Screening and evaluation of PGPR strains having multiple PGP traits from hilly terrain

Plant growth-promoting rhizobacteria (PGPR) with multiple beneficial traits serve as potentially, ecofriendly,and cost-effective alternatives to chemical fertilizers and pesticides. They have both direct and indirectaffirmative impacts on overall plant growth and health. PGPRs are well known to directly improve the plantgrowth by phytohormone production and availability of minerals in soil. A total of nine soil samples were takenfrom near the rhizospheric zone of different crops and 56 rhizobacterial strains were isolated. Only 16 out of56 rhizobacterial strains were found positive for more than one beneficial trait that included solubilization ofphosphate, indole acetic acid (IAA), siderophore, ammonia and H2S production. Among all PGPR strains,RKM15 was observed having the highest phosphate solubilizing index (3.4), solubilized phosphorus (339mg L−1) and also siderophore unit (70.54 %). The maximum IAA production was observed by RKM25 strain(35.56 µg ml−1). The most promising RKM15 isolate was identified as Pantoea dispersa (MN629239) through16S rRNA gene sequencing technique. This characterized PGPR strain may be used for the development ofbiofertilizers to enhance crop productivity and improvement in soil fertility

Endophytic Bacillus strains enhance pearl millet growth and nutrient uptake under low-P

Abstract Bacterial endophytes are considered to have a beneficial effect on host plants, improving their growth by different mechanisms. The objective of this study was to investigate the capacity of four endophytic Bacillus strains to solubilize iron phosphate (Fe-P), produce siderophores and indole-acetic acid (IAA) in vitro, and to evaluate their plant growth promotion ability in greenhouse conditions by inoculation into pearl millet cultivated in a P-deficient soils without P fertilization, with Araxá rock phosphate or soluble triple superphosphate. All strains solubilized Fe-P and three of them produced carboxylate-type siderophores and high levels of IAA in the presence of tryptophan. Positive effect of inoculation of some of these strains on shoot and root dry weight and the N P K content of plants cultivated in soil with no P fertilization might result from the synergistic combination of multiple plant growth promoting (PGP) traits. Specifically, while B1923 enhanced shoot and root dry weight and root N P content of plants cultivated with no P added, B2084 and B2088 strains showed positive performance on biomass production and accumulation of N P K in the shoot, indicating that they have higher potential to be microbial biofertilizer candidates for commercial applications in the absence of fertilization.

Endophytic Bacillus strains enhance pearl millet growth and nutrient uptake under low-P

Abstract Bacterial endophytes are considered to have a beneficial effect on host plants, improving their growth by different mechanisms. The objective of this study was to investigate the capacity of four endophytic Bacillus strains to solubilize iron phosphate (Fe-P), produce siderophores and indole-acetic acid (IAA) in vitro, and to evaluate their plant growth promotion ability in greenhouse conditions by inoculation into pearl millet cultivated in a P-deficient soils without P fertilization, with Araxá rock phosphate or soluble triple superphosphate. All strains solubilized Fe-P and three of them produced carboxylate-type siderophores and high levels of IAA in the presence of tryptophan. Positive effect of inoculation of some of these strains on shoot and root dry weight and the N P K content of plants cultivated in soil with no P fertilization might result from the synergistic combination of multiple plant growth promoting (PGP) traits. Specifically, while B1923 enhanced shoot and root dry weight and root N P content of plants cultivated with no P added, B2084 and B2088 strains showed positive performance on biomass production and accumulation of N P K in the shoot, indicating that they have higher potential to be microbial biofertilizer candidates for commercial applications in the absence of fertilization.

Promotion of iron nutrition and growth on peanut by Paenibacillus illinoisensis and Bacillus sp. strains in calcareous soil

ABSTRACT This study aimed to explore the effects of two siderophore-producing bacterial strains on iron absorption and plant growth of peanut in calcareous soil. Two siderophore-producing bacterial strains, namely, YZ29 and DZ13, isolated from the rhizosphere soil of peanut, were identified as Paenibacillus illinoisensis and Bacillus sp., respectively. In potted experiments, YZ29 and DZ13 enhanced root activity, chlorophyll and active iron content in leaves, total nitrogen, phosphorus and potassium accumulation of plants and increased the quality of peanut kernels and plant biomass over control. In the field trial, the inoculated treatments performed better than the controls, and the pod yields of the three treatments inoculated with YZ29, DZ13, and YZ29 + DZ13 (1:1) increased by 37.05%, 13.80% and 13.57%, respectively, compared with the control. Based on terminal restriction fragment length polymorphism analysis, YZ29 and DZ13 improved the bacterial community richness and species diversity of soil surrounding the peanut roots. Therefore, YZ29 and DZ13 can be used as candidate bacterial strains to relieve chlorosis of peanut and promote peanut growth. The present study is the first to explore the effect of siderophores produced by P. illinoisensis on iron absorption.

