Iron-rich Environments Research Articles

Zero-Valent Iron Sand Filtration Can Reduce Human and Plant Pathogenic Bacteria While Increasing Plant Growth Promoting Bacteria in Reclaimed Water

The increasing use of reclaimed water for irrigation in areas lacking access to advanced wastewater treatment and reclaimed water distribution systems calls for an examination of irrigation-site-based treatment technologies that can improve the quality of this alternative water source. To address this need, we investigated the impact of zero-valent iron (ZVI)-sand filtration on the bacterial community structure and functional potential of conventionally treated reclaimed water utilized in downstream applications. Over a two-month period, reclaimed water was collected from a tertiary wastewater treatment plant in the Mid-Atlantic, U.S. and trucked to our greenhouse facility. The water was stored in rain barrels and then filtered through one ZVI-sand filter every five days. Filtrate was then subjected to enumeration, phylotyping, shiga toxin screening and antimicrobial susceptibility testing of Escherichia coli. Aliquots of filtrate were also DNA extracted, and purified DNA was subjected to 16S rRNA gene sequencing and metagenomic shotgun sequencing. The genera Dechloromonas, Desulfotomaculum, Leptonema and Thermomonas, which contain denitrifying and sulfate reducing species, commonly used in bioremediation, and known to increase the inherent reactivity of ZVI, were significantly more relatively abundant in ZVI-sand filtered reclaimed water compared to reclaimed water. The concentration of E. coli in ZVI-sand filtered reclaimed water was significantly lower compared to that of reclaimed water, and cefoxitin- and tetracycline-resistant E. coli were undetectable after ZVI-sand filtration. ZVI-sand filtration reduced the occurrence of human as well as plant pathogenic genera (Aeromonas, Mycobacterium, Shewanella, Acidovorax, Agrobacterium, Clavibacter) but increased the proportion of Azospira, a nitrogen fixing bacterial genera, in the microbial community. Our exploratory functional analysis showed a modest non-significant increase in the proportion of open reading frames for genes associated with iron uptake, oxidative stress, as well as defense and repair mechanisms after ZVI-sand filtration. These data indicate an iron rich environment in the filter causing an oxidative stress response by the bacterial community present in the reclaimed water. Our findings demonstrate that ZVI-sand filtration effectively filters conventionally treated reclaimed water. Longer-term, field-based studies are needed to evaluate the effectiveness of the filter in agricultural settings and inform the development of future agricultural water reuse regulations.

Simulating Mars Drilling Mission for Searching for Life: Ground-Truthing Lipids and Other Complex Microbial Biomarkers in the Iron-Sulfur Rich Río Tinto Analog.

Sulfate and iron oxide deposits in Río Tinto (Southwestern Spain) are a terrestrial analog of early martian hematite-rich regions. Understanding the distribution and drivers of microbial life in iron-rich environments can give critical clues on how to search for biosignatures on Mars. We simulated a robotic drilling mission searching for signs of life in the martian subsurface, by using a 1m-class planetary prototype drill mounted on a full-scale mockup of NASA's Phoenix and InSight lander platforms. We demonstrated fully automated and aseptic drilling on iron and sulfur rich sediments at the Río Tinto riverbanks, and sample transfer and delivery to sterile containers and analytical instruments. As a ground-truth study, samples were analyzed in the field with the life detector chip immunoassay for searching microbial markers, and then in the laboratory with X-ray diffraction to determine mineralogy, gas chromatography/mass spectrometry for lipid composition, isotope-ratio mass spectrometry for isotopic ratios, and 16S/18S rRNA genes sequencing for biodiversity. A ubiquitous presence of microbial biomarkers distributed along the 1m-depth subsurface was influenced by the local mineralogy and geochemistry. The spatial heterogeneity of abiotic variables at local scale highlights the importance of considering drill replicates in future martian drilling missions. The multi-analytical approach provided proof of concept that molecular biomarkers varying in compositional nature, preservation potential, and taxonomic specificity can be recovered from shallow drilling on iron-rich Mars analogues by using an automated life-detection lander prototype, such as the one proposed for NASA's IceBreaker mission proposal.

