Abstract
The type VI secretion system (T6SS) is a class of sophisticated cell contact-dependent apparatus with anti-eukaryotic or anti-bacterial function. Klebsiella pneumoniae is one of the most common bacterial pathogens with resistance to the carbapenem antibiotics. However, little is known about the antibacterial T6SS in K. pneumoniae. Using core-component protein searches, we identified a putative T6SS gene cluster on the chromosome of the carbapenemase-producing K. pneumoniae (CRKP) strain HS11286. Intraspecies and interspecies competition assays revealed an antibacterial function of the HS11286 T6SS. The phospholipase Tle1KP was found to be an effector protein that is transferred by T6SS. The overexpression of this effector gene in the periplasm caused severe growth inhibition of Escherichia coli. A sub-inhibitory concentration of β-lactam antibiotics stimulated the expression and secretion of the HS11286 T6SS and enhanced T6SS-dependent killing. It suggested that the antibiotics might be an impact factor for the T6SS secretion and antibacterial activity.
Highlights
The type VI secretion system (T6SS) is structurally related to the cell-puncturing device of tailed bacteriophages and functions as a contractile injection machinery that perforates eukaryotic and prokaryotic target membranes (Pukatzki et al, 2006; Kapitein and Mogk, 2013; Alteri and Mobley, 2016)
We detected an entire 23-gene T6SS cluster (KPHS_2297023190) on the chromosome of K. pneumoniae strain HS11286 (Supplementary Table 4). This T6SS consisted of 12 core components (Figure 1)
We found a 4.7 kb insertion region that contained KPHS_23060-23110, which is located between the core component genes icmF and vgrG
Summary
The type VI secretion system (T6SS) is structurally related to the cell-puncturing device of tailed bacteriophages and functions as a contractile injection machinery that perforates eukaryotic and prokaryotic target membranes (Pukatzki et al, 2006; Kapitein and Mogk, 2013; Alteri and Mobley, 2016). T6SS gene cluster contains the core component genes and variable regions that encode effector and immunity proteins (Zhang et al, 2012; see the comprehensive review of Russell et al, 2014). ClpV (a class of ATPases) is required to disassemble the Antibacterial T6SS in Klebsiella pneumoniae contracted VipA/VipB sheath (Bönemann et al, 2009; Basler and Mekalanos, 2012). Hcp and VgrG, have frequently been used as markers to investigate the T6SS translocation of secreted effectors (Pukatzki et al, 2006, 2009; Li et al, 2016)
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