Differential Spo0A-mediated effects on transcription and replication of the related Bacillus subtilis phages Nf and Φ29 explain their different behaviours in vivo

Abstract

Members of groups 1 (e.g. Φ29) and 2 (e.g. Nf) of the Φ29 family of phages infect the spore forming bacterium Bacillus subtilis. Although classified as lytic phages, the lytic cycle of Φ29 can be suppressed and its genome can become entrapped into the B. subtilis spore. This constitutes an alternative infection strategy that depends on the presence of binding sites for the host-encoded protein Spo0A in the Φ29 genome. Binding of Spo0A to these sites represses Φ29 transcription and prevents initiation of DNA replication. Although the Nf genome can also become trapped into B. subtili s spores, in vivo studies showed that its lytic cycle is less susceptible to spo0A-mediated suppression than that of Φ29. Here we have analysed the molecular mechanism underlying this difference showing that Spo0A differently affects transcription and replication initiation of the genomes of these phages. Thus, whereas Spo0A represses all three main early promoters of Φ29, it only represses one out of the three equivalent early promoters of Nf. In addition, contrary to Φ29, Spo0A does not prevent the in vitro initiation of Nf DNA replication. Altogether, the differences in Spo0A-mediated regulation of transcription and replication between Φ29 and Nf explain their different behaviours in vivo. © 2009 The Author(s).