Expression, purification and spin labelling of the ferrous iron transporter FeoB from Escherichia coli BL21 for EPR studies

Functional Characterization of FeoAB in Iron Acquisition and Pathogenicity in Riemerella anatipestifer

The bacterium Riemerella anatipestifer requires iron for growth, but the mechanism of iron uptake is not fully understood. In this study, we disrupted the Feo system and characterized its function in iron import in R. anatipestifer ATCC 11845. Compared to the parent strain, the growth of the ΔfeoA, ΔfeoB, and ΔfeoAB strains was affected under Fe3+-limited conditions, since the absence of the feo system led to less intracellular iron than in the parent strain. In parallel, the ΔfeoAB strain was shown to be less sensitive to streptonigrin, an antibiotic that requires free iron to function. The sensitivity of the ΔfeoAB strain to hydrogen peroxide was also observed to be diminished compared with that of the parent strain, which could be related to the reduced intracellular iron content in the ΔfeoAB strain. Further research revealed that feoA and feoB were directly regulated by iron through the Fur regulator and that the transcript levels of feoA and feoB were significantly increased in medium supplemented with 1 mM MnCl2, 400 μM ZnSO4, and 200 μM CuCl2. Finally, it was shown that the ΔfeoAB strain of R. anatipestifer ATCC 11845 was significantly impaired in its ability to colonize the blood, liver, and brain of ducklings. Taken together, these results demonstrated that FeoAB supports ferrous iron acquisition in R. anatipestifer and plays an important role in R. anatipestifer colonization. IMPORTANCE In Gram-negative bacteria, the Feo system is an important ferrous iron transport system. R. anatipestifer encodes an Feo system, but its function unknown. As iron uptake may be required for oxidative stress protection and virulence, understanding the contribution of iron transporters to these processes is crucial. This study showed that the ΔfeoAB strain is debilitated in its ability to import iron and that its intracellular iron content was constitutively low, which enhanced the resistance of the deficient strain to H2O2. We were surprised to find that, in addition to responding to iron, the Feo system may play an important role in sensing manganese, zinc, and copper stress. The reduced colonization ability of the ΔfeoAB strain also sheds light on the role of iron transporters in host-pathogen interactions. This study is important for understanding the cross talk between iron and other metal transport pathways, as well as the pathogenic mechanism in R. anatipestifer.

A general protocol for the expression and purification of the intact transmembrane transporter FeoB

Ferrous iron (Fe²⁺) transport is an essential process that supports the growth, intracellular survival, and virulence of several drug-resistant pathogens, and the ferrous iron transport (Feo) system is the most important and widespread protein complex that mediates Fe²⁺ transport in these organisms. The Feo system canonically comprises three proteins (FeoA/B/C). FeoA and FeoC are both small, accessory proteins localized to the cytoplasm, and their roles in the Fe²⁺ transport process have been of great debate. FeoB is the only wholly-conserved component of the Feo system and serves as the inner membrane-embedded Fe²⁺ transporter with a soluble G-protein-like N-terminal domain. In vivo studies have underscored the importance of Feo during infection, emphasizing the need to better understand Feo-mediated Fe²⁺ uptake, although a paucity of research exists on intact FeoB. To surmount this problem, we designed an overproduction and purification system that can be applied generally to a suite of intact FeoBs from several organisms. Importantly, we noted that FeoB is extremely sensitive to excess salt while in the membrane of a recombinant host, and we designed a workflow to circumvent this issue. We also demonstrated effective protein extraction from the lipid bilayer through small-scale solubilization studies. We then applied this approach to the large-scale purifications of Escherichia coli and Pseudomonas aeruginosa FeoBs to high purity and homogeneity. Lastly, we show that our protocol can be generally applied to various FeoB proteins. Thus, this workflow allows for isolation of suitable quantities of FeoB for future biochemical and biophysical characterization.

Study of Antibacterial Chemical Substances and Molecular Investigation among Sulfamethoxazole-trimethoprim (SXT)-Resistant Escherichia coli Isolates

Background

Escherichia coli (E. coli) remains one of the leading agents of urinary tract infection (UTIs), it has become resistant to many drugs. Current work aimed to evaluate some chemical substances as antibacterial agents and molecular study of virulence factors associated with UTIs.

