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Understanding the global diversity of extracellular Contractile Injection Systems: nanoscale machines used by bacteria to control both friends and foe

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  • Bacteria are key plays in all aspects of life on this planet
  • How they interact with other organisms is vital to our understanding of environmental, health and economic issues
  • Understanding the tools bacteria use to control their relationships with other organisms is becoming increasingly important in controlling disease.

Researchers from the University of Warwick and the Beijing Friendship Hospital, China, have described the diversity and complexity of an astonishing new bacterial molecular injection machine, likely to play crucial roles in the life styles of many bacteria.

Bacteria are everywhere. They are fundamental components of any environment, interacting with every other organism on the planet. Therefore, it is crucial to understand how they manage these relationships. The predominant tools they use for this are proteins. A variety of different bacterial protein secretion systems have been identified for the transfer of proteins either out of the cell into the surrounding environment or directly into the cells of other organisms, including man.

The best-described secretion machines fall into the so-called types I-VII systems. These secretion systems play key roles in the life cycles of all bacteria, mediating interactions that range from symbiotic to pathogenic relationships. For example, the type VI secretion systems (T6SSs) are capable of targeting both eukaryotic and bacterial cells, either for pathogenesis or to provide a growth advantage against competing bacteria.

A far less well-characterized system, a bacteriophage-tail-like contractile nanomachine was identified in the insect pathogen Serratia entomophila, and designated the anti-feeding prophage (AFP). AFP causes cessation of feeding and death of infected grass grub larvae, the natural host of S. entomophila. A similar AFP-like system, the Photorhabdus virulence cassettes (PVCs) discovered by the Waterfield group, was shown to have potent insecticidal activity against moth larvae. Subsequently, a more distantly related cousin of the AFP/PVC-type devices was identified in the marine bacterium Pseudoalteromonas luteoviolacea. This system, metamorhosis-associated contractile (MAC) structure, triggers metamorphosis of a marine worm, Hydroides elegans. Together this family of molecular machines have been designated extracellular Contractile Injection Systems (or eCIS).

Increasing numbers of publications are emerging implicating a role of eCIS systems in very diverse bacteria. Therefore, in collaboration with researchers in the Beijing Friendship Hospital, the Waterfield group at Warwick Medical School (WMS) have performed a survey of the genes required to elaborate these astonishing eCIS devices in the available complete bacterial genome sequences found in the public DNA databases.

The recent publication by the Waterfield group in Cell Reports; “Genome-wide Identification and Characterization of a Superfamily of Bacterial Extracellular Contractile Injection Systems” highlights the widespread distribution and genetic diversity of this system. The work reveals that eCIS genes can be found in examples of most groups of bacteria, even in the enigmatic archaea.

Furthermore, in collaboration with members of Prof. Achtman (WMS) we have delved deeper into one specific genus of important human pathogen, Salmonella. Using their cutting edge Enterobase bioinformatics facility the researchers examined over 100 thousand Salmonella genome sequences and showed that these devices can also be found in two specific subgroups of this genus of clinically important bacteria. In this recent publication they also present a public access fully searchable database, allowing researchers in any field to look for eCIS devices in their bacteria of interest (http://www.mgc.ac.cn/dbeCIS/)

“Genome-wide Identification and Characterization of a Superfamily of Bacterial Extracellular Contractile Injection Systems” in Cell Reports. 2019 Oct 8;29(2):511-521.e2. doi: 10.1016/j.celrep.2019.08.096.

Mon 21 Oct 2019, 11:57 | Tags: BMS