UNUSUAL PATTERN OF BACTERIAL ICE NUCLEATION GENE EVOLUTION

Bacterial ice nucleation activity (INA(+) phenotype) can be traced to the product of a single gene, ina. A remarkably sparse distribution of this phenotype within three bacterial genera indicates that the ina g ene may have followed an unusual evolutionary path. Southern blot anal yses, coupled with assays for ice-nucleating ability, revealed that wi thin four bacterial species an ina gene is present in some strains but absent from others. Results of hybridization experiments using DNA fr agments that flank the ina gene suggested that the genotypic dimorphis m of ina may be anomalous. A phylogenetic analysis of 16S ribosomal RN A gene sequences from a total of 14 ina(+) and ina(-) bacterial strain s indicated that the ina(+) bacteria are not monophyletic but instead phylogenetically interspersed among ina(-) bacteria. The relationships of ina(+) bacteria inferred from ina sequence did not coincide with t hose inferred from the 16S data. These results suggest the possibility of horizontal transfer in the evolution of bacterial ina genes.