Siderophore-producing Bacteria Research Articles

Effects of disinfection efficiency on microbial communities and corrosion processes in drinking water distribution systems simulated with actual running conditions

The effects of disinfection efficiency on microbial communities and the corrosion of cast iron pipes in drinking water distribution systems (DWDSs) were studied. Two annular reactors (ARs) that simulated actual running conditions with UV/Cl2 disinfection and chlorination alone were used. High chlorine consumption and corrosion rate were found in the AR with UV/Cl2. According to functional genes and pyrosequencing tests, a high percentage of iron recycling bacteria was detected within the biofilm of the AR with Cl2 at early running stage, whereas siderophore-producing bacteria were dominant in the biofilm of the AR with UV/Cl2. At the early running stage, the sequential use of UV light and an initial high chlorine dosage suppressed the biomass and iron-recycling bacteria in both bulk water and biofilms, thereby forming less protective scales against further corrosion, which enhanced chlorine consumption. Non-metric multidimensional scaling analysis showed that the bacterial communities in the ARs shaped from within rather than being imported by influents. These results indicate that the initial high disinfection efficiency within the distribution system had not contributed to the accumulation of iron-recycling bacteria at the early running stages. This study offer certain implications for controlling corrosion and water quality in DWDSs.

Characterization of sponge-associated actinobacteria with potential to promote plant growth on tidal swamps

Tidal swamps have become one of the highlighted topics in agricultural land development. Rice productivity in a tidal swamp is still low due to the high concentration of Fe, Al, and low pH. Siderophore-producing bacteria were known to alleviate the toxicity of heavy metals for plants. However, the potential of sponge-associated actinobacteria has been rarely reported in siderophore production. This work aimed to characterize the sponge-associated actinobacteria based on their tidal swamps characters and their potency to produce plant growth promoter on stressful tidal swamp imposed characters. The in vitro assay showed that, at the presence of Fe and Al, Car21t isolate produced a dry weight of mycelium reaching up to 289 mg and 204 mg in Yeast Malt Extract medium, respectively. Interestingly, all isolates were able to grow in relatively high salinity condition (7%). Indeed, under stress condition, inoculum of five actinobacteria isolates could produce Indole Acetic Acid and siderophore. These experimental results suggested that all potential isolates provided beneficial effects on the host plant, as evidenced by the rise of root length (9.86%), shoot length (9.44%), and root number (13.93%). Subsequently, our experimental data also indicated that these potential isolates belonged to the genus Streptomyces.

SIDO-CHAR SEBAGAI PEMBENAH KERACUNAN Fe PADA TANAH SAWAH

Solok Regency is known as a food production centre of the community of West Sumatra and has extensive volcanic paddy fields. Paddy fields have problems of one that is the toxicity of Fe at the time of the decrease in pH, thereby resulting in low available P (Phosphate) and can decrease the production of rice. This research aimed to get the right combination of siderophore-producing bacteria by growing rice husk bio-char media in overcoming toxicity of iron (Fe) in the land of paddy fields in Solok Regency, and to get a pure siderophore bacterial isolate without the use of the media biochar in overcoming toxicity of Fe on paddy fields. The results of this research showed that the addition of the siderophore bacteria by using rice husk biochar could reduce the toxicity of Fe as well as improving soil available P content of paddy field. The best combination was obtained for 10 ml of siderophore bacterial isolate and 25 g of rice husk biochar.

Exploring the links between bacterial communities and magnetic susceptibility in bulk soil and rhizosphere of beech (Fagus sylvatica L.)

