To avert frequent viral infections, prokaryotes have developed numerous defense systems. It was found that in bacterial and archaeal genomes phage defense systems tend to be clustered in regions called "defense islands" [1]. This observation led to identification of novel antiviral systems by examining uncharacterized genes located in close vicinity to genes encoding well-known bacterial defense systems. One of recently discovered systems that assists bacteria to conquer phage infection is named Septu [2].
Septu defense system, isolated from bacteria of Bacillus genus, consists of two proteins – PtuA, which contains ATPase domain, and HNH nuclease PtuB [2]. Surprisingly, Septu system of B. thuringiensis provides protection from not only B. subtilis but also E. coli phages [3]. In this study we present results of purification of proteins encoded by PtuAB operon and in vivo activity against E. coli phages of B. thuringiensis Septu defense system.