<p>Protective role of antioxidative enzymes and antioxidants against iron-induced oxidative stress in the cyanobacterium <em>Anabaena sphaerica</em> isolated from iron rich paddy field of Chhattisgarh, India</p>

Iron, as an essential element for plants and microorganisms, plays a significant role in photosynthesis, photopigment synthesis, nitrogen fixation, nucleic acid synthesis, etc. However, in iron rich environments, it causes stress by affecting various physiological activities including ROS generation and detoxification machineries. Here, we investigated the protective role of antioxidative enzymes and antioxidants against iron-induced oxidative stress in the cyanobacteria, Anabaena sphaerica from the iron rich regions of Chhattisgarh. We evaluated various morpho-physiological modifications at different concentrations of iron (0, 20, 50, 75 and 100 µM FeCl 3 ). Microscopic and physiological characterization showed highest order of structural deformities, reactive oxygen species (ROS) generation and lipid peroxidation at 100 µM FeCl 3 but growth was reduced only by 28%. Possibly, maximum superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities along with highest level of antioxidants (carotenoid, proline, cysteine and non protein thiol) played a major role in protecting the growth. As compared to 20 µM FeCl 3 treated cells of A. sphaerica , almost equal growth and no structural alterations at 50 and 75 µM FeCl 3 may be correlated with minimum ROS, electrolyte leakage and malondialdehyde (MDA) content along with an activation of efficient ROS detoxification machinery i.e. enhanced level of antioxidative enzymes and antioxidants. Thus, the inherited property of A. sphaerica to grow at iron enriched condition make it more efficient microbe for improvement of the nitrogen status in the soil.

A Combinational Analysis of Acidophilic Bacterial Diversity of an Iron-Rich Environment

Microbial diversity, same as mineral deposits has been evaluated to be among the underground riches of a country. New data on microbial diversity are thought to be of potential economic value. Acid drainage waters are characterized by low pH and high concentrations of metals. Therefore, these acidic habitats are perfect places for quantitative and genomic-based analyses related to microbial ecology and community functions. The samplings were collected from the Kahramanmaras. The microbiological and molecular techniques were applied to determine the acidophilic community of these regions. Water samples were rich in iron (808.2 ppm, 1086.6 ppm, 2264.7 ppm), gold (1.4 ppm, 1.6 ppm, 2.5 ppm), aluminum (218.5 ppm, 265.5 ppm, 464.3 ppm), manganese (994.1 ppm, 945.6 ppm, 1643.4 ppm), sulfur (3432 ppm, 3971 ppm, 6399 ppm) and zinc (93.9 ppm, 10.8 ppm, 169.5 ppm), respectively for three seasons. The isolates were obtained as Acidiphilium sp., Acidithiobacillus sp., and Leptospirillum ferrooxidans. The predominant bacteria were found to be the members of Acidiphilium, Metallibacterium, Acidithiobacillus, Leptospirillum genera according to the results of the community fingerprint and clone library. 16S amplicon sequencing was analyzed and the diversity results were given at the genus level. Combined culture-dependent and culture-independent techniques were used to identify indigenous bacteria in the iron-rich acid mine ponds. The chemolithotrophic and heterotrophic acidophiles were isolated.

Critical Role for Molecular Iron in Coxiella burnetii Replication and Viability.

Coxiella burnetii, the causative agent of Query (Q) fever in humans, is a highly infectious obligate intracellular bacterium. Following uptake into a host cell, C. burnetii replicates within a phagolysosome-derived compartment referred to as the Coxiella-containing vacuole (CCV). During infection, C. burnetii exhibits tropism for tissues related to iron storage and recycling (e.g., the liver and splenic red pulp), suggesting that pathogen physiology is linked to host iron metabolism. Iron has been described to have a limited role in C. burnetii virulence regulation, despite evidence that C. burnetii-infected host cells increase expression of transferrin receptors, thereby suggesting that active iron acquisition by the bacterium occurs upon infection. Through the use of host cell-free culture, C. burnetii was separated from the host cell in order to directly assess the role of different forms of iron in C. burnetii replication and viability, and therefore virulence. Results indicate that C. burnetii tolerates molecular iron over a broad concentration range (i.e., ∼0.001 to 1 mM) and undergoes gross loss of viability upon iron starvation. C. burnetii protein synthesis and energy metabolism, however, occur nearly uninhibited under iron concentrations not permissive to replication. Despite the apparent absence of genes related to acquisition of host-associated iron-containing proteins, C. burnetii replication is supported by hemoglobin, transferrin, and ferritin, likely due to release of iron from such proteins under acidic conditions. Moreover, chelation of host iron pools inhibited pathogen replication during infection of cultured cells.IMPORTANCE Host organisms restrict the availability of iron to invading pathogens in order to reduce pathogen replication. To counteract the host's response to infection, bacteria can rely on redundant mechanisms to obtain biologically diverse forms of iron during infection. C. burnetii appears specifically dependent on molecular iron for replication and viability and exhibits a response to iron akin to bacteria that colonize iron-rich environments. Physiological adaptation of C. burnetii to the unique acidic and degradative environment of the CCV is consistent with access of this pathogen to molecular iron.

