Characterization of the major control region of Vibrio cholerae bacteriophage K139: Immunity, exclusion, and integration

The temperate bacteriophage K139 is highly associated with pathogenic 01 Vi brio cholerae strains. The nucleotide sequence of the major control region of K139 was determined. The sequences of four (cox, cII, cI, and int) of th e six deduced open reading frames and their gene order indicated that K139 is related to the P2 bacteriophage family. Two genes of the lysogenic trans cript from the mapped promoter P-L encode homologs to the proteins CI and I nt, with deduced functions in prophage formation and maintenance. Between t he d and int genes, two additional genes were identified: orf2, which has n o significant. similarity to any other gene, and the formerly characterized gene glo. Further analysis revealed that Orf2: is involved in preventing s uperinfection. In a previous report, we described that mutations in glo cau se an attenuation effect in the cholera mouse model (J.Reidl and J. J. Meka lanos, Mel. Microbiol. 18:685-701, 1995). In this report,we present strong evidence that Glo participates in phage exclusion. Glo was characterized to encode a 13.6-kDa periplasmic protein which inhibits phage infection at an early step, hence preventing reinfection of vibriophage K139 into K139 lys ogenic cells. Immediately downstream of gene int, the attP site was identif ied. Upon analysis of the corresponding attB site within the V. cholerae ch romosome, it became evident that phage K139 is integrated between the flage llin genes flaA and flaC of O1 E1 Tor and O139 V.cholerae lysogenic strains .