Study of lipoprotein export in Bacteroidetes

  • Elisabeth BALAND

    Student thesis: Master typesMaster en microbiologie moléculaire, à finalité approfondie

    Résumé

    In Gram-negative bacteria, lipoproteins are major components of the outer
    membrane where they play a variety of roles, from the involvement in β-barrel assembly to virulence. Bacteroidetes, a widespread phylum of Gram-negative bacteria, including freeliving organisms, commensals and pathogens spanning from soil or fresh-water environments to the human and animal microbiota, encode an exceptionally high number of outer membrane lipoproteins. These proteins are crucial in this phylum mainly because they are key components of SUS-like nutrient acquisition systems as well as of the Type IX secretion and gliding motility machineries. The transport of lipoproteins to the outer membrane has mainly been studied in E. coli and relies on the Lol system, composed of the inner membrane extraction machinery LolCDE, the periplasmic carrier LolA and the outer membrane lipoprotein LolB. While most Lol proteins are essential and conserved across Gram-negative bacteria, to date, no LolB homologs have been identified outside of γ- and βproteobacteria. How lipoproteins reach and are inserted in the outer membrane of Bacteroidetes is not known and might involve different pathways. This master thesis aims at
    characterizing lipoprotein transport to the outer membrane of the environmental
    Bacteroidetes F. johnsoniae. In particular, my work focused first at identifying LolB homologs and then at characterizing the role of LolA and LolB in F. johnsoniae. We identified for the first time LolB homologs in Bacteroidetes and disclosed the co-existence of several LolA and LolB homologs in several species. We showed that LolA1 and LolB1 of F. johnsoniae might be devoted to targeting gliding and T9SS lipoproteins to the outer membrane. A proteomic analysis of the outer membrane composition of the lolA1 deletion strain supports these
    evidences. In contrast, we could not provide any evidence for a role of LolA2 and/or LolB2 on lipoprotein transport and further investigations are required to precisely determine their function. Furthermore, we show that, while LolB1 and, to a lesser extent LolA1, have conserved functions in Bacteroidetes, they are functionally different from their E. coli counterparts. Finally, the finding that in the absence of LolA and LolB homologs lipoproteins still localize to the outer membrane, strongly suggests the presence in Bacteroidetes of a yet
    unidentified Lol-alternative transport pathway. In conclusion, Bacteroidetes seem to have evolved different and probably more complex lipoprotein transport pathways than other Gram-negative bacteria and further research is required to uncover their complexity.
    la date de réponse22 janv. 2021
    langue originaleAnglais
    L'institution diplômante
    • Universite de Namur
    SuperviseurFrancesco Renzi (Promoteur)

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