A first aspect of the present invention is an isolated nucleic acid encoding a phage abortive defense protein, the isolated nucleic acid selected from the group consisting of: (a) isolated nucleic acid having the sequence or coding sequence given in SEQ ID NO: 1 (by "coding sequence" is meant nucleotides 373 to 1668 therein); (b) isolated nucleic acid encoding a phage abortive defense protein and which hybridizes to an nucleic acid having the sequence or coding sequence given in SEQ ID NO: 1, and/or having a sequence at least 60, 70, 80, 90, 92 or 95 percent identical to the sequence or coding sequence given in SEQ ID NO: 1; and (c) isolated nucleic acid encoding a phage abortive defense protein encoded by an isolated nucleic acid of (a) or (b) above, but differing in sequence therefrom due to the degeneracy of the genetic code (e.g., a nucleic acid encoding the protein given in SEQ ID NO: 2).