areas affected by convection agriculture; and isolates capable of dissolving cellulose — from the soil of organic farming. Conclusions. The initial identification of certain isolates allowed us to classify them as Bacillus and Trichoderma. These isolates are important for further research with the prospect of creating a complex biological preparation with fungicidal properties and the ability to mobilize organic and inorganic phosphorus compounds.

Phosphate solubilization by Antarctic yeasts isolated from lichens.

Antarctica has a great diversity of microorganisms with biotechnological potential but is not very well Known about yeasts with phosphate solubilization activity. Thus, the aim of this study was to evaluate the ability of yeasts from Antarctica lichens to solubilize phosphate in vitro. In the screening, 147 yeasts were tested and 43 (29%) showed P solubilization in solid NBRIP medium at 15.0°C, with a higher prevalence of positive genera Vishniacozyma, followed by Cystobasidium. Most of the positive yeasts were isolated from Usnea auratiacoatra, followed by Polycauliona regalis and Lecania brialmontii. Two strains with better activity after screening were selected for the solubilization in the liquid medium, Vishniacozyma victoriae 2.L15 and A.L6 (unidentified). Vishniacozyma victoriae 2.L15 exhibiting activities at 25.0°C (29.91mg/L of phosphate and pH 6.85) and at 30.0°C (619.04mg/L of phosphate and pH 3.73) and A.L6 strain at 25.0°C (25.05mg/L of phosphate and pH 6.69) and at 30.0°C (31.25mg/L of phosphate and pH 6.47). Of eight organic acids tested by HPLC, tartaric and acetic acids were detected during phosphate solubilization, with greater release in the period of 144 (2.13mg/L) and 72 (13.72mg/L) hours, respectively. Future studies to elucidate the presence of functional genes for P metabolism in lichens, as well as studies in the field of proteomics for the discovery of yeast proteins related to P solubilization are needed. Thus, the high prevalence of lichen-associated yeast communities probably contributed to the high frequency of phosphate-solubilizing isolates in this study.

Isolation and characterization of phosphate solubilizing bacteria naturally colonizing legumes rhizosphere in Morocco.

Low-cost and environmentally friendly agricultural practices have received increasing attention in recent years. Developing microbial inoculants containing phosphate (P) solubilizing bacteria (PSB) represents an emerging biological solution to improve rhizosphere P availability. The present study aims to explore PSB strains isolated from soils located at different bioclimatic stages in Morocco and present in various legumes rhizosphere to improve agronomic microbial fertilizer’s effectiveness. It was also aimed to test the isolated strains for their ability to solubilize P in NBRIP medium with Tricalcium P (Ca3 (PO4)2) (TCP), rock phosphate (RP), and their combination as a source of phosphorus, by (22) experiment design. Bacterial strains with a high P solubility index (PSI) were selected, characterized, and compared to commercial control. The vanadate-molybdate method was used to estimate P solubilization activity. Stress tolerance to salinity, acidity, drought, and temperature was tested. From all isolated strains (64), 12 were screened as promising biotechnological interest because of their P solubilization and their good resistance to different drastic conditions. Besides, the strain WJEF15 showed the most P solubility efficiency in NBRIP solid medium with a PSI of 4.1; while the WJEF61 strain was located as the most efficient strain in NBRIP-TCP liquid medium by releasing 147.62 mg.l–1 of soluble P. In contrast, in the NBRIP-RP medium, the strain WJEF15 presented maximum solubilization with 25.16 mg.l–1. The experiment design showed that a combination of RP and TCP with max level progressively increases P solubilization by 20.58%, while the WJEF63 strain has the most efficient concentration of 102.69 mg.l–1. Indeed, among the selected strains, four strains were able to limit tested fungi growth. Thus, results reveal a potential effect of selecting PSBs to support cropping cultures as plant growth-promoting rhizobacteria (PGPR).

