Different responses to Spo0A-mediated suppression of the related Bacillus subtilis phages Nf and φ29

The φ29 family of phages is divided in three groups. Members of groups 1 and 2 infect the spore-forming bacterium Bacillus subtilis . Previous studies showed that group 1 phage φ29 adapts its infection strategy to the physiological state of the host. Thus, the lytic cycle of φ29 is suppressed when cells are infected during the early stages of sporulation and the infecting genome becomes trapped into the spore. A major element of this adaptive strategy is a very sensitive response to the host-encoded Spo0A protein, the key regulator for sporulation activation, which is directly responsible for suppression of φ29 development. Here we analysed if this adaptation is conserved in phage Nf belonging to group 2. The results obtained show that although Nf also possesses the alternative infection strategy, it is clearly less sensitive to Spo0A-mediated suppression than φ29. Sequence determination of the Nf genome revealed striking differences in the number of Spo0A binding site sequences. The results provide evidence that the life style of two highly related phages is distinctly tuned by differences in binding sites for a host-encoded regulatory protein, being a good example of how viruses have evolved to optimally exploit features of their host.