SP10 Infectivity Is Aborted after Bacteriophage SP10 Infection Induces nonA Transcription on the Prophage SP Region of the Bacillus

Bacteria have developed various strategies for phage resistance. Infection with phage induces the transcription of part of the phage resistance gene, but the regulatory mechanisms of such transcription remain largely unknown. The phage resistance gene nonA is located on the SP prophage region of the Bacillus subtilisMarburg strain genome. The nonA transcript was detected at the late stage of SP10 infection but is undetectable in noninfected cells. The nonA transcript was detected after the induction of the sigma factor Orf199-Orf200 (Orf199-200), when sigma factors encoded in the SP10 genome were expressed from a xylose-in-ducible plasmid. Thus, the SP10 sigma factor is an activator of a set of SP10 genes and nonA. The nonA gene encodes a 72-amino-acid protein with a transmembrane motif and has no significant homology with any protein in any database. NonA overexpres-sion halted cell growth and reduced the efficiency of B. subtilis colony formation and respiration activity. In addition, SP10 virion protein synthesis was inhibited in the nonA strain, and SP10 virion particles were scarce in it. These results indicate that NonA is a novel protein that can abort SP10 infection, and its transcription was regulated by SP10 sigma factor. Bacteriophages (phages) frequently attack bacteria in almost allenvironments. Phages outnumber bacteria by approximately 1- to 10-fold, and1025 phages initiate infection per second on a global scale (1–3). Bacteria have evolved various systems to resist phage predation, and phages in turn have developed strategies to evade such resistance (4). Thus, constant infection with phages lead