Screening of Compounds Secreted by Local Isolates of Phosphate Solubilizing Fungi (PSF) by GC-MS Analysis

Background: Microorganisms are an important factor in solubility of nutrition minerals; phosphate solubilizing fungi (PSF) considered one of the main sources of sustainability of agriculture production systems. Some fungi are well known for their natural capability to produce various organic acids, due to the lowering pH in the soil. The study amid to isolate PSF from rhizosphere soil and some plant residue and identify its secrenning compound using GC-MS analysis. Methods: in laboratory investigation during 2016, isolates of PSF and check their solubilizing activities using selective artificial media PVK and NBRIP in soild and broth form. The secrening of secondary organic compound in broth culture extracted and identify using GC-MS analysis. Result: the results inventory six isolates, among these isolates Aspergillus niger AD-A2 and AG-B1 were Distinguished by formed halo-clear zones around their colonies as a result of their phosphate-solubilizing ability in soild PVK and NBRIP media. pH decrese of the final product of PSF isolate in broth medium. Various compounds formed by submerged fermentation of A. niger isolates were 1,3-dioxan-5-ol (96.47%); octanoic acid, 4-chlorobenzyl ester (0.14%); 1,3,5-cycloheptatriene (0.58%); Crotonic acid (2.64%); 2-Propanone, 1,1-diethoxy (0.18%); 2-Butanone, 4-hydroxy (13.11%); 1-Tetrazol-2-ylethanone (86.4%); Propanethioamide (0.49%); Acetic acid, ethyl ester; Acetidin (100%); Methylolacetone (100%) and Trichoderma hamatum (T-113) were identified: Ethane, 1,1-diethoxy (100%) and 2-Butanone, 4-hydroxy-(100%).

Identification of the Phosphorus-Solubilizing Bacteria Strain JP233 and Its Effects on Soil Phosphorus Leaching Loss and Crop Growth.

Phosphorus (P) is one of the most limiting nutrients in global agricultural ecosystems, and phosphorus-solubilizing bacteria (PSB) can convert insoluble P into soluble P, thereby improving the absorption and use of soil P by plants. Increasing leaching loss of soil P due to PSB that could lead to water eutrophication is a major concern, although no direct experimental evidence is available to evaluate these effects. In this study, a highly efficient PSB strain, Pseudomonas sp. JP233, was isolated from soil and its P-solubilizing agent was identified by metabolomics and HPLC analyses. The effects of JP233 on P contents in soil leachates were also analyzed by microcosm leaching experiments in the absence and presence of maize. JP233 could solubilize insoluble P into soluble forms, and the molybdate reactive phosphorus (MRP) content reached 258.07 mg/L in NBRIP medium containing 5 g/L Ca3(PO4)2 within 48 h. Metabolomics analysis demonstrated that the organic acid involved in JP233 P solubilization was primarily 2-keto gluconic acid (2KGA). Further, HPLC analysis revealed that 2KGA contents rapidly accumulated to 19.33 mg/mL within 48 h. Microcosm leaching experiments showed that MRP and total phosphorus (TP) contents in soil leaching solutions were not significantly higher after JP233 inoculation. However, inoculation with JP233 into maize plant soils significantly decreased MRP and TP contents in the soil leaching solutions on days 14 (P < 0.01), 21 (P < 0.01), and 28 (P < 0.05). Inoculation with strain JP233 also significantly increased the biomass of maize aerial components and that of whole plants (P < 0.05). Thus, strain JP233 exhibited a significant plant-growth-promoting effect on maize development. In conclusion, the application of PSB into soils does not significantly increase P leachate loss. Rather, the application of PSB can help reduce P leachate loss, while significantly promoting plant absorption and use of soil P.

EXPLORING POTENTIAL OF METAL RESISTANT AND PGP ATTRIBUTES OF PHOSPHATE SOLUBILIZING RHIZOBACTERIA ISOLATED FROM SOUTHERN PUNJAB, PAKISTAN

Phosphorus is highly required nutrient for proper plant functioning and growth but due to its highly reactive nature it changed its form after short period of time when we applied as fertilizer and become unavailable for plant uptake while Phosphate solubilizing rhizobacteria are powerful candidates that solubilize the P that is already present in soil. So, the present research based on the hypothesis to isolating, screening and optimizing the phosphate solubilizing rhizobacteria with potential of metalresistant and multiple PGPR attributes. Total 55 PSR strains were isolated out of which 20 strains (WUSB1,WUSB2, WUSB3, WUSB4, WUSB5, WUSB6, WUSB7, WUSB8, WUSB9, WUSB10, WUSB11, WUSB12, WUSB13, WUSB14, WUSB15, WUSB16, WUSB17, WUSB18, WUSB19, WUSB20) were selected with 4-8 (PSI) and 30-122?g/ml phosphate solubilization in NBRIP medium for one weekincubation at 370C. These strains were further analyzed for their physiochemical attributes, metal resistant, extracellular enzyme production and PGP attributes. Final results showed that one candidate designated the name as WUSB16 produce significant results i.e. having capacity to solubilize P 5.46 (PSI) on agar plate assay and 105?g/ml in broth assay, Acid and alkaline phosphatase production 20?mol PNPb ml-1 hr-1 or 15?mol PNP ml-1 hr-1 respectively. It showed metal resistant against ZnSO4, MnSO4 and CuSO4. Evaluation of PGP attributes indicated that the capacity of WUSB16 strain for auxin production was 100?g/ml, for siderophore and nitrogen fixation was stronger (+++), for Hydrogen Cyanide and ammonia production was medium (++) and for ACC deaminase was negative (-). From above results we can conclude that WUSB16 PSR strain with multifaceted PGP traits is the best candidate that have potential to utilized as Phosphate solubilizing bioinoculant.

