Lsr2 Is an Important Determinant of Intracellular Growth and Virulence in Mycobacterium abscessus

Vincent Le Moigne,Frédéric Crémazy,Alexandre Pawlik,Laurent Kremer,Albertus Viljoen,Fabienne Misguich,Christian Dupont,Jean-Louis Gaillard,Audrey Bernut,Jean-Louis Herrmann,Mélanie Cortès

doi:10.3389/fmicb.2019.00905

Abstract

Mycobacterium abscessus, a pathogen responsible for severe lung infections in cystic fibrosis patients, exhibits either smooth (S) or rough (R) morphotypes. The S-to-R transition correlates with inhibition of the synthesis and/or transport of glycopeptidolipids (GPLs) and is associated with an increase of pathogenicity in animal and human hosts. Lsr2 is a small nucleoid-associated protein highly conserved in mycobacteria, including M. abscessus, and is a functional homolog of the heat-stable nucleoid-structuring protein (H-NS). It is essential in Mycobacterium tuberculosis but not in the non-pathogenic model organism Mycobacterium smegmatis. It acts as a master transcriptional regulator of multiple genes involved in virulence and immunogenicity through binding to AT-rich genomic regions. Previous transcriptomic studies, confirmed here by quantitative PCR, showed increased expression of lsr2 (MAB_0545) in R morphotypes when compared to their S counterparts, suggesting a possible role of this protein in the virulence of the R form. This was addressed by generating lsr2 knock-out mutants in both S (Δlsr2-S) and R (Δlsr2-R) variants, demonstrating that this gene is dispensable for M. abscessus growth. We show that the wild-type S variant, Δlsr2-S and Δlsr2-R strains were more sensitive to H2O2 as compared to the wild-type R variant of M. abscessus. Importantly, virulence of the Lsr2 mutants was considerably diminished in cellular models (macrophage and amoeba) as well as in infected animals (mouse and zebrafish). Collectively, these results emphasize the importance of Lsr2 in M. abscessus virulence.

Highlights

Mycobacterium abscessus is a rapidly growing mycobacterium (RGM) increasingly acknowledged as a serious non-tuberculous mycobacterial (NTM) pathogen (Mougari et al, 2016; Diel et al, 2017)
Because Lsr2 appears to be involved in the virulence and the antibiotic resistance of M. tuberculosis (Colangeli et al, 2009; Gordon et al, 2010), we reasoned that induction of Lsr2 expression in the R strain may explain, at least in part, the increase of virulence in the R over the S variant
Lsr2 filaments are found at the promoters of 401 and 272 genes in M. tuberculosis and M. smegmatis, respectively, often extending into their coding regions (Gordon et al, 2010)

Summary

Introduction

Mycobacterium abscessus is a rapidly growing mycobacterium (RGM) increasingly acknowledged as a serious non-tuberculous mycobacterial (NTM) pathogen (Mougari et al, 2016; Diel et al, 2017). Mycobacterium abscessus presents either smooth (S) or rough (R) colony morphotypes leading to different clinical outcomes (Howard et al, 2006; Catherinot et al, 2009; Medjahed and Reyrat, 2009; Ripoll et al, 2009; Roux et al, 2011) They exhibit different morphological aspects (Howard et al, 2006; Sánchez-Chardi et al, 2011) and virulence phenotypes (Byrd and Lyons, 1999; Catherinot et al, 2007; Bernut et al, 2014a). The S-to-R transition, which occurs essentially in vivo and is responsible for a significant increase in pathogenicity (Jönsson et al, 2007; Rottman et al, 2007; Bernut et al, 2014b) likely represents an evolutionary adaptation mechanism to the host immune response (Pawlik et al, 2013; Roux et al, 2016)

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