Dr. Meriyem Aktas (PI)

Biological role of outer membrane vesicle-associated small proteins of the phytopathogen Agrobacterium tumefaciens

Ruhr University Bochum (Germany), Institute of Microbial Biology

Bacterial extracellular membrane vesicles are considered as novel players in various cell communication systems. Outer membrane vesicles (OMVs) are released from the outer membrane of many Gram-negative bacteria. The cargo of these extracellular nanostructures comprises distinct biomolecules such as small compounds, genetic material, proteins and peptides, which are involved in intra- and inter-species communication and pathogenicity [1-2].

We have recently demonstrated that the phytopathogen Agrobacterium tumefaciens, the causative agent of crown gall disease, releases OMVs into the culture supernatant during growth. A proteome study of the OMV fractions obtained under different growth conditions identified about 60 proteins including the two conserved small proteins Atu2614 and Atu8019 with unknown functions. Both proteins contain a predicted N-terminal signal peptidase II sequence with a C-terminal consensus lipobox, a hallmark of lipoproteins [3-4]. The mature form of Atu2614 is expected to contain 67 aa and comprises a highly hydrophobic domain with several extended glycine-zipper motifs commonly found in pore-forming membrane proteins [5]. Atu8019 (mature size: 32 aa) shares sequence similarities to entericidin antidote/toxin peptides [6-7].

In this proposal, we aim at elucidating the biological roles of these two OMV-associated small proteins in Agrobacterium by combining genetic and biochemical approaches. With these studies, we expect to obtain new valuable insights into the physiological relevance of OMV-associated small lipoproteins in bacteria.

  1. Schwechheimer C, Kuehn MJ. 2015. Outer-membrane vesicles from Gram-negative bacteria: biogenesis and functions. Nat Rev Microbiol 13:605-619
  2. Mashburn-Warren LM, Whiteley M. 2006. Special delivery: vesicle trafficking in prokaryotes. Mol Microbiol 61:839-846.
  3. Nakayama H, Kurokawa K, Lee BL. 2012. Lipoproteins in bacteria: structures and biosynthetic pathways. FEBS J 279:4247-4268.
  4. Kovacs-Simon A, Titball RW, Michell SL. 2011. Lipoproteins of bacterial pathogens. Infect Immun 79:548-561.
  5. Kim S, Jeon TJ, Oberai A, Yang D, Schmidt JJ, Bowie JU. 2005. Transmembrane glycine zippers: physiological and pathological roles in membrane proteins. Proc Natl Acad Sci U S A 102:14278-14283.
  6. Bishop RE, Leskiw BK, Hodges RS, Kay CM, Weiner JH. 1998. The entericidin locus of Escherichia coli and its implications for programmed bacterial cell death. J Mol Biol 280:583-596.
  7. Schubiger CB, Orfe LH, Sudheesh PS, Cain KD, Shah DH, Call DR. 2015. Entericidin is required for a probiotic treatment (Enterobacter sp. strain C6-6) to protect trout from cold-water disease challenge. Appl Environ Microbiol 81:658-665.