Soil magnetic properties are sensitive indicators of pedogenetic processes. Although many of the processes that increase soil magnetism are well documented, the role of microbial communities and the metabolic characteristics of Fe-reducing bacteria are still largely unknown. For this work, two soils with contrasting magnetic properties were identified in a beech forest on Monte Zuccarello (central Italy). Samples of bulk soil and rhizosphere were obtained from A (0–7 cm), AB (7–16 cm), Bw1 (16–22 cm) and Bw2 (22–29 cm) horizons of both soils, and were analysed for their physicochemical characteristics, the amount of magnetic minerals, and the composition of total and culturable bacterial communities, focusing on siderophore-producing bacteria (SPB). Analyses confirmed that the magnetic soil (MS) have a higher content of maghemite and magnetite association, compared to non-magnetic soil (NMS). Since the formation of maghemite can occur through different processes, we investigated on the possible role of soil bacteria in the formation of this magnetic mineral. As soil maghemite generally contains small amounts of Fe2+, the formation of which has been attributed to the combustion of organic matter, SPB have been isolated and identified. MS samples showed the highest number of SPB (mainly Micrococcaceae, Bacillaceae, and Pseudomonadaceae), suggesting a significant increase in Fe-reducing bacteria. High-throughput sequencing analysis revealed a separation in terms of the total composition of the bacterial community between bulk and rhizosphere of both MS and NMS, dominated by Proteobacteria, Actinobacteria, Acidobacteria, and Verrucomicrobia phyla. Interestingly, Gamma and Delta Proteobacteria, as well as Nitrospirae, were usually more abundant in MS than in NMS, confirming that the MS was predominantly characterized by groups of magnetotactic bacteria and SPB, and potentially contributing to enhance the soil magnetic properties.

Isolation of a novel Co2+-resistant bacterium and the application of its siderophore in Co2+ recovery from an aqueous solution.

Siderophores are considered to have a good potential as decontamination agents owing to their metal-chelating abilities. In order to confirm whether siderophores can be used in the recovery of metal ions, a siderophore (or metallophore) exhibiting Co2+-chelating activity was screened to demonstrate its ability to recover Co2+ from an aqueous solution. A siderophore-producing bacterium, Pandoraea sp. HCo-4B, was identified from a screen of Co2+-resistant bacteria grown in an aerobic enrichment culture with a Co2+-supplemented medium. After incubation of the crude extracted siderophore in a Co2+-containing solution, the Co2+-siderophore complex was adsorbed on to a C18 column. The bound Co2+ was eluted from the column by the addition of 10 mM H2SO4. The recovered amount of Co2+ was proportional to the amount of the added siderophore. We observed that the siderophore identified in this study binds to Co2+ at a 1:1 ratio.

Co-cultivation of siderophore-producing bacteria Idiomarina loihiensis RS14 with Chlorella variabilis ATCC 12198, evaluation of micro-algal growth, lipid, and protein content under iron starvation

Co-cultivation systems offer the potential to commercialize microalgae biomass. The key purpose of the study was to understand the relationship between siderophore-producing bacterium Idiomarina loihiensis RS14 and Chlorella variabilis ATCC 12198 strain for Chlorella growth enhancement. After observing growth enhancement in C. variabilis by adding metal chelator deferroxamine mesylate (siderophore standard) and purified siderophore from I. loihiensis (1 mg mL−1), a co-cultivation system was designed where axenic microalgae and co-cultured (microalgae + bacteria) aliquots were grown in (1:9, 9:1, 1:1) volumetric inoculum ratio (mL) under iron-sufficient and iron-deficient conditions. The co-culture volumetric ratio 1:1 (microalgae/bacteria) showed bleaching of microalgae and 1:9 showed less biomass (310 mg L−1) comparatively with 9:1 that increased 35% of biomass, i.e., 650 mg L−1 (axenic) to 1000 mg L−1 (co-cultured) in iron-deficient media. The inoculum ratios were optimized in 100 mL shake flask and 9:1 ratio was further scaled up with the similar conditions, and the co-culture showed 20% increase in biomass, i.e., 285.6 mg L−1 (axenic) to 356 mg L−1 (co-cultured). The co-cultured biomass contains 19.70% lipid content compared with axenic algae, i.e., 18.41% which shows 7% of increase in co-culture. Protein content increased to 30% in co-culture microalgae compared with axenic microalgae. Scanning electron microscope images show crumpled surface of Chlorella cells in co-cultured compared with its axenic cells. This finding is of interest for biofuel production from microalgae, often attained through nutrient-starvation processes leading to oil accumulation.