Molecular Insights into Pathogenesis and Infection with Aspergillus Fumigatus

The virulence of fungi is dependent on multiple factors, including the immune status of patients and biological features of fungi. In particular, the virulence of Aspergillus fumigatus is due to the complex interaction among various molecules involved in thermotolerance (such as ribosomal biogenesis proteins, α-mannosyltransferase and heat shock proteins), pigment production (DHN-melanin), immune evasion (like melanin and hydrophobin) and nutrient uptake (such as siderophores and zinc transporters). Other molecules also play important roles in the virulence of A. fumigatus, including cell wall components and those which maintain its integrity (for instance β-1-3 glucan, α-1-3 glucan, chitin, galactomannan and mannoproteins) and adhesion (such as hydrophobins), as well as various hydrolytic enzymes (such as serine and aspartic protease, phospholipases, metalloproteinase and dipeptidyl peptidases). Signalling molecules (including G-protein, cAMP, Ras protein and calcineurin) also increase the virulence through altering the metabolic response to stress conditions and toxins (such as gliotoxin, fumitremorgins, fumagatin and helvolic acid).

Genes Involved in the Biosynthesis and Transport of Acinetobactin in Acinetobacter baumannii

Pathogenic bacteria survive in iron-limited host environments by using several iron acquisition mechanisms. Acinetobacter baumannii, causing serious infections in compromised patients, produces an iron-chelating molecule, called acinetobactin, which is composed of equimolar quantities of 2,3-dihydroxybenzoic acid (DHBA), L-threonine, and N-hydroxyhistamine, to compete with host cells for iron. Genes that are involved in the production and transport of acinetobactin are clustered within the genome of A. baumannii. A recent study showed that entA, located outside of the acinetobactin gene cluster, plays important roles in the biosynthesis of the acinetobactin precursor DHBA and in bacterial pathogenesis. Therefore, understanding the genes that are associated with the biosynthesis and transport of acinetobactin in the bacterial genome is required. This review is intended to provide a general overview of the genes in the genome of A. baumannii that are required for acinetobactin biosynthesis and transport.

The ferric aerobactin receptor IutA, a protein isolated on agarose column, is not essential for uropathogenic Escherichia coli infection / O receptor de aerobactina IutA, uma proteína isolada em coluna de agarose, não é essencial para a infecção por Escherichia coli uropatogênica / El receptor de aerobactina IutA, una proteína aislada en columna de agarosa, no es esencial para la infección por Escherichia coli uropatógena

Although many proteins have been described involved in Escherichia coli colonization and infection, only few reports have shown lectins as important components in these processes. Because the mechanisms underlying E. coli colonization process involving lectins are not fully understood, we sought to identify the presence of other non-described lectins in E. coli. Here, we isolated a 75-kDa protein from E. coli on Sepharose column and identified it as ferric aerobactin receptor (IutA). Since IutA is controversially associated with virulence of some E. coli strains, mainly in uropathogenic E. coli (UPEC), we evaluated the presence of iutA gene in UPEC isolated from patients with urinary infection. This gene was present in only 38% of the isolates, suggesting a weak association with virulence. Because there is a redundancy in the siderophore-mediated uptake systems, we suggest that IutA can be advantageous but not essential for UPEC.

Apenas alguns relatos na literatura demonstram que lectinas são importantes nos processos de colonização e infecção por Escherichia coli. A falta de compreensão clara dos mecanismos envolvendo lectinas, no processo de colonização por E. coli, motivou a realização deste estudo para se identificar a presença de outras lectinas não descritas em E. coli. Neste trabalho, isolou-se uma proteína de 75kDa de E. coli em coluna de Sepharose, correspondente ao receptor de aerobactina férrica (IutA). A associação de IutA com virulência de cepas de E. coli é controversa, principalmente em E. coli uropatogênica (UPEC), o que levou a se avaliar a presença do gene iutA em UPECs isoladas de pacientes com infecção urinária. O gene estava presente em 38% dos isolados, sugerindo fraca associação com virulência. Devido à existência de redundância nos sistemas de captura de ferro, sugere-se, aqui, que IutA possa ser vantajosa, mas não essencial para UPEC.

