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  • 1. Campos, Manuel
    et al.
    Cisneros, David A.
    Institut Pasteur, Molecular Genetics Unit, Department of Microbiology, 75015 Paris, France.
    Nivaskumar, Mangayarkarasi
    Francetic, Olivera
    The type II secretion system: a dynamic fiber assembly nanomachine2013In: Research in Microbiology, ISSN 0923-2508, E-ISSN 1769-7123, Vol. 164, no 6, p. 545-555Article in journal (Refereed)
    Abstract [en]

    Type II secretion systems (T2SSs) share common origins and structure with archaeal flagella (archaella) and pili, bacterial competence systems and type IV pili. All of these systems use a conserved ATP-powered machinery to assemble helical fibers that are anchored in the plasma membrane. The T2SSs assemble pseudopili, periplasmic filaments that promote extracellular secretion of folded periplasmic proteins. Comparative analysis of T2SSs and related fiber assembly nanomachines might provide important clues on their functional specificities and dynamics. This review focuses on recent developments in the study of pseudopilus structure and biogenesis, and discusses mechanistic models of pseudopilus function in protein secretion.

  • 2. Kupka, Daniel
    et al.
    Liljeqvist, Maria
    Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).
    Nurmi, Pauliina
    Puhakka, Jaakko A
    Tuovinen, Olli H
    Dopson, Mark
    Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology).
    Oxidation of elemental sulfur, tetrathionate and ferrous iron by the psychrotolerant Acidithiobacillus strain SS3.2009In: Research in Microbiology, ISSN 0923-2508, E-ISSN 1769-7123, Vol. 160, no 10, p. 767-74Article in journal (Refereed)
    Abstract [en]

    Mesophilic iron and sulfur-oxidizing acidophiles are readily found in acid mine drainage sites and bioleaching operations, but relatively little is known about their activities at suboptimal temperatures and in cold environments. The purpose of this work was to characterize the oxidation of elemental sulfur (S(0)), tetrathionate (S4O6(2-)) and ferrous iron (Fe2+) by the psychrotolerant Acidithiobacillus strain SS3. The rates of elemental sulfur and tetrathionate oxidation had temperature optima of 20 degrees and 25 degrees C, respectively, determined using a temperature gradient incubator that involved narrow (1.1 degrees C) incremental increases from 5 degrees to 30 degrees C. Activation energies calculated from the Arrhenius plots were 61 and 89 kJ mol(-1) for tetrathionate and 110 kJ mol(-1) for S(0) oxidation. The oxidation of elemental sulfur produced sulfuric acid at 5 degrees C and decreased the pH to approximately 1. The low pH inhibited further oxidation of the substrate. In media with both S(0) and Fe2+, oxidation of elemental sulfur did not commence until all available ferrous iron was oxidized. These data on sequential oxidation of the two substrates are in keeping with upregulation and downregulation of several proteins previously noted in the literature. Ferric iron was reduced to Fe2+ in parallel with elemental sulfur oxidation, indicating the presence of a sulfur:ferric iron reductase system in this bacterium.

  • 3.
    Liu, Junfa
    et al.
    Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology). Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Thanikkal, Edvin
    Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology). Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Obi, Ikenna
    Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology). Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Francis, Matthew
    Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology). Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Elevated CpxR~P levels repress the Ysc-Yop type III secretion system of Yersinia pseudotuberculosis2012In: Research in Microbiology, ISSN 0923-2508, E-ISSN 1769-7123, Vol. 163, no 8, p. 518-530Article in journal (Refereed)
    Abstract [en]

    One way that Gram-negative bacteria respond to extracytoplasmic stress is through the CpxA-CpxR system. An activated CpxA sensor kinase phosphorylates the CpxR response regulator to instigate positive auto-amplification of Cpx pathway activation, as well as synthesis of various bacterial survival factors. In the absence of CpxA, human enteropathogenic Yersinia pseudotuberculosis accumulates high CpxR~P levels aided by the action of low molecular weight phosphodonors such as acetyl~P. Critically, these bacteria are also defective for plasmid encoded Ysc-Yop-dependent type III synthesis and secretion, an essential determinant of virulence. Herein, we investigated whether elevated CpxR~P levels account for lost Ysc-Yop function. Decisively, reducing CpxR~P in Yersinia defective for CpxA phosphatase activity - through incorporating second-site suppressor mutations in ackA-pta or cpxR - dramatically restored Ysc-Yop T3S function. Moreover, the repressive effect of accumulated CpxR~P is a direct consequence of binding to the promoter regions of the T3S genes. Thus, Cpx pathway activation has two consequences in Yersinia; one, to maintain quality control in the bacterial envelope, and the second, to restrict ysc-yop gene expression to those occasions where it will have maximal effect.

  • 4.
    Otto, Karen
    Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
    Biophysical approaches to study the dynamic process of bacterial adhesion.2008In: Research in Microbiology, ISSN 0923-2508, E-ISSN 1769-7123, Vol. 159, no 6, p. 415-22Article in journal (Refereed)
    Abstract [en]

    Recent applications of biophysical techniques to the study of adhesion and biofilm formation are playing an important role in broadening our understanding of bacterial interactions. While non-invasive methods enable measurement of adhesion kinetics in real time, single-cell approaches provide information about adhesion forces mediated by specific cell surface structures. Promising approaches are presented in this review.

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