Effector–Immunity Pairs Provide the T6SS Nanomachine its Offensive and Defensive Capabilities

Abstract

Type VI protein secretion systems (T6SSs) are specialized transport apparatus which can target both eukaryotic and prokaryotic cells and play key roles in host–pathogen–microbiota interactions. Therefore, T6SSs have attracted much attention as a research topic during the past ten years. In this review, we particularly summarized the T6SS antibacterial function, which involves an interesting offensive and defensive mechanism of the effector–immunity (E–I) pairs. The three main categories of effectors that target the cell wall, membranes, and nucleic acids during bacterial interaction, along with their corresponding immunity proteins are presented. We also discuss structural analyses of several effectors and E–I pairs, which explain the offensive and defensive mechanisms underpinning T6SS function during bacterial competition for niche-space, as well as the bioinformatics, proteomics, and protein–protein interaction (PPI) methods used to identify and characterize T6SS mediated E–I pairs. Additionally, we described PPI methods for verifying E–I pairs.

Type VI Secretion Systems Present New Insights on Pathogenic Yersinia

“…Bacteria could utilize T6SS to intimately interface with other bacteria, efficiently killing or inhibiting competitors with T6SS toxins and protecting itself with immune proteins, which has been reported in P. aeruginosa (HSI-1) (Hood et al, 2010 ), B. thailandensis (T6SS-1) (Schwarz et al, 2010 ), V. cholerae (MacIntyre et al, 2010 ; Ishikawa et al, 2012 ), and Serratia marcescens (Murdoch et al, 2011 ). Different from the traditional offensive and defensive model of T6SS mediated bacterial competition (Russell et al, 2012 ; Lien and Lai, 2017 ; Yang et al, 2018 ), swarming Proteus mirabilis discriminate non-identical population via T6SS-dependent delivery of toxic effectors, thus forming a visible demarcation line (Dienes line) between different Proteus isolates (Alteri et al, 2013 ). Although this phenomenon of self-recognition during swarming in P. mirabilis has been known for decades it was only ascribed to the T6SS recently.…”

Accumulation of dead cells from contact killing facilitates coexistence in bacterial biofilms

“…In all cases, the relative abundance of killer cells initially increases quickly, followed by a substantially slower increase after 3 hours. phenomenon is reminiscent of domain formation observed in populations of mutual 64 killer strains (i.e, both strains are T6SS+) [24], even though in our current experiments 65 one strain -the target strain -is engineered to be defective at T6SS killing. While we 66 observe that domains of the T6SS+ strain expand quickly at early times, domain 67 growth later slows substantially (Fig.…”

“…The barrier 298 may be removed when dead cell debris is consumed by predators[60], broken down by 299 secreted enzymes (such as lipases or DNAses), removed via shear flow[61], or dispersed 300 by mechanical perturbations, among other potential mechanisms. The rate at which 301 dead cell debris breaks down may also be impacted by the action of the delivered toxins 302 themselves[62], which are known to exhibit a wide range of effects, from growth 303 inhibition to lysis[20,21,35,63,64]. Further, while we observe similar characteristics of 304 cell debris accumulation across different co-culture competitions containing V. cholerae, 305 E. cloacae, and V. harveyi, the material and physical characteristics of dead cell debris 306 may vary across different combinations of competing strains or species, impacting the 307 stability of the barrier.…”

Diagnostic approaches and contribution of next-generation sequencing technologies in genomic investigation of Vibrio parahaemolyticus that caused acute hepatopancreatic necrosis disease (AHPND)

“…Although the pir vp toxin genes are the primary causes of AHPND, there might be other virulence components or antibiotic resistant genes that play important roles during shrimp infection. Previous studies reported that the VP AHPND strains possess a T6SS protein secretion apparatus that is known to play a role in inter-bacterial competition (Yang et al 2018 ; Yu et al 2020 ). The T6SS possesses antibacterial activities mediated by delivery of toxic effectors into neighbouring cells and therefore the acquisition T6SS might confer a fitness advantage to VP AHPND strains over other competing bacteria and facilitates shrimp infection (Yang et al 2018 ).…”