The presence of complete but masked freezing nuclei in various artificially constructed ice nucleation-active proteobacteria

Disparate gamma-subdivision proteobacteria artifically endowed with the same ice gene of enteric origin acquired water-freezing potential at −12°C, but expressed it to varying extents under identical conditions of culture as well as after being subjected to certain post-culture treatments. Varying rates of cell-bound ice nucleus synthesis were probably not the root cause of these observed interspecies differences in nucleation-active cell frequency because potentially functional but masked ice-forming templates were found in the outer cell envelope of even initially inactive individuals taken from physiologically uniform populations of virtually all tested species. We therefore propose that the extent of bacterial ice nucleation generally reflects species-specified extent of ice nucleus sequestration.