From Striking Out to Striking Gold: Discovering that Type VI Secretion Targets Bacteria (original) (raw)
Related papers
mBio, 2017
The ability to detect and measure danger from an environmental signal is paramount for bacteria to respond accordingly, deploying strategies that halt or counteract potential cellular injury and maximize survival chances. Type VI secretion systems (T6SSs) are complex bacterial contractile nanomachines able to target toxic effectors into neighboring bacteria competing for the same colonization niche. Previous studies support the concept that either T6SSs are constitutively active or they fire effectors in response to various stimuli, such as high bacterial density, cell-cell contact, nutrient depletion, or components from dead sibling cells. For Serratia marcescens , it has been proposed that its T6SS is stochastically expressed, with no distinction between harmless or aggressive competitors. In contrast, we demonstrate that the Rcs regulatory system is responsible for finely tuning Serratia T6SS expression levels, behaving as a transcriptional rheostat. When confronted with harmless...
Type VI secretion delivers bacteriolytic effectors to target cells
Nature, 2011
Peptidoglycan is the major structural constituent of the bacterial cell wall, forming a meshwork outside the cytoplasmic membrane that maintains cell shape and prevents lysis. In Gram-negative bacteria, peptidoglycan is located in the periplasm, where it is protected from exogenous lytic enyzmes by the outer membrane. Here we show that the type VI secretion system (T6SS) of Pseudomonas aeruginosa breaches this barrier to deliver two effector proteins, Tse1 and Tse3, to the periplasm of recipient cells. In this compartment, the effectors hydrolyze peptidoglycan, thereby providing a fitness advantage for P. aeruginosa cells in competition with other bacteria. To protect itself from lysis by Tse1 and Tse3, P. aeruginosa utilizes specific periplasmicallylocalized immunity proteins. The requirement for these immunity proteins depends on intercellular self-intoxication through an active T6SS, indicating a mechanism for export whereby effectors do not access donor cell periplasm in transit. Competition among bacteria for niches is widespread, fierce and deliberate. These organisms elaborate factors ranging in complexity from small diffusible molecules, to exported proteins, to multicomponent machines, in order to inhibit the proliferation of rival cells 1,2. A common target of such factors is the peptidoglycan cell wall 3-6. The conserved, essential, and accessible nature of this molecule makes it an Achilles heel of bacteria.
A Widespread Bacterial Type VI Secretion Effector Superfamily Identified Using a Heuristic Approach
Cell Host & Microbe, 2012
Sophisticated mechanisms are employed to facilitate information exchange between interfacing bacteria. A type VI secretion system (T6SS) of Pseudomonas aeruginosa was shown to deliver cell wall-targeting effectors to neighboring cells. However, the generality of bacteriolytic effectors, and moreover, of antibacterial T6S, remained unknown. Using parameters derived from experimentally validated bacterial T6SS effectors and informatics, we identified a phylogenetically disperse superfamily of T6SS-associated peptidoglycan-degrading effectors. The effectors separate into four families composed of peptidoglycan amidase enzymes of differing specificities. Effectors strictly co-occur with cognate immunity proteins, indicating that selfintoxication is a general property of antibacterial T6SSs and effector delivery by the system exerts a strong selective pressure in nature. The presence of antibacterial effectors in a plethora of organisms, including many that inhabit or infect polymicrobial niches in the human body, suggests that the system could mediate interbacterial interactions of both environmental and clinical significance.
The rise of the Type VI secretion system
F1000prime reports, 2013
Bacterial cells have developed multiple strategies to communicate with their surrounding environment. The intracellular compartment is separated from the milieu by a relatively impermeable cell envelope through which small molecules can passively diffuse, while larger macromolecules, such as proteins, can be actively transported. In Gram-negative bacteria, the cell envelope is a double membrane, which houses several supramolecular protein complexes that facilitate the trafficking of molecules. For example, bacterial pathogens use these types of machines to deliver toxins into target eukaryotic host cells, thus subverting host cellular functions. Six different types of nanomachines, called Type I - Type VI secretion systems (T1SS - T6SS), can be readily identified by their composition and mode of action. A remarkable feature of these protein secretion systems is their similarity to systems with other biological functions, such as motility or the exchange of genetic material. The T6SS...
