Purification and partial characterization of two azoreductases from Shigella dysenteriae Type 1

Two azoreductases (I and II) were purified to homogeneity from extracts of Shigella dysenteriae (type 1). Azoreductase I was a dimer of identical subunits of M(r) 28,000, whereas azoreductase II was a monomer of 11,000 M(r). Both were flavoproteins, each containing 1 mol of FMN per mol enzyme. Both NADH and NADPH functioned as electron donors for the azoreductases. Azoreductase I used Ponceau SX, Tartrazine, Amaranth and Orange II as substrates. Azoreductase II utilized all the dyes except Amaranth.     

Treatment of HeLa cells with bacterial water extracts inhibits Shigella flexneri invasion

Abstract Pathogenesis mediated by Shigella flexneri requires invasion of the gastrointestinal epithelium. It has been previously shown that HeLa cells challenged with S. flexneri show alterations in their phosphotyrosine-containing protein profile. In this report, we demonstrated that bacterial water extracts (WE) abrogated the invasion of HeLa cells by S. flexneri in a dose-dependent manner. A proteinaceous component of S. flexneri was shown to be responsible for this inhibitory activity. Proteins encoded on the 140-MDa plasmid were not responsible for the observed inhibition. WE from other Gram-negative bacteria also inhibited Shigella invasion of HeLa cells. HeLa cells pretreated with WE showed changes in the profile and the intensity of phosphotyrosine-containing protein bands. These data were consistent with a surface protein component in WE which initiated aberrant host cell signaling at the membrane which may account for the inhibition of bacterial entry.     

The history of septin biology and bacterial infection

Investigation of cytoskeleton during bacterial infection has significantly contributed to both cell and infection biology. Bacterial pathogens Listeria monocytogenes and Shigella flexneri are widely recognised as paradigms for investigation of the cytoskeleton during bacterial entry, actin‐based motility, and cell‐autonomous immunity. At the turn of the century, septins were a poorly understood component of the cytoskeleton mostly studied in the context of yeast cell division and human cancer. In 2002, a screen performed in the laboratory of Pascale Cossart identified septin family member MSF (MLL septin‐like fusion, now called SEPT9) associated with L. monocytogenes entry into human epithelial cells. These findings inspired the investigation of septins during L. monocytogenes and S. flexneri infection at the Institut Pasteur, illuminating important roles for septins in host–microbe interactions. In this review, we revisit the history of septin biology and bacterial infection, and discuss how the comparative study of L. monocytogenes and S. flexneri has been instrumental to understand septin roles in cellular homeostasis and host defence.     

Proteomes of pathogenic Escherichia coli/Shigella group surveyed in their host environments

Proteomic studies on Shigella dysenteriae, Shigella flexneri, enterohemorrhagic Escherichia coli and uropathogenic E. coli (UPEC) are reviewed. UPEC causes infections in the urogenital tract, whereas the other species colonize and, to varying degrees, invade the intestinal tract. Type III secretion systems used to breach the mucosal barrier by the intestinal pathogens revealed distinct expression patterns in different host environments. Dynamic adaptations to changes in nutrient availability and oxygen were observed, including increased reliance on anaerobic respiration and mixed acid fermentation in vivo. Utilization of carbon and nitrogen resources by the bacteria varied considerably depending on the host model investigated. Shigellae and UPEC adapted to metal ion sequestration in the mammalian host by enhancing expression of various receptors and transporters for iron and zinc. This appears to reflect the preferred intracellular life stage of Shigella spp. and responses of UPEC to high levels of lipocalin and lactotransferrin in the urinary tract.     

In vitro selection of a DNA aptamer targeted against Shigella dysenteriae

To identify DNA aptamers demonstrating binding specificity for Shigella dysenteriae, a whole-bacterium Systemic Evolution of Ligands by Exponential enrichment (SELEX) method was applied to a combinatorial library of single-stranded DNA (ssDNA) molecules. After several rounds of selection using S. dysenteriae as the target, the highly enriched oligonucleotide pool was sequenced and then grouped into different families based on primary sequence homologies and similarities in the secondary structures. Aptamer S 1, which showed particularly high binding affinity in preliminary studies, was chosen for further characterisation. This aptamer displayed a dissociation constant (K_d value) of 23.47 ± 2.48 nM. Binding assays to assess the specificity of aptamer S 1 showed high binding affinity for S. dysenteriae and low apparent binding affinity for other bacteria. The ssDNA aptamers generated may serve as a new type of molecular probe for microbial pathogens, as it has the potential to overcome the tedious isolation and purification requirements for complex targets.     

