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  • 1.
    Aliashkevich, Alena
    et al.
    Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS). Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
    Alvarez, Laura
    Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS). Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
    Cava, Felipe
    Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS). Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
    New Insights Into the Mechanisms and Biological Roles of D-Amino Acids in Complex Eco-Systems2018In: Frontiers in Microbiology, ISSN 1664-302X, E-ISSN 1664-302X, Vol. 9, article id 683Article, review/survey (Refereed)
    Abstract [en]

    In the environment bacteria share their habitat with a great diversity of organisms, from microbes to humans, animals and plants. In these complex communities, the production of extracellular effectors is a common strategy to control the biodiversity by interfering with the growth and/or viability of nearby microbes. One of such effectors relies on the production and release of extracellular D-amino acids which regulate diverse cellular processes such as cell wall biogenesis, biofilm integrity, and spore germination. Non-canonical D-amino acids are mainly produced by broad spectrum racemases (Bsr). Bsr's promiscuity allows it to generate high concentrations of D-amino acids in environments with variable compositions of L-amino acids. However, it was not clear until recent whether these molecules exhibit divergent functions. Here we review the distinctive biological roles of D-amino acids, their mechanisms of action and their modulatory properties of the biodiversity of complex eco-systems.

  • 2.
    Alvarez, Laura
    et al.
    Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Aliashkevich, Alena
    Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    de Pedro, Miguel A.
    Cava, Felipe
    Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS).
    Bacterial secretion of D-arginine controls environmental microbial biodiversity2018In: The ISME Journal, ISSN 1751-7362, E-ISSN 1751-7370, Vol. 12, no 2, p. 438-450Article in journal (Refereed)
    Abstract [en]

    Bacteria face tough competition in polymicrobial communities. To persist in a specific niche, many species produce toxic extracellular effectors to interfere with the growth of nearby microbes. These effectors include the recently reported non-canonical D-amino acids (NCDAAs). In Vibrio cholerae, the causative agent of cholera, NCDAAs control cell wall integrity in stationary phase. Here, an analysis of the composition of the extracellular medium of V. cholerae revealed the unprecedented presence of D-Arg. Compared with other D-amino acids, D-Arg displayed higher potency and broader toxicity in terms of the number of bacterial species affected. Tolerance to D-Arg was associated with mutations in the phosphate transport and chaperone systems, whereas D-Met lethality was suppressed by mutations in cell wall determinants. These observations suggest that NCDAAs target different cellular processes. Finally, even though virtually all Vibrio species are tolerant to D-Arg, only a few can produce this D-amino acid. Indeed, we demonstrate that D-Arg may function as part of a cooperative strategy in vibrio communities to protect non-producing members from competing bacteria. Because NCDAA production is widespread in bacteria, we anticipate that D-Arg is a relevant modulator of microbial subpopulations in diverse ecosystems.

  • 3. Howell, Matthew
    et al.
    Aliashkevich, Alena
    Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS). Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
    Salisbury, Anne K.
    Cava, Felipe
    Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS). Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine).
    Bowman, Grant R.
    Brown, Pamela J. B.
    Absence of the Polar Organizing Protein PopZ Results in Reduced and Asymmetric Cell Division in Agrobacterium tumefaciens2017In: Journal of Bacteriology, ISSN 0021-9193, E-ISSN 1098-5530, Vol. 199, no 17, article id UNSP e00101-17Article in journal (Refereed)
    Abstract [en]

    Agrobacterium tumefaciens is a rod-shaped bacterium that grows by polar insertion of new peptidoglycan during cell elongation. As the cell cycle progresses, peptidoglycan synthesis at the pole ceases prior to insertion of new peptidoglycan at midcell to enable cell division. The A. tumefaciens homolog of the Caulobacter crescentus polar organelle development protein PopZ has been identified as a growth pole marker and a candidate polar growth-promoting factor. Here, we characterize the function of PopZ in cell growth and division of A. tumefaciens. Consistent with previous observations, we observe that PopZ localizes specifically to the growth pole in wild-type cells. Despite the striking localization pattern of PopZ, we find the absence of the protein does not impair polar elongation or cause major changes in the peptidoglycan composition. Instead, we observe an atypical cell length distribution, including minicells, elongated cells, and cells with ectopic poles. Most minicells lack DNA, suggesting a defect in chromosome segregation. Furthermore, the canonical cell division proteins FtsZ and FtsA are misplaced, leading to asymmetric sites of cell constriction. Together, these data suggest that PopZ plays an important role in the regulation of chromosome segregation and cell division. IMPORTANCE A. tumefaciens is a bacterial plant pathogen and a natural genetic engineer. However, very little is known about the spatial and temporal regulation of cell wall biogenesis that leads to polar growth in this bacterium. Understanding the molecular basis of A. tumefaciens growth may allow for the development of innovations to prevent disease or to promote growth during biotechnology applications. Finally, since many closely related plant and animal pathogens exhibit polar growth, discoveries in A. tumefaciens may be broadly applicable for devising antimicrobial strategies.

  • 4. Howell, Matthew
    et al.
    Aliashkevich, Alena
    Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS). Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine). Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Sundararajan, Kousik
    Daniel, Jeremy J.
    Lariviere, Patrick J.
    Goley, Erin D.
    Cava, Felipe
    Umeå University, Faculty of Medicine, Molecular Infection Medicine Sweden (MIMS). Umeå University, Faculty of Medicine, Department of Molecular Biology (Faculty of Medicine). Umeå University, Faculty of Medicine, Umeå Centre for Microbial Research (UCMR).
    Brown, Pamela J. B.
    Agrobacterium tumefaciens divisome proteins regulate the transition from polar growth to cell division2019In: Molecular Microbiology, ISSN 0950-382X, E-ISSN 1365-2958, Vol. 111, no 4, p. 1074-1092Article in journal (Refereed)
    Abstract [en]

    The mechanisms that restrict peptidoglycan biosynthesis to the pole during elongation and re-direct peptidoglycan biosynthesis to mid-cell during cell division in polar-growing Alphaproteobacteria are largely unknown. Here, we explore the role of early division proteins of Agrobacterium tumefaciens including three FtsZ homologs, FtsA and FtsW in the transition from polar growth to mid-cell growth and ultimately cell division. Although two of the three FtsZ homologs localize to mid-cell, exhibit GTPase activity and form co-polymers, only one, FtsZ(AT), is required for cell division. We find that FtsZ(AT) is required not only for constriction and cell separation, but also for initiation of peptidoglycan synthesis at mid-cell and cessation of polar peptidoglycan biosynthesis. Depletion of FtsZ(AT) in A. tumefaciens causes a striking phenotype: cells are extensively branched and accumulate growth active poles through tip splitting events. When cell division is blocked at a later stage by depletion of FtsA or FtsW, polar growth is terminated and ectopic growth poles emerge from mid-cell. Overall, this work suggests that A. tumefaciens FtsZ makes distinct contributions to the regulation of polar growth and cell division.

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