Research Publications (Food Safety)

Enterohemorrhagic Escherichia coli (EHEC), an enteropathogen that colonizes in the intestine, causes severe diarrhea and hemorrhagic colitis in humans by the expression of the type III secretion system (T3SS) and Shiga‐like toxins (Stxs). However, how EHEC can sense and respond to the changes in the alimentary tract and coordinate the expression of these virulence genes remains elusive.

DNA gyrase is an essential type II topoisomerase that is composed of two subunits, GyrA and GyrB and has an A2B2 structure. Although the A and B subunits are required in equal proportions to form DNA gyrase, the gyrA and gyrB genes that encode them in Salmonella (and in many other bacteria) are at separate locations on the chromosome, are under separate transcriptional control, and are present in different copy numbers in rapidly growing bacteria.

Certain stresses or conditions induce production or import of putrescine and/or cadaverine. Once stress is relieved or conditions change, the polyamines need to be exported via PaeA. Failure to export leads to high polyamine concentrations that are lethal under certain conditions. Abstract Salmonella and E. coli synthesize, import, and export cadaverine, putrescine, and spermidine to maintain physiological levels and provide pH homeostasis.

This paper presents the first evidence of a heterodimer formation between the periplasmic domains of ToxR and ToxS, two main regulators of the cholera causative Vibrio cholerae. The interaction establishes a protection of ToxR against proteolysis. The atomic resolution structure of ToxRp shows an αβ‐fold followed by a long unstructured C‐terminal stretch which plays a significant role in the stability of ToxRp.

A regulatory circuit indicates the interplay between the major outer membrane porin OmpU, periplasmic stress stimuli and the σE response pathway in Vibrio cholerae. This study reveals a negative feedback regulation resulting in fine‐tuning of the ompU expression level, balancing stress response and survival. Putative factor(s) operating on the negative feedback regulation on ompU expression is shown in burgundy colour.

Vibrio cholerae cytolysin is a potent membrane‐damaging toxin that perforates cell membranes by forming oligomeric β‐barrel pores. We have shown that a key tyrosine residue in the hinge region of the pore‐forming motif plays a crucial role in regulating the oligomeric pore‐formation mechanism of the toxin. Such a regulatory mechanism has not been documented earlier in the structurally‐related β‐barrel pore‐forming toxins.

The most lethal malaria parasite, Plasmodium falciparum, rapidly adapts to acquire drug resistance. For the first time, we report that highly resistant Plasmodium parasites carry additional copies of resistance‐conferring genes separate from the genome, which are known as extra‐chromosomal DNA (ecDNA). This finding provides a new model to study a fundamental mechanism of adaptation that is relevant in many microbes and may lead to a new way to target malaria.

HMP‐P synthase (Thi5) is a critical enzyme in the biosynthesis of thiamine pyrophosphate in yeast. A Thi5 homolog from Legionella pneumophila, which contributes to HMP synthesis in its native host, is an enzyme that binds pyridoxal‐5’‐phosphate and releases HMP when the purified protein is incubated with iron. In a heterologous system Thi5 from Saccharomyces cerevisiae and L.

The majority of M. tuberculosis infections result in latent tuberculosis where bacteria are dormant and exhibit phenotypic drug tolerance. Mycobacterial cell envelope lipids, or their biosynthetic precursors, are exported from the cytoplasm by MmpL transporters. We showed previously that MmpL11 exports lipids that are important for biofilm formation and non‐replicating persistence, two phenotypes associated with dormancy.

We describe a protein secretion system in Gram‐negative bacteria that uses a holin membrane protein in tandem with a cell wall editing enzyme. The pairing of holins from different families with various types of peptidoglycan hydrolases suggests that this secretion pathway evolved multiple times. We propose that the pathway be named the Type 10 Secretion System (TXSS). Summary Gram‐negative bacteria have evolved numerous pathways to secrete proteins across their complex cell envelopes.

Sulfane sulfur such as glutathione persulfide (GSSH) is produced from H2S oxidation or from L‐cysteine metabolism. It accumulates inside Pseudomonas aeruginosa PAO1 during the stationary phase of growth, inactivating a repressor to increase the expression of a major multidrug efflux pump. The finding explains why the bacterium is relatively resistant to antibiotics at the stationary phase of growth.

ES24, but not nitrofurantoin, inhibits SecYEG‐dependent protein transport in bacteria and exhibits anti‐bacterial activity towards various clinically relevant strains. In addition, ES24 affects many other processes important to E. coli, hinting at a multifaceted mode of action of ES24. Summary Eeyarestatin 1 (ES1) is an inhibitor of endoplasmic reticulum (ER) associated protein degradation, Sec61‐dependent Ca2+ homeostasis and protein translocation into the ER.

