Secrets of Secretion

Responsible for causing tuberculosis, a disease affecting millions of people worldwide, Mycobacterium tuberculosis can infect macrophages, immune cells which normally engulf and destroy pathogens. Critical to the bacterium’s success is a sophisticated secretion system, enabling it to transport useful compounds into host cells. Multiple proteins make up this system but their specific roles are difficult to disentangle, so researchers are investigating them in a closely-related pathogen, Mycobacterium marinum, causing tuberculosis in fish. They found especially intriguing results for one protein, named EspH. While bacteria lacking EspH were less effective at infecting macrophages in the lab, they were very virulent when infecting zebrafish larvae, forming aggregates inside and around zebrafish blood vessels, a phenomenon known as cording (pictured, with bacteria in red, blood vessels in green and macrophages in blue).This suggests that host factors interact with the bacterium’s own proteins, adding another layer of complexity to the processes behind tuberculosis infections.

Written by Emmanuelle Briolat

Emmanuelle Briolat

Writer

A researcher specialising in visual signals in Lepidoptera, camouflage and the effects of light pollution, Emmanuelle’s writing covers a range of topics, from biomedical research to children’s books about moth defences.

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• Image from work by Trang H. Phan and Lisanne M. van Leeuwen, and colleagues
• Department of Medical Microbiology and Infection Control, Amsterdam University Medical Centers; and Section Molecular Microbiology, Amsterdam Institute of Molecules, Medicines & Systems, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands
• Image originally published under a Creative Commons Licence (BY 4.0)
• Published in PLOS Pathogens, August 2018