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Intercellular communication and conjugation are mediated by ESX secretion systems in mycobacteria

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Science  21 Oct 2016:
Vol. 354, Issue 6310, pp. 347-350
DOI: 10.1126/science.aag0828

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Conseting mycobacteria

Mycobacteria encompass several slow-growing pathogens, including organisms that cause leprosy and tuberculosis. Mycobacteria use a component of their ESX (or Type VII) secretion system for a distinctive form of genetic exchange called distributive conjugal DNA transfer. Gray et al. investigated a quicker-growing model species, Mycobacterium smegmatis. They found that the secretory apparatus, ESX-4, is essential for DNA transfer into the recipient but is not required for donor cells to pass along their DNA. The ESX-1 secretory apparatus was required in the recipient for ESX-4 induction, but it did not appear to provide the physical channel for DNA. Rather, ESX-1 may secrete cell-surface “mating factor” receptors. More research will be needed to understand the details of this intriguing means of DNA exchange in mycobacteria.

Science, this issue p. 347

Abstract

Communal bacterial processes require intercellular communication mediated by secretion systems to coordinate appropriate molecular responses. Intercellular communication has not been described previously in mycobacteria. Here we show that the ESX secretion-system family member ESX-4 is essential for conjugal recipient activity in Mycobacterium smegmatis. Transcription of esx4 genes in the recipient requires coculture with a donor strain and a functional ESX-1 apparatus in the recipient. Conversely, mutation of the donor ESX-1 apparatus amplifies the esx4 transcriptional response in the recipient. The effect of ESX-1 on esx4 transcription correlates with conjugal DNA transfer efficiencies. Our data show that intercellular communication via ESX-1 controls the expression of its evolutionary progenitor, ESX-4, to promote conjugation between mycobacteria.

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