Phosphate Solubilization Index Research Articles

Halophilic Phosphate-Solubilizing Microbes (Priestia megaterium and Bacillus velezensis) Isolated from Arabian Sea Seamount Sediments for Plant Growth Promotion.

Arabian Sea is a highly productive Ocean owing to deep upwelling with reports on phosphorus cycling in ocean sediments. In this study, microbes from sea mounts of the Arabian Sea at varying depths (400m, 900m) were screened to isolate and characterize phosphate-solubilizing bacteria (PSB) with plant growth-promoting properties. Out of the seven morphologically different PSBs, two bacterial strains with maximum phosphate solubilization index were identified as Priestia megaterium (H1) and Bacillus velezensis (H2) based on biochemical and molecular characteristics. Different factors influencing phosphatase production were optimized, which showed maximum solubilization at temperature of 30°C (97.5μg/mL), glucose as best carbon source (70µg/mL), 1-M NaCl (114.1µg/mL), and pH 8 (134.3µg/mL) indicating their halophilic and alkaliphilic characteristics. Alkaline phosphatase enzyme was extracted and partially purified from both PSBs wherein H2 strains showed greater specific activity (24.83 U/mg). Metabolomics studies through HPLC revealed maximum production of gluconic acid (483.75mg/L) in addition to lactic, oxalic, acetic, and succinic acid during solubilization. Biopriming effect of PSBs on tomato seed germination showed high germination index (80%) in consortia of both isolates which was also validated through root colonization by SEM analysis. Further studies using pot assay experiments also showed comparable results in marine PSB consortia with positive control (Phosphobacteria) for plant growth attributes including root height and weight. These findings suggest that the halophilic PSB strains from marine sediments could be used as potential bio-inoculants to enhance plant growth and combat saline stress for sustainable Agriculture.

Plant growth promotion of crops using phosphate solubilizing bacterial strains derived from insects

The aim of this study was to investigate insect derived bacteria for the ability to dissolve insoluble soil phosphate to release soluble phosphorus compounds, available to plants. Bacterial isolates were obtained from Diabrotica virgifera, Hermetia illucens, Oulema melanopus, and Ostrinia nubilalis. An in vitro evaluation of phosphate solubilization ability on Pikovskaya’s medium was done and the phosphate solubilizing index (PSI) was calculated for each isolate. Bacteria were tested in a greenhouse experiment on seeds of oats, wheat, triticale, barley and soybeans. After incubation, the weight and length of their aerial plant parts were measured. The highest increase in the weight of aerial parts was recorded for oats after using strain Om046 for inoculation (88.98%), then, wheat (Dv097, 31.43%), soybean (strain 96, 53.79%), and triticale (bacterial consortium, 36.9%). Bacteria used were identified as Lactococcus lactis (strains Om030 and Om046), Acinetobacter sp. (Dv123), Lactococcus garvieae (Dv097) and Rothia kristinae (strains 90 and 96). We showed that a successful application of insect derived bacteria for phosphate solubilization in soil, to promote plant growth, is possible. Innovative agriculture requires constant improvements in increasing crop growth. Thus, new sources of bacterial strains effectively promoting plant growth, are needed. We described a new source of plant growth-promoting bacteria that can be used in agriculture.

Effects of Plant Growth Promoting Halotolerant Pseudomonas Aeruginosa JCM 5962 with Hydrocarbon Degradation Ability, Isolated from Sundarbans Mangrove Area in West Bengal, on Abelmoschus esculentus (Okra) Plant Growth

