Unique Substrates Secreted by the Type VI Secretion System of Francisella tularensis during Intramacrophage Infection

Gram-negative bacteria have evolved sophisticated secretion machineries specialized for the secretion of macromolecules important for their life cycles. The Type VI secretion system (T6SS) is the most widely spread bacterial secretion machinery and is encoded by large, variable gene clusters, often...

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Main Authors:	Bröms, Jeanette E., Meyer, Lena, Sun, Kun, Lavander, Moa, Sjöstedt, Anders
Format:	Online
Language:	English
Published:	Public Library of Science 2012
Online Access:	https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3502320/

id	pubmed-3502320
recordtype	oai_dc
spelling	pubmed-35023202012-11-26 Unique Substrates Secreted by the Type VI Secretion System of Francisella tularensis during Intramacrophage Infection Bröms, Jeanette E. Meyer, Lena Sun, Kun Lavander, Moa Sjöstedt, Anders Research Article Gram-negative bacteria have evolved sophisticated secretion machineries specialized for the secretion of macromolecules important for their life cycles. The Type VI secretion system (T6SS) is the most widely spread bacterial secretion machinery and is encoded by large, variable gene clusters, often found to be essential for virulence. The latter is true for the atypical T6SS encoded by the Francisella pathogenicity island (FPI) of the highly pathogenic, intracellular bacterium Francisella tularensis. We here undertook a comprehensive analysis of the intramacrophage secretion of the 17 FPI proteins of the live vaccine strain, LVS, of F. tularensis. All were expressed as fusions to the TEM β-lactamase and cleavage of the fluorescent substrate CCF2-AM, a direct consequence of the delivery of the proteins into the macrophage cytosol, was followed over time. The FPI proteins IglE, IglC, VgrG, IglI, PdpE, PdpA, IglJ and IglF were all secreted, which was dependent on the core components DotU, VgrG, and IglC, as well as IglG. In contrast, the method was not directly applicable on F. novicida U112, since it showed very intense native β-lactamase secretion due to FTN_1072. Its role was proven by ectopic expression in trans in LVS. We did not observe secretion of any of the LVS substrates VgrG, IglJ, IglF or IglI, when tested in a FTN_1072 deficient strain of F. novicida, whereas IglE, IglC, PdpA and even more so PdpE were all secreted. This suggests that there may be fundamental differences in the T6S mechanism among the Francisella subspecies. The findings further corroborate the unusual nature of the T6SS of F. tularensis since almost all of the identified substrates are unique to the species. Public Library of Science 2012-11-20 /pmc/articles/PMC3502320/ /pubmed/23185631 http://dx.doi.org/10.1371/journal.pone.0050473 Text en © 2012 Bröms et al http://creativecommons.org/licenses/by/4.0/ This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are properly credited.
repository_type	Open Access Journal
institution_category	Foreign Institution
institution	US National Center for Biotechnology Information
building	NCBI PubMed
collection	Online Access
language	English
format	Online
author	Bröms, Jeanette E. Meyer, Lena Sun, Kun Lavander, Moa Sjöstedt, Anders
spellingShingle	Bröms, Jeanette E. Meyer, Lena Sun, Kun Lavander, Moa Sjöstedt, Anders Unique Substrates Secreted by the Type VI Secretion System of Francisella tularensis during Intramacrophage Infection
author_facet	Bröms, Jeanette E. Meyer, Lena Sun, Kun Lavander, Moa Sjöstedt, Anders
author_sort	Bröms, Jeanette E.
title	Unique Substrates Secreted by the Type VI Secretion System of Francisella tularensis during Intramacrophage Infection
title_short	Unique Substrates Secreted by the Type VI Secretion System of Francisella tularensis during Intramacrophage Infection
title_full	Unique Substrates Secreted by the Type VI Secretion System of Francisella tularensis during Intramacrophage Infection
title_fullStr	Unique Substrates Secreted by the Type VI Secretion System of Francisella tularensis during Intramacrophage Infection
title_full_unstemmed	Unique Substrates Secreted by the Type VI Secretion System of Francisella tularensis during Intramacrophage Infection
title_sort	unique substrates secreted by the type vi secretion system of francisella tularensis during intramacrophage infection
description	Gram-negative bacteria have evolved sophisticated secretion machineries specialized for the secretion of macromolecules important for their life cycles. The Type VI secretion system (T6SS) is the most widely spread bacterial secretion machinery and is encoded by large, variable gene clusters, often found to be essential for virulence. The latter is true for the atypical T6SS encoded by the Francisella pathogenicity island (FPI) of the highly pathogenic, intracellular bacterium Francisella tularensis. We here undertook a comprehensive analysis of the intramacrophage secretion of the 17 FPI proteins of the live vaccine strain, LVS, of F. tularensis. All were expressed as fusions to the TEM β-lactamase and cleavage of the fluorescent substrate CCF2-AM, a direct consequence of the delivery of the proteins into the macrophage cytosol, was followed over time. The FPI proteins IglE, IglC, VgrG, IglI, PdpE, PdpA, IglJ and IglF were all secreted, which was dependent on the core components DotU, VgrG, and IglC, as well as IglG. In contrast, the method was not directly applicable on F. novicida U112, since it showed very intense native β-lactamase secretion due to FTN_1072. Its role was proven by ectopic expression in trans in LVS. We did not observe secretion of any of the LVS substrates VgrG, IglJ, IglF or IglI, when tested in a FTN_1072 deficient strain of F. novicida, whereas IglE, IglC, PdpA and even more so PdpE were all secreted. This suggests that there may be fundamental differences in the T6S mechanism among the Francisella subspecies. The findings further corroborate the unusual nature of the T6SS of F. tularensis since almost all of the identified substrates are unique to the species.
publisher	Public Library of Science
publishDate	2012
url	https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3502320/
_version_	1611933910706421760

Unique Substrates Secreted by the Type VI Secretion System of Francisella tularensis during Intramacrophage Infection

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