Characterisation of iron oxide encrusted microbial fossils

Robust methods for the characterisation of microbial biosignatures in geological matrices is critical for developing mineralogical biosignatures. Studying microbial fossils is fundamental for our understanding of the role microorganisms have played in elemental cycling in modern and ancient environments on Earth and potentially Mars. Here, we aim to understand what promotes the fossilisation of microorganisms after the initial stages of biomineralisation, committing bacteriomorphic structures to the geological record within iron-rich environments. Mineral encrusted cell envelope structures were routinely identified within a goethite-rich vein that cross-cut the saprolite (iron ore) of a weathered banded iron formation (BIF) system in the Quadrilátero Ferrífero, Brazil. The preservation of potential organic and mineralogical biosignatures associated with these fossils was characterised using the following high-resolution analytical techniques: scanning and transmission electron microscopy, focused ion beam scanning electron microscopy, nanoscale secondary ion mass spectrometry, synchrotron-based Fourier transform infrared spectroscopy and Raman spectroscopy. Electron microscopy demonstrated that mineral nucleation associated with a range of cell envelope structures typically followed the extant cell templates. These biologically-influenced iron-rich minerals are microcrystalline with minimal secondary growth. In contrast, intracellular mineralisation formed larger minerals that grew inward from the cell membrane to infill intracellular voids after cell death. A three dimensional reconstruction of encrusted cell envelopes in a fossilised biofilm suggests that microorganisms may be able to replicate, during the initial stages of mineralisation. Carbon and nitrogen signatures are preserved associated with the cell envelope structures; however, there were no conclusive mineralogical biosignatures associated with the mineralised cell envelopes highlighting the classical importance of morphology and elemental biosignatures in determining the biogenicity of bacteriomorphic structures.

Paspalum urvillei and Setaria parviflora, two grasses naturally adapted to extreme iron-rich environments

Paspalum urvillei and Setaria parviflora are two plant species naturally adapted to iron-rich environments such as around iron mines wastes. The aim of our work was to characterize how these two species cope with these extreme conditions by comparing them with related model species, Oryza sativa and Setaria viridis, that appeared to be much less tolerant to Fe excess. Both Paspalum urvillei and Setaria parviflora were able to limit the amount of Fe accumulated within roots and shoots, compared to the less tolerant species. Perls/DAB staining of Fe in root cross sections indicated that Paspalum urvillei and Setaria parviflora responded through the build-up of the iron plaque (IP), suggesting a role of this structure in the limitation of Fe uptake. Synchrotron μXRF analyses showed the presence of phosphorus, calcium, silicon and sulfur on IP of Paspalum urvillei roots and μXANES analyses identified Fe oxyhydroxide (ferrihydrite) as the main Fe form. Once within roots, high concentrations of Fe were localized in the cell walls and vacuoles of Paspalum urvillei, Setaria parviflora and O. sativa whereas Setaria viridis accumulated Fe in ferritins. The Fe forms translocated to the shoots of Setaria parviflora were identified as tri-iron complexes with citrate and malate. In leaves, all species accumulated Fe in the vacuoles of bundle sheath cells and as ferritin complexes in plastids. Taken together, our results strongly suggest that Paspalum urvillei and Setaria parviflora set up mechanisms of Fe exclusion in roots and shoots to limit the toxicity induced by Fe excess.