Growth and Fatty Acid Profile of the Aspergillus terreus in Different Culture Media and Temperatures

Fungi are a promising alternative source of oil to produce biodiesel, still very little known. The identification of a species with desirable characteristics is a fundamental component to achieve the economic viability of the process. The study aimed to carry out the evaluation of the fungus Aspergillus terreus in different culture media and different temperatures, the production of fungal biomass and in line with obtaining the profile of methyl esters of fatty acids. The fungal biomass revealed that in the NBRIP medium at both a temperature of 29 ºC and 36 ºC, it resulted in a great potential in the production of saturated fatty acids (SFA), which have excellent combustion properties, reaching values of 35.89 and 34,89%, respectively. For most species, the fuel would need to be mixed to make up culture conditions to be optimized and achieve the correct lipid profile, so that the fungal fuel meets European biodiesel production standards (EN 14214). Aspergillus terreus from iron ore tailings proved to be a promising microbial biomass as an energy source in the production of biodiesel.

Isolation and characterization of plant growth-promoting endophytic bacteria of wild legumes growing on sandy soils of Binh Thuan province, Vietnam

The roots of two legume species (Tephrosia purpurea and Tephrosia villosa) that grew wild on dry sandy soils of Binh Thuan province were sources for isolating plant growth-promoting endophytic bacteria. Semi-solid LGI medium was used for the isolation of nitrogen-fixing bacteria from root extracts. All bacterial isolates isolates were evaluated for their ability to solubilize calcium orthophosphate on solid NBRIP medium and their ability to produce IAA in Burk's liquid medium supplemented with 100 mg/L tryptophan. The possibilities of nitrogen fixation, phosphate solubilization and IAA synthesis were all quantitative examined by colorimetric method. Twenty-two bacterial isolates of T. purpurea and 18 isolates of T. villosa were capable of nitrogen fixation in the range of 1.94 to 2.81 mg/L NH4+, whereas only 18 isolates of T. purpurea and 16 isolates of T. villosa showed phosphate solubilization in the range of 12.30 – 48.90 mg/L P2O5, and IAA production in the range of 0.38 – 12.72 mg/L. Sixteen outstanding bacterial isolates of the two legume species were identified by MALDI-TOF technique. The results showed that 13 isolates had high similarity with five bacterial genera including Klebsiella, Cronobacter, Enterobacter, Burkholderia, and Bacillus with score values in the range of 2.070 – 2.411.

Qualitative and quantitative estimation for phosphate solubilizing ability of Trichoderma isolates: A natural soil health enhancer

India is an agricultural country. Nearly 70% of the populations thrive in rural areas, engaged in agriculture making the backbone of our economy. The Trichoderma genus is widely distributed and provides an alternative to chemical pesticides in crops and plants growth. Trichoderma species are free living and commonly found in soil and root ecosystems. Root colonization by Trichoderma also regularly promotes growth and development of plants. They also perform beneficial and significant role in enhancing crop productivity, fight against pathogens, resistant to abiotic stress and increase of nutrients uptake from soil. The present study was undertaken to investigate quantitative and qualitative estimation of phosphate solubilizer by using nineteen isolates of Trichoderma grown on Pikovskaya’s Agar and NBRIP media. It was found that all isolates were capable of differentially utilizing 5 g/L TCP in NBRIP broth. This was indicated by the soluble phosphate concentrations and increase in acidity of growth medium. Out of 19 isolates, all isolates were capable in phosphate solubilization. However, the P- solubilizing efficiency was found higher in case of the isolate number-59 and 89. While isolate number-102 was the strongest and isolate number-23 was the weakest P-solubilizer. Minimum Phosphate solubilization concentration was observed in 3rd day (0%) that simultaneously increased on 7th day (52.63%) followed by 9th day (100%) and remaining all days 13th, 17th and 21st days also observed 100% efficiency.

