Research Publications (Food Safety)

Two of the primary virulence regulators of Vibrio cholerae, ToxR and TcpP, function together with cognate effector proteins. ToxR undergoes regulated intramembrane proteolysis (RIP) during late stationary phase in response to nutrient limitation at alkaline pH, however, the specific function of its cognate ToxS remains unresolved.

The cereal pathogen Fusarium graminearum threatens food and feed production worldwide. It reduces the yield and poisons the remaining kernels with mycotoxins, notably deoxynivalenol (DON). We analyzed the importance of gamma-aminobutanoic acid (GABA) metabolism for the life cycle of this fungal pathogen. GABA metabolism in F. graminearum is partially regulated by the global nitrogen regulator AreA.

Rod-shaped bacterial cells are polarized, with many organelles confined to a polar cellular site. In polar flagellates, FlhF and FlhG, a multiple-domain (B-N-G) GTPase and a MinD-like ATPase respectively, function as a cognate pair to regulate flagellar localization and number as revealed in Vibrio and Pseudomonas species.

Thermophilic Campylobacter species colonize the intestine of agricultural and domestic animals commensally, but cause severe gastroenteritis in humans. In contrast to other enteropathogenic bacteria, Campylobacter have been considered to be non-glycolytic, a metabolic property originally used for their taxonomic classification. Contrary to this dogma, we demonstrate that several Campylobacter coli strains are able to utilize glucose as a growth substrate.

Campylobacters are a leading cause of gastrointestinal morbidity worldwide and the majority of human infections are triggered by eating foods contaminated with Campylobacter jejuni or Campylobacter coli. Campylobacters are equally notorious for their ability to mimic human glycoconjugate structures and for their capacity to synthesize both N- and O-linked glycoproteins.

Campylobacter jejuni, one of the most common causes of gastroenteritis worldwide, is transmitted to humans through poultry. We previously reported that Lactobacillus gasseri SBT2055 (LG2055) reduced C. jejuni infection in human epithelial cells in vitro and inhibited pathogen colonization of chickens in vivo.

Spatiotemporal regulation of cell polarity plays a role in many fundamental processes in bacteria and often relies on ‘landmark’ proteins which recruit the corresponding clients to their designated position. Here, we explored the localization of two multi-protein complexes, the polar flagellar motor and the chemotaxis array, in Shewanella putrefaciens CN-32. We demonstrate that polar positioning of the flagellar system, but not of the chemotaxis system, depends on the GTPase FlhF.

Trivalent organoarsenic compounds are far more toxic than either pentavalent organoarsenicals or inorganic arsenite. Many microbes methylate inorganic arsenite (As(III)) to more toxic and carcinogenic methylarsenite (MAs(III)). Additionally, monosodium methylarsenate (MSMA or MAs(V)) has been used widely as an herbicide and is reduced by microbial communities to MAs(III).

As it became evident recently, extracellular DNA could be a versatile nutrient source of the facultative pathogen Vibrio cholerae along the different stages of its life cycle. By the use of two extracellular nucleases and periplasmic phosphatases, V. cholerae degrades extracellular DNA to nucleosides. In this study, we investigated the nucleoside uptake via identification and characterization of VCA0179, VC1953 and VC2352 representing the three nucleoside transport systems in V. cholerae.

Phosphate is essential for life, being used in many core processes such as signal transduction and synthesis of nucleic acids. The waterborne agent of cholera, Vibrio cholerae, encounters phosphate limitation in both the aquatic environment and human intestinal tract. This bacterium can utilize extracellular DNA (eDNA) as a phosphate source, a phenotype dependent on secreted endo- and exonucleases. However, no transporter of nucleotides has been identified in V.

Small RNAs are principal elements of bacterial gene regulation and physiology. Two small RNAs in Brucella abortus, AbcR1 and AbcR2, are required for wild-type virulence. Examination of the abcR loci revealed the presence of a gene encoding a LysR-type transcriptional regulator flanking abcR2 on chromosome 1. Deletion of this lysR gene (bab1_1517) resulted in the complete loss of abcR2 expression, while no difference in abcR1 expression was observed. The B.

The class-II AP-endonuclease (XthA) acts on abasic sites of damaged DNA in bacterial base excision repair. We identified that the sliding DNA β-clamp forms in vivo and in vitro complexes with XthA in Mycobacterium tuberculosis. A novel 239QLRFPKK245 motif in the DNA-binding domain of XthA was found to be important for the interactions. Likewise, the peptide-binding-groove (PBG) and the C-terminal of β-clamp located on different domains, interact with XthA.

Vibrio cholerae cytolysin (VCC) permeabilises target cell membranes by forming transmembrane oligomeric β-barrel pores. VCC has been shown to associate with the target membranes via amphipathicity-driven spontaneous partitioning into the membrane environment. More specific interaction(s) of VCC with the membrane components have also been documented.

