Iron Stress Conditions Research Articles

Investigating the Role of Known Arabidopsis Iron Genes in a Stress Resilient Soybean Line

Genes involved in iron deficiency responses have been well characterized in Arabidopsis thaliana, but their roles in crop species have not been well explored. Reliance on model species may fail to identify novel iron stress mechanisms present within crop species, likely selected by hundreds of years of selection. Fiskeby III (PI 438471) is a soybean line from Sweden that demonstrates high levels of resilience to numerous stresses. Earlier Fiskeby III studies have identified a suite of genes responding to iron deficiency stress in Fiskeby III that are also associated with Arabidopsis iron deficiency responses. We were interested in determining how canonical iron genes function in Fiskeby III under normal and iron stress conditions. To investigate this, we used virus-induced gene silencing to knock down gene expression of three iron deficiency response genes (FER-like iron deficiency induced transcription factor (FIT), elongated hypocotyl 5 (HY5) and popeye (PYE)) in Fiskeby III. Analyses of RNAseq data generated from silenced plants in iron-sufficient and -deficient conditions found silencing FIT and HY5 altered general stress responses but did not impact iron deficiency tolerance, confirming Fiskeby III utilizes novel mechanisms to tolerate iron deficiency stress.

Novel candidate genes for environmental stresses response in Synechocystis sp. PCC 6803 revealed by machine learning algorithms.

Cyanobacteria have developed acclimation strategies to adapt to harsh environments, making them a model organism. Understanding the molecular mechanisms of tolerance to abiotic stresses can help elucidate how cells change their gene expression patterns in response to stress. Recent advances in sequencing techniques and bioinformatics analysis methods have led to the discovery of many genes involved in stress response in organisms. The Synechocystis sp. PCC 6803 is a suitable microorganism for studying transcriptome response under environmental stress. Therefore, for the first time, we employed two effective feature selection techniques namely and support vector machine recursive feature elimination (SVM-RFE) and LASSO (Least Absolute Shrinkage Selector Operator) to pinpoint the crucial genes responsive to environmental stresses in Synechocystis sp. PCC 6803. We applied these algorithms of machine learning to analyze the transcriptomic data of Synechocystis sp. PCC 6803 under distinct conditions, encompassing light, salt and iron stress conditions. Seven candidate genes namely sll1862, slr0650, sll0760, slr0091, ssl3044, slr1285, and slr1687 were selected by both LASSO and SVM-RFE algorithms. RNA-seq analysis was performed to validate the efficiency of our feature selection approach in selecting the most important genes. The RNA-seq analysis revealed significantly high expression for five genes namely sll1862, slr1687, ssl3044, slr1285, and slr0650 under ion stress condition. Among these five genes, ssl3044 and slr0650 could be introduced as new potential candidate genes for further confirmatory genetic studies, to determine their roles in their response to abiotic stresses.

Production of iron-rich biomass using Chlorella vulgaris cultivation under iron stress

Fertilizers play a crucial role in enhancing the yield of agricultural crops and their market value. Therefore, it is essential to have large-scale, low cost, eco-friendly, broad-spectrum, and clean production of fertilizers. This study aims to prepare an iron-rich biomass, which holds the potential to serve as a biofertilizer, through the cultivation of Chlorella vulgaris microalgae under iron stress conditions. To attain this objective, three different iron sources were examined by supplementing them to the microalgal growth culture medium, namely ammonium ferric citrate, FeCl3, and EDDHA-Fe, each at varying concentrations of iron. The experimental findings revealed that, under iron stress conditions, the addition of ammonium ferric citrate as the iron source to the microalgal growth culture medium resulted in a microalgal biomass with a maximum iron content of 4.88 % by weight. However, the iron content of the obtained biomass from the culture media sourced from FeCl3 and EDDHA-Fe reached a maximum of only 2.01 % and 3.55 % by weight, respectively. Ultimately, the efficacy of the iron-rich microalgal biomass was evaluated by utilizing it during corn cultivation, in conjunction with regular microalgal biomass, ammonium ferric citrate, and the iron-deficient soil (as control) samples. The dry weight of the corn stem cultured with iron-rich biomass was 13 %, 55 %, and 152 % higher, compared to those cultured with regular microalgal biomass, ammonium ferric citrate, and the iron-deficient soil, respectively.

