Genomics of glycopeptidolipid biosynthesis in Mycobacterium abscessus and M. chelonae

Fabienne Ripoll,Jean-Louis Gaillard,Jean-Luc Beretti,Françoise Laval,Jean-Marc Reyrat,Caroline Deshayes,Mamadou Daffé,Gilles Etienne,Franck Biet,Jean-Loup Risler,Sophie Pasek

doi:10.1186/1471-2164-8-114

Abstract

BackgroundThe outermost layer of the bacterial surface is of crucial importance because it is in constant interaction with the host. Glycopeptidolipids (GPLs) are major surface glycolipids present on various mycobacterial species. In the fast-grower model organism Mycobacterium smegmatis, GPL biosynthesis involves approximately 30 genes all mapping to a single region of 65 kb.ResultsWe have recently sequenced the complete genomes of two fast-growers causing human infections, Mycobacterium abscessus (CIP 104536T) and M. chelonae (CIP 104535T). We show here that these two species contain genes corresponding to all those of the M. smegmatis "GPL locus", with extensive conservation of the predicted protein sequences consistent with the production of GPL molecules indistinguishable by biochemical analysis. However, the GPL locus appears to be split into several parts in M. chelonae and M. abscessus. One large cluster (19 genes) comprises all genes involved in the synthesis of the tripeptide-aminoalcohol moiety, the glycosylation of the lipopeptide and methylation/acetylation modifications. We provide evidence that a duplicated acetyltransferase (atf1 and atf2) in M. abscessus and M. chelonae has evolved through specialization, being able to transfer one acetyl at once in a sequential manner. There is a second smaller and distant (M. chelonae, 900 kb; M. abscessus, 3 Mb) cluster of six genes involved in the synthesis of the fatty acyl moiety and its attachment to the tripeptide-aminoalcohol moiety. The other genes are scattered throughout the genome, including two genes encoding putative regulatory proteins.ConclusionAlthough these three species produce identical GPL molecules, the organization of GPL genes differ between them, thus constituting species-specific signatures. An hypothesis is that the compact organization of the GPL locus in M. smegmatis represents the ancestral form and that evolution has scattered various pieces throughout the genome in M. abscessus and M. chelonae.

Highlights

The outermost layer of the bacterial surface is of crucial importance because it is in constant interaction with the host
By exploiting available data concerning the genetic basis of the GPL biosynthetic pathway in the rapidly growing mycobacteria (RGM) model organism, M. smegmatis, we identified and analysed the genetic regions encoding enzymes involved in GPL biosynthesis in M. chelonae and M. abscessus
Biochemical analysis of the glycopeptidolipid produced by M. abscessus and M. chelonae Since GPL molecules may differ at a structural level, we first assessed the GPL status of the strains used in this study for comparative genomic analysis: M. smegmatis mc2155, M. chelonae CIP 104535T and M. abscessus CIP 104536T

Summary

Introduction

The outermost layer of the bacterial surface is of crucial importance because it is in constant interaction with the host. Glycopeptidolipids (GPLs) are surface lipids found on a number of mycobacterial species including both RGM (e.g., M. smegmatis, M. chelonae, M. abscessus) and slow growing mycobacteria These molecules can make up more than 70% of the lipids exposed at the bacterial surface (for a review see [3,4,5]) They have a glycosylated lipopeptide core that is variably modified by O-methylation and O-acetylation (Fig. 1). The GPL structure is based on a tripeptideaminoalcohol (D-Phe-D-allo-Thr-D-Ala-L-alaninol) Nlinked to a long chain fatty acyl residue This lipopeptide core is substituted by a 6-deoxytalosyl (dTal) unit linked to the allo-Thr residue and by an O-methylated rhamnosyl unit linked to the terminal alaninol residue. The dTal residue can be O-acetylated on positions 3 and 4, further glycosylated on position 2 in M. avium, whereas the fatty acyl moiety and the rhamnosyl residue can be modified with one and three methyl groups on positions 2, 3, or 4, respectively and in some cases further glycosylated by the addition of an extra rhamnosyl unit [3,11,6] (Fig. 1)

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Conclusion