Manipulating the type VI secretion system spike to shuttle passenger proteins

The type VI secretion system (T6SS) is a contractile injection apparatus that translocates a spike loaded with various effectors directly into eukaryotic or prokaryotic target cells. Pseudomonas aeruginosa can load either one of its three T6SSs with a variety of toxic bullets using different but specific modes. The T6SS spike, which punctures the bacterial cell envelope allowing effector transport, consists of a torch-like VgrG trimer on which sits a PAAR protein sharpening the VgrG tip. VgrG itself sits on the Hcp tube and all elements, packed into a T6SS sheath, are propelled out of the cell and into target cells. On occasion, effectors are covalent extensions of VgrG, PAAR or Hcp proteins, which are then coined “evolved” components as opposed to canonical. Here, we show how various passenger domains could be fused to the C terminus of a canonical VgrG, VgrG1a from P. aeruginosa, and be sent into the bacterial culture supernatant. There is no restriction on the passenger type, although the efficacy may vary greatly, since we used either an unrelated T6SS protein, β-lactamase, a covalent extension of an “evolved” VgrG, VgrG2b, or a Hcp-dependent T6SS toxin, Tse2. Our data further highlights an exceptional modularity/flexibility for loading the T6SS nano-weapon. Refining the parameters to optimize delivery of passenger proteins of interest would have attractive medical and industrial applications. This may for example involve engineering the T6SS as a delivery system to shuttle toxins into either bacterial pathogens or tumour cells which would be an original approach in the fight against antimicrobial resistant bacteria or cancer

Breaking free from home: biofilm dispersal by a glycosidase from Desulfovibrio vulgaris

descripción no proporcionada por scopu

Protect thy host: Pf4 phages shield Pseudomonas aeruginosa from antibiotics

Bacterial viruses or bacteriophages exert profound effects on host cell lifestyle and evolution. The prophage Pf4 in Pseudomonas aeruginosa is highly induced in biofilms and is shown to confer antibiotic resistance to the bacterium. A novel study has now revealed that Pf4 forms crystalline structures that serve to physically wall off antibiotics from the bacterium. This represents an entirely novel mechanism involving liquid–liquid phase separation in prokaryotic systems. Furthermore, the toxin-antitoxin system PfiAT, which is encoded within the prophage Pf4, represents a unique production mechanism for Pf4. Combined, these two studies broadened our knowledge on the antibiotic resistance mechanisms used by P. aeruginosa

Protect thy host: Pf4 phages shield Pseudomonas aeruginosa

Bacterial viruses or bacteriophages exert profound effects on host cell lifestyle and evolution. The prophage Pf4 in Pseudomonas aeruginosa is highly induced in biofilms and is shown to confer antibiotic resistance to the bacterium. A novel study has now revealed that Pf4 forms crystalline structures that serve to physically wall off antibiotics from the bacterium. This represents an entirely novel mechanism involving liquid–liquid phase separation in prokaryotic systems. Furthermore, the toxin-antitoxin system PfiAT, which is encoded within the prophage Pf4, represents a unique production mechanism for Pf4. Combined, these two studies broadened our knowledge on the antibiotic resistance mechanisms used by P. aeruginosa

Some have it all: multicellularity, magnetotaxis and photokinesis in one bacterium

Bacteria developed many different ways to orient themselves in the environment. Magnetoreception with following motility along Earth's magnetic field lines and photoreception with subsequent positive or negative phototaxis allow bacteria to optimally position themselves for survival and growth. Some bacteria show both magnetotactic and photoresponsive behaviour and additionally live in a multicellular organism adding another layer of complexity. A novel study by Qian and colleagues visualized different species of multicellular magnetotactic bacteria and shed light on their reproductive as well as photoresponsive behaviour. This study paves the way towards understanding the evolutionary advantage of multicellular lifestyle of prokaryotes

Should I kill or should I go: T6SS regulation networks in Vibrio

This work was funded by the Spanish Ministry of Economy and Competitiveness (MINECO) Grant BIO2017-83763-

Death in a sphere: Chromobacterium violaceum secretes outer membrane vesicles filled with antibiotics

descripción no proporcionada por scopu

Delivery of the Pseudomonas aeruginosa phospholipase effectors PldA and PldB in a VgrG- and H2-T6SS-dependent manner