Transposable temperate phages promote the evolution of divergent social strategies in Pseudomonas aeruginosa populations

Transposable temperate phages randomly insert into bacterial genomes, providing increased supply and altered spectra of mutations available to selection, thus opening alternative evolutionary trajectories. Transposable phages accelerate bacterial adaptation to new environments, but their effect on adaptation to the social environment is unclear. Using experimental evolution of Pseudomonas aeruginosa in iron-limited and iron-rich environments, where the cost of producing cooperative iron-chelating siderophores is high and low, respectively, we show that transposable phages promote divergence into extreme siderophore production phenotypes. Iron-limited populations with transposable phages evolved siderophore over-producing clones alongside siderophore non-producing cheats. Low siderophore production was associated with parallel mutations in pvdgenes, encoding pyoverdine biosynthesis, and pqs genes, encoding quinolone signaling, while high siderophore production was associated with parallel mutations in phenazine-associated gene clusters. Notably, some of these parallel mutations were caused by phage insertional inactivation. These data suggest that transposable phages, which are widespread in microbial communities, can mediate the evolutionary divergence of social strategies.

Transposable temperate phages promote the evolution of divergent social strategies in Pseudomonas aeruginosa populations.

Transposable temperate phages randomly insert into bacterial genomes, providing increased supply and altered spectra of mutations available to selection, thus opening alternative evolutionary trajectories. Transposable phages accelerate bacterial adaptation to new environments, but their effect on adaptation to the social environment is unclear. Using experimental evolution of Pseudomonas aeruginosa in iron-limited and iron-rich environments, where the cost of producing cooperative iron-chelating siderophores is high and low, respectively, we show that transposable phages promote divergence into extreme siderophore production phenotypes. Iron-limited populations with transposable phages evolved siderophore overproducing clones alongside siderophore non-producing cheats. Low siderophore production was associated with parallel mutations in pvd genes, encoding pyoverdine biosynthesis, and pqs genes, encoding quinolone signalling, while high siderophore production was associated with parallel mutations in phenazine-associated gene clusters. Notably, some of these parallel mutations were caused by phage insertional inactivation. These data suggest that transposable phages, which are widespread in microbial communities, can mediate the evolutionary divergence of social strategies.

3187 Rare Presentation of Hereditary Hemochromatosis Brought to Light by Disseminated Mycoplasmosis

INTRODUCTION: Hereditary hemochromatosis is commonly caused by mutation of the HFE protein (C282Y/H63D), leading to iron overload and deposition in the liver, heart, pancreas, and pituitary. Manifestations of Hereditary hemochromatosis differ based on the primary site of iron deposition, ranging from cirrhosis, cardiomyopathy, to diabetes and immunosuppression. which increases susceptibility to opportunistic infections including disseminated mycoplasma. Even with its estimated prevalence of 15% of all community acquired pneumonias, mycoplasma pneumonia is not well recognized for its multitude of rare extrapulmonary manifestations (Figure 1). CASE DESCRIPTION/METHODS: 43 year old male was found unresponsive at home. On admission, diffuse mucosal sloughing and bleeding with numerous small, flat, erythematous lesions on the trunk and extremities. Throat swab Polymerase Chain Reaction: positive for mycoplasma pneumonia, with IgM serum confirmatory test. These skin lesions would blister and ulcerate on following days. Skin biopsy revealed Steven Johnson Syndrome. On hospital day 6 patient was noted to have left hemiplegia, Head imaging, Right Middle Cerebral Artery ischemic stroke and hemorrhagic conversion. Cardiac Imaging showed No patent Foramen Ovale, no atrial thrombi or valvular pathology, leading to a diagnosis of cryptogenic stroke. In the presence of elevated liver function testing and diffuse hyperattenuation of the liver on non-contrast CT, Iron studies were obtained. Ferritin of 10,086 ng/ml, % Iron saturation of 78.7. Genetic testing returned homozygous for C282Y gene. Liver biopsy confirmed hemochromatosis. Appropriate antibiotics and serial phlebotomies started, after which he clinically improved. DISCUSSION: The liver plays a central role in the clearance of bacteria from the bloodstream as hepatic phagocytosis accounts for more than 80% of all reticuloendothelial system function. In hemochromatosis, patients have increased portocaval shunting from liver injury. Therefore, bypassing the liver, and reducing clearance of mycoplasma, predisposing patients to a more virulent clinical course. Mycoplasma's activity in an Iron rich environment is poorly understood. It is known that mycoplasma binds to lactoferrin, a protein largely responsible for iron sequestration in the body for bacteriostasis. This leaves room for further research regarding its evolutionary pathogenicity. Therefore, patients with unexplained opportunistic infections and elevated transaminases should be investigated for hemochromatosis.

