A broadly distributed predicted helicase/nuclease confers phage resistance via abortive infection

There is strong selection for the evolution of systems that protect bacterial populations from viral attack. We report a single phage defense protein, Hna, that provides protection against diverse phages in Sinorhizobium meliloti, a nitrogen-fixing alpha-proteobacterium. Homologs of Hna are distributed widely across bacterial lineages, and a homologous protein from Escherichia coli also confers phage defense. Hna contains superfamily II …