Characterization of Pseudomonas bacteria of Piper tuberculatum regarding the production of potentially bio-stimulating compounds for plant growth

ABSTRACT Despite advances in the identification and characterization of endophytic bacteria in various plant species worldwide, little is known about such microorganisms in plants from the Amazon region. Previous studies reported that Piper tuberculatum endophytic Pseudomonas (isolates Pt12 and Pt13, identified as Pseudomonas putida and Pseudomonas sp., respectively) were able to inhibit the in vitro growth of Fusarium solani f. sp. piperis, which causes root rot in black pepper (Piper nigrum), and that Pt13 promoted the growth of P. nigrum. Therefore, the aim here was to characterize these bacteria regarding their ability to produce plant growth-promoting substances [siderophores, indol acetic acid (IAA) and soluble phosphate]. Chrome azurol S assays were performed for the detection of siderophores. For qualitative and quantitative assays of IAA production and phosphate solubilization, Salkowski´s reagent and NBRIP medium with molybdenum blue reagent, respectively, were used. Results revealed that Pt12 and Pt13 were able to synthesize IAA, mainly under a high concentration of L-tryptophan, indicating that they are IAA-producing bacteria, probably through a tryptophan-dependent biosynthesis pathway. The presence of P. nigrum extract positively influenced the IAA production by Pt12 and Pt13, with highest values of 125 and 90 µg mL-1, respectively. In addition, Pt12 was positive for the production of siderophores and produced 56.56 µg mL-1 of soluble phosphate. In contrast, Pt13 showed no ability to produce siderophores or to solubilize phosphate. Besides their potential in controlling plant diseases, Pt12 and Pt13 have potential as biofertilizers, favoring sustainable agriculture.

Antarctic lichens as a source of phosphate-solubilizing bacteria

In association with lichens, bacteria can play key roles in solubilizing sources of inorganic phosphates that are available in the environment. In this study, the potential of bacteria isolated from 15 Antarctic lichen samples for phosphate solubilization was investigated. From 124 bacteria tested, 66 (53%) were positive for phosphate solubilization in solid NBRIP medium, with a higher prevalence of Pseudomonas, followed by Caballeronia and Chryseobacterium. Most of the phosphate-solubilizing bacteria were isolated from Usnea auratiacoatra, followed by Caloplaca regalis and Xanthoria candelaria. Two isolates showed outstanding performance, Pseudomonas sp. 11.LB15 and Pseudomonas sp. 1.LB34, since they presented solubilization in the temperature range from 15.0 to 30.0°C, and maximum quantification of soluble phosphate at 25.0°C was 511.21 and 532.07mg/L for Pseudomonas sp. 11.LB15 and Pseudomonas sp. 1.LB34, respectively. At 30.0°C soluble phosphate yield was 639.43 and 518.95mg/L with pH of 3.74 and 3.87 for Pseudomonas sp. 11.LB15 and Pseudomonas sp. 1.LB34, respectively. Fumaric and tartaric acids were released during the solubilization process. Finally, bacteria isolated from Antarctic lichens were shown to have the potential for phosphate solubilization, opening perspectives for future application in the agricultural sector and contributing to reduce the use of chemical fertilizers.

The Screening of Potassium- and Phosphate-Solubilizing Actinobacteria and the Assessment of Their Ability to Promote Wheat Growth Parameters.

Soil fertility and plant nutrition require an adequate management of essential macronutrients such as potassium (K) and phosphorus (P), which are mandatory for plant development. Bioleaching of K and P bearing minerals improves their chemical weathering and increases the performance of the biofertilization strategies. In this study, in vitro and greenhouse experiments were carried out to investigate P and K solubilization traits of nine Actinobacteria (P13, P14, P15, P16, P17, P18, BC3, BC10, and BC11) under fertilization with rock phosphate (RP). K and P solubilization were evaluated on Alexandrov and NBRIP media containing mica and six RP samples, respectively. The actinobacterial strains were able to solubilize K in Alexandrov medium supplemented with RP. However, when soluble P was used instead of RP, only four strains of Actinobacteria (Streptomyces alboviridis P18–Streptomyces griseorubens BC3–Streptomyces griseorubens BC10 and Nocardiopsis alba BC11) solubilized K. The solubilization values of K ranged from 2.6 to 41.45 mg/L while those of P varied from 0.1 to 32 mg/L. Moreover, all strains were able to produce IAA, siderophore, HCN, and ammonia and significantly improved the germination rate and the vigor index of wheat. The pot experiments revealed that four strains (Streptomyces alboviridis P18, Streptomyces griseorubens BC3, Streptomyces griseorubens BC10, and Nocardiopsis alba BC11) significantly improved the growth parameters of wheat, namely root length (1.75–23.84%), root volume (41.57–71.46%), root dry weight (46.89–162.41%), shoot length (8.92–23.56%), and shoot dry weight (2.56–65.68%) compared to the uninoculated control. These findings showed that Streptomyces griseorubens BC10 and Nocardiopsis alba BC11 are promising candidates for the implementation of efficient biofertilization strategies to improve soil fertility and plant yield under rock P and rock K fertilization.