The making of natural iron sulfide nanoparticles in a hot vent snail

Biomineralization in animals exclusively features oxygen-based minerals with a single exception of the scaly-foot gastropod Chrysomallon squamiferum, the only metazoan with an iron sulfide skeleton. This unique snail inhabits deep-sea hot vents and possesses scales infused with iron sulfide nanoparticles, including pyrite, giving it a characteristic metallic black sheen. Since the scaly-foot is capable of making iron sulfide nanoparticles in its natural habitat at a relatively low temperature (∼15 °C) and in a chemically dynamic vent environment, elucidating its biomineralization pathways is expected to have significant industrial applications for the production of metal chalcogenide nanoparticles. Nevertheless, this biomineralization has remained a mystery for decades since the snail's discovery, except that it requires the environment to be rich in iron, with a white population lacking in iron sulfide known from a naturally iron-poor locality. Here, we reveal a biologically controlled mineralization mechanism employed by the scaly-foot snail to achieve this nanoparticle biomineralization, through δ34 S measurements and detailed electron-microscopic investigations of both natural scales and scales from the white population artificially incubated in an iron-rich environment. We show that the scaly-foot snail mediates biomineralization in its scales by supplying sulfur through channel-like columns in which reaction with iron ions diffusing inward from the surrounding vent fluid mineralizes iron sulfides.

The interaction of Hemin and Sestrin2 modulates oxidative stress and colon tumor growth

Several large epidemiological and animal studies demonstrate a direct correlation between dietary heme iron intake and/or systemic iron levels and cancer risk in several cancers including colorectal cancer (CRC). However, the precise mechanisms for how heme iron contributes to CRC and how cancer cells respond to heme iron-induced stress are still unclear. Previously we have shown that one of the stress-inducible proteins, Sestrin2 (SESN2), is a novel tumor suppressor in colon by limiting endoplasmic reticulum stress and mammalian target of rapamycin complex 1 (mTORC1) signaling and tumor growth. But the relationship between heme iron and SESN2, especially in the context of colon carcinogenesis, was not investigated previously. Here, we found that hemin dose-dependently increased SESN2 expression in an oxidative stress and nuclear factor (erythroid-derived 2)-like 2 (NFE2L2, NRF2)-dependent manner. Since SESN2 overexpression reduced hemin-induced oxidative stress, SESN2 could be an important target of NRF2 exerting antioxidant function. Indeed, expression of several oxidative stress responsive proteins such as NRF2 and its target genes was reduced by SESN2. Although we formerly reported that SESN2 expression was reduced after p53 mutation in colon tumors, mouse colon tumors, which have intact p53 and NRF2, induced SESN2 expression in response to iron stimulus. Although SESN2 overexpression decreased murine colon tumor cell growth both in vitro and in vivo, it rendered colon cancer cells more resistant to hemin-induced apoptosis and therefore promoted tumor growth during hemin treatment. Taken together, although SESN2 generally suppresses tumorigenesis, it can produce tumor-promoting role in iron-rich environment by suppressing oxidative stress-associated cancer cell death.

Patterns of soft tissue and cellular preservation in relation to fossil bone tissue structure and overburden depth at the Standing Rock Hadrosaur Site, Maastrichtian Hell Creek Formation, South Dakota, USA

Recovery of soft tissues and cells from fossil bones is becoming increasingly common, with structures morphologically consistent with vertebrate osteocytes, blood vessels, fibrous/collagenous matrix, and potential intravascular contents now recognized from specimens dating back to the Permian. However, it largely remains unclear how bone tissue structure, early diagenetic regimes, and many other taphonomic variables influence or control the preservation potential of soft tissues in vertebrate fossils. To explore the influence of a few of these factors, we tested a suite of fossils from the Standing Rock Hadrosaur Site, a vast Edmontosaurus annectens bonebed in the Maastrichtian Hell Creek Formation of South Dakota, for preservation of cellular and tissue components. Demineralization of bone samples from each specimen yielded abundant microstructures morphologically consistent with vertebrate osteocytes, blood vessels, and collagenous matrix. This includes the first recovery of osteocytes and vessels from a fossil vertebral centrum and ossified tendons. Perhaps surprisingly, no correlation was found between soft tissue/cellular recovery and either bone tissue structure type (cortical vs. cancellous) or overburden depth at the time of discovery. A traditional taphonomic survey of the site, conducted in parallel and reported previously, affords a clear and detailed history of these remains, both pre- and postburial. Cumulative taphonomic evidence indicates the Edmontosaurus individuals died in a mass mortality event and their disarticulated remains were buried rapidly in a shallow floodplain pond during a crevasse splay event. Oxygenated flood waters and/or groundwater oxidized initially sideritic concretions to goethite during early diagenesis, facilitating rapid cementation of portions of the sediment that likely aided stabilization of soft tissues by shielding regions of the bones from prolonged exposure to pore fluids. Our findings support cancellous bone as a viable target for cellular analyses, corroborate previous propositions that iron-rich environments and rapid burial facilitate soft tissue preservation, and provide new details into early diagenetic environments conducive to such preservation.