Oligomeric states of the Shigella translocator protein IpaB provide structural insights into formation of the type III secretion translocon

The Shigella flexneri Type III secretion system (T3SS) senses contact with human intestinal cells and injects effector proteins that promote pathogen entry as the first step in causing life threatening bacillary dysentery (shigellosis). The Shigella Type III secretion apparatus (T3SA) consists of an anchoring basal body, an exposed needle, and a temporally assembled tip complex. Exposure to environmental small molecules recruits IpaB, the first hydrophobic translocator protein, to the maturing tip complex. IpaB then senses contact with a host cell membrane, forming the translocon pore through which effectors are delivered to the host cytoplasm. Within the bacterium, IpaB exists as a heterodimer with its chaperone IpgC; however, IpaB's structural state following secretion is unknown due to difficulties isolating stable protein. We have overcome this by coexpressing the IpaB/IpgC heterodimer and isolating IpaB by incubating the complex in mild detergents. Interestingly, preparation of IpaB with n‐octyl‐oligo‐oxyethylene (OPOE) results in the assembly of discrete oligomers while purification in N,N‐dimethyldodecylamine N‐oxide (LDAO) maintains IpaB as a monomer. In this study, we demonstrate that IpaB tetramers penetrate phospholipid membranes to allow a size‐dependent release of small molecules, suggesting the formation of discrete pores. Monomeric IpaB also interacts with liposomes but fails to disrupt them. From these and additional findings, we propose that IpaB can exist as a tetramer having inherent flexibility, which allows it to cooperatively interact with and insert into host cell membranes. This event may then lay the foundation for formation of the Shigella T3SS translocon pore.     

志贺菌基因组进化研究进展

志贺菌属(Shigella)是引起全球范围内细菌性痢疾的重要病原菌.近年来,多重耐药型和新血清型志贺菌的不断出现给志贺菌的监测和防控带来了新的挑战.基因组学的快速发展为深入了解志贺菌的进化来源、变异机制及传播规律等提供了极大的帮助,对控制细菌性痢疾的蔓延具有重要的科学意义.本文首先从遗传来源角度探讨志贺菌与大肠杆菌的进化关系及其可能的分子机制,随后对福氏、宋内和1型痢疾志贺菌的基因组进化进展进行了总结,详细描述了它们的时空分布特点以及耐药基因变异在进化中所发挥的作用,以期为志贺菌的研究和防控提供参考.     

Detection of Shiga-like toxin on the outer membranes of Shigella species and Escherichia coli K-12

Abstract Outer membranes of Shigella species and E. coli K-12 carrying large invasive plasmids and isogenic non-invasive strains without plasmids were analyzed by SDS-PAGE. The immunoblotting analysis of the outer membrane proteins of these bacteria was performed with monoclonal antibody (mAb) made against A and B subunits of Shiga-like toxin (SLT). The SLT was detected in the outer membranes of S. dysenteriae 1 IDBM11, S. sonnei PNS20, S. flexneri M90T, S. dysenteriae 60R, and E. coli K-12 strain AB2463. The two other E. coli K-12 strains, C600 and 933J were included as controls for low and high toxin producers respectively. The outer membrane protein band of molecular weight 70 kDa was common to all bacterial strains studied. The most prominent band of 70 kDa protein was seen to be present in the high toxin producing plasmidless strain of S. dysenteriae 60R and the lysogenic strain of E. coli 933J. The invasive strains of S. dysenteriae 1 and S. flexneri M90T which carry the large invasive plasmids showed the least prominent band of 70 kDa protein.
The immunoblotting analysis of Shiga-toxin partially purified from the S. dysenteriae 60R strain revealed the absence of 70 kDa band on SDS-PAGE, instead the two dissociated subunits were seen. Furthermore, periplasmic Shiga-toxin proteins also showed the complete dissociation into A and B subunits. However, under the same denaturing conditions, the 70 kDa protein band cross-reacting with mAb against A and B subunits was still present in the outer membranes of all different strains.     

The expression of lipopolysaccharide by strains of Shigella dysenteriae, Shigella flexneri and Shigella boydii and their cross-reacting strains of Escherichia coli

Strains of Shigella dysenteriae, Shigella flexneri and Shigella boydii express lipopolysaccharides, that enable the serotyping of strains based on their antigenic structures. Certain strains of S. dysenteriae, S. flexneri and S. boydii are known to share epitopes with strains of Escherichia coli ; however, the lipopolysaccharide profiles of the cross-reacting organisms have not been compared by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) lipopolysaccharides profiling. In the present study, type strains of these bacteria were examined using SDS-PAGE/silver staining to compare their respective lipopolysaccharide profiles. Strains of S. dysenteriae, S. boydii and S. flexneri all expressed long-chain lipopolysaccharide, with distinct profile patterns. The majority of strains of Shigella spp., known to cross-react with strains of E. coli , had lipopolysaccharide profiles quite distinct from the respective strain of E. coli . It was concluded that while cross-reacting strains of Shigella spp. and E. coli may express shared lipopolysaccharide epitopes, their lipopolysaccharide structures are not identical.