Quantitative Determination of Antibacterial Activity During Bacterial Coculture.

Antibacterial activity assays are an important tool in the assessment of the ability of one bacterium to kill or inhibit the growth of another, for example, during the study of the Type VI secretion system (T6SS) and the antibacterial toxins it secretes. The method we describe here can detect the ability of a bacterial strain to kill or inhibit other bacterial cells in a contact-dependent manner when cocultured on an agar surface. It is particularly useful since it enumerates the recovery of viable target cells and thus enables quantification of the antibacterial activity.

Rhs NADase effectors and their immunity proteins are exchangeable mediators of inter-bacterial competition in Serratia.

Many bacterial species use Type VI secretion systems (T6SSs) to deliver anti-bacterial effector proteins into neighbouring bacterial cells, representing an important mechanism of inter-bacterial competition. Specific immunity proteins protect bacteria from the toxic action of their own effectors, whilst orphan immunity proteins without a cognate effector may provide protection against incoming effectors from non-self competitors. T6SS-dependent Rhs effectors contain a variable C-terminal toxin domain (CT), with the cognate immunity protein encoded immediately downstream of the effector.

The accessory protein TagV is required for full Type VI secretion system activity in Serratia marcescens.

The bacterial Type VI secretion system (T6SS) is a dynamic macromolecular structure that promotes inter- and intra-species competition through the delivery of toxic effector proteins into neighbouring cells. The T6SS contains 14 well-characterised core proteins necessary for effector delivery (TssA-M, PAAR). In this study, we have identified a novel accessory component required for optimal T6SS activity in the opportunistic pathogen Serratia marcescens, which we name TagV.

The genus Serratia revisited by genomics.

The genus Serratia has been studied for over a century and includes clinically-important and diverse environmental members. Despite this, there is a paucity of genomic information across the genus and a robust whole genome-based phylogenetic framework is lacking. Here, we have assembled and analysed a representative set of 664 genomes from across the genus, including 215 historic isolates originally used in defining the genus.

The ecological impact of a bacterial weapon: microbial interactions and the Type VI secretion system.

Bacteria inhabit all known ecological niches and establish interactions with organisms from all kingdoms of life. These interactions are mediated by a wide variety of mechanisms and very often involve the secretion of diverse molecules from the bacterial cells. The Type VI secretion system (T6SS) is a bacterial protein secretion system that uses a bacteriophage-like machinery to secrete a diverse array of effectors, usually translocating them directly into neighbouring cells.

Activation of a [NiFe]-hydrogenase-4 isoenzyme by maturation proteases.

Maturation of [NiFe]-hydrogenases often involves specific proteases responsible for cleavage of the catalytic subunits. HycI is the protease dedicated to maturation of the Hydrogenase-3 isoenzyme, a component of formate hydrogenlyase-1. In this work, it is demonstrated that a HycI homologue, HyfK, is required for hydrogenase-4 activity, a component of formate hydrogenlyase-2, in that bacterium.

Type VI secretion system effector proteins: Effective weapons for bacterial competitiveness.

The Type VI secretion system (T6SS) is a protein translocation nanomachine widespread among Gram-negative bacteria and used as a means to deliver effectors directly into target bacterial or eukaryotic cells. These effectors have a wide variety of functions within target cells that ultimately help the secreting cell gain a competitive fitness advantage. Here, we discuss the different ways in which these effectors can be delivered by the T6SS and the diverse mechanisms by which they exert their noxious action upon recipient cells.

A family of Type VI secretion system effector proteins that form ion-selective pores.

Type VI secretion systems (T6SSs) are nanomachines widely used by bacteria to deliver toxic effector proteins directly into neighbouring cells. However, the modes of action of many effectors remain unknown. Here we report that Ssp6, an anti-bacterial effector delivered by a T6SS of the opportunistic pathogen Serratia marcescens, is a toxin that forms ion-selective pores.

The plant pathogen Pectobacterium atrosepticum contains a functional formate hydrogenlyase-2 complex.

Pectobacterium atrosepticum SCRI1043 is a phytopathogenic Gram-negative enterobacterium. Genomic analysis has identified that genes required for both respiration and fermentation are expressed under anaerobic conditions. One set of anaerobically expressed genes is predicted to encode an important but poorly understood membrane-bound enzyme termed formate hydrogenlyase-2 (FHL-2), which has fascinating evolutionary links to the mitochondrial NADH dehydrogenase (Complex I).

A New Front in Microbial Warfare-Delivery of Antifungal Effectors by the Type VI Secretion System.

Microbes typically exist in mixed communities and display complex synergistic and antagonistic interactions. The Type VI secretion system (T6SS) is widespread in Gram-negative bacteria and represents a contractile nano-machine that can fire effector proteins directly into neighbouring cells. The primary role assigned to the T6SS is to function as a potent weapon during inter-bacterial competition, delivering antibacterial effectors into rival bacterial cells.

Killing with proficiency: Integrated post-translational regulation of an offensive Type VI secretion system.

The Type VI secretion system (T6SS) is widely used by bacterial pathogens as an effective weapon against bacterial competitors and is also deployed against host eukaryotic cells in some cases. It is a contractile nanomachine which delivers toxic effector proteins directly into target cells by dynamic cycles of assembly and firing. Bacterial cells adopt distinct post-translational regulatory strategies for deployment of the T6SS.

The type VI secretion system deploys antifungal effectors against microbial competitors.