Methods

This work involved 133 urine specimens obtained from females' patients suffering from UTIs, Methods of well diffusion and disk diffusion were achieved to assay the effect of some chemical substances and antibiogram profiles toward Sulfamethoxazole-trimethoprim (SXT)-resistant E. coli respectively. Virulence genes were done based on the technique of Polymerase Chain Reaction (PCR).

Results

The results recorded 49/133 (36.84%) E. coli among women suffering UTIs, 28/49 (57.14%) were resistant to SXT drug. imipenem, meropenem, and nitrofurantoin were recorded more effectively. Chemicals substances at the concentration 0.3 (g/ml) recorded percentages of inhibition, reaching 9.143±1.442, 15.36±0.5914, and 21.82±0.8699 for NaHCO3, Ch4c, and Viroxide Super™ respectively. PCR demonstrated that 28/28 (100%) of SXT-resistant E. coli isolates were harbored Sul-2, FeoB and PapC genes, while 14/28 (50%), 15/28 (53.57%), 19/28 (67.85%) and 26/28 (92.85%) in U250 (pet), FumC, Sul-1 and IutA genes, respectively. Sul-3 gene was not observed.

Conclusion

Observed a high percentage of E. coli that were resistant to SXT drug, and having several virulence genes, poses a real threat, it requires a real pause to create substitutions to limit the spreading of this threat.

A fusion of the Bacteroides fragilis ferrous iron import proteins reveals a role for FeoA in stabilizing GTP-bound FeoB

Iron is an essential element for nearly all organisms, and under anoxic and/or reducing conditions, Fe²⁺ is the dominant form of iron available to bacteria. The ferrous iron transport (Feo) system is the primary prokaryotic Fe²⁺ import machinery, and two constituent proteins (FeoA and FeoB) are conserved across most bacterial species. However, how FeoA and FeoB function relative to one another remains enigmatic. In this work, we explored the distribution of feoAB operons encoding a fusion of FeoA tethered to the N-terminal, G-protein domain of FeoB via a connecting linker region. We hypothesized that this fusion poises FeoA to interact with FeoB to affect function. To test this hypothesis, we characterized the soluble NFeoAB fusion protein from Bacteroides fragilis, a commensal organism implicated in drug-resistant infections. Using X-ray crystallography, we determined the 1.50-Å resolution structure of BfFeoA, which adopts an SH3-like fold implicated in protein–protein interactions. Using a combination of structural modeling, small-angle X-ray scattering, and hydrogen–deuterium exchange mass spectrometry, we show that FeoA and NFeoB interact in a nucleotide-dependent manner, and we mapped the protein–protein interaction interface. Finally, using guanosine triphosphate (GTP) hydrolysis assays, we demonstrate that BfNFeoAB exhibits one of the slowest known rates of Feo-mediated GTP hydrolysis that is not potassium-stimulated. Importantly, truncation of FeoA from this fusion demonstrates that FeoA–NFeoB interactions function to stabilize the GTP-bound form of FeoB. Taken together, our work reveals a role for FeoA function in the fused FeoAB system and suggests a function for FeoA among prokaryotes.

Light-Induced Pulsed EPR Dipolar Spectroscopy on a Paradigmatic Hemeprotein

Light-induced pulsed EPR dipolar spectroscopic methods allow the determination of nanometer distances between paramagnetic sites. Here we employ orthogonal spin labels, a chromophore triplet state and a stable radical, to carry out distance measurements in singly nitroxide-labeled human neuroglobin. We demonstrate that Zn-substitution of neuroglobin, to populate the Zn(II) protoporphyrin IX triplet state, makes it possible to perform light-induced pulsed dipolar experiments on hemeproteins, extending the use of light-induced dipolar spectroscopy to this large class of metalloproteins. The versatility of the method is ensured by the employment of different techniques: relaxation-induced dipolar modulation enhancement (RIDME) is applied for the first time to the photoexcited triplet state. In addition, an alternative pulse scheme for laser-induced magnetic dipole (LaserIMD) spectroscopy, based on the refocused-echo detection sequence, is proposed for accurate zero-time determination and reliable distance analysis.

Comparative genomic analysis of 127 Escherichia coli strains isolated from domestic animals with diarrhea in China

Background

Escherichia coli is an important pathogen that causes diarrhea in both humans and animals. To determine the relationships between putative virulence factors and pathotypes or host taxa, many molecular studies on diarrhea-associated E. coli have been reported. However, little is known regarding genome-wide variation of E. coli from animal hosts. In this study, we performed whole genome sequencing of 127 E. coli isolates from sheep and swine with diarrhea in China. We compared isolates to explore the phylogenomic relatedness based on host origin. We explored the relationships of putative virulence factors across host taxa and pathotypes. Antimicrobial resistance was also tested.