Interactive effect of Fe and Mn deficiencies on physiological, biochemical, nutritional and growth status of soybean

Iron (Fe) deficiency is one of the most common problems of soybean. It causes upper leaves yellowing, interveinal chlorosis, stunted growth and yield loss. Manganese (Mn) deficiency affects the reactions in the oxygen evolving complex (OEC) of photosystem II and increase the accumulation of reactive oxygen species (ROS). The aim of this research is to study the effect of Fe and Mn deficiencies applied separately and simultaneously on physiological, biochemical, nutritional and growth (morphological) parameters of soybean cultivars (Glycine max L.). The experiment was conducted in nutrient hydroponic solution lacking Fe or Mn or both Fe and Mn. Chlorophyll content index (CCI) and chlorophyll a fluorescence were measured through time to detect nutritional disorders at an early growth stage before the apparition of visual symptoms. The results showed that Fe and Mn deficiencies had a significant negative effect on the photosynthetic efficiency, CCI, stomatal conductance, protein content and shoot/root nutrient uptakes. Iron and manganese stress conditions were found to enhance the accumulation of secondary metabolites and increase the antioxidant activity such as total polyphenol content (TPC), malondialdehyde (MDA) and superoxide dismutase (SOD). These impacts were more accentuated when Fe and Mn stress were applied simultaneously than when any of the deficiencies was applied alone. More than that, Mn stress alone did not significantly affect the biomass accumulation. The obtained results showed that, in hydroponic conditions, iron and manganese rational fertilization can improve the studied parameters.

Genome-Wide Identification of Cassava Glyoxalase I Genes and the Potential Function of MeGLYⅠ-13 in Iron Toxicity Tolerance.

Glyoxalase I (GLYI) is a key enzyme in the pathway of the glyoxalase system that degrades the toxic substance methylglyoxal, which plays a crucial part in plant growth, development, and stress response. A total of 19 GLYI genes were identified from the cassava genome, which distributed randomly on 11 chromosomes. These genes were named MeGLYI-1–19 and were systematically characterized. Transcriptome data analysis showed that MeGLYIs gene expression is tissue-specific, and MeGLYI-13 is the dominant gene expressed in young tissues, while MeGLYI-19 is the dominant gene expressed in mature tissues and organs. qRT-PCR analysis showed that MeGLYI-13 is upregulated under 2 h excess iron stress, but downregulated under 6, 12, and 20 h iron stress. Overexpression of MeGLYI-13 enhanced the growth ability of transgenic yeast under iron stress. The root growth of transgenic Arabidopsis seedlings was less inhibited by iron toxicity than that of the wild type (WT). Potted transgenic Arabidopsis blossomed and podded under iron stress, but flowering of the WT was significantly delayed. The GLYI activity in transgenic Arabidopsis was improved under both non-iron stress and iron stress conditions compared to the WT. The SOD activity in transgenic plants was increased under iron stress, while the POD and CAT activity and MDA content were decreased compared to that in the WT. These results provide a basis for the selection of candidate genes for iron toxicity tolerance in cassava, and lay a theoretical foundation for further studies on the functions of these MeGLYI genes.

In vitro plant growth promoter assay of actinobacteria potential for tidal land farming

The use of tidal land for agricultural still faces constraints, mainly due to high iron content. Actinobacteria produce bioactive compound with many functions. The aim of this work was to assess the growth of actinobacteria at various iron concentrations and its capability as plant growth promoter. Four actinobacteria isolates (Cal31t, Dbi28t, Crc32t and Cal24h) were grown at various iron concentrations. The isolates were examined for their capability to produce IAA and fix N2 under in vitro assay. The growth of actinobacteria under stress conditions was examined by cultivating them in ISP2 medium at pH 4, 3% NaCl, 750 mg.L−1 AlCl3 and 8 concentrations of FeCl3, i.e. 0, 500, 1000, 2000, 4000, 8000, 16000, 32000 mg.L−1. Actinobacteria isolates were able to grow under iron stress condition up to 32.000 mg.L−1. Both Cal3t and Dbi28t produced higher cell biomass compared with the other two tested isolates. All isolates produced IAA when grown under iron stress condition up to 4000 mg.L−1 of FeCl3, were able to grow under N-free medium and capable to produce ammonia at various concentrations. Crc32t produced the highest number of ammonia (0,354 mg.L−1). Cal31t and Crc32t isolates have the potency as plant growth promoter in tidal land farming.