The potential contribution of siderophore producing bacteria on growth and Fe ion concentration of sunflower (Helianthus annuus L.) under water stress

ABSTRACTIn the present study, 100 bacterial strains were isolated from the soil and tested for siderophore producing ability. Among siderophore producing bacteria, three superior isolates with the highest level of siderophore (F13, F58 and F66) selected for further study. Production of lecithinase, arginine dehydrolase, catalase, oxidase, hydrogen cyanide, indole acetic acid, solubilization of phosphate, gelatin hydrolysis, oxidative/fermentative, motility and gram staining by these strains was evaluated. In greenhouse experiment, the ability of selected isolates in solubilizing insoluble iron-containing compounds was examined at three moisture levels (0.45–0.6, 0.6–0.7 and 0.7–0.85 field capacity). Results showed that isolates F13 and F66 have greatest effects on chlorophyll amount and shoot dry weight compared to isolate F58. On average, iron concentration of sunflower in the presence of bacteria was 2.85-fold more than control, while it was 1.88-fold for roots. In addition, bacterial treatments enhanced resistance to water stress in sunflower. Based on biochemical tests and by comparison of 16S rRNA sequences, the F13, F58 and F66 isolates were closely related to Pseudomonas spp., Enterobacter spp. and Bacillus Sporothernodurans, respectively.

Isolation and Characterization of Rumex acetosa-Associated Mineral-Weathering Bacteria

ABSTRACTA total of 121 bacterial strains were isolated from the rhizosphere soils, root and stem interiors of Rumex acetosa to characterize the microenvironment-related changes in the mineral-weathering effectiveness, weathering mechanisms and populations of the bacteria. Among the 121 bacterial strains, 118 bacterial strains were found to weather biotite. The relative abundance of the highly effective mineral-weathering bacteria was different among the rhizosphere soils, root and stem interiors. Notably, the highest and lowest relative abundances of the highly effective mineral-weathering bacteria were observed in the stem and root interiors, respectively. Furthermore, the relative abundance of the highly acid-producing bacteria was significantly higher in the rhizosphere soils and stem interiors, while the highest and lowest relative abundances of the highly siderophore-producing bacteria were found in the stem interiors and rhizosphere soils, respectively. The mineral-weathering bacteria from the rhizosphere soils, root and stem interiors were affiliated with 11, 7 and 4 genera, respectively. In addition, 25–73% of the bacterial genera were specific to the plant-associated environments. The results showed diverse mineral-weathering bacteria in the plant-associated environments and microenvironment-related changes in weathering effectiveness and pattern and populations of the mineral-weathering bacteria. The results also suggested the different biotite-weathering mechanisms used by the bacteria among the plant-associated environments.

Metagenomic insights into the influence of salinity and cytostatic drugs on the composition and functional genes of microbial community in forward osmosis anaerobic membrane bioreactors

Wastewater treatment using forward osmosis anaerobic membrane bioreactors (FO-AnMBR) has a number of advantages over traditional wastewater treatment approaches. Previous studies have investigated the overall performance of lab-scale FO-AnMBR in treating synthetic wastewater. Due to enhanced physical rejection of osmosis membrane, salinity gradually increased and emerging contaminants such as cytostatic drugs in wastewater would also be accumulated during operation. The objective of this study was to investigate the influence of increased salinity and the accumulation of cytostatic drugs on the composition and function of the microbial community in FO-AnMBR through a metagenomics approach. We found that salinity increase in FO-AnMBR was the key factor driving compositional and functional transitions in microbial community. At high salinity condition, methane-producing archaea (MPA) became less competitive than sulphate-reducing bacteria (SRB), resulting in a reduced methane yield rate. The reduced methane production could be restored in the next successive cycle and salt-tolerant MPA was continuously enriched in the entire operation. Relative abundance of genes involved in nitrogen metabolism, cell attachment and biofilm related signalling increased from low salinity to high salinity condition, while those for methanogenesis and iron metabolism were found to decrease. The presence of cytostatic drugs caused the inhibition of microbial metabolism and increased extracellular polymeric substances (EPS) concentration. Due to their differential influences on community members, the evenness of community decreased after drug treatment. After the drug treatment, biofilm-forming and siderophore-producing bacteria were found to be more dominant in the microbial community.