Interactions between bacterial and fungal cells shape many polymicrobial communities. Bacteria elaborate diverse strategies to interact and compete with other organisms, including the deployment of protein secretion systems. The type VI secretion system (T6SS) delivers toxic effector proteins into host eukaryotic cells and competitor bacterial cells, but, surprisingly, T6SS-delivered effectors targeting fungal cells have not been reported.

Dual Role for DsbA in Attacking and Targeted Bacterial Cells during Type VI Secretion System-Mediated Competition.

Incorporation of disulfide bonds into proteins can be critical for function or stability. In bacterial cells, the periplasmic enzyme DsbA is responsible for disulfide incorporation into many extra-cytoplasmic proteins. The type VI secretion system (T6SS) is a widely occurring nanomachine that delivers toxic effector proteins directly into rival bacterial cells, playing a key role in inter-bacterial competition.

Quantitative Determination of Anti-bacterial Activity During Bacterial Co-culture.

Anti-bacterial activity assays are an important tool in the assessment of the ability of one bacterium to kill or inhibit the growth of another, for example during the study of the Type VI secretion system (T6SS) and the anti-bacterial toxins it secretes. The method we describe here can detect the ability of a bacterial strain to kill or inhibit other bacterial cells in a contact-dependent manner when co-cultured on an agar surface. It is particularly useful since it enumerates the recovery of viable target cells and thus enables quantification of the anti-bacterial activity.

VgrG and PAAR Proteins Define Distinct Versions of a Functional Type VI Secretion System.

The Type VI secretion system (T6SS) is widespread among bacterial pathogens and acts as an effective weapon against competitor bacteria and eukaryotic hosts by delivering toxic effector proteins directly into target cells. The T6SS utilises a bacteriophage-like contractile machinery to expel a puncturing device based on a tube of Hcp topped with a VgrG spike, which can be extended by a final tip from a PAAR domain-containing protein. Effector proteins are believed to be delivered by specifically associating with particular Hcp, VgrG or PAAR proteins, either covalently ('specialised') or non-covalently ('cargo' effectors).

Aim, Load, Fire: The Type VI Secretion System, a Bacterial Nanoweapon.

Bacteria utilise specialised protein secretion systems to interact with host organisms, competitor bacteria, and the environment. The Type VI secretion system (T6SS) is a versatile weapon deployed by many bacterial species to target either host cells or rival bacteria. The widespread occurrence and significance of the T6SS is becoming increasingly appreciated, as is its intriguing mode of action.

Molecular weaponry: diverse effectors delivered by the Type VI secretion system.

The Type VI secretion system is a widespread bacterial nanomachine, used to deliver toxins directly into eukaryotic or prokaryotic target cells. These secreted toxins, or effectors, act on diverse cellular targets, and their action provides the attacking bacterial cell with a significant fitness advantage, either against rival bacteria or eukaryotic host organisms. In this review, we discuss the delivery of diverse effectors by the Type VI secretion system, the modes of action of the so-called 'anti-bacterial' and 'anti-eukaryotic' effectors, the mechanism of self-resistance against anti-bacterial effectors and the evolutionary implications of horizontal transfer of Type VI secretion system-associated toxins.

Visualization of the Serratia Type VI Secretion System Reveals Unprovoked Attacks and Dynamic Assembly.

The Type VI secretion system (T6SS) is a bacterial nanomachine that fires toxic proteins into target cells. Deployment of the T6SS represents an efficient and widespread means by which bacteria attack competitors or interact with host organisms and may be triggered by contact from an attacking neighbor cell as a defensive strategy. Here, we use the opportunist pathogen Serratia marcescens and functional fluorescent fusions of key components of the T6SS to observe different subassemblies of the machinery simultaneously and on multiple timescales in vivo.

Intraspecies Competition in Serratia marcescens Is Mediated by Type VI-Secreted Rhs Effectors and a Conserved Effector-Associated Accessory Protein.

Unlabelled: The type VI secretion system (T6SS) is widespread in Gram-negative bacteria and can deliver toxic effector proteins into eukaryotic cells or competitor bacteria. Antibacterial T6SSs are increasingly recognized as key mediators of interbacterial competition and may contribute to the outcome of many polymicrobial infections. Multiple antibacterial effectors can be delivered by these systems, with diverse activities against target cells and distinct modes of secretion.

A holin and an endopeptidase are essential for chitinolytic protein secretion in Serratia marcescens.

Pathogenic bacteria adapt to their environment and manipulate the biochemistry of hosts by secretion of effector molecules. Serratia marcescens is an opportunistic pathogen associated with healthcare-acquired infections and is a prolific secretor of proteins, including three chitinases (ChiA, ChiB, and ChiC) and a chitin binding protein (Cbp21). In this work, genetic, biochemical, and proteomic approaches identified genes that were required for secretion of all three chitinases and Cbp21.

Communication, cooperation, and social interactions: a report from the third Young Microbiologists Symposium on microbe signalling, organisation, and pathogenesis.

The third Young Microbiologists Symposium took place on the vibrant campus of the University of Dundee, Scotland, from the 2nd to 3rd of June 2014. The symposium attracted over 150 microbiologists from 17 different countries. The significant characteristic of this meeting was that it was specifically aimed at providing a forum for junior scientists to present their work.

Genome evolution and plasticity of Serratia marcescens, an important multidrug-resistant nosocomial pathogen.

Serratia marcescens is an important nosocomial pathogen that can cause an array of infections, most notably of the urinary tract and bloodstream. Naturally, it is found in many environmental niches, and is capable of infecting plants and animals. The emergence and spread of multidrug-resistant strains producing extended-spectrum or metallo beta-lactamases now pose a threat to public health worldwide.