Plant growth promoting rhizobacteria (PGPR) play a key role in sustainable agricultural practices leading to increased crop productivity. Moreover, PGPR with ability to diminish abiotic stresses like salinity and hydrocarbon contamination in soil, can be developed into potent biofertilizers with maximum ecological benefits. Sundarbans mangrove region in West Bengal, a natural reservoir of diverse microbiota is an important source of PGPR adapted to high salinity and other abiotic stresses like hydrocarbon contamination due to oil spillage and water transport systems, rendering the soil unsuitable for farming. In the present study, a potent PGPR has been isolated from rhizospheric soil of Matla riverbed in mangrove areas of Sundarbans, with simultaneous nitrogen fixing, phosphate solubilizing and plant hormone like indole acetic acid (IAA) producing properties as well as high salt tolerance and hydrocarbon bioremediation abilities. The strain has been identified as Pseudomonas aeruginosa JCM 5962 (NCBI Accession number MK544832.1) on the basis of 16S rRNA analysis. The isolated Pseudomonas aeruginosa strain showed atmospheric nitrogen fixation (3612 ± 2 mg N/ Kg of soil), highest phosphate solubilization index of 3.0 ± 0.06 and 37.14 µg/mL of IAA production. This potent strain also showed salt tolerance upto 7% in culture broth and an uptake of 18.72% of salt. Highest hydrocarbon degradation was shown by this strain in presence of diesel as the sole carbon source. The isolated Pseudomonas aeruginosa strain showed overall improvement in growth of Abelmoschus esculentus (Okra) plants in pot experiments in different conditions like absence of any abiotic stress, presence of 5% salt stress and presence of 1% diesel contaminant. These results indicate that Pseudomonas aeruginosa JCM 5962 can be developed as a potent biofertilizer to be used in agricultural lands of Sundarbans mangrove regions and other areas which are plagued by high salinity and increasing hydrocarbons, particularly petroleum contamination.

Molecular Characterization Reveals Biodiversity and Biopotential of Rhizobacterial Isolates of Bacillus Spp

Bacillus species appearas the most attractive plant growth-promoting rhizobacteria (PGPR) and alternative to synthetic chemical pesticides. The present study examined the antagonistic potential of spore forming-Bacilli isolated from organic farm soil samples of Allahabad, India. Eighty-seven Bacillus strains were isolated and characterized based on their morphological, plant growth promoting traits and molecular characteristics. The diversity analysis used 16S-rDNA, BOX-element, and enterobacterial repetitive intergenic consensus. Two strains, PR30 and PR32, later identified as Bacillus sp., exhibited potent in vitro antagonistic activity against Ralstonia solanaceorum. These isolates produced copious amounts of multiple PGP traits, such as indole-3-acetic acid (40.0 and 54.5 μg/mL), phosphate solubilization index (PSI) (4.4 and 5.3), ammonia, siderophore (3 and 4 cm), and 1-aminocyclopropane-1-carboxylate deaminase (8.1and 9.2 μM/mg//h) and hydrogen cyanide. These isolates were subjected to the antibiotic sensitivity test. The two potent isolates based on the higher antagonistic and the best plant growth-promoting ability were selected for plant growth-promoting response studies in tomatoe, broccoli, and chickpea. In the pot study, Bacillus subtilis (PR30 and PR31) showed significant improvement in seed germination (27–34%), root length (20–50%), shoot length (20–40%), vigor index (50–75%), carotenoid content (0.543–1.733), and lycopene content (2.333–2.646 mg/100 g) in tomato, broccoli, and chickpea. The present study demonstrated the production of multiple plant growth-promoting traits by the isolates and their potential as effective bioinoculants for plant growth promotion and biocontrol of phytopathogens.

Comparing the population density, colony diversity, and phosphate solubilization ability between rice root endophytic and rice rhizospheric soil bacteria from organic wetland

Abstract Phosphate-solubilizing bacteria (PSB) play important roles in the agricultural systems. The present study aims to compare the population density, colony diversity, and phosphate solubilization ability between rice root endophytic bacteria (RRoEB) and rice rhizospheric soil bacteria (RRzSB) from organic wetland. By spread plate method, bacteria were isolated directly using Pikovskaya’s agar and indirectly through other media, namely Nutrient Agar (NA), Starch Casein Agar (SCA), Jensen, and Yeast Extract Mannitol Agar (YEMA). Each distinct colony based on the morphology on the respective media was screened for phosphate solubilization ability by subculturing on Pikovskaya’s agar. The phosphate solubilizing index (PSI) was measured from the halo zone formation. The results showed that by direct isolation, 6 RRoEB and 5 RRzSB were able to phosphate solubilization. By indirect isolation from NA, SCA, Jensen, and YEMA, 2, 3, 1, and 3 isolates of RRoEB and 4, 3, 1, and 3 isolates of RRzSB showed the capability as phosphate solubilizer. Although the highest colony diversity of PSB was obtained from direct isolation, however the highest PSI was yielded from indirect isolation, namely isolates J1R1 (3.53) and Y1S1 (2.48). The highest PSI from direct isolation was obtained by P1R5 (1.90) and P1S1 (1.51).