Correlation of over-expression of rv1900c with enhanced survival of M. smegmatis under stress conditions: Modulation of cell surface properties.

Mycobacterium tuberculosis has distinct cell wall composition that helps in intracellular survival of bacteria. Rv1900c, a two domain protein, has been grouped in lip gene family. The expression of rv1900c was upregulated under acidic, nutritive and iron stress conditions in M. tuberculosis H37Ra. To investigate the biological effect of Rv1900c in mycobacterium physiology, rv1900c gene was cloned in M. smegmatis, a surrogate host. Its counterpart MSMEG_4477 in M. smegmatis demonstrated 38% protein similarity with Rv1900c. MSMEG_4477 gene was knocked out in M. smegmatis by homologous recombination. rv1900c and MSMEG_4477 genes, cloned in pVV16, were expressed in the M. smegmatis knockout strain (M. smegmatis ΔMSMEG_4477). Gene knockout significantly altered colony morphology and growth kinetics of M. smegmatis. M. smegmatis ΔMSMEG_1900 (pVV16::rv1900c) colonies were less wrinkled and had smooth surface as compared to M. smegmatis ΔMSMEG_4477. The changes were reverted back to normal upon expression of MSMEG_4477 in knockout strain M. smegmatis ΔMSMEG_4477 (pVV16::MSMEG_4477). The expression of rv1900c enhanced the biofilm formation and survival of bacteria under various in vitro stresses like acidic, nutritive stress, including lysozyme, SDS and multiple antibiotics treatment in comparison to control. On the other hand the expression of rv1900c decreased the cell wall permeability. The resistance provided by M. smegmatis ΔMSMEG_4477 (pVV16::MSMEG_4477) was comparable to M. smegmatis having vector alone (MS_vec). The lipid content of M. smegmatis ΔMSMEG_1900 (pVV16::rv1900c) was observed to be different from M. smegmatis ΔMSMEG_4477 (pVV16::MSMEG_4477). M. smegmatis ΔMSMEG_1900 (pVV16::rv1900c) was more tolerant to stress conditions in comparison to M. smegmatis ΔMSMEG_4477 (pVV16::MSMEG_4477). Expression of rv1900c enhanced the intracellular survival of mycobacteria. Therefore, the present study suggested an association of Rv1900c to the stress tolerance by cell wall modification that might have resulted in enhanced intracellular survival of the mycobacteria.

The Mycobactin Biosynthesis Pathway: A Prospective Therapeutic Target in the Battle against Tuberculosis.

The alarming rise in drug-resistant clinical cases of tuberculosis (TB) has necessitated the rapid development of newer chemotherapeutic agents with novel mechanisms of action. The mycobactin biosynthesis pathway, conserved only among the mycolata family of actinobacteria, a group of intracellularly surviving bacterial pathogens that includes Mycobacterium tuberculosis, generates a salicyl-capped peptide mycobactin under iron-stress conditions in host macrophages to support the iron demands of the pathogen. This in vivo essentiality makes this less explored mycobactin biosynthesis pathway a promising endogenous target for novel lead-compounds discovery. In this Perspective, we have provided an up-to-date account of drug discovery efforts targeting selected enzymes (MbtI, MbtA, MbtM, and PPTase) from the mbt gene cluster (mbtA-mbtN). Furthermore, a succinct discussion on non-specific mycobactin biosynthesis inhibitors and the Trojan horse approach adopted to impair iron metabolism in mycobacteria has also been included in this Perspective.

