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function is also unknown. The sheer size of the tem, composed of the genes jetABCD, which is mostly defined as “domains of unknown func-
Druantia system (12 kb of genomic DNA) sug- common in microbial genomes and is very fre- tion,” structural modeling using Phyre2 (41)
gests a complex function, and the near-complete quently found next to defense genes (Fig. 5A). showed structural homology between JetA, JetB,
absence of recognizable domains in its genes Three instances representing three different types and JetC and genes belonging to the housekeep-
suggests a new mode of defense not shared by of Wadjet (see below) were cloned from three ing condensin system MukF, MukE, and MukB,
prokaryotic defense systems whose mechanism separate Bacillus species into B. subtilis BEST7003. respectively. Bacterial condensins are chromosome-
is currently understood. Although none of these systems provided pro- organizing complexes that are responsible for
tection against any of the 10 Bacillus phages in DNA condensation and accurate segregation
Defense against plasmid transformation our array, all three consistently and significantly during replication (42), and mutations in the
Some of the putative defense systems that we reduced transformation efficiency of the episomal housekeeping condensins lead to severe defects
experimentally tested did not show any anti- plasmid pHCMC05 (Fig.5C).These results sug- in chromosome segregation and viability (43).
phage activity despite being strongly associated gest that Wadjet may be a defense system spe- Several versions of housekeeping condensins
with known defense genes. We reasoned that cifically targeting foreign plasmids. appear in bacterial genomes: SMC, MukBEF, and
some of these systems may defend against other We identified three different domain compo- MksBEF (44); the Wadjet system was previously
forms of foreign DNA. To test this hypothesis, sitions, each encoding a different set of pfams, noted as a distant homolog of the MksBEF sys-
we selected one such system, which we denote but all with common sequence signatures mark- tem described in P. aeruginosa (45).
Wadjet (god protector of ancient Egypt), for fur- ing them as three types of Wadjet (Fig. 5B). Although the domain organization of the
ther experimentation. Wadjet is a four-gene sys- Whereas the pfam domains of Wadjet genes are jetABC genes may lead to the hypothesis that Downloaded from

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Fig. 5. The Wadjet system provides protection against plasmid trans- of Wadjet systems were taken from B. cereus Q1 (type I), B. vireti LMG 21834 on March 1, 2018
formation in B. subtilis. (A) Representative instances of the Wadjet system (type II), and B. thuringiensis serovar finitimus YBT-020 (type III) (table S4) and
and their defense island context. Genes known to be involved in defense are cloned into B. subtilis BEST7003. Gene deletions and point mutations are of
orange. RM, restriction-modification; TA, toxin-antitoxin; Abi, abortive infection. the B. cereus Q1 type I Wadjet. Transformation efficiency of plasmid pHCMC05
(B) Domain organization of the three types of Wadjet. Pfam and COG into Wadjet-containing strains is presented as a percentage of the transfor-
domains were assigned according to the information in the IMG database (48). mation efficiency to B. subtilis BEST7003 carrying an empty vector instead of
(C) Wadjet reduces plasmid transformation efficiency in B. subtilis.Instances the Wadjet system. Average of three replicates; error bars, mean ± SD.

Doron et al., Science 359, eaar4120 (2018) 2 March 2018 7of 11