title: Three separate classes of bacterial ice nucleation structures.
abstract: Studies of the properties of the ice nucleation structure exposed on the surfaces of various bacteria such as Pseudomonas syringae, Erwinia herbicola, or various strains of Ice+ recombinant Escherichia coli have shown that there are clearly three major related but chemically distinct types of structures on these cells. First, the ability of Ice+ cells to nucleate super-cooled D2O has been examined, and it has been found that this ability (relative to the ability of the same cells to nucleate super-cooled H2O) exhibited three characteristic nucleating patterns. The rarest structure, called class A, is found on only a small fraction of cells in a culture, nucleates H2O at temperatures above -4.4 degrees C, and is an effective nucleator of super-cooled D2O. A second class of structure, called class B, is found on a larger portion of the cells, nucleates H2O between -4.8 and -5.7 degrees C, and is a relatively poor nucleator of super-cooled D2O. The class C structure is found on almost all cells and nucleates at -7.6 degrees C or colder. These three classes of structures were also differentiated by their sensitivities to low concentrations of water-miscible organic solvents such as dioxane or dimethyl sulfoxide. Depending on the specific bacterial strain, the addition of these solvents to bacterial suspensions lowered the nucleation activity of the class A structure by 1,000-fold or more. The nucleation activities of class B structures in the same culture were highly resistant to these compounds and were lowered only by 20 to 40%. The class C structures were more sensitive than Class B structures were, and the nucleation activities decreased 70 to 90%. Finally, the pH sensitivity of these three classes of structures was examined. The class A structure was destroyed in buffers at pH 4.5 lower but was stable in buffers at higher pHs. The class B structure was less sensitive to acidic buffers but was destroyed at pH 5.5 or lower and was stable at higher pHs. However, the class C structure was unaffected by incubation in buffers with pHs of 3.5 to 9.0. Suggestions for the actual nucleation structures of the three classes are proposed.
authors.affiliation: Department of Microbiology, University of California, San Francisco 94143-0404.
authors.forename: M A
authors.initials: MA
authors.lastname: Turner
authors.forename: F
authors.initials: F
authors.lastname: Arellano
authors.forename: L M
authors.initials: LM
authors.lastname: Kozloff
mesh_terms: D003903:Deuterium; D017666:Deuterium Oxide; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D004146:Dioxanes / Q000494:pharmacology; D004885:Erwinia / Q000187:drug effects / Q000502:physiology*; D004926:Escherichia coli / Q000187:drug effects / Q000502:physiology*; D005615:Freezing; D006863:Hydrogen-Ion Concentration; D007053:Ice; D011549:Pseudomonas / Q000187:drug effects / Q000502:physiology*; D013045:Species Specificity; D014867:Water
chemical_list: D004146:Dioxanes; D007053:Ice; D014867:Water; D003903:Deuterium; D017666:Deuterium Oxide; C025223:1,4-dioxane; D004121:Dimethyl Sulfoxide