Effects of two new siderophore-producing rhizobacteria on growth and iron content of maize and canola plants

ABSTRACTSiderophore-producing rhizobacteria beneficially affect plant growth by providing available iron to plants. In this study, bacteria were isolated from the rhizosphere of canola (Brassica napus L.) plants grown in the central fields in Iran, for the presence of siderophore-producing bacteria. A total of 45 distinct isolates were found to produce siderophore using qualitative chrome azurol sulfonate (CAS)-agar assay. Of them, ten isolates, based on the highest halo diameter/colony diameter ratios, were selected to quantify the rate of siderophore production using CAS-liquid assay. A variety of biochemical assays was used to determine the type(s) of siderophores produced by each of the ten isolates. The best isolates, based on production of the highest rates of either hydroxamates or carboxylates, were identified and used in further studies. Based on 16S ribosomal ribonucleic acid (rRNA) sequence analysis and a variety of phenotypic properties, the isolates were identified as Micrococcus yunnanensis YIM 65004 (T) and Stenotrophomonas chelatiphaga LPM-5 (T). We also studied the plant growth-promoting effect of the most promising isolates (YIM 65004 and LPM-5) on canola and maize plants under greenhouse conditions. The results of this study showed that M. yunnanensis and S. chelatiphaga increased gain weight and iron (Fe) content of roots and shoots significantly, in comparison with control, indicating beneficial effects of these rhizobacteria on plant growth and development. This study reports M. yunnanensis and S. chelatiphaga, as new records for Iran. The latter is reported for the first time from plant (canola) rhizosphere. Besides, the ability of both M. yunnanensis and S. chelatiphaga to produce siderophores is documented for the first time.

SELECTION AND CHARACTERIZATION OF SIDEROPHORE-PRODUCING RHIZOBACTERIA AND POTENTIAL ANTAGONISTIC ACTIVITY TOWARD Ralstonia solanacearum

Ralstonia solanacearum is an important disease of tomato. An alternative method to control the disease is the application of biocontrol agents. Plant Growth-Promoting Rhizobacteria (PGPR) could be used as potential biocontrol agents. PGPR with siderophores is among compounds having important role in disease suppression. This experiment was conducted to select and characterize the siderophore-producing rhizobacteria from tomato and to determine their potential as antagonistic agents for R. solanacearum. Candidates of the PGPR were isolated from tomato grown in West Java Province, Indonesia. The isolates were detected as siderophore-producing bacteria using CAS medium. Among 29 isolates producing siderophore and having negative result on hypersensitivity reaction, two isolates provided the widest diameter of inhibition zone toward R. solanacearum. Both isolates were CP1C and CP2D with diameter of inhibition zone up to 3.6 and 7.0 mm, respectively. Based on the sequence of 16S rDNA, isolate CP1C was identified as Brevundimonas sp., while isolate CP2D was identified as Enterobacter sp. Both bacteria did not cause negative effect on the increasing plant height and dry weight of the plants, compared with control.

Effect of heavy-metal on synthesis of siderophores by Pseudomonas aeruginosa ZGKD3

Most siderophore-producing bacteria could improve the plant growth. Here, the effect of heavy-metal on the growth, total siderophore and pyoverdine production of the Cd tolerance Pseudomonas aeruginosa ZGKD3 were investigated. The results showed that ZGKD3 exhibited tolerance to heavy metals, and the metal tolerance decreased in the order Mn2+>Pb2+>Ni2+>Cu2+>Zn2+>Cd2+. The total siderophore and pyoverdine production of ZGKD3 induced by metals of Cd2+, Cu2+, Zn2+, Ni2+, Pb2+ and Mn2+ were different, the total siderophore and pyoverdine production reduced in the order Cd2+>Pb2+>Mn2+>Ni2+>Zn2+ >Cu2+ and Zn2+>Cd2+>Mn2+>Pb2+>Ni2+>Cu2+, respectively. These results suggested that ZGKD3 could grow in heavy-metal contaminated soil and had the potential of improving phytoremediation efficiency in Cd and Zn contaminated soils.

