Identification of Novel Acinetobacter baumannii Type VI Secretion System Antibacterial Effector and Immunity Pairs release_2rlqh6jbwrgqlncj56ym7graye

Abstract

<jats:title>ABSTRACT</jats:title> The type VI secretion system (T6SS) is a macromolecular machine that delivers protein effectors into host cells and/or competing bacteria. The effectors may be delivered as noncovalently bound cargo of T6SS needle proteins (VgrG/Hcp/PAAR) or as C-terminal extensions of these proteins. Many <jats:named-content content-type="genus-species">Acinetobacter baumannii</jats:named-content> strains produce a T6SS, but little is known about the specific effectors or how they are delivered. In this study, we show that <jats:named-content content-type="genus-species">A. baumannii</jats:named-content> AB307-0294 encodes three <jats:italic>vgrG</jats:italic> loci, each containing a <jats:italic>vgrG</jats:italic> gene, a T6SS toxic effector gene, and an antitoxin/immunity gene. Each of the T6SS toxic effectors could kill <jats:named-content content-type="genus-species">Escherichia coli</jats:named-content> when produced in <jats:italic>trans</jats:italic> unless the cognate immunity protein was coproduced. To determine the role of each VgrG in effector delivery, we performed interbacterial competitive killing assays using <jats:named-content content-type="genus-species">A. baumannii</jats:named-content> AB307-0294 <jats:italic>vgrG</jats:italic> mutants, together with <jats:named-content content-type="genus-species">Acinetobacter baylyi</jats:named-content> prey cells expressing pairs of immunity genes that protected against two toxic effectors but not a third. Using this approach, we showed that AB307-0294 produces only three T6SS toxic effectors capable of killing <jats:named-content content-type="genus-species">A. baylyi</jats:named-content> and that each VgrG protein is specific for the carriage of one effector. Finally, we analyzed a number of <jats:named-content content-type="genus-species">A. baumannii</jats:named-content> genomes and identified significant diversity in the range of encoded T6SS VgrG and effector proteins, with correlations between effector types and <jats:named-content content-type="genus-species">A. baumannii</jats:named-content> global clone lineages.
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