(FBIOyF) Departamento de Microbiología

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https://rephip.unr.edu.ar/handle/2133/2564

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Examinando (FBIOyF) Departamento de Microbiología por Autor "Altabe, Silvia Graciela"

Mostrando 1 - 4 de 4
  • Miniatura
    ÍtemAcceso Abierto
    Cerulenin inhibits unsaturated fatty acids synthesis in Bacillus subtilis by modifying the input signal of DesK thermosensor
    (Wiley, 2014-04-09) Porrini, Lucía; Cybulski, Larisa Estefanía; Altabe, Silvia Graciela; Mansilla, María Cecilia; De Mendoza, Diego
    Bacillus subtilis responds to a sudden decrease in temperature by transiently inducing the expression of the des gene encoding for a lipid desaturase, Δ5-Des, which introduces a double bond into the acyl chain of preexisting membrane phospholipids. This Δ5-Des-mediated membrane remodeling is controlled by the cold-sensor DesK. After cooling, DesK activates the response regulator DesR, which induces transcription of des. We show that inhibition of fatty acid synthesis by the addition of cerulenin, a potent and specific inhibitor of the type II fatty acid synthase, results in increased levels of short-chain fatty acids (FA) in membrane phospholipids that lead to inhibition of the transmembrane-input thermal control of DesK. Furthermore, reduction of phospholipid synthesis by conditional inactivation of the PlsC acyltransferase causes significantly elevated incorporation of long-chain FA and constitutive upregulation of the des gene. Thus, we provide in vivo evidence that the thickness of the hydrophobic core of the lipid bilayer serves as one of the stimulus sensed by the membrane spanning region of DesK.
  • Miniatura
    ÍtemAcceso Abierto
    MapB, the Brucella suis TamB homologue, is involved in cell envelope biogenesis, cell division and virulence
    (Springer Nature, 2019-02-15) Bialer, Magalí Graciela; Ruiz-Ranwez, Verónica; Sycz, Gabriela; Estein, Silvia Marcela; Russo, Daniela Marta; Altabe, Silvia Graciela; Sieira, Rodrigo; Zorreguieta, Ángeles; De Bolle, Xavier: provide the anti-OMPs and anti-LPS antibodies; Ugalde, Juan: provide the anti-OMPs and anti-LPS antibodies; Cassataro, Juliana: provide the anti-OMPs and anti-LPS antibodies; Spera, Juan Manuel: provide the PQE31-3xFLAG plasmid; Bravo, Marta: DNA sequencing
    Brucella species are Gram-negative, facultative intracellular pathogens responsible for a worldwide zoonosis. The envelope of Brucella exhibits unique characteristics that make these bacteria furtive pathogens and resistant to several host defence compounds. We have identified a Brucella suis gene (mapB) that appeared to be crucial for cell envelope integrity. Indeed, the typical resistance of Brucella to both lysozyme and the cationic lipopeptide polymyxin B was markedly reduced in a ∆mapB mutant. MapB turned out to represent a TamB orthologue. This last protein, together with TamA, a protein belonging to the Omp85 family, form a complex that has been proposed to participate in the translocation of autotransporter proteins across the outer membrane (OM). Accordingly, we observed that MapB is required for proper assembly of an autotransporter adhesin in the OM, as most of the autotransporter accumulated in the mutant cell periplasm. Both assessment of the relative amounts of other specific outer membrane proteins (OMPs) and a proteome approach indicated that the absence of MapB did not lead to an extensive alteration in OMP abundance, but to a reduction in the relative amounts of a protein subset, including proteins from the Omp25/31 family. Electron microscopy revealed that ∆mapB cells exhibit multiple anomalies in cell morphology, indicating that the absence of the TamB homologue in B. suis severely affects cell division. Finally, ∆mapB cells were impaired in macrophage infection and showed an attenuated virulence phenotype in the mouse model. Collectively, our results indicate that the role of B. suis TamB homologue is not restricted to participating in the translocation of autotransporters across the OM but that it is essential for OM stability and protein composition and that it is involved in cell envelope biogenesis, a process that is inherently coordinated with cell division.
  • Miniatura
    ÍtemAcceso Abierto
    Structural determinant of functionality in acyl lipid desaturases
    (Elsevier, 2018-10) Sastre, Diego Emiliano; Saita, Emilio Adolfo; Uttaro, Antonio Domingo; De Mendoza, Diego; Altabe, Silvia Graciela
    Little is known about the structure-function relationship of membrane-bound lipid desaturases. Using a domain-swapping strategy, we found that the N terminus (comprising the two first transmembrane segments) region of Bacillus cereus DesA desaturase improves Bacillus subtilis Des activity. In addition, the replacement of the first two transmembrane domains from Bacillus licheniformis inactive open reading frame (ORF) BL02692 with the corresponding domain from DesA was sufficient to resurrect this enzyme. Unexpectedly, we were able to restore the activity of ORF BL02692 with a single substitution (Cys40Tyr) of a cysteine localized in the first transmembrane domain close to the lipidwater interface. Substitution of eight residues (Gly90, Trp104, Lys172, His228, Pro257, Leu275, Tyr282, and Leu284) by site-directed mutagenesis produced inactive variants of DesA. Homology modeling of DesA revealed that His228 is part of the metal binding center, together with the canonical His boxes. Trp104 shapes the hydrophobic tunnel, whereas Gly90 and Lys172 are probably involved in substrate binding/recognition. Pro257, Leu275, Tyr282, and Leu284 might be relevant for the structural arrangement of the active site or interaction with electron donors. This study reveals the role of the N-terminal region of 5 phospholipid desaturases and the individual residues necessary for the activity of this class of enzymes.
  • Miniatura
    ÍtemAcceso Abierto
    The role of cell-envelope synthesis for envelope growth and cytoplasmic density in Bacillus subtilis
    (Oxford University Press, 2022-07-26) Kitahara, Yuki; Oldewurtel, Enno R.; Wilson, Sean; Sun, Yingjie; Altabe, Silvia Graciela; De Mendoza, Diego; Garner, Ethan C.; Van Teeffelen, Sven; http://orcid.org/0000-0001-8034-9058; http://orcid.org/0000-0002-2813-0259; http://orcid.org/0000-0002-7216-9804; http://orcid.org/0000-0002-1309-753X; http://orcid.org/0000-0003-0141-3555; http://orcid.org/0000-0002-0877-1294
    All cells must increase their volumes in response to biomass growth to maintain intracellular mass density within physiologically permissive bounds. Here, we investigate the regulation of volume growth in the Gram-positive bacterium Bacillus subtilis. To increase volume, bacteria enzymatically expand their cell envelopes and insert new envelope material. First, we demonstrate that cell-volume growth is determined indirectly, by expanding their envelopes in proportion to mass growth, similarly to the Gram-negative Escherichia coli, despite their fundamentally different envelope structures. Next, we studied, which pathways might be responsible for robust surface-to-mass coupling: We found that both peptidoglycan synthesis and membrane synthesis are required for proper surface-tomass coupling. However, surprisingly, neither pathway is solely rate-limiting, contrary to wide-spread belief, since envelope growth continues at a reduced rate upon complete inhibition of either process. To arrest cell-envelope growth completely, the simultaneous inhibition of both envelope-synthesis processes is required. Thus, we suggest that multiple envelope-synthesis pathways collectively confer an important aspect of volume regulation, the coordination between surface growth, and biomass growth.