SCREENING OF SOIL BACTERIA FOR PLANT GROWTH PROMOTION ACTIVITIES IN VITRO

Fourteen isolates of soil bacteria, including two known plant growth promoting rhizobacteria (PGPR) strains, Azotobacter vinelandii Mac 259 and Bacillus cereus UW 85, were tested in vitro. Parameters assessed were indoleacetic acid (IAA) production, phosphate solubilization, dinitrogen fixation, and siderophore (Fe-III chelating agent) production. IAA production was assayed colorimetrically using ferric chlorideperchloric acid reagent. Phosphate-solubilization and siderophore production were tested qualitatively by plating the bacteria in Pikovskaya and chrome azurol S agar, respectively. The ability to fix dinitrogen was measured based on nitrogenase activity of the bacteria by gas chromatography. The results showed that twelve isolates produced IAA, ranged from 2.09 to 33.28 µmol ml-1. The ability to solubilize precipitated phosphate was positively exhibited by four isolates (BS 58, BTS, TCaR 61, and BTCaRe 65). Seven isolates including Mac 259 positively produced siderophore. None of the isolates showed nitrogenase activity. Only one isolate (TS 3) did not exhibit any of the traits tested. Isolate TCeRe 60 and reference strain Mac 259 were found to have IAA- and siderophore-producing traits. Four P-solubilizing bacteria (BS 58, BTS, TCaR 61, and BTCaRe 65) were also IAA- and siderophore-producing bacteria. Potential use of these PGPR isolates needs further test in enhancing plant growth.

SCREENING OF SOIL BACTERIA FOR PLANT GROWTH PROMOTION ACTIVITIES IN VITRO

Fourteen isolates of soil bacteria, including two known plant growth promoting rhizobacteria (PGPR) strains, Azotobacter vinelandii Mac 259 and Bacillus cereus UW 85, were tested in vitro. Parameters assessed were indoleacetic acid (IAA) production, phosphate solubilization, dinitrogen fixation, and siderophore (Fe-III chelating agent) production. IAA production was assayed colorimetrically using ferric chlorideperchloric acid reagent. Phosphate-solubilization and siderophore production were tested qualitatively by plating the bacteria in Pikovskaya and chrome azurol S agar, respectively. The ability to fix dinitrogen was measured based on nitrogenase activity of the bacteria by gas chromatography. The results showed that twelve isolates produced IAA, ranged from 2.09 to 33.28 µmol ml-1. The ability to solubilize precipitated phosphate was positively exhibited by four isolates (BS 58, BTS, TCaR 61, and BTCaRe 65). Seven isolates including Mac 259 positively produced siderophore. None of the isolates showed nitrogenase activity. Only one isolate (TS 3) did not exhibit any of the traits tested. Isolate TCeRe 60 and reference strain Mac 259 were found to have IAA- and siderophore-producing traits. Four P-solubilizing bacteria (BS 58, BTS, TCaR 61, and BTCaRe 65) were also IAA- and siderophore-producing bacteria. Potential use of these PGPR isolates needs further test in enhancing plant growth.

Insect Gut Bacteria: A Novel Source for Siderophore Production

Insect gut microbial community is known to produce biotechnologically important products. Present study is focussed on isolation of bacteria and screening of siderophore producing strains of Sathrophyllia femorata collected from Western Ghats region near Pune, Maharashtra, India (19°20′N and 73°47′E). Total 207 bacteria were isolated from gut of 2 different specimens (DM and EM) of grasshopper belonging to S. femorata. Out of 207 bacterial isolates, 166 (79 %) isolates produced siderophore during their submerged growth in iron deficient succinic acid medium. Among these, 24 isolates produced copious amount of siderophore and hence selected for further study. Further analysis of these isolates showed absorption maxima either at 240 or at 250 nm depending on type of siderophore. Molecular identification of these siderophore producing bacteria based on 16S rRNA gene sequencing confirms their affiliation to 37 species representing 19 genera. Dominance of phylum Proteobacteria followed by Firmicutes was observed. Among 19 genera, gammaproteobacteria like Acinetobacter, Klebsiella and Pseudomonas showed abundance over other genera like Serratia, Stenotrophomonas and Yokenella. Some of these bacteria have been used in plant growth promotion and as biocontrol agents against insect pests of plants. Siderophore producing bacteria having insecticidal activity against the insect pests promoting plant growth can serve as green bioinoculants for sustainable agriculture.

