Nooks and Crannies in Type VI Secretion Regulation

Abstract

Type VI secretion systems (T6SS) are macromolecular, transenvelope machines encoded within the genomes of most Gram-negative bacteria, including plant, animal, and human pathogens, as well as soil and environmental isolates. T6SS are involved in a broad variety of functions: from pathogenesis to biofilm formation and stress sensing. This large array of functions is reflected by a vast diversity of regulatory mechanisms: repression by histone-like proteins and regulation by quorum sensing, transcriptional factors, two-component systems, alternative sigma factors, or small regulatory RNAs. Finally, T6SS may be produced in an inactive state and are turned on through the action of a posttranslational cascade involving phosphorylation and subunit recruitment. The current data reviewed here highlight how T6SS have been integrated into existing regulatory networks and how the expression of the T6SS loci is precisely modulated to adapt T6SS production to the specific needs of individual bacteria.

Type VI Secretion System-Associated Gene Clusters Contribute to Pathogenesis of Salmonella enterica Serovar Typhimurium

“…However, in S. Typhimurium and other T6SS-harboring organisms, no evolved tailspike protein is present (5). In addition to the core genes, organisms that possess a T6SS typically encode less-well-conserved, T6SS-associated genes that differ extensively in their number and location throughout the genome, and some of these genes have been reported to act as effector or regulatory proteins (2,14,43). Recently, a set of genes encoding T6SS-secreted toxin proteins were identified in Pseudomonas aeruginosa that are involved in interbacterial competition (45).…”

A multidrug resistance plasmid contains the molecular switch for type VI secretion in Acinetobacter baumannii

“…Its biogenesis follows energetically costly cycles of assembly/disassembly, and therefore, in most bacteria, T6SS appears to be exquisitely regulated. T6SS is silenced in most strains and only activated under specific conditions, such as an attack from another bacterium or in environments leading to membrane perturbations (16)(17)(18)(19). Many Acinetobacter spp.…”

Phytobacterial Type VI Secretion System - Gene Distribution, Phylogeny, Structure and Biological Functions

“…The T6SS regulation involves various transcriptional activators such as AraC, TetR-, and MarR-like proteins, σ 54 -like factors and heat-stable nucleoid-structural (H-NS) proteins (Bernard et al, 2010). Likewise, two-component systems, like the ferric uptake regulator Fur and the Quorum sensing (QS) related regulators like LuxI, LuxR and acyl homoserine lactones (AHL) are reported to be involved in regulation of T6SS expression (Bernard et al, 2010).…”

“…Likewise, two-component systems, like the ferric uptake regulator Fur and the Quorum sensing (QS) related regulators like LuxI, LuxR and acyl homoserine lactones (AHL) are reported to be involved in regulation of T6SS expression (Bernard et al, 2010). It has been also reported (Mougous et al, 2007) that the regulation of the HSI-1 in P. aeruginosa PAO1 is influenced by the sensor kinases RedS and the LadS, resulting in opposite patterns of regulation for the type III and type VI secretion systems in this bacterium, as in S. enterica (Parsons & Heffron 2005).…”