Selection of Potential Bacteria in Termite Nest and Gut for Sustainable Agriculture

In this study, bacteria with the best abilities in cellulose degradation, siderophore production, phosphate solubility, and Pythium parasitica inhibition were selected from termite nests and guts. The isolate BTNASP 5-2, BTPK 5-3 and BTNA 5-1 from termite guts exhibited highest in siderophore production index (SPI) (4.16 ± 0.21), phosphate solubilizing index (PSI) (2.10 ± 0.14) and percentage inhibition of radial growth (PIRG) (67.07 ± 4.02 %), respectively. The BGNACMC 4-3 isolated from termite nest gave the highest cellulolytic index (CI) of 5.17 ± 0.24. Bacterial classification was performed using 16s rRNA gene sequencing. The isolates BTPK 5-3, BGNACMC 4-3 and BTNA 5-1 were found closely related to Bacillus cereus, whereas the bacterial isolate BTNASP 5-2 was closely related to Bacillus subtilis. It is also suggested that the Bacillus cereus exhibited a variety of biological activities, denoting the highest cellulase, phosphate-solubilizing and antifungal activities, while Bacillus subtilis produced only a siderophore. The results obtained suggest that the bacteria selected will be used to develop bio-compost to promote plant growth, leading to sustainable farming. HIGHLIGHTS Bacillus cereus exhibited a variety of biological activities, denoting the highest cellulase, phosphate-solubilizing, and antifungal activities Bacillus subtilis produced a siderophore The highest cellulose-degrading bacteria ( cereus BGNACMC4-3) found in termite mound nest GRAPHICAL ABSTRACT

Characterization of Azotobacter beijerinckii for PGP properties isolated from tomato rhizosphere of Darjeeling Hills

The rhizosphere soil is the habitat of a various kind of microorganisms that play a key role in the enhancement of plant growth. The present study was carried out to screen the abundance of free-living dinitrogen-fixing microorganisms from the tomato rhizosphere of Darjeeling Hills. The bacteria that could fix nitrogen from the atmosphere and grow on media devoid of nitrogen were isolated. One of the potent strains was selected and identified as Azotobacter beijerinckii through molecular characterization using 16S rRNA homology at NCMR-NCCS, Pune. In-vitro production of IAA was 27 (?g/mL), Gibberellic acid was 48 (?g/mL) and the Phosphate solubilization index (SI) was 2.86. The plant growth promotion test was performed on rice seeds using the strain. The results showed that the % increase in germination over control was 7.52%.

Isolation and screening of stress tolerant and plant growth promoting root nodulating rhizobial bacteria from some wild legumes of Nagaland, India

Wild legumes are widely distributed and better adapted to extreme agro-climatic conditions because of their soil microbiota. In the present study, Root Nodulating Bacteria (RNB) were isolated from wild legumes and analysed for their abiotic stress tolerant and Plant Growth Promoting Traits (PGPT). Rhizobial strains were identified based on their 16S rRNA sequences. A total of 14 rhizobial species were characterized based, of which six were Rhizobium (AIS3, AIS9, AIR14, LUMCR3, LUMVRW4, LUMVRW8), four belongs to Burkholderia (AIS12, MOLKCS15, CHMP9, CHMP10) and one each of genera Cupriavidus (LUMMD12), Herbaspirillum (LUMVRW4), Paraburkholderia (CHMP1) and Ralstonia (LUMDes9). Stress tolerance analysis found most of the strains are to be tolerant to alkaline pH (9–11) where highest tolerance exhibited by Rhizobium sp. (strain AIS9) and Burkholderia territorii (strain MOKCS15). Seven Rhizobial strains were able to thrive at lower temperature stress (10 and 20 °C); while, strains AIS9, CHMP1 and LUMMD21 were able to grow at higher temperature (40 and 50 °C). Most of the isolate could tolerate salinity stress up to 1.5 %; but, only isolates AIS9, AIS12 and LUMMD12 could tolerate 2 and 2.5 % salt concentrations. The PGPT analyses found LUMCR3 having the highest IAA production potentiality (102.5 µg/ml); while, isolate MOKCS15 exhibited highest phosphate solubilizing activity (4.1 Phosphate Solubilization Index). The RNB isolates in the present study exhibited both stress tolerance and PGP traits indicating their potential use as biofertilizer under extreme agronomic conditions to improve productivity.