Study the Effects of Siderophore-Producing Bacteria on Zinc and Phosphorous Nutrition of Canola and Maize Plants

ABSTRACTPlant growth-promoting rhizobacteria (PGPR) are soil bacteria that are able to colonize rhizosphere and to enhance plant growth by means of a wide variety of mechanisms. In the present study, Myristica yunnanensis and Stenotrophomonas chelatiphaga strains were recognized as new records in Iran flora. According to the results, these strains significantly affected plants’ zinc and phosphorous contents which could be due to the production of phytosiderophore. Siderophore-producing bacteria increased canola zinc (Zn) content as strategy-I plant, while in maize, it can be said that probably the effect of phytosiderophore produced by plant on increasing root and shoot Zn content was more than siderophore produced by bacteria. These isolates could be used as bio-input for improving the plant productivity as a substitute to chemical fertilizers and also to correct the nutrient deficiencies in canola and maize for sustainable agriculture.

Zinc treatment increases the titre of 'Candidatus Liberibacter asiaticus' in huanglongbing-affected citrus plants while affecting the bacterial microbiomes.

Huanglongbing (HLB)-affected citrus often display zinc deficiency symptoms. In this study, supplemental zinc was applied to citrus to determine its effect on Candidatus Liberibacter asiaticus (Las) titre, HLB symptoms, and leaf microbiome. HLB-affected citrus were treated with various amounts of zinc. The treatments promoted Las growth and affected microbiomes in citrus leaves. Phylochip(™) -based results indicated that 5475 of over 50000 known Operational Taxonomic Units (OTUs) in 52 phyla were detected in the midribs of HLB-affected citrus, of which Proteobacteria was the most abundant, followed by Firmicutes and Actinobacteria. In comparison, the microbiomes of zinc-treated diseased plants had overall more OTUs with higher amounts of Proteobacteria, but decreased percentages of Firmicutes and Actinobacteria. In addition, more OTUs of siderophore-producing bacteria were present. Only zinc-sensitive Staphylococcaceae had higher OTU's in the diseased plants without zinc treatments. Although HLB-affected citrus appear zinc deficient, zinc amendments increased the pathogen levels and shifted the microbiome. HLB is currently the most devastating disease of citrus worldwide. Zinc is often applied to HLB-affected citrus due to zinc deficiency symptoms. This study provided new insights into the potential effects of zinc on HLB and the microbial ecology of citrus.

Swarming motility is modulated by expression of the putative xenosiderophore transporter SppR-SppABCD in Pseudomonas aeruginosa PA14.

In the present study, we characterised the putative peptide ABC transporter SppABCD, which is co-transcribed with the TonB-dependent receptor SppR in Pseudomonas aeruginosa PA14. However, our data show that this transporter complex is not involved in the uptake of peptides. The fact that the TonB-dependent receptor SppR is regulated by an iron starvation ECF sigma factor suggested that this transporter is probably involved in the uptake of xenosiderophores. Therefore, we screened culture supernatants of 23 siderophore-producing bacteria for their ability to induce the expression of the SppR-regulating ECF sigma factor. However, none of them had an effect on the expression of this ECF sigma factor. Since the spp operon is not expressed under standard laboratory conditions, we overexpressed it from plasmids in PA14, which led to an impairment of its swarming motility on semisolid agar. Since we excluded the possibility that the uptake of a culture medium component was responsible for the observed phenotype, we hypothesize that the Spp transport system is involved in the uptake of a compound from the periplasmic space or a compound secreted by P. aeruginosa. Furthermore, we found that rhamnolipid synthesis was decreased while biofilm and exopolysaccharide synthesis was slightly increased upon overexpression of the spp operon. Moreover, we observed an impact of spp overexpression on regulation of genes involved in siderophore and phenazine biosynthesis.