La falta de una clara comprensión de los mecanismos de participación de las lectinas en el proceso de colonización por Escherichia coli, nos motivó a identificar la presencia de otras lectinas que no han sido descritas en E. coli. En este estudio, se aisló una proteína de 75kDa de E. coli en una columna de Sepharosa, correspondiente al receptor de aerobactina (IutA). La asociación de IutA con cepas virulentas de E coli es controvertido, especialmente en E. coli uropatógena (UPEC), lo que nos llevó a evaluar la presencia del gen iutA en UPECs aisladas de pacientes con infección urinaria. El gen estaba presente en 38% de los aislamientos, lo que sugiere una débil asociación con la virulencia. Debido a la existencia de redundancia en los sistemas de captura de hierro, se sugiere que IutA puede ser una ventaja, sin embargo no es esencial para la UPEC.

Comparison between Pseudomonas aeruginosa siderophores and desferrioxamine for iron acquisition from ferritin

Background: Siderophore is an iron chelator produced by microorganism. Pseudomonas aeruginosa produces two siderophores (pyoverdin and pyochelin). Desferrioxamine is a siderophore used in thalassemia patients to treat an iron overload of vital organs. Objective: Compare the ability of pyoverdin, pyochelin, and desferrioxamine for iron mobilization from ferritin. Materials and Methods: In vitro experiment, the ability of P. aeruginosa siderophores and desferrioxamine for iron mobilization from ferritin was compared by using a dialysis membrane assay at pH values of 7.4 and 6.0. Stimulation of P. aeruginosa PAO1 growth by all siderophores was studied in glucose minimum medium. Results: All three compounds were capable of iron mobilization at both pHs. At pH 6.0, the most effectiveness compound was desferrioxamine (31.6%), followed by pyoverdin (21.5%) and pyochelin (13.7%) compared on weight basis, each at 10 μg/mL. At equimolar concentration, their activities were desferrioxamine (38.5±1.2%), followed by pyoverdin (32.0±4.8%) and pyochelin (26.7±1.9%), respectively. Conclusion: The most effective compound in iron mobilization from ferritin was desferrioxamine, followed by pyoverdin and pyochelin respectively.

Isolation of siderophore- producing strains of rhizobacterial fluorescent pseudomonads and their biocontrol against rice fungal pathogens.

Rice blast caused by Magnaporthe grisea and sheath blight caused by Rhizoctonia solani are the major diseases affecting the rice production. Application of beneficial bacteria as seed or seedling root dip to protect these diseases may be an alternative strategies to chemical control. In this study, fluorescent Pseudomonads isolated from rice seedlings were used to screen for their antagonistic ability and siderophore mediated antibiosis under in-vitro conditions against these pathogens. Among 10 isolates, strain P.f 003 gave significantly higher inhibition of mycelial growth of M. grisea and R. solani. Strains of P.f 001, P.f 003, P.f 005 and P.f 007 produced siderophores when grown on Fe deficient and Fe fortified King’s B medium. These strains again tested for their in-vitro antagonistic activity against M. grisea and R. solani on King’s B media with or without FeCl3. Our results showed that all these strains significantly reduced the growth of M. grisea and R. solani with FeCl3 in the media compared to without FeCl3. Strain P.f 003 activity was superior compared to other strains evaluated.

Growth and Siderophore Production of Staphylococci in Human Peritoneal Dialysate

Although activity of iron uptake system (IUS) was thought to play an important role in staphylococcal growth in human peritoneal dialysate (HPD) solution, siderophore production, one of the well-known IUS, was not yet detected directly in HPD solution. Therefore, we tried to detect siderophore production directly in HPD solution by using a newly developed chrome azurol S (CAS) agar diffusion assay and to investigate the effect of IUS activity on bacterial growth in HPD solution. According to the susceptibility test for streptonigrin and the productivity of siderophore in the iron-deficient (ID) medium, Staphylococcus aureus ATCC 6538 strain and Staphylococcus epidermidis clinical isolate had higher IUS activity and grew better than S. aureus ATCC 25923 strain in the ID medium. These bacteria did not grow and produce siderophore in the unused chronic ambulatory peritoneal dialysis solution. However, these bacteria grew and produced siderophore in the HPD solution. Moreover, S. aureus ATCC 25923 strain with lower activity of IUS grew poorly and produced smaller amount of siderophore in HPD compared to S. aureus ATCC 6538 strain and S. epidermidis clinical isolate with higher activity of IUS like in the ID medium. To the best of our knowledge, this is the first report that sidero-phore production is directly detected in the HPD by CAS agar diffusion assay. These results indicated that activity of IUS plays an important role in bacterial growth in the HPD solution and pathogenesis of continuous ambulatory peritoneal dialysis peritonitis.