Differential responses to iron stress in blackgram (Vigna mungo L.) varieties

The intention behind conducting this study was to evaluate the toxicological response of black gram (Vigna mungo) varieties exposed to iron stress at an early seedling stage. Iron is a micronutrient required to plant for various metabolic activity. However, its toxicity or deficiency can cause harmful effects to the plants. The experiment was conducted in the Department of Life Science and Bioinformatics of Assam University, Silchar during kharif season of 2019. Two blac gram varieties and three iron concentrations (control, 10µM and 2mM) were evaluated in laboratory conditions.The results clearly showed that significant difference was observed in the growth of roots and shoots and total biomass of the plants grown in three different iron conditions. An enhancement was observed in MDA, H2O2, and O2- and in IPU-073 than in Shekhar-1. At iron-deficiency, H2O2, MDA, O2- radical content of IPU-073 increased by 88.3, 79 and 50.1% whereas, in Shekhar-1, it increased by 70.5, 26.8 and 36.6% in roots respectively which was found to be higher than Fe-excess condition in both roots and shoots. The reduction rate of Chlorophyll content was lower in Shekhar-1 (9.1%) than IPU 073 (31.8%). The comparison between these two varieties showed that Shekhar-1 performed better than IPU-073 under different iron stress condition

Examining Short-Term Responses to a Long-Term Problem: RNA-Seq Analyses of Iron Deficiency Chlorosis Tolerant Soybean.

Iron deficiency chlorosis (IDC) is a global crop production problem, significantly impacting yield. However, most IDC studies have focused on model species, not agronomically important crops. Soybean is the second largest crop grown in the United States, yet the calcareous soils across most of the upper U.S. Midwest limit soybean growth and profitability. To understand early soybean iron stress responses, we conducted whole genome expression analyses (RNA-sequencing) of leaf and root tissue from the iron efficient soybean (Glycine max) cultivar Clark, at 30, 60 and 120 min after transfer to iron stress conditions. We identified over 10,000 differentially expressed genes (DEGs), with the number of DEGs increasing over time in leaves, but decreasing over time in roots. To investigate these responses, we clustered our expression data across time to identify suites of genes, their biological functions, and the transcription factors (TFs) that regulate their expression. These analyses reveal the hallmarks of the soybean iron stress response (iron uptake and homeostasis, defense, and DNA replication and methylation) can be detected within 30 min. Furthermore, they suggest root to shoot signaling initiates early iron stress responses representing a novel paradigm for crop stress adaptations.

Deconstructing the genetic architecture of iron deficiency chlorosis in soybean using genome-wide approaches

BackgroundIron (Fe) is an essential micronutrient for plant growth and development. Iron deficiency chlorosis (IDC), caused by calcareous soils or high soil pH, can limit iron availability, negatively affecting soybean (Glycine max) yield. This study leverages genome-wide association study (GWAS) and a genome-wide epistatic study (GWES) with previous gene expression studies to identify regions of the soybean genome important in iron deficiency tolerance.ResultsA GWAS and a GWES were performed using 460 diverse soybean PI lines from 27 countries, in field and hydroponic iron stress conditions, using more than 36,000 single nucleotide polymorphism (SNP) markers. Combining this approach with available RNA-sequencing data identified significant markers, genomic regions, and novel genes associated with or responding to iron deficiency. Sixty-nine genomic regions associated with IDC tolerance were identified across 19 chromosomes via the GWAS, including the major-effect quantitative trait locus (QTL) on chromosome Gm03. Cluster analysis of significant SNPs in this region deconstructed this historically prominent QTL into four distinct linkage blocks, enabling the identification of multiple candidate genes for iron chlorosis tolerance. The complementary GWES identified SNPs in this region interacting with nine other genomic regions, providing the first evidence of epistatic interactions impacting iron deficiency tolerance.ConclusionsThis study demonstrates that integrating cutting edge genome wide association (GWA), genome wide epistasis (GWE), and gene expression studies is a powerful strategy to identify novel iron tolerance QTL and candidate loci from diverse germplasm. Crops, unlike model species, have undergone selection for thousands of years, constraining and/or enhancing stress responses. Leveraging genomics-enabled approaches to study these adaptations is essential for future crop improvement.

The response of East Kalimantan, Indonesia local rice cultivars against iron stress

