Abstract

Recent evidence shows that mycobacteria have developed novel and specialized secretion systems for the transport of extracellular proteins across their hydrophobic, and highly impermeable, cell wall. Strikingly, mycobacterial genomes encode up to five of these transport systems. Two of these systems, ESX-1 and ESX-5, are involved in virulence — they both affect the cell-to-cell migration of pathogenic mycobacteria. Here, we discuss this novel secretion pathway and consider variants that are present in various Gram-positive bacteria. Given the unique composition of this secretion system, and its general importance, we propose that, in line with the accepted nomenclature, it should be called type VII secretion.

Author affiliations

1. Abdallah M. Abdallah, Christina M. J. E. Vandenbroucke-Grauls, Ben J. Appelmelk and Wilbert Bitter are at the Department of Medical Microbiology, VU medical centre, Amsterdam 1081BT, The Netherlands.
2. Patricia A. DiGiuseppe Champion and Jeffery Cox are at the Department of Microbiology and Immunology, University of California, San Francisco, California 4143-2200, USA.
3. Nicolaas C. Gey van Pittius is at the DST/NRF Centre of Excellence in Biomedical Tuberculosis Research, US/MRC Centre for Molecular and Cellular Biology, Division of Molecular Biology and Human Genetics, Department of Biomedical Sciences, Stellenbosch University, Tygerberg 7505, South Africa.
4. Joen Luirink is at the Department of Molecular Microbiology, Vrije Universiteit, Amsterdam 1081HV, The Netherlands.

Correspondence to: Wilbert Bitter¹ Email: w.bitter@vumc.nl

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