Responses of Acidithiobacillus thiooxidans A01 to Individual and Joint Nickel (Ni2+) and Ferric (Fe3+)

Acidithiobacillus thiooxidans A01 is widely used in bioleaching processes and commonly thrives in most metal-rich environments. However, interactions between different heavy metals remain obscure. In this study, we elaborated the effect of ferric iron on the growth and gene expression of At. thiooxidans A01 under the stress of nickel. The results showed that 600 mM Ni2+ completely inhibited the growth and sulfur metabolism of At. thiooxidans A01. However, trace amounts of Fe3+ (0.5 mM) facilitated the growth of At. thiooxidans A01 in the presence of 600 mM Ni2+. With the addition of 5 mM Fe3+, the maximum cell density reached 1.84 × 108 cell/mL, and pH value was 0.95. In addition, metal resistance-related and sulfur metabolism genes were significantly up regulated with extra ferric iron. Taking the whole process into account, the promoting effect of Fe3+ addition can be attributed to the following: (1) alleviation of the effects of Ni2+ toxicity and restoring the growth of At. thiooxidans A01, (2) a choice of multiple pathways to export nickel ion and producing precursor of chelators of heavy metals. This can suggest that microorganisms may widely exhibit metabolic activity in iron-rich environments with heavy metals. Our study will facilitate the technique development for the processing of ore bodies with highly challenging ore compositions.

The role of aluminium in the preservation of microbial biosignatures

Demonstrating the biogenicity of presumptive microfossils in the geological record often requires supporting chemical signatures, including isotopic signatures. Understanding the mechanisms that promote the preservation of microbial biosignatures associated with microfossils is fundamental to unravelling the palaeomicrobiological history of the material. Organomineralization of microorganisms is likely to represent the first stages of microbial fossilisation and has been hypothesised to prevent the autolytic degradation of microbial cell envelope structures. In the present study, two distinct fossilisation textures (permineralised microfossils and iron oxide encrusted cell envelopes) identified throughout iron-rich rock samples were analysed using nanoscale secondary ion mass spectrometry (NanoSIMS). In this system, aluminium is enriched around the permineralised microfossils, while iron is enriched within the intracellularly, within distinct cell envelopes. Remarkably, while cell wall structures are indicated, carbon and nitrogen biosignatures are not preserved with permineralised microfossils. Therefore, the enrichment of aluminium, delineating these microfossils appears to have been critical to their structural preservation in this iron-rich environment. In contrast, NanoSIMS analysis of mineral encrusted cell envelopes reveals that preserved carbon and nitrogen biosignatures are associated with the cell envelope structures of these microfossils. Interestingly, iron is depleted in regions where carbon and nitrogen are preserved. In contrast aluminium appears to be slightly enriched in regions associated with remnant cell envelope structures. The correlation of aluminium with carbon and nitrogen biosignatures suggests the complexation of aluminium with preserved cell envelope structures before or immediately after cell death may have inactivated autolytic activity preventing the rapid breakdown of these organic, macromolecular structures. Combined, these results highlight that aluminium may play an important role in the preservation of microorganisms within the rock record.

Regulation of the Synthesis and Secretion of the Iron Chelator Cyclodipeptide Pulcherriminic Acid in Bacillus licheniformis.