Effect of Iron - Uptake Mechanisms of Staphylococcus Aureus on the Growth in Human Body Fluids / 감염

BACKGROUND: We could establish a streptonigrin-resistant strain called SR-1 strain from Staphylococcus aureus ATCC 6538 as a parental strain and characterize SR-1 strain as defective in the iron-uptake mechanisms including production of siderophores and expression of transferrin-binding protein on the cell wall. We performed this study to elucidate effect of the iron-uptake mechanisms on the growth in human body fluids. METHODS: Growth kinetics of SR-1 strain were compared with those of the parental strain and the increase of unsaturated iron-binding capacity (UIBC) was measured. Siderophore production and expression of transferrin-binding protein were detected by CAS diffusion assay and ligand-blot method probed with human transferrin conjugated horseradish peroxidase, respectively, as the strains were cultivated in normal pooled sera, ascitic fluid and pleural effusion. RESULTS: Siderophores activity in the body fluids could not be detected by the CAS diffusion assay. The parental strain expressed the transferrin-binding protein on the cell wall during the growth in ascites and pleural effusion except the sera whereas SR-1 strain did not. Growth kinetics showed that SR-1 strain grew sluggish compared to the parental strain. The peak of increase of UIBC of the parental strain was observed at the mid-exponential growth phase and the increase of UIBC of SR-1 strain was either lower than that of the parental strain or not changed. CONCLUSION: The iron-uptake mechanisms of S. aureus, especially expression of transferrin-binding protein, play a significant role in growing in the body fluids.

Improvement and Analysis in Over- siderophores Production Bacteria Filtrating and Detecting / 微生物学通报

A novel stable blue agar plate which is convenient to preparing and more effective than the universal chrome azurol sulfonate (CAS) assay established by Schwyn and Neilands was designed by replacing MM9 growth medium and pipes with certain concentrate of phosphorus buffer solution which pH could be stabled at 6.8. It is more suitable for screening over- siderophores production bacteria. Since OD_ 630 of the sample is usually out of the range of spectrophotometer with CAS assay solution when quantifying the siderophores and the outcome is not steady,the measuring wavelength had been changed to 680 nm corresponding to the middle of max absorbance and the correlation between siderophores concentrations and OD was unchanged. But the detecting sensitivity is elevated by enlarged the absorbance differences among samples with different productivity of siderophores at 680 nm .

Study on Effect Factor of the Production of Catechol-type Siderophores Secreted by a Strain of Soil Bacteria / 微生物学通报

Catechol-type siderophores secreted by a strain of soil bacteria in three different medium were assayed by two high-resolution TLC.The results showed different medium had a significant effect on the secretion of catechol-type siderophores,and in three different medium strain S1 produced different catechol-type siderophores.The effect of Al~(3+) on Catechol-type siderophores by S1 were also assayed.The results showed Al~(3+)had a significant stimulation on the secretion of catechol-type siderophores.Moreover,Al~(3+)could to some extent counteract the repression of Fe~(2+)on siderophores production.In KMB medium four catechol-type siderophores were identified and all ones except for 2,3-dihydroxybenzoic acid(2,3-DHBA) had high affinity for Al~(3+).

Detection of Siderophore from Halophilic Archaea with Two-layer Plate / 微生物学通报

A two-layer plate was developed for in situ detection of siderophore from halophilic archaea. Halophilic archaea could grow on the upper nutrient layer without addition of iron and excrete siderophore under iron-limited stress.The lower layer was the detection agar,which contained universal blue-coloured ferric-CAS complex.The presence of the siderophore was indicated by the decolorization of the blue complex, resulting in a yellow-orange halo around colonies growing on the upper nutrient layer,when the excreted siderophore penetrated from the upper nutrient layer into the lower detection agar.The results showed that the two-layer plate method was applicable to the detection of siderophore from halophilic archaea, which was more convenient and definite than former approach for halophilic archaea siderophore detection.