Several Fusarium species produce the polyketide mycotoxin zearalenone (ZEA), a causative agent of hyperestrogenic syndrome in animals that is often found in F. graminearum-infected cereals in temperate regions. The ZEA biosynthetic cluster genes PKS4, PKS13, ZEB1, and ZEB2 encode a reducing polyketide synthase, a nonreducing polyketide synthase, an isoamyl alcohol oxidase, and a transcription factor, respectively.

Vibrio cholerae uses a multiprotein transcriptional regulatory cascade to control expression of virulence factors cholera toxin and toxin-coregulated pilus. Two proteins in this cascade are ToxR and TcpP – unusual membrane-localized transcription factors with relatively undefined periplasmic domains and transcription activator cytoplasmic domains.

Salmonellae survive and propagate in macrophages to cause serious systemic disease. Periplasmic superoxide dismutase plays a critical role in this survival by combating phagocytic superoxide. Salmonella Typhimurium strain 14028 produces two periplasmic superoxide dismutases, SodCI and SodCII. Although both proteins are produced during infection, only SodCI is functional in the macrophage phagosome.

H-NS is a well-established silencer of virulence gene transcription in the human pathogen Vibrio cholerae. Biofilm formation aids V. cholerae in colonizing both its host and its external environments and H-NS silences biofilm gene expression. Cyclic-di-guanosine monophosphate acts through the DNA binding proteins VpsR and VpsT to overcome H-NS-mediated repression of biofilm genes, driving a transition between a planktonic and a colonial/biofilm lifestyle.

Expression of Vibrio cholerae genes required for the biosynthesis of exopolysacchide (vps) and protein (rbm) components of the biofilm matrix is enhanced by cyclic diguanylate (c-di-GMP). In a previous study, we reported that the H-NS protein represses the transcription of vpsA, vpsL and vpsT.

The diarrheal pathogen Vibrio cholerae contains 3 gene clusters that encode chemotaxis-related proteins, but only cluster II appears to be required for chemotaxis. Here, we present the first characterization of V. cholerae's “cluster III” chemotaxis system. We found that cluster III proteins assemble into foci at bacterial poles, like those formed by cluster II proteins, but the two systems assemble independently and do not colocalize.

Salmochelins are glucosylated forms of enterobactin (enterochelin) and contribute to virulence of Salmonella enterica and some extra-intestinal pathogenic E. coli (ExPEC). Fes, IroD and IroE esterases degrade salmochelins and enterobactin to release iron. We investigated the apparently redundant role of these esterases in virulence and in salmochelin production and utilisation of the ExPEC strain χ7122.

Gram-negative bacteria survive harmful environmental stressors by modifying their outer membrane. Much of this protection is afforded upon remodeling of the lipid A region of the major surface molecule lipopolysaccharide (LPS). For example, the addition of cationic substituents, such as 4-amino-4-deoxy-L-arabinose (L-Ara4N) and phosphoehthanolamine (pEtN) at the lipid A phosphate groups, is often induced in response to specific environmental flux stabilizing the outer membrane.

Second messengers are key components of many signal transduction pathways. In addition to cyclic AMP, ppGpp, and cyclic di-GMP, many bacteria use also cyclic di-AMP as a second messenger. This molecule is synthesized by distinct classes of diadenylate cyclases and degraded by phosphodiesterases. The control of the intracellular c-di-AMP pool is very important since both a lack of this molecule and its accumulation can inhibit growth of the bacteria.

Autotransporters are a superfamily of virulence factors secreted by Gram negative bacteria. They are comprised of an N-terminal passenger domain that is translocated across the outer membrane, and a C-terminal domain that inserts into the outer membrane forming a β-barrel anchor. It is still poorly understood how the passenger is efficiently translocated in the absence of external energy inputs.

An exoprotease of Vibrio vulnificus, VvpS, exhibits an autolytic function during the stationary phase. To understand how vvpS expression is controlled, the regulators involved in vvpS transcription and their regulatory mechanisms were investigated. LeuO was isolated in a ligand-fishing experiment, and experiments using a leuO-deletion mutant revealed that LeuO represses vvpS transcription. LeuO bound the extended region including LeuO-binding site (LBS)-I and LBS-II.

The microaerophilic food-borne pathogen Campylobacter jejuni uses complex cytochrome-rich respiratory chains for growth and host colonization. Cytochrome c biogenesis requires haem ligation to reduced apocytochrome cysteines, catalysed by the cytochrome c synthase, CcsBA. While ccsBA could not be deleted, we showed that the thiol reductase DsbD and the CcsX homologue Cj1207 are involved in, but not essential for, cytochromes c biogenesis.