The cyclodipeptide pulcherriminic acid synthesized by Bacillus licheniformis is an iron chelator that antagonizes certain pathogens by removing iron from the environment. But since the insoluble iron-pulcherriminic acid complex cannot act as an iron carrier as siderophores do, excessive synthesized pulcherriminic acid causes iron starvation for the producer cells. At present, the regulation of pulcherriminic acid synthesis and the mechanism by which B. licheniformis strikes a balance between biocontrol and self-protection from excessive iron removal remain unclear. This study provides insights into the regulatory network and explains the mechanism of pulcherriminic acid biosynthesis. The yvmC-cypX synthetic gene cluster was directly negatively regulated by three regulators: AbrB, YvnA, and YvmB. Within the regulatory network, YvnA expression was repressed not only by AbrB but also by iron-limiting environments, while YvmB expression was repressed by YvnA. The transporter gene yvmA is repressed by YvmB and is required for pulcherriminic acid secretion. The biosynthesis window is determined by the combined concentration of the three regulators in an iron-rich environment. Under iron-limiting conditions, cells close the pulcherriminic acid synthesis pathway by downregulating YvnA expression.IMPORTANCE The cyclodipeptides are widespread in nature and exhibit a broad variety of biological and pharmacological activities. The cyclodipeptide scaffold is synthesized by nonribosomal peptide synthetases (NRPSs) and cyclodipeptide synthases (CDPSs). At present, it is clear that CDPSs use aminoacyl tRNAs as substrates to synthesize the two peptide bonds, and the pulcherriminic acid synthase YvmC is a member of the eight identified CDPSs. However, little is known about the regulation of cyclodipeptide synthesis and secretion. In this study, we show that AbrB, which is considered to be the main regulator of NRPS-dependent pathways, is also involved in the regulation of CDPS genes. However, AbrB is not the decisive factor for pulcherriminic acid synthesis, as the expression of YvnA determines the fate of pulcherriminic acid synthesis. With this information on how CDPS gene transcription is regulated, a clearer understanding of cyclodipeptide synthesis can be developed for B. licheniformis Similar approaches may be used to augment our knowledge on CDPSs in other bacteria.

Petrography, lithostratigraphy and major element geochemistry of Mesoarchean metamorphosed banded iron formation-hosted Nkout iron ore deposit, north western Congo craton, Central West Africa

The Nkout banded iron formation (BIF) or iron deposit is located in the northwestern margin of the Congo Craton (CC) and is hosted within high-grade metamorphic Ntem complex. It is mainly made up of metamorphosed banded iron formations with resource estimation of 1.8 Bt @ 32.6% Fe indicated, and 0.9 Bt @ 30.3% Fe inferred. Nkout iron deposit is subdivided into three prospects namely East, Centre and West deposits. Results from lithostratigraphic studies allow detailed correlations between units in the Nkout succession. The litho-package from the top to the base stratigraphy comprises iron-rich member and the gneissic member. The first member forms the upper and middle units while the second member forms the lower unit and represents the footwall of the deposit. The upper unit is ∼200 m deep and consists of oxidized (hematite) and un-oxidized (fresh metamorphosed BIF) ore types. The middle unit is approximately 150 m thick and consists of fresh metamorphosed BIF with minor intercalation of biotite gneiss. The lower unit is made up of garnet-magnetite micaschist, biotite gneiss and pyroxene-biotite gneiss.The Nkout banded iron formation belongs to oxide facies magnetite-rich type which has suffered greenschist to amphibolite facies metamorphism, leading to recrystallization of chlorite, amphibole and garnet minerals. Its overall major oxide bulk chemistry is very similar to that of most Archaean iron-formations worldwide, with high SiO2 and Fe2O3 contents. However, the garnet-rich BIF has higher contents of Al2O3 (8.73 wt%), TiO2 (0.27 wt%), K2O (2.37 wt%) relative to magnetite-rich BIF, suggesting clastic contamination, thus a depositional environment closer to the continent. Furthermore, the absence of carbonate facies BIF in the entire Nkout deposit suggests deep water distal depositional setting, in an area of little or no organic carbon supplies.The lithostratigraphic correlation of metamorphosed BIF unit reveals both thicknesses and depth variations from West to the East, inferring a folded structure for the Nkout deposit. However the occurrence of BIF units in the entire deposit supports the fact that BIF deposition took place on a basin-wide scale. Considering the extent of the Ntem basin, it is suggested that a huge amount of Fe2+ in sea water was required. Thus, the deposition of Nkout BIF probably involved an iron rich environment of reduced Fe2+ rich hydrothermal fluid in chemically stratified sea water, similar to the depositional model proposed for the Minas BIF Supergroup of Quadrilátero Ferrífero in Brazil.