Impact of Phanerochaete chrysosporium on the Functional Diversity of Bacterial Communities Associated with Decaying Wood.

Bacteria and fungi naturally coexist in various environments including forest ecosystems. While the role of saprotrophic basidiomycetes in wood decomposition is well established, the influence of these fungi on the functional diversity of the wood-associated bacterial communities has received much less attention. Based on a microcosm experiment, we tested the hypothesis that both the presence of the white-rot fungus Phanerochaete chrysosporium and the wood, as a growth substrate, impacted the functional diversity of these bacterial communities. Microcosms containing sterile sawdust were inoculated with a microbial inoculum extracted from a forest soil, in presence or in absence of P. chrysosporium and subsequently, three enrichment steps were performed. First, bacterial strains were isolated from different microcosms previously analyzed by 16S rRNA gene-based pyrosequencing. Strains isolated from P. chrysosporium mycosphere showed less antagonism against this fungus compared to the strains isolated from the initial forest soil inoculum, suggesting a selection by the fungus of less inhibitory bacterial communities. Moreover, the presence of the fungus in wood resulted in a selection of cellulolytic and xylanolytic bacterial strains, highlighting the role of mycospheric bacteria in wood decomposition. Additionally, the proportion of siderophore-producing bacteria increased along the enrichment steps, suggesting an important role of bacteria in iron mobilization in decaying-wood. Finally, taxonomic identification of 311 bacterial isolates revealed, at the family level, strong similarities with the high-throughput sequencing data as well as with other studies in terms of taxonomic composition of the wood-associated bacterial community, highlighting that the isolated strains are representative of the wood-associated bacterial communities.

Increased iron-stress resilience of maize through inoculation of siderophore-producing Arthrobacter globiformis from mine.

Iron deficiency is common among graminaceous crops. Ecologically successful wild grasses from iron-limiting habitats are likely to harbour bacteria which secrete efficient high-affinity iron-chelating molecules (siderophores) to solubilize and mobilize iron. Such siderophore-producing rhizobacteria may increase the iron-stress resilience of graminaceous crops. Considering this, 51 rhizobacterial isolates of Dichanthium annulatum from iron-limiting abandoned mine (∼84% biologically unavailable iron) were purified and tested for siderophore production; and efficacy of Arthrobacter globiformis inoculation to increase iron-stress resilience of maize and wheat was also evaluated. 16S rRNA sequence analyses demonstrated that siderophore-producing bacteria were taxonomically diverse (seven genera, nineteen species). Among these, Gram-positive Bacillus (eleven species) was prevalent (76.92%). A. globiformis, a commonly found rhizobacterium of graminaceous crops was investigated in detail. Its siderophore has high iron-chelation capacity (ICC: 13.0 ± 2.4 μM) and effectively dissolutes diverse iron-complexes (FeCl3 : 256.13 ± 26.56 μM/ml; Fe2 O3 red: 84.3 ± 4.74 μM/ml; mine spoil: 123.84 ± 4.38 μM/ml). Siderophore production (ICC) of A. globiformis BGDa404 also varied with supplementation of different iron complexes. In plant bioassay with iron-deficiency sensitive species maize, A. globiformis inoculation triggered stress-associated traits (peroxidase and proline) in roots, enhanced plant biomass, uptake of iron and phosphate, and protein and chlorophyll contents. However, in iron deficiency tolerant species wheat, growth improvement was marginal. The present study illustrates: (i) rhizosphere of D. annulatum colonizing abandoned mine as a "hotspot" of siderophore-producing bacteria; and (ii) potential of A. globiformis BGDa404 inoculation to increase iron-stress resilience in maize. A. globiformis BGDa404 has the potential to develop as bioinoculant to alleviate iron-stress in maize.