Nurhasanah, lestari HS, Sunaryo W. 2019. The response of East Kalimantan, Indonesia local rice cultivars against iron stress. Biodiversitas 20: 273-282. Iron (Fe) toxicity is one of the most problematic metal elements in acidic soil. Besides being as an essential micronutrient, an excessive iron can cause mineral and nutrients absorption disorder which leads to disruption of plant metabolism and cell development. Reduction of plant growth and yield will be the further consequences of the excessive soil iron content. This study aimed to evaluate the response of East Kalimantan local rice cultivars and to screen rice genotypes tolerant to iron stress. Twenty-five rice genotypes were used in this study, consisted of twenty-three local rice cultivars of East Kalimantan and two control of iron sensitive (IR64) and tolerant (Mekongga) varieties. Uniform sprouts (3 days old) having 1-1.5 cm root length were used for iron stress experiment. The seedlings were grown in nutrient solution using hydroponic system in an aerobic condition. The seedlings were treated for one week in iron stress condition by adding an extra iron source of 100 and 200 ppm FeSO4.7H2O (pH 4.0). The seedlings grown in the nutrient solution without an extra iron treatment at normal acidity growth condition (pH 5.8) were used as the control. The growth responses were observed from root, shoot, and biomass of the plants. The tolerance index of the plant growth characters was calculated to classify the rice genotypes into tolerant, moderate, and sensitive to iron stress. The results showed that 100 and 200 ppm of FeSO4.7H2O treatments inhibited the root and shoot growth and also reduced the plant biomass. The plant growth reduction was in parallel with the increase of iron concentration. There was a significant differential response of East Kalimantan local rice genotypes to iron stress treatment. Some genotypes showed an extreme reduction of plant growth, whereas several genotypes had an increased growth under stressed situation. In the contrary, the sensitive genotype IR 64 was consistently sensitive based on the tolerance index of the root, shoot, and plant biomass characters. Among all growth parameters, the most selective character for iron toxicity screening was maximal root length character. This character caused the most severe symptoms for most of the genotypes. Two local rice genotypes, Bentian and Bogor Hitam, were consistently tolerant based on the maximal root growth, total root growth, shoot length and plant biomass.

Iron Homeostasis in Rice: Deficit and Excess

Rice is the major food crop grown in all over the world mitigating 60–70% requirement of calories. However, its growth has always been challenged under different abiotic stress. Iron is one such important micronutrient, which pose hazardous effects to its yield and quality under both iron (Fe) deficient and excess condition. Recent research studies have attempted to overcome these iron stress constraints by understanding the function of homeostatic genes involved in it and modulating their expression through developed molecular technologies. These technologies involved overexpression of genes in iron uptake, transport, storage, along with the transcriptomics analysis of whole genome to develop a better quality of rice progenies which can withstand various adverse effects of iron stress. Iron homeostasis pathway involves Strategy I and Strategy II followed by dicotyledonous and monocotyledonous plants. However, in the case of rice, several genes involved in both strategies have found to be responsive under Fe-deficient and excess condition. Interaction of other metals present in the soil along with pH can affect the iron uptake in rice. Transgenic rice can become a strong contender in iron stress condition controlling iron uptake, translocation and storage.

Drosophila multicopper oxidase 3 is a potential ferroxidase involved in iron homeostasis

Multicopper oxidases (MCOs) are a specific group of enzymes that contain multiple copper centers through which different substrates are oxidized. Main members of MCO family include ferroxidases, ascorbate oxidases, and laccases. MCO type of ferroxidases is key to iron transport across the plasma membrane. In Drosophila, there are four potential multicopper oxidases, MCO1–4. No convincing evidence has been presented so far to indicate any of these, or even any insect multicopper oxidase, to be a ferroxidase. Here we show Drosophila MCO3 (dMCO3) is highly likely a bona fide ferroxidase. In vitro activity assay with insect-cell-expressed dMCO3 demonstrated it has potent ferroxidase activity. Meanwhile, the ascorbate oxidase and laccase activities of dMCO3 are much less significant. dMCO3 expression in vivo, albeit at low levels, appears mostly extracellular, reminiscent of mammalian ceruloplasmin in the serum. A null dMCO3 mutant, generated by CRISPR/Cas9 technology, showed disrupted iron homeostasis, evidenced by increased iron level and reduced metal importer Mvl expression. Notably, dMCO3-null flies phenotypically are largely normal at normal or iron stressed-conditions. We speculate the likely existence of a similar iron efflux apparatus as the mammalian ferroportin/ferroxidase in Drosophila. However, its importance to fly iron homeostasis is greatly minimized, which is instead dominated by another iron efflux avenue mediated by the ZIP13-ferritin axis along the ER/Golgi secretion pathway.