Nutrient availability and the ultimate control of the biological carbon pump in the western tropical South Pacific Ocean

Abstract. Surface waters (0–200 m) of the western tropical South Pacific (WTSP) were sampled along a longitudinal 4000 km transect (OUTPACE cruise, DOI: 10.17600/15000900) during the austral summer (stratified) period (18 February to 3 April 2015) between the Melanesian Archipelago (MA) and the western part of the SP gyre (WGY). Two distinct areas were considered for the MA, the western MA (WMA), and the eastern MA (EMA). The main carbon (C), nitrogen (N), and phosphorus (P) pools and fluxes provide a basis for the characterization of the expected trend from oligotrophy to ultra-oligotrophy, and the building of first-order budgets at the daily and seasonal timescales (using climatology). Sea surface chlorophyll a well reflected the expected oligotrophic gradient with higher values obtained at WMA, lower values at WGY, and intermediate values at EMA. As expected, the euphotic zone depth, the deep chlorophyll maximum, and nitracline depth deepen from west to east. Nevertheless, phosphaclines and nitraclines did not match. The decoupling between phosphacline and nitracline depths in the MA allows for excess P to be locally provided in the upper water by winter mixing. We found a significant biological “soft tissue” carbon pump in the MA sustained almost exclusively by dinitrogen (N2) fixation and essentially controlled by phosphate availability in this iron-rich environment. The MA appears to be a net sink for atmospheric CO2, while the WGY is in quasi-steady state. We suggest that the necessary excess P, allowing the success of nitrogen fixers and subsequent carbon production and export, is mainly brought to the upper surface by local deep winter convection at an annual timescale rather than by surface circulation. While the origin of the decoupling between phosphacline and nitracline remains uncertain, the direct link between local P upper water enrichment, N2 fixation, and organic carbon production and export, offers a possible shorter timescale than previously thought between N input by N2 fixation and carbon export. The low iron availability in the SP gyre and P availability in the MA during the stratified period may appear as the ultimate control of N input by N2 fixation. Because of the huge volume of water to consider, and because the SP Ocean is the place of intense denitrification in the east (N sink) and N2 fixation in the west (N source), precise seasonal C, N, P, and iron (Fe) budgets would be of prime interest to understand the efficiency, at the present time and in the future, of the oceanic biological carbon pump.

Genomic Organization and Expression of Iron Metabolism Genes in the Emerging Pathogenic Mold Scedosporium apiospermum.

The ubiquitous mold Scedosporium apiospermum is increasingly recognized as an emerging pathogen, especially among patients with underlying disorders such as immunodeficiency or cystic fibrosis (CF). Indeed, it ranks the second among the filamentous fungi colonizing the respiratory tract of CF patients. However, our knowledge about virulence factors of this fungus is still limited. The role of iron-uptake systems may be critical for establishment of Scedosporium infections, notably in the iron-rich environment of the CF lung. Two main strategies are employed by fungi to efficiently acquire iron from their host or from their ecological niche: siderophore production and reductive iron assimilation (RIA) systems. The aim of this study was to assess the existence of orthologous genes involved in iron metabolism in the recently sequenced genome of S. apiospermum. At first, a tBLASTn analysis using A. fumigatus iron-related proteins as query revealed orthologs of almost all relevant loci in the S. apiospermum genome. Whereas the genes putatively involved in RIA were randomly distributed, siderophore biosynthesis and transport genes were organized in two clusters, each containing a non-ribosomal peptide synthetase (NRPS) whose orthologs in A. fumigatus have been described to catalyze hydroxamate siderophore synthesis. Nevertheless, comparative genomic analysis of siderophore-related clusters showed greater similarity between S. apiospermum and phylogenetically close molds than with Aspergillus species. The expression level of these genes was then evaluated by exposing conidia to iron starvation and iron excess. The expression of several orthologs of A. fumigatus genes involved in siderophore-based iron uptake or RIA was significantly induced during iron starvation, and conversely repressed in iron excess conditions. Altogether, these results indicate that S. apiospermum possesses the genetic information required for efficient and competitive iron uptake. They also suggest an important role of the siderophore production system in iron uptake by S. apiospermum.

Iron's grip on malaria

Iron Homeostasis Malaria parasites have coevolved with their human and mammalian hosts. These Plasmodium species invade the iron-rich environment of red blood cells. Zhang et al. found that the iron transporter ferroportin persists on the surface of mature mammalian red blood cells. Red blood cells