Synthesis of nanoparticles using Trichoderma Harzianum, characterization, antifungal activity and impact on Plant Growth promoting Bacteria.

Globally cultivated cereals are frequently threatened by various plant pathogenic agents such as Fusarium fungi. To combat these pathogens, researchers have made nanoparticles as potential agricultural pesticides. In this study, selenium and titanium dioxide NPs were synthesized using Trichoderma harzianum metabolites. Characterization of the NPs indicated varying size and shapes of both NPs and functional groups existence to constitute both NPs. The evaluation of antifungal activity of NPs against plant pathogenic fungi, Fusarium culmorum, indicated both NPs maximum antifungal activity at concentration of 100mg/L. The impacts of nanoparticles on some beneficial plant growth promoting bacteria (PGPB) were evaluated and showed their inhibition effect on optical density of PGPB at a concentration of 100mg/L but they did not have any impact on nitrogen fixation by bacteria. Existence of TiO2NPs reduced the intensity of color change to pink compared to the control indicating auxin production. Both NPs demonstrated different impact on phosphate solubilization index. This study suggests that the synthesized nanoparticles have the potential to serve as antifungal compounds at special concentration against plant diseases without significantly reducing the potential of PGPB at low concentrations.

Identification of Plant Growth-Promoting Rhizobacteria for the Development of Probiotic Consortia


 Soil infertility is one of the major challenges in agriculture. Although chemical fertilizers provide promising solution for crop growth in infertile soil, excessive application cause negative impacts on the natural systems such as soil and water. Moreover, these fertilizers can be converted into insoluble forms soon after application which often result in increasing the application frequency and the quantity. Hence, for decades plant growth-promoting rhizobacteria (PGPR) have been considered as an environmentally friendly alternative for chemical fertilizers. In this context, the present study was focused on the identification of candidate PGPRs for the development of probiotic packages for chilli (Capsicum annuum L.) which is one of the most widely grown and highly demanding vegetable crops in Sri Lanka. Rhizobacteria were isolated from the roots of healthy, young chilli plants grown in Angunakolapelessa, Sri Lanka and their rhizosphere soil. In total, 75 morphologically distinct strains were isolated, and they were inoculated into different nutrient media to screen their ability to solubilize insoluble mineral nutrient sources. Those media were National-Botanical-Research-Institute's phosphate agar [NBRIP-agar] with Ca3(PO4)2 as the P source, modified-Aleksandrov-agar containing mica as the K source and zinc-solubilizing-agar containing ZnCO3 as the Zn source. Further, bacteria were screened for N fixation in the nitrogen- fixing-bacteria (NfB) medium. Sixteen P-solubilizing-bacteria (PSB), 4 K-solubilizing-bacteria (KSB), 15 Zn-solubilizing-bacteria (ZnSB) and 10 N-fixing strains were identified. We noticed that all KSB strains also have the capacity to solubilize Ca3(PO4)2. All PSB strains, except CSTM10, can solubilize ZnCO3. The phosphate solubilizing index (PSI) was calculated to rank the P-solubilizing efficiency (PSE) of PSB. The highest PSI was found in CSTM40 and CSTM6. We further screened all mineral-solubilizing strains for the indole-3-acidic acid (IAA) production which is a PGP hormone. Cultures were induced for IAA production by supplementing the medium with 0.2% (w/v) tryptophan and IAA concentration was determined using the Salkowski's method. Nine strains were capable of producing IAA. The CSTM6 and CSTM21 showed the highest IAA production of
 181.94 and 178.59 mg/L respectively. In conclusion, bacterial strains, CSTM6, CSTM14, CSTM21, CSTM24, CSTM40, CMTM1, CMTM2 and CSTM10 showed multiple PGP characteristics and they were selected as candidates for the developing probiotic consortia. They can be viewed as promising strains in sustainable agriculture since they perhaps can enhance the availability of mineral nutrients in soil and promote plant growth.
 