The bacterial pathogen Pseudomonas aeruginosa uses three type VI secretion systems (T6SSs) to drive a multitude of effector proteins into eukaryotic or prokaryotic target cells. The T6SS is a supramolecular nanomachine, involving a set of 13 core proteins, which resembles the contractile tail of bacteriophages and whose tip is considered as a puncturing device helping to cross membranes. Effectors can attach directly to the T6SS spike which is composed of a VgrG (valine-glycine-rich proteins) trimer, of which P. aeruginosa produces several. We have previously shown that the master regulator RsmA controls the expression of all three T6SS gene clusters (H1-, H2- and H3-T6SS) and a range of remote vgrG and effector genes. We also demonstrated that specific interactions between VgrGs and various T6SS effectors are prerequisite for effector delivery in a process we called “à la carte delivery”. Here, we provide an in-depth description on how the two H2-T6SS-dependent effectors PldA and PldB are delivered via their cognate VgrGs, VgrG4b and VgrG5, respectively. We show that specific recognition of the VgrG C terminus is required and effector specificity can be swapped by exchanging these C-terminal domains. Importantly, we established that effector recognition by a cognate VgrG is not always sufficient to achieve successful secretion, but it is crucial to provide effector stability. This study highlights the complexity of effector adaptation to the T6SS nanomachine and shows how the VgrG tip can possibly be manipulated to achieve effector delivery

Role of regulated proteolysis in the communication of bacteria with the environment

For bacteria to flourish in different niches, they need to sense signals from the environment and translate these into appropriate responses. Most bacterial signal transduction systems involve proteins that trigger the required response through the modification of gene transcription. These proteins are often produced in an inactive state that prevents their interaction with the RNA polymerase and/or the DNA in the absence of the inducing signal. Among other mechanisms, regulated proteolysis is becoming increasingly recognized as a key process in the modulation of the activity of these signal response proteins. Regulated proteolysis can either produce complete degradation or specific cleavage of the target protein, thus modifying its function. Because proteolysis is a fast process, the modulation of signaling proteins activity by this process allows for an immediate response to a given signal, which facilitates adaptation to the surrounding environment and bacterial survival. Moreover, regulated proteolysis is a fundamental process for the transmission of extracellular signals to the cytosol through the bacterial membranes. By a proteolytic mechanism known as regulated intramembrane proteolysis (RIP) transmembrane proteins are cleaved within the plane of the membrane to liberate a cytosolic domain or protein able to modify gene transcription. This allows the transmission of a signal present on one side of a membrane to the other side where the response is elicited. In this work, we review the role of regulated proteolysis in the bacterial communication with the environment through the modulation of the main bacterial signal transduction systems, namely one- and two-component systems, and alternative σ factors.This work was funded by the FEDER and the Spanish Ministry of Economy with grant BIO2017-83763-P. We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI

Solving the puzzle: connecting a heterologous Agrobacterium tumefaciens T6SS effector to a Pseudomonas aeruginosa spike complex

The type VI secretion system (T6SS) is a contractile injection apparatus that translocates a spike loaded with various effectors directly into eukaryotic and prokaryotic target cells. Such T6SS spike consists of a needle-shaped trimer of VgrG proteins topped by a conical and sharp PAAR protein that facilitates puncturing of the target membrane. T6SS-delivered effector proteins can be either fused to one of the two spike proteins or interact with either in a highly specific manner. In Agrobacterium tumefaciens the T6SS effector Tde1 is targeted to its cognate VgrG1 protein. Here, we attempted to use a VgrG shuttle to deliver a heterologous T6SS effector by directing Tde1 onto a T6SS spike in Pseudomonas aeruginosa. For this, we designed chimeras between VgrG1 from A. tumefaciens and VgrG1a from P. aeruginosa and showed that modification of the spike protein hampered T6SS functionality in the presence of the Tde1 effector complex. We provide evidence suggesting that Tde1 specifically binds to the VgrG spike in the heterologous environment and propose that there are additional requirements to allow proper effector delivery and translocation. Our work sheds light on complex aspects of the molecular mechanisms of T6SS delivery and highlights some limitations on how effectors can be translocated using this nanomachine