Staphylococcus hominis YJILJH and Staphylococcus epidermidis YJ101 promote the growth of white clover (Trifolium repens L.) by increasing available phosphorus

Phosphorus is critical for the regulation of numerous metabolic processes in plants, and so understanding the mechanisms by which plants acquire phosphorus is important. Phosphate solubilizing bacteria (PSB) are thought to promote the uptake of phosphorus by plants. The effects of PSB YJILJH and YJ101 strains on the growth of white clover (Trifolium repens L.) were investigated through the production of the plant hormone IAA and the change of available phosphorus content in the soil. Two strains of YJILJH and YJ101 were selected from the rhizosphere soil of white clover among rows of apple orchards. Combined with 16S rDNA and next-generation sequencing (NGS), the strains were identified as Staphylococcus hominis and Staphylococcus epidermidis, respectively. The two strains had strong phosphate solubilizing ability, and had solubilization index (SI) values of 4.39 and 3.95, respectively. The dissolved amounts of soy lecithin were 351.2 and 387.3 mg/L in liquid medium, respectively. The amount of Ca3(PO4)2 dissolved reached 506.3 and 789.8 mg/L, respectively. The pot experiment showed that the biomass of white clover after adding the two strains increased by 21.17% and 36.49%, the total phosphorus (TP) content increased by 28.87% and 30.41%, and the soil available phosphorus (AP) content increased by 86.63% and 47.16%, respectively. This study also found that both strains can produce IAA content reaching 55.95 and 54.33 pmol / L in 72 h. In regard to relative gene expression, trpD and trpA genes were expressed in the different treatments, while ipdC was only expressed in Luria-Bertani broth (LB broth) and NBRIP media (+ soy lecithin). It is speculated that the pathway of IAA synthesis by both strains may be related to the tryptophan side chain pathway and the indole-3-pyruvate pathway. The IAA produced by the two bacteria strains is an important reason to promote the growth of white clover and participate in the process of reducing the environmental pH of the growth medium.

Characteristics of plant growth-promoting rhizobacteria SCPG-7 and its effect on the growth of Capsicum annuum L.

The strain SCPG-7 was isolated from saline soil in a cotton field. It is confirmed that the strain SCPG-7 is Pseudomonas sp. by means of the analysis of its phenotypic features and 16S rRNA sequence. SCPG-7 was capable of dissolving mineral tri-calcium phosphate (Ca3(PO4)2) and tri-magnesium phosphate (Mg3(PO4)2). In contrast, no showing iron phosphate (FePO4) or aluminum phosphate (AlPO4) solubilizing activities were detected by this experimental approach. The ratio of the dissolved P diameter to the colony diameter was 1.86. To study the phosphate dissolving mechanisms of the strain, we analyzed the changes of the pH value, the soluble phosphate content, the concentration of alkaline phosphatase, and the production of organic acid in the insoluble phosphate liquid medium. 2-keto-D-gluconicacid, α-ketoglutaric acid, succinic acid, etc. were characterized by LC-MS/MS in NBRIP medium. The concentration of 2-keto-D-gluconicacid increased to 88.6 mg/L after being cultured for 216 h. The strain decreased the pH value of the medium from 7.4 to 4.7 and the released soluble phosphate up to 516 mg/L, which proved the production of organic acids and alkaline phosphatase to be mechanism for solubilizing P. Under low phosphorus stress, Pseudomonas global regulatory protein PhoB regulates the transcription of the alkaline phosphatase gene. IAA and siderophore were secreted by SCPG-7. After treatment with SCPG-7, the individual plant height and dry weight of pepper increased by 23.3 and 31.2%, respectively, compared to the control group. The results show that the strain SCPG-7 has the potential to convert insoluble inorganic phosphorus to plant-available phosphorus. It can enhance soil phosphorus release through biological pathways, thereby increasing crop yield, and providing germplasm resources for the development of biological fertilizers.