Results

The E. coli genomes in this study were diverse with clear differences in the SNP, MLST, and O serotypes. Seven putative virulence factors (VFs) were prevalent (> 95%) across the isolates, including Hcp, csgC, dsdA, feoB, fepA, guaA, and malX. Sixteen putative VFs showed significantly different distributions (P < 0.05) in strains from sheep and swine and were primarily adhesion- and toxin-related genes. Some putative VFs were co-occurrent in some specific pathotypes and O serotypes. The distribution of 4525 accessory genes of the 127 strains significantly differed (P < 0.05) between isolates obtained from the two animal species. The 127 animal isolates sequenced in this study were each classified into one of five pathotypes: EAEC, ETEC, STEC, DAEC, and EPEC, with 66.9% of isolates belonging to EAEC. Analysis of stx subtypes and a minimum spanning tree based on MLST revealed that STEC isolates from sheep and EAEC isolates from sheep and swine have low potential to infect humans. Antibiotic resistance analysis showed that the E. coli isolates were highly resistant to ampicillin and doxycycline. Isolates from southeast China were more resistant to antibiotics than isolates from northwest China. Additionally, the plasmid-mediated colist in resistance gene mcr-1 was detected in 15 isolates, including 4 from sheep in Qinghai and 11 from swine in Jiangsu.

Conclusions

Our study provides insight into the genomes of E. coli isolated from animal sources. Distinguishable differences between swine and sheep isolates at the genomic level provides a baseline for future investigations of animal E. coli pathogens.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5588-2) contains supplementary material, which is available to authorized users.

Toward a mechanistic understanding of Feo-mediated ferrous iron uptake

Virtually all organisms require iron and have evolved to obtain this element in free or chelated forms. Under anaerobic or low pH conditions commonly encountered by numerous pathogens, iron predominantly exists in the ferrous (Fe2+) form. The ferrous iron transport (Feo) system is the only widespread mechanism dedicated solely to bacterial ferrous iron import, and this system has been linked to pathogenic virulence, bacterial colonization, and microbial survival. The canonical feo operon encodes for three proteins that comprise the Feo system: FeoA, a small cytoplasmic β-barrel protein; FeoB, a large, polytopic membrane protein with a soluble G-protein domain capable of hydrolyzing GTP; and FeoC, a small, cytoplasmic protein containing a winged-helix motif. While previous studies have revealed insight into soluble and fragmentary domains of the Feo system, the chief membrane-bound component FeoB remains poorly studied. However, recent advances have demonstrated that large quantities of intact FeoB can be overexpressed, purified, and biophysically characterized, revealing glimpses into FeoB function. Two models of full-length FeoB have been published, providing starting points for hypothesis-driven investigations into the mechanism of FeoB-mediated ferrous iron transport. Finally, in vivo studies have begun to shed light on how this system functions as a unique multicomponent complex. In light of these new data, this review will summarize what is known about the Feo system, including recent advancements in FeoB structure and function.

Studies on the X-Ray and Solution Structure of FeoB from Escherichia coli BL21

The ferrous iron transporter FeoB is an important factor in the iron metabolism of many bacteria. Although several structural studies have been performed on its cytosolic GTPase domain (NFeoB), the full-length structure of FeoB remains elusive. Based on a crystal packing analysis that was performed on crystals of NFeoB, a trimeric structure of the FeoB channel was proposed, where the transport pore runs along the trimer axis. Because this trimer has not been observed in some subsequently solved structures of NFeoB homologs, it remains unclear whether or not the trimer is indeed functionally relevant. Here, pulsed electron-electron double resonance spectroscopy, negative stain electron microscopy, and native mass spectrometry are used to analyze the oligomeric state of different soluble and full-length FeoB constructs. The results show that the full-length protein is predominantly monomeric, whereas dimers and trimers are formed to a small percentage. Furthermore, the solution structure of the switch I region is analyzed by pulsed electron-electron double resonance spectroscopy and a new, to our knowledge, crystal structure of NFeoB from Escherichia coli BL21 is presented.