Identification of a Contact-Dependent Growth Inhibition (CDI) System That Reduces Biofilm Formation and Host Cell Adhesion of Acinetobacter baumannii DSM30011 Strain.

Morgane Roussin,Christian Lesterlin,Sedera Rabarioelina,Laurence Cluzeau,Suzana P Salcedo,Julien Cayron,Sarah Bigot

doi:10.3389/fmicb.2019.02450

Abstract

Acinetobacter baumannii is a multidrug-resistant nosocomial opportunistic pathogen that is becoming a major health threat worldwide. In this study, we have focused on the A. baumannii DSM30011 strain, an environmental isolate that retains many virulence-associated traits. We found that its genome contains two loci encoding for contact-dependent growth inhibition (CDI) systems. These systems serve to kill or inhibit the growth of non-sibling bacteria by delivering toxins into the cytoplasm of target cells, thereby conferring the host strain a significant competitive advantage. We show that one of the two toxins functions as a DNA-damaging enzyme, capable of inducing DNA double-stranded breaks to the chromosome of Escherichia coli strain. The second toxin has unknown catalytic activity but stops the growth of E. coli without bactericidal effect. In our conditions, only one of the CDI systems was highly expressed in the A. baumannii DSM30011 strain and was found to mediate interbacterial competition. Surprisingly, the absence of this CDI system promotes adhesion of A. baumannii DSM30011 to both abiotic and biotic surfaces, a phenotype that differs from previously described CDI systems. Our results suggest that a specific regulation mediated by this A. baumannii DSM30011 CDI system may result in changes in bacterial physiology that repress host cell adhesion and biofilm formation.

Highlights

In Gram-negative bacteria, the two-partner secretion (TPS) pathway, known as type Vb secretion system (T5bSS), mediates the translocation across the outer membrane of large, mostly virulence-related, TpsA proteins (Guérin et al, 2017)
TpsA proteins can be phylogenetically classified into at least five subfamilies with distinct functions: (i) the contact-dependent growth inhibition (CDI) CdiA proteins (Aoki et al, 2005), (ii) the hemolysins/cytolysins such as ShlA of Serratia marcescens (Braun et al, 1992), (iii) the adhesins such as filamentous hemagglutinin (FHA) of Bordetella pertussis (Relman et al, 1989), (iv) HxuA-type proteins involved in iron acquisition (Fournier et al, 2011), and (v) TpsA with unknown specific activities (Faure et al, 2014)
The blast search revealed that the CDI system subfamily is predominantly represented within A. baumannii strains with the exception of some genomes comprising Hxu system homologues

Summary

INTRODUCTION

In Gram-negative bacteria, the two-partner secretion (TPS) pathway, known as type Vb secretion system (T5bSS), mediates the translocation across the outer membrane of large, mostly virulence-related, TpsA proteins (Guérin et al, 2017). Contact-dependent growth inhibition systems are widespread among Gram-negative bacteria, as cdi gene clusters are found in several α-, β-, and γ-proteobacteria They have been extensively studied in Enterobacteria and Burkholderia species, and recent work investigated their role in Acinetobacter species (Harding et al, 2017). Our in silico analysis revealed that these two adhesins associated with their respective CdiB and CdiI partners constitute putative CDI systems, suggesting a potential involvement of these systems in the virulence of A. baumannii This is in line with studies in other organisms suggesting a role for CDI systems beyond bacterial competition. We show that only one CDI system is expressed in A. baumannii DSM30011 and promotes interbacterial competition but is surprisingly a limiting factor for the adhesion process

RESULTS

DISCUSSION

EXPERIMENTAL PROCEDURES

DATA AVAILABILITY STATEMENT