Contact-Dependent Growth Inhibition Proteins in Acinetobacter baylyi ADP1

Eliana De Gregorio,Eliana Pia Esposito,Raffaele Zarrilli,Pier Paolo Di Nocera

doi:10.1007/s00284-018-1540-y

Eliana De Gregorio, Eliana Pia Esposito + Show 2 more

Open Access

https://doi.org/10.1007/s00284-018-1540-y

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Journal: Current Microbiology	Publication Date: Jul 17, 2018
Citations: 22	License type: open-access

Affiliation: University of Naples Federico II

Abstract

Bacterial contact-dependent growth inhibition (CDI) systems are two-partner secretion systems in which toxic CdiA proteins are exported on the outer membrane by cognate transporter CdiB proteins. Upon binding to specific receptors, the C-terminal toxic (CT) domain, detached from CdiA, is delivered to neighbouring cells. Contacts inhibit the growth of not-self-bacteria, lacking immunity proteins co-expressed with CdiA, but promote cooperative behaviours in “self” bacteria, favouring the formation of biofilm structures. The Acinetobacter baylyi ADP1 strain features two CdiA, which differ significantly in size and have different CT domains. Homologous proteins sharing the same CT domains have been identified in A. baumannii. The growth inhibition property of the two A. baylyi CdiA proteins was supported by competition assays between wild-type cells and mutants lacking immunity genes. However, neither protein plays a role in biofilm formation or adherence to epithelial cells, as proved by assays carried out with knockout mutants. Inhibitory and stimulatory properties may be similarly uncoupled in A. baumannii proteins.

Highlights

Gram-negative bacteria exploit six secretion systems to secrete proteins outside the cell [8]
CdiA2784 and CdiA940 share an extended signal peptide region (ESPR) domain at the NH2 side, which is recognized by the Sec-translocation machinery and eventually cleaved during the export through the inner membrane (IM), and a two-partner secretion (TPS) domain involved in CdiA–CdiB interactions, but differ in length and organization
CdiA2784 features a domain of unknown function (DUF637, PF04830), and a PT-VENN domain (PF04829), located, as in CdiA from many bacterial species [20], immediately upstream of the C-terminal toxic (CT) region

Summary

Introduction

Gram-negative bacteria exploit six secretion systems (types I–VI) to secrete proteins outside the cell [8]. Most secretion machineries are complex structures which span both the inner membrane (IM) and the outer membrane (OM). In the type V secretion system, proteins cross the IM through the Sec system and subsequently the OM either alone, in the auto-transporter pathway, or assisted by dedicated proteins, in the two-partner secretion (TPS) pathway [17]. The secreted proteins may remain onto the OM, be released into the extracellular milieu, or be injected into target cells. Secreted proteins are involved in different processes which include adhesion to cells or abiotic surfaces, iron acquisition, invasion of eukaryotic cells, environmental adaptation.

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