Binding of proton and iron to lignite humic acid size-fractions in aqueous matrix

The bioavailability of trivalent iron (Fe3+) to plants can be enhanced using fertilizer solutions containing humic acids (HA) as manifested from the increased crop yield at an iron stress conditions. The lignite-derived HA (HAlignite) facilitates higher diffusion of Fe3+ between the soil layers as attributable to more number of reactive sites in the assemblage compared to those from other origins. In the current work, the proton-binding of HAlignite size-fractions (5–10, 10–30, 30–100, and >100 kDa), as segmented based on the molecular weight distribution, and their complexation with Fe3+ have been studied at varying pH ranging from low to high. The protonation or formation of Fe3+-complexes exhibited a comparable pattern despite the differences in the conformational distribution of HAlignite size-fractions. The protonation behavior specified that the behavior of HAlignite size-fractions has similarity with that of a dibasic acid. The results are interpreted using reactive structural units (RSU) concept to show that the carboxyl and phenolic-hydroxyl groups in the HAlignite size-fractions simultaneously available as the Fe3+-binding sites. The stability constants for larger MW fractions of HAlignite (>100 kDa) was the lowest, as attributed to the increased aggregation rate in an aqueous matrix. The trend in conditional stability constants of HAlignite-size fractions and other Fe-chelators point to a better Fe-binding capability of HAlignite (30–100 kDa) size-fraction than the biodegradable alternatives (GLDA, HIDS, EDDS, IDSA, or NTA), while the Fe-interaction was stronger with classical synthetic chelators (EDTA, DTPA, or EDDHA).

BIOASSAY, CHARACTERIZATION AND ESTIMATION OF SIDEROPHORES FROM SOME IMPORTANT ANTAGONISTIC FUNGI

The primary mechanisms of plant disease suppression by biological control agents are by production of antimicrobial secondary metabolites like siderophores, antibiotics, volatile substances etc. Siderophores are low molecular iron chelating compounds produced by fungi and bacteria under iron stress condition. The present study is focused on the detection, estimation and characterisation of siderophores from different soil borne fungal biocontrol agents like Trichoderma spp., Beauveria spp. and Metarhizium spp. Isolates of Trichoderma have shown positive results in CAS agar plate whereas Beauveria and Metarhizium have shown negative results. The isolates with positive results were opted for characterization and quantitative estimation of siderophore. T. harzianum produced a maximum percentage of siderophore (85.00%), followed by T. viride (65.50%), T. asperellum (60.27%) and T. longibrachiatum (45.50%). While studying the typification of siderophores, it was found that T. harzianum recorded with maximum hydroxymate and carboxylate production whereas T. viride, T. asperellum and T. longibrachiatum recorded with lesser production of hydroxymate and carboxylate as confirmed by color intensity. But none of the isolates was recorded with catecholate production. Through spectrophotometric analysis, it has been found that slightly alkaline pH was more favorable for the siderophore production for different spp. of Trichoderma. The productions of siderophore from Trichoderma spp. not only scavenge iron which lead to inactivation of those enzymes of the pathogen where iron plays the critical role as cofactor which supplies that iron to the host plant resulting in plantgrowth promotion. Siderophore also has a high degree of influence on medical science in MRI imaging. So mapping of different strains of Trichoderma with high antagonistic efficacy along with profound potency of siderophore production will encourage eco friendly management of fungal diseases on crops, crop improvement and enrichment of medical science

Production, optimization and probiotic characterization of potential lactic acid bacteria producing siderophores.

The aim of the study was to characterize the probiotic qualities and siderophore production of Enterococcus and Bacillus isolates for possible application for iron nutrition in human and animals strains were selectively isolated from different dairy sources and infant faecal matter. Isolates SB10, JC13 and IFM22 were found to produce maximum siderophore ranging from 65–90% at an optimum pH 7, incubation period of 96 h, agitation speed of 150 rpm and inoculum volume of 15%. SB10 and JC13 were found to show high homology with Enterococcus spp. and IFM22 with Bacillus spp., using partial 16S rRNA sequencing and biochemical characterization. All the three isolates produced hydroxymate type of siderophores under iron stressed conditions and screened for probiotic characters as per WHO guidelines. Strains have shown excellent tolerance to acid, bile salt, sodium chloride and phenol. They were non-haemolytic in nature and exhibited high hydrophobicity and autoaggregation. Our isolates proved to be potent probiotic strains due to their survival under highly acidic conditions and higher tolerance to bile salt. In addition, its colonization efficiency was proved by exhibiting high autoaggregation and hydrophobicity.