 Keywords: Biofertilizer, Capsicum annuum, Plant growth-promoting rhizobacteria
 
 Financial assistance from Indo-Sri Lanka Joint Research Programme 2019 funded by the State Ministry of Skill Development, Vocational Education, Research and Innovation, Sri Lanka is acknowledged.

PRODUCTION OF ORGANIC ACID AND SOLUBILIZATION OF INORGANIC PHOSPHATE BY A BACTERIUM ISOLATED FROM CONTAMINATED SOIL

Many agricultural soils have significant phosphorus (P) reserves, much of which builds up because of frequent P fertilizer applications. However, roughly 95 to 99% of soil phosphorus is found as insoluble phosphates and is therefore unavailable for plant uptake. The current investigation characterized a bacterial strain that was obtained from contaminated soil and showed the ability to solubilize insoluble inorganic phosphates. An efficient phosphate-solubilizing bacterium was isolated in polluted soil in Mumbai. The phosphate solubilization index of this isolate was assessed using tribasic calcium phosphate-supplemented Pikovskaya’s (PVK) medium. After growing under constant agitation for seven days, the medium pH decreased from 7.0 to 3.5 units. Based on the colony morphology, microscopic analysis, and MALDI-TOF sequencing, the bacterial isolate was identified as Klebsiella pneumoniae. Phosphate solubilization was linked to a pH drop caused by bacterial growth in a medium with glucose as a carbon source. The secretion of organic acids by these phosphate-solubilizing bacteria is responsible for their ability to solubilize inorganic phosphate. GC-MS analysis revealed the presence of carbamic acid, dodecanoic acid, tetra decanoic acid, and trifluoroacetic acid in the culture supernatant. The amount of phosphate solubilized by the bacterium was determined by phosphomolybdate assay and was found to be 667.0 ug/ml which was much higher than the control bacterium S. aureus which was 131.0 ug/ml. To the best of our knowledge, this is the first report mentioning the isolation of phosphate solubilizing bacterium from polluted soil in Mumbai.

Exploration and Characterization of High-Efficiency Phosphate-Solubilizing Bacteria Isolates from Chickpea Rhizospheric Soil

The study was conducted during April, 2021 to June, 2022 to study the isolation and identification of high effective strains of phosphate solubilizing bacteria and evaluation the ability to solubilize tricalcium phosphate in vitro. Microorganisms that live in soil are actively involved in the carbon, nitrogen, sulphur, and phosphorus cycles in nature, enabling them to maintain ecological balance. Phosphate-solubilizing microbes are used as agricultural biofertilizers and play an essential role in plant nutrition by enhancing phosphate uptake. Phosphate is one of the most important macronutrients necessary for the growth and development of plants. Numerous microorganisms present in the rhizosphere solubilize insoluble phosphorus, making it readily available to plants. Fourteen phosphate-solubilizing bacterial colonies were identified on Pikovskaya’s agar medium, containing insoluble tricalcium phosphate (TCP) from rhizospheric soil. Among them, eight colonies showing clear halo zones around the microbial growth were considered as phosphate-solubilizing. All isolates showing the highest phosphate solubilization index (PSI), ranging from 2.8 to 4.03, were selected for further qualitative and quantitative studies. Out of these eight potent isolates, two strains showed the maximum PSI: V7 (4.03) and V8 (3.85) in agar plates, along with a high production of soluble phosphate, measuring 448.03 and 441.43 mg l-1, and a greater reduction in pH in the broth culture. The morphological, biochemical, and molecular identification of V7 and V8 strains revealed them to belong the Acinetobacter and Paenibacillus genera, respectively, and were phylogenetically close to Acinetobacter baumannii and Paenibacillus lautus species.

