CHARACTERIZATION AND POSSIBLE FUNCTIONS OF A NEW FILAMENTOUS BACTERIOPHAGE FROM VIBRIO-CHOLERAE O139

The emergence and rapid rise to dominance of Vibrio cholerae O139 in I ndia and Bangladesh in 1992 led to the consideration that choleraphage might serve as both a selective mechanism and a means for horizontal transmission of genetic information. A filamentous phage '493' from O1 39 strain AJ27-493 has been purified and partially characterized. The phage was inactive on classical biotype V. cholerae O1 but it was acti ve on El Tor biotype strains isolated prior to 1994 when El Tor re-eme rged in Bangladesh. More recent El Tor isolates were all resistant to the phage. The phage was also active on O139 strains. Unlike the filam entous ctx phi, the receptor for 493 is not TcpA. The phage genome was a 9.3 kb closed circular single-stranded molecule containing a 0.4 kb double-stranded stem supporting a 2 kb single-stranded loop. A 283 bp fragment was cloned and used as a probe in Southern hybridization, in parallel with total phage 493 DNA. These probes hybridized both chrom osomally and extrachromosomally with most O139 strains, but not with O 1 strains. Infection of hybridization-negative El Tor or O139 strains resulted in the presence of hybridizing loci (both plasmid and chromos omal), in the appearance of an 18 kDa protein, and in marked alteratio ns in colonial morphology. Phage 493 is clearly distinct from other O1 39 choleraphages which have been described. Phage 493 DNA hybridized w ith an encapsulated non-O1 (O31) strain (NRT36S) which was isolated be fore O139 was recognized. NRT36S also produces a phage which can infec t Fl Tor strains with low efficiency. Further studies may reveal wheth er bacteriophage play a role in the emergence and the territoriality o f new choleragenic vibrios.