Nonribosomal peptide synthetase with a unique iterative-alternative-optional mechanism catalyzes amonabactin synthesis in Aeromonas.

Based on the exploration of data generated by genome sequencing, a bioinformatics approach has been chosen to identify the biosynthetic pathway of the siderophores produced by Aeromonas species. The amonabactins, considered as a virulence factor, represent a family of four variants of catechol peptidic siderophores containing Dhb, Lys, Gly, and an aromatic residue either Trp or Phe in a D-configuration. The synthesis operon is constituted of seven genes named amoCEBFAGH and is iron-regulated. The cluster includes genes encoding proteins involved in the synthesis and incorporation of the Dhb monomer, and genes encoding specific nonribosomal peptide synthetases, which are responsible for the building of the peptidic moiety. The amonabactin assembly line displays a still so far not described atypical mode of synthesis that is iterative, alternative, and optional. A disruption mutant in the adenylation domain of AmoG was unable to synthesize any amonabactin and to grow in iron stress conditions while a deletion of amoH resulted in the production of only two over the four forms. The amo cluster is widespread among most of the Aeromonas species, only few species produces the enterobactin siderophore.

Quantitative proteomic analysis of cell envelope preparations under iron starvation stress in Aeromonas hydrophila.

BackgroundIron homeostasis is an essential process over the entire lives of both hosts and bacterial pathogens, and also plays roles in many other metabolic functions. Currently, knowledge is limited on the iron scavenging mechanism of the cell envelope in the aquatic pathogen, Aeromonas hydrophila. To understand the iron homeostasis mechanism in A. hydrophila, a dimethyl labelling based quantitative proteomics method was used to compare the differential expression of cell envelope proteins under iron starvation.ResultsA total of 542 cell envelope proteins were identified by LC-MS/MS, with 66 down-regulated and 104 up-regulated proteins. Bioinformatics analysis showed that outer membrane siderophores, heme and iron receptors, periplasmic iron binding proteins, inner membrane ABC transporters and H+-ATP synthase subunits increased in abundance while iron-cluster proteins, electron transport chain and redox proteins were down-regulated. Further q-PCR validation, in vivo addition of exogenous metabolites, and an enzyme inhibition assay revealed that redox, the energy generation process, and ATP synthase elevated the susceptibility of A. hydrophila to iron starvation.ConclusionsOur study demonstrates that the redox and energy generation process, and ATP synthase in A. hydrophila may play critical roles in iron acquisition under conditions of iron-stress. An understanding of the iron scavenging mechanism may be helpful for the development of strategies for preventing and treating A. hydrophila infection.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-016-0769-5) contains supplementary material, which is available to authorized users.

Effect of Iron Availability on the Survival of Carbapenem-Resistant Acinetobacter baumannii: a Proteomic Approach

Acinetobacter baumannii is a notorious pathogen and is known to cause hospital-acquired nosocomial infections. Presently, carbapenems are most effective antibiotics against A. baumannii, however, emerging carbapenem resistance by A. baumannii further made it difficult to treat the infections. One of the requirements of for successful invasion and colonization of A. baumannii is the essential micronutrient iron inside the human host. However, the bioavailability of iron is sequestered due to the nutritional immunity of host, which acts as an important virulence factor. Present study is an attempt to identify membrane proteins in response to in vitro iron-overload and iron-limiting conditions by using Differential In-Gel Electrophoresis (DIGE) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). Carbapenem-resistant clinical strain of A. baumannii under iron-stress conditions, showed high expression of Fhu E receptor, ferric acinetobactin receptor, ferrienterchelin receptor, ferric siderophore receptor, bacterioferritin and cell division inhibitor suggesting their correlation in iron circumvention inside human host. On contrary, in presence of iron, proteins such as ATP synthase, malate dehydrogenase, acetyl-CoA carboxylase, ribosomal protein, EF-Ts etc are elevated indicating their role in facilitating the metabolism of carbohydrate, amino acid, fatty acid and nucleic acid. Present results indicate the adaptability of carbapenem-resistant A. baumannii to iron availability by differentially expressing some of its membrane proteins.