Isolation and Characterization of Phosphate Solubilizing Bacteria from Upland Rice Cultivation Areas in Bangka Regency

The availability of phosphorus (P) in ultisol acid soils presents a significant challenge due to its attachment to aluminum (Al) or iron (Fe) compounds. A potential solution to address this issue is the utilization of phosphate solubilizing bacteria (PSB). Therefore, this study aimed to analyze the potential of PSB originating from upland rice cultivation on ultisol soils. The bacterial isolates were obtained from soil samples taken from the rhizosphere area and root tissue of upland rice plants cultivated in Payabenua and Saing Villages, Bangka Regency. The pathogenicity testing encompassed hypersensitivity and hemolysis tests, while the P solubilization included the evaluation of the phosphate solubilizing index (PSI) and P dissolution. Subsequently, the selected isolates were subjected to phosphatase enzyme and organic acid content assessment. The results showed a total of 120 isolates, predominantly distributed in the Payabenua area and primarily consisting of endophytic bacteria. Among the six selected isolates, genus Burkholderia dominated four isolates, while the remaining isolates belonged to genus Serratia. Furthermore, in Burkholderia vietnamiensis, the solubility value of P in AlPO4 and Ca3(PO4)2 liquid media exhibited a range of 0.0013 to 0.0344% and 0.0008 to 0.1842%, respectively.

Selection of multi-purpose native rhizobia from a new red clover cultivar developed in Brazil

Red clover is an important forage legume in the livestock sector in southern Brazil, but regional climatic conditions compromise its management. Therefore, UFRGS and EMBRAPA have developed the cultivar URS BRS Mesclador adapted to the southern region of Brazil, but efficient rhizobia for it is still missing. This study aimed to select symbiotic rhizobia for the URS BRS Mesclador and evaluate their efficiency in biological nitrogen fixation in red clover and growth promotion in the rye. Seven rhizobia isolates from red clover nodules of the new cultivar and nine strains from the SEMIA Rhizobia Culture Collection were evaluated for their ability to promote plant growth. Certain strains exhibited notable abilities among the studied rhizobia, such as Rhizobium changzhiense Tp46 producing indole compounds (5.33 μg ml−1), Semia 2076 with a phosphate solubilization index of 2.4, and R. leguminosarum Tp57 and Tp34, SEMIA 2038, and SEMIA 276 with high siderophore production index. Isolates Tp46 and Tp34 demonstrated potential by displaying high biological nitrogen fixation efficiency in red clover and promoting rye growth. These promising results warrant further investigation for field studies with a long-term goal of developing inoculants for red clover cultivation in Brazil.

Eksplorasi Potensi Bacillus spp. sebagai Bakteri Pemacu Pertumbuhan Tanaman di Hutan Primer Resort Kembang Kuning

Kembang Kuning resort is one of the Mount Rinjani National Park Resorts that have high biodiversity, so it has the potential for plant growth-promoting bacteria. Bacillus sp. is one species of bacteria that has great potential as a plant growth-promoting bacteria. The purpose of this study was to isolate and determine the ability of phosphate solubilization, nitrogen-fixing and anti-fungal activity of Bacillus spp. isolated from the Primary Forest of Kembang Kuning Resort, Gunung Rinjani National Park. This research is an exploratory study consisting of the isolation of Bacillus sp., phosphate solubilization test with spot inoculation method on Pikovskaya Agar media, qualitative nitrogen fixing test using Jensen's Nitrogen - Free media, and anti-fungal activity test against Fusarium sp. with dual culture method. There were 21 isolates of the genus Bacillus successfully isolated in this study. The phosphate solubilization test showed that 16 bacterial isolates could solubilize phosphate, where the highest phosphate solubilization index was produced by isolate P3.1 namely 0,52. A total of one isolate, namely isolate P3.1, can fix nitrogen on Jensen's Nitrogen-Free medium. In the anti-fungal test against Fusarium sp., three bacterial isolates were obtained that were able to inhibit the growth of Fusarium sp., where the highest antagonism was produced by isolate P2.8 which was 46,66%. Bacillus spp. isolated from Kembang Kuning Resort has potential as PGPB in terms of crop protection.

