<em>Acinetobacter baumannii</em> Utilizes a Type VI Secretion System for Bacterial Competition

<div><p>Type VI secretion systems (T6SS) are a class of macromolecular secretion machines that are utilized by a number of bacteria for inter-bacterial competition or to elicit responses in eukaryotic cells. <i>Acinetobacter baumannii</i> is an opportunistic pathogen that causes severe infections in humans. These infections, including pneumonia and bacteremia, are important, as they are often associated with hospitals and medical-settings where they disproportionally affect critically ill patients like those residing in intensive care units. While it is known that <i>A. baumannii</i> genomes carry genes whose predicted products have homology with T6SS-associated gene products from other bacteria, and secretion of a major T6SS structural protein Hcp has been demonstrated, no additional work on an <i>A. baumannii</i> T6SS has been reported. Herein, we demonstrated that <i>A. baumannii</i> strain M2 secretes Hcp and this secretion was dependent upon TssB, an ortholog of a bacteriophage contractile sheath protein, confirming that strain M2 produces a functional T6SS. Additionally, we demonstrated that the ability of strain M2 to out-compete <i>Escherichia coli</i> was reliant upon the products of <i>tssB</i> and <i>hcp.</i> Collectively, our data have provided the first evidence demonstrating function in inter-bacterial competition, for a T6SS produced by <i>A. baumannii.</i></p>