Vibrio cholerae, the causative agent of the acute diarrheal disease cholera, is able to thrive in diverse habitats such as natural water bodies and inside human hosts. To ensure their survival, these bacteria rely on chemosensory pathways to sense and respond to changing environmental conditions. These pathways constitute a highly sophisticated cellular control system in Bacteria and Archaea. Reflecting the complex life cycle of V.

Copper is essential, but highly toxic. Direct responses of bacteria to excess copper, collectively termed copper homeostasis systems, are well known, but how copper causes toxicity is unclear. This review summarizes how both direct copper homeostasis responses, and indirect accessory stress‐response pathways are essential to resisting copper toxicity among enterobacteria. Abstract Copper is a required micronutrient for bacteria and an essential cofactor for redox‐active cuproenzymes.

Our data suggest a model in which L. monocytogenes ΔspxA1 produces less cytochrome bd than wt, generating ROS from the incomplete electron transport chain. This would normally be readily detoxified but ΔspxA1 is deficient in catalase production and is thus more sensitive to peroxide‐mediated toxicity. Therefore, the severe ΔspxA1 aerobic growth defect is the result of increased ROS in the absence of catalase and heme.

The membrane‐bound transcription regulator ToxR controls housekeeping and virulence gene expression in V. cholerae. The activity and stability of ToxR strongly depends on its operon partner ToxS, the redox state of its periplasmic cysteine residues and environmental stimuli. Here, ToxR‐ToxR PPIs are key for its activity, which is influenced by ToxS, DNA binding capabilities, bile and the disulfide bond forming enzymes DsbA/C, which induce intra‐ or intermolecular disulfide bonds.

The ATP binding cassette (ABC) transporter LptB2FGC extracts LPS from the inner membrane and powers the transport of the glycolipid to the cell surface in Gram‐negative bacteria. Our study shows that changes to the LPS structure and the transporter can affect how the function of the cytoplasmic LptB ATPase is coupled to the extraction of LPS by LptFG by either promoting or interfering with the collapse of the substrate‐binding cavity.

Overlapping transcription between the mRNAs of the neighbouring genes is a common process in bacteria. The resulting paired RNAs are digested genome‐wide by the action of the double‐stranded endoribonuclease RNase III. New examples of gene arrangements where overlapping transcription plays a key role are summarised to explain our current understanding regarding how overlapping transcription may serve a general purpose of coordinating the bacterial gene expression.

Contrary to other human bacterial pathogens, most strains of the human pathogen L. monocytogenes have preserved along decades susceptibility to the key‐drugs used to treat human infections. L. monocytogenes has a large core‐genome (present in all strains of the species), allowing to adapt to multiple environmental niches without the need of recruiting accessory genes from other species by horizontal gene transfer.

Serovar 4b strains of L. monocytogenes possess galactosylated WTAs and LTAs. We show that two different genes, gtlB and gttB encode two distinct glycosyltransferases required for the galactosylation of LTA and WTA respectively. Deletion of these genes reveals that the galactose decoration on WTA but not LTA is responsible for the surface retention and function of the important virulence factor InlB.

The universe of Molecular Microbial Pathogenesis is filled with many female and male stars. But there are two particularly bright shining supernovae‐like stars: the late Stanley Falkow and the very lively and creative Pascale Cossart. These two outstanding luminaries, surrounded by numerous planets, do not only belong to different scientific generations but their splendor also comes from very different scientific concepts.

Mycobacteria use type VII secretion systems (T7SSs) to translocate proteins across their diderm cell envelope. We previously showed that the Mycobacterium tuberculosis ESX‐5 T7SS is unable to complement secretion in a Mycobacterium marinum esx‐5 mutant, suggesting species‐specificity in secretion. In this study, we established that a specific domain, i.e. linker 2, of the membrane ATPase EccC5 is responsible for this.

In Vibrio parahaemolyticus, the iron uptake regulator Fur represses genes involved in iron acquisition and swarming. The Fur regulon also includes a previously uncharacterized regulator fcrX. Overproduction of FcrX, which is a small tetratricopeptide repeat‐containing protein, affects phenotypes in multiple bacterial species. FcrX interacts with V. parahaemolyticus and Escherichia coli Fur. Through this interaction, FcrX may serve as an insulator to inhibit the repressive function of Fur.

Many pathogenic bacteria use different types of thermosensors to sense increased temperature once inside the host. In this review, we are describing the identification of protein, DNA and RNA thermosensors that took place around 20 years ago. In particular, we describe the events leading to the discovery of the prfA thermosensor in Listeria monocytogenes (depicted). Abstract An outstanding question regards the ability of organisms to sense their environments and respond in a suitable way.

While exposure to high levels of toxic metals such as cadmium and arsenic is only experienced in a handful of special habitats and ecosystems, Listeria and other Gram‐positive bacteria have evolved an impressively diverse array of genetic tools for acquiring enhanced tolerance to such metals.