Fungal endophytic species Fusariumannulatum and Fusariumsolani: identification, molecular characterization, and study of plant growth promotion properties

Research on endophytic fungi has gained significant interest due to their potential to enhance plant growth directly by producingphytohormones, solubilizing macronutrients, fixing nitrogen, or indirectly inhibiting phytopathogens growth by producing ammonia, siderophore, hydrogen cyanide, or extracellular enzymes, thereby acting as biocontrol agents. The present study aimed to isolate fungal endophytes from Alternantheraphiloxeroidesand evaluate their plant growth promotion and antimicrobial activity. In total, nine fungal endophytic strains were isolated from different parts of A. philoxeroides such as leaves, roots, and stems. The results demonstrate that the strains MEFAphS1 and MEFAphR3 exhibited positive plant growth promotion properties,including phosphate solubilization, and IAA (Indoleacetic acid) production, and ammonia production. The IAA production was highest for MEFAphS1, with a concentration of 46.635±1.04 µg/mL, while MEFAphR3 displayed the highest ammonia production (0.903±0.01 µg/mL). The phosphate solubilization index (PSI) is the maximum for MEFAphS1 (1.5±0.10). MEFAphS1 also exhibited antibacterial activity against Vibrio vulnificus, Streptococcus pneumoniae, and V.parahaemolyticus,with the most substantial inhibition zone observed against V.vulnificus(28±1 mm). In contrast, MEFAphR3 showed an inhibition zone of 8±1.53 mm against V. parahaemolyticus. Molecular identification revealed the identity of the isolates MEFAphS1 and MEFAphR3 as Fusariumsolaniand F.annulatum. These results thus confirm the possible applications of the fungal endophytes as plant biofertilizers and bio-enhancers to increase crop productivity.

Unraveling the new member Bacillus pumilus SH-9 of Bacillaceae family and its potential role in seed biopriming to mitigate drought stress in Oryza sativa

Rice is an important cereal crop cultivated worldwide to meet the need of hungry populations. Drought stress is a major problem that reduces crop productivity by up to 50 %. Beneficial microbes have the potential to mitigate drought stress in various crops. The use of beneficial microorganisms in seed biopriming techniques enhances germination potential through the production of antioxidants and phytohormones. In this study, the novel bacterial strain SH-9 was isolated and screened for various biological and stress tolerance assays. SH-9 exhibited plant growth-promoting characteristics such as abscisic acid production (2.18 ± 0.05 ng/ml), phosphate solubilization index (4.69 ± 0.30), and sucrose production (0.72 ± 0.05 mg/ml). The oxidative stress tolerance assay also revealed remarkable production of the antioxidant molecules catalase, superoxide dismutase, and ascorbate peroxidase. Germination metrics were also measured through seed biopriming in the experimental plant (Oryza sativa) treated with SH-9. Surprisingly, SH-9 was found to be significantly drought-tolerant as it could tolerate drought up to 35 % PEG 6000. Seed biopriming enhanced the germination potential by up to 90 % and improved the seed vigor index, germination energy, and germination rate index. It also improved the seedling characteristics of rice compared with the control group. This study demonstrated that SH-9 has excellent potential to enhance the germination metrics even under stress. Molecular identification revealed that SH-9 is a new member of the Bacillaceae family with the gene accession number ON753949. Overall, it is expected that further research on seed biopriming employing SH-9 strain in plants will lead to this technique being employed as a form of sustainable management in agriculture.

Enterobacter sp. DBA51 produces ACC deaminase and promotes the growth of tomato (Solanum lycopersicum L.) and tobacco (Nicotiana tabacum L.) plants under greenhouse condition

Bacterial isolated from rhizospheric soil associated with the semi-desertic plant Coronilla juncea L. were screened for 1-aminocyclopropane-1-carboxylate deaminase (ACCD) activity, a common trait for plant-growth-promoting rhizobacteria (PGPR). Among bacterial isolates, strain DBA51 showed phosphate solubilizing index (PSI), producing indole acetic acid (IAA), and with the hemolysis-negative test. Sequencing and analysis of the 16S rDNA gene identified DBA51 as Enterobacter. DBA51 did not show antagonistic activity in vitro against bacterial (Clavibacter michiganensis, Pseudomonas syringae pv. tomato DC3000 and Pectobacterium cacticidum FHLGJ22) and fungal phytopathogens (Alternaria sp., Fusarium oxysporum fsp. lycopersici, Fusarium oxysporum fsp. cubense M5, and Rhizoctonia sp.). Root inoculations with DBA51 in tomato (Solanum lycopersicum L.) and tobacco (Nicotiana tabacum L.) plants were performed under greenhouse conditions. Plant height (20 %) and root biomass (40 %) were significantly enhanced in tomato plants inoculated with DBA51 compared to non-inoculated plants, although for tobacco plants, only root biomass (27 %) showed significant differences with DBA51. In addition, physiological parameters such as photosynthetic rate (µmol CO2 m−2 s-1), stomatal conductance (mol H2O m−2 s−1), and transpiration rate (mmol H2O m−2 s−1) were also evaluated, and no differences were detected between DBA51-inoculated and control treatment in tomato and tobacco leaves. The observed results indicate that the DBA51 strain could be used as a biofertilizer to improve yields of horticultural crops.

