Journal of Bacteriology (2020) PubMed PMID: 32958633; PubMed Central PMCID: .

Abstract

The arms-race between bacteria and their competitors has produced an astounding variety of conflict systems that are shared via horizontal gene transfer across bacterial populations. In this issue of Journal of Bacteriology, Burroughs and Aravind investigate how these biological conflict systems have been mixed-and-matched into new configurations, often with novel protein domains. The authors additionally characterize the evolutionary history of genes in eukaryotes that appear to have been acquired from these prokaryotic defense systems.

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Citation

Kibby EM, Whiteley AT. J Bacteriol. 2020 Nov 19;202(24). doi: 10.1128/JB.00507-20. Print 2020 Nov 19. PubMed PMID: 32958633; PubMed Central PMCID: PMC7685558.

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Mol Cell. 2020 Jan 6. pii: S1097-2765(19)30923-2. doi: 10.1016/j.molcel.2019.12.010. [Epub ahead of print]

Abstract

Bacteria possess an array of defenses against foreign invaders, including a broadly distributed bacteriophage defense system termed CBASS (cyclic oligonucleotide-based anti-phage signaling system). In CBASS systems, a cGAS/DncV-like nucleotidyltransferase synthesizes cyclic di- or tri-nucleotide second messengers in response to infection, and these molecules activate diverse effectors to mediate bacteriophage immunity via abortive infection. Here, we show that the CBASS effector NucC is related to restriction enzymes but uniquely assembles into a homotrimer. Binding of NucC trimers to a cyclic tri-adenylate second messenger promotes assembly of a NucC homohexamer competent for non-specific double-strand DNA cleavage. In infected cells, NucC activation leads to complete destruction of the bacterial chromosome, causing cell death prior to completion of phage replication. In addition to CBASS systems, we identify NucC homologs in over 30 type III CRISPR/Cas systems, where they likely function as accessory nucleases activated by cyclic oligoadenylate second messengers synthesized by these systems' effector complexes.

Keywords: 

CD-NTase; Endonuclease; abortive infection; bacteriophage immunity; second messenger signaling

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