Proceedings of the National Academy of Sciences, 2012
Interbacterial interaction pathways play an important role in defining the structure and complexity of bacterial associations. A quantitative description of such pathways offers promise for understanding the forces that contribute to community composition. We developed time-lapse fluorescence microscopy methods for quantitation of interbacterial interactions and applied these to the characterization of type VI secretion (T6S) in Pseudomonas aeruginosa. Our analyses allowed a direct determination of the efficiency of recipient cell lysis catalyzed by this intercellular toxin delivery pathway and provided evidence that its arsenal extends beyond known effector proteins. Measurement of T6S apparatus localization revealed correlated activation among neighboring cells, which, taken together with genetic data, implicate the elaboration of a functional T6S apparatus with a marked increase in susceptibility to intoxication. This possibility was supported by the identification of T6S-inactivating mutations in a genome-wide screen for resistance to T6S-mediated intoxication and by time-lapse fluorescence microscopy analyses showing a decreased lysis rate of recipient cells lacking T6S function. Our discoveries highlight the utility of singlecell approaches for measuring interbacterial phenomena and provide a foundation for studying the contribution of a widespread bacterial interaction pathway to community structure.
Multicellular Bacteria Deploy the Type VI Secretion System to Preemptively Strike Neighboring Cells
PLoS Pathogens, 2013
The Type VI Secretion System (T6SS) functions in bacteria as a contractile nanomachine that punctures and delivers lethal effectors to a target cell. Virtually nothing is known about the lifestyle or physiology that dictates when bacteria normally produce their T6SS, which prevents a clear understanding of how bacteria benefit from its action in their natural habitat. Proteus mirabilis undergoes a characteristic developmental process to coordinate a multicellular swarming behavior and will discriminate itself from another Proteus isolate during swarming, resulting in a visible boundary termed a Dienes line. Using transposon mutagenesis, we discovered that this recognition phenomenon requires the lethal action of the T6SS. All mutants identified in the genetic screen had insertions within a single 33.5-kb region that encodes a T6SS and cognate Hcp-VrgG-linked effectors. The identified T6SS and primary effector operons were characterized by killing assays, by construction of additional mutants, by complementation, and by examining the activity of the type VI secretion system in real-time using live-cell microscopy on opposing swarms. We show that lethal T6SS-dependent activity occurs when a dominant strain infiltrates deeply beyond the boundary of the two swarms. Using this multicellular model, we found that social recognition in bacteria, underlying killing, and immunity to killing all require cell-cell contact, can be assigned to specific genes, and are dependent on the T6SS. The ability to survive a lethal T6SS attack equates to ''recognition''. In contrast to the current model of T6SS being an offensive or defensive weapon our findings support a preemptive mechanism by which an entire population indiscriminately uses the T6SS for contact-dependent delivery of effectors during its cooperative mode of growth.
Large-scale discovery of candidate type VI secretion effectors with antibacterial activity
2021
Type VI secretion systems (T6SS) are common bacterial contractile injection systems that inject toxic effector proteins into neighboring cells. Effector discovery is generally done manually, and computational approaches used for effector discovery depend on genetic linkage to T6SS genes and/or sequence similarity to known effectors. We bioinformatically investigated T6SS in more than 11,832 genomes of Gram negative bacteria. We found that T6SS encoding bacteria are host-associated and pathogenic, enriched in specific human and plant tissues, while depleted in marine, soil, and engineered environments. Analysis of T6SS cores with C-terminal domains ("evolved" cores) showed "evolved" HCP are rare, overwhelmingly encoded in orphan operons, and are largely restricted to Escherichia. Using the wealth of data generated from our bioinformatic analysis, we developed two algorithms for large-scale discovery of T6SS effector proteins (T6Es). We experimentally validated ten...
The Versatile Type VI Secretion System
Microbiology Spectrum
Bacterial type VI secretion systems (T6SSs) function as contractile nanomachines to puncture target cells and deliver lethal effectors. In the 10 years since the discovery of the T6SS, much has been learned about the structure and function of this versatile protein secretion apparatus. Most of the conserved protein components that comprise the T6SS apparatus itself have been identified and ascribed specific functions. In addition, numerous effector proteins that are translocated by the T6SS have been identified and characterized. These protein effectors usually represent toxic cargoes that are delivered by the attacker cell to a target cell. Researchers in the field are beginning to better understand the lifestyle or physiology that dictates when bacteria normally express their T6SS. In this article, we consider what is known about the structure and regulation of the T6SS, the numerous classes of antibacterial effector T6SS substrates, and how the action of the T6SS relates to a giv...