Isolation And Characterization Of Phosphate Solving Bacteria From Swamp Soil With High Levels Of Acidity

Phosphate solubilizing bacteria (PSB) are one of the microbes that play an important role in soil and plant cycles. Phosphate (P) is a very important macronutrient for plants. In soil, most of the P element is found to be unavailable to plants because it is fixed by Ca, Al or Fe. This research aims to identify BPF in acid soil which has the potential to dissolve phosphate elements. The method used in this research is the isolation of BPF from acid soil using the National Botanical Research Institute's Phosphate (NBRIP) medium, phosphate dissolution index test and UV Visual. Soils from overflow type C (TLC) swamps have higher diversity compared to TLB soils. The abundance of BPF in TLC soil was higher (5,4 107 CFU per gram) compared to soil from overflow zone B (TLB) (2,9 107 CFU per gram) because TLC soil had a lower acidity level than TLB. There were 55 BPF isolates obtained from these two types of soil. Two isolates (TLB1 and TLB2) had a better phosphate solubilization index and all potential isolates that were extracted and subjected to gDNA amplification showed a DNA band at 1330-1500 bp.

Mineral Solubilizing Rhizobacterial Strains Mediated Biostimulation of Rhodes Grass Seedlings.

Minerals play a dynamic role in plant growth and development. However, most of these mineral nutrients are unavailable to plants due to their presence in fixed forms, which causes significant losses in crop production. An effective strategy to overcome this challenge is using mineral solubilizing bacteria, which can convert insoluble forms of minerals into soluble ones that plants can quickly assimilate, thus enhancing their availability in nutrient-depleted soils. The main objective of the present study was to isolate and characterize mineral solubilizing rhizobacteria and to assess their plant growth-promoting potential for Rhodes grass. Twenty-five rhizobacterial strains were isolated on a nutrient agar medium. They were characterized for solubilization of insoluble minerals (phosphate, potassium, zinc, and manganese), indole acetic acid production, enzymatic activities, and various morphological traits. The selected strains were also evaluated for their potential to promote the growth of Rhodes grass seedlings. Among tested strains, eight strains demonstrated strong qualitative and quantitative solubilization of insoluble phosphate. Strain MS2 reported the highest phosphate solubilization index, phosphate solubilization efficiency, available phosphorus concentration, and reduction in medium pH. Among tested strains, 75% were positive for zinc and manganese solubilization, and 37.5% were positive for potassium solubilization. Strain MS2 demonstrated the highest quantitative manganese solubilization, while strains MS7 and SM4 reported the highest solubilization of zinc and potassium through acidifying their respective media. The strain SM4 demonstrated the most increased IAA production in the presence and absence of L-tryptophan. The majority of strains were positive for various enzymes, including urease, catalase protease, and amylase activities. However, these strains were negative for coagulase activity except strains SM7 and MS7. Based on 16S rRNA gene sequencing, six strains, namely, SM2, SM4, SM5, MS1, MS2, and MS4, were identified as Bacillus cereus, while strains SM7 and MS7 were identified as Staphylococcus saprophyticus and Staphylococcus haemolyticus. These strains significantly improved growth attributes of Rhodes grass, such as root length, shoot length, and root and shoot fresh and dry biomasses compared to the uninoculated control group. The present study highlights the significance of mineral solubilizing and enzyme-producing rhizobacterial strains as potential bioinoculants to enhance Rhodes grass growth under mineral-deficient conditions sustainably.