Small-molecule communication between virusesWe discovered that phages that infect Bacillus subtilis can use small molecule communication to coordinate lysis/lysogeny decisions (Erez et al, Nature 2017). During infection of its host cell, the phage produces a 6aa communication peptide that is released to the medium. In subsequent infections, progeny phages measure the concentration of this peptide and lysogenize if the concentration is sufficiently high. We found that different phages encode different versions of the communication peptide, demonstrating a phage-specific peptide communication code for lysogeny decisions. We termed this communication system the "arbitrium" system (Erez et al, Nature 2017). We found that such communication commonly guides lysogeny decisions in more than 1000 phages that infect soil bacteria, as well as those infecting pathogens (Stokar-Avihail, Tal et al, Cell Host & Microbe 2019).
a) Dynamics of arbitrium accumulation during infection of a bacterial culture by phage.
b) At the first encounter of a phage with a bacterial population, the early genes aimR and aimP are expressed immediately upon infection. AimR, as a dimer activates AimX expression. AimX is an inhibitor of lysogeny, directing the phage to a lytic cycle. At the same time AimP is expressed, secreted and processed extracellularly to produce the mature communication peptide.
c) At later stages of the infection dynamics, the arbitrium peptide accumulates in the medium and is internalized into the bacteria by the OPP transporter. Now when the phage infects the bacterium, the expressed AimR receptor binds the arbitrium molecules and cannot activate the expression of AimX, leading to lysogeny preference.
(Figure taken from Erez et al, Nature 2017).