Saul A. Yankofsky

Some Basic Characteristics of Bacterial Freezing Nuclei

Abstract Freezing spectra of INA bacteria from different parts of the world were compared. A slight increase in efficiency of freezing nuclei produced by strains from warmer climates was observed. Whole cells of the most efficient strain produced nuclei active at temperatures ranging from −2 to −10°C, whereas fragments from these cells exhibited activity only at −8 to −10°C. In all cases, the frequency of active cells in a population proved low. Thus, activity at −8 to −10°C was evidenced by 1 cell in about 300, the corresponding ratio being 1 in 104 at −2 to −4°C. It was shown in several ways that the variety of “freezer” individuals was not due to a need for multicell aggregation or any other cooperative process. Also, the time at which a given individual in a cell population expressed its latent freezing potential was shown to vary with time and cell physiological state.

Contact Versus Immersion Freezing of Freely Suspended Droplets by Bacterial Ice Nuclei

Abstract Droplets freely suspended in the air stream of a wind tunnel were nucleated with dedicated bacterial cells in either the contact or immersion mode. Immersion freezing seemed to give a noncontinuous frequency distribution of freezing with temperature whereas the corresponding curve for contact was monotonic. Although the latter nucleation mode was more efficient by ∼2°C, the temperature ranges over which droplets froze by either mode of nucleation were closer to 0°C than those so far published for nonbiogenic ice nuclei of natural origin.

Association with citrus of ice-nucleating bacteria and their possible role as causative agents of frost damage

Two distinct bacteria capable of freezing nucleus activity at temperatures as warm as −2.5°C were repeatedly isolated from citrus and avocado plants in Israel. Phage typing has shown them to be related to each other and to one of the two groups of ice-nucleation-active bacteria already described by other workers. Evidence suggesting that these organisms can cause frost damage to the plants they inhabit at temperatures not far below freezing was also obtained.

Solid-phase assay for d-biotin on avidin-cellulose disks

Abstract Filter-paper disks of uniform size were chemically modified by the introduction of isonitrile functional groups. Avidin was then covalently linked to the disks in a four-component condensation reaction involving disk isonitrile groups and avidin carboxyl groups in the presence of a water-soluble aldehyde and an amine. Quantitative assay of unknown d -biotin solutions could be conveniently carried out with such avidin-cellulose disks by a two-step procedure: (i) immersion in the unknown sample, and (ii) exposure to an excess of radioactive biotin. Based on the known total capacity of the disks for biotin, the amount of unlabeled biotin extracted from solution by avidin-cellulose disks could be easily estimated.

Possible Application of Bacterial Condensation Freezing to Artificial Rainfall Enhancement

Abstract Both gram-positive and gram-negative bacteria become excellent condensation nuclei when lyophilized to dryness. The same freeze-dry procedure does not inactivate the highly effective freezing nuclei produced by ice nucleation active bacteria. Therefore, irrespective of their contact nucleation potential, ice nucleation-active bacteria ought to effect condensation freezing at −10°C of warmer in cloud systems. Output from a numerical cloud model suggests that the condensation freezing capability of ice nucleation-active bacteria at warmer temperatures could be exploited to produce rainfall from clouds too warm to respond positively to inorganic nucleants like silver iodide.

Induction of latent freezing nucleus capability in an ice nucleation-active bacterium

The normally very low frequency of ice nucleation-active individuals in populations of Bacterium M1 could be raised as high as 100% by treatments having perturbation of cellular DNA metabolism as their common denominator. The process whereby inactive cells acquired efficient freezing nuclei after induction was shown to require ongoing synthesis of RNA and protein. It was probably also promoted by a rapid rate of DNA synthesis.

Isolation and characterization of a ColE1 plasmid containing the entire Bio gene cluster of Escherichia coli K12

SummaryColE1 amp plasmids carrying the entire bio gene cluster were constructed in vitro using ColE1 amp as the cloning vehicle and a λ transducing phage, λatt2,as the source of bio DNA. Restriction endonuclease EcoRI digests of ColE1amp and λatt2DNA were joined by polynucleotide ligase and plasmids bearing the entire bio gene cluster were selected, after transformation, in bio deletion strains of E. coli. Recombinant DNA moleules contained one ColE1amp fragment (7.4×106 daltons) and one λatt2DNA fragment (5.4×106 daltons). Clones carrying ColE1 amp-bio plasmids produce elevated levels of biotin and biotin synthetase activity.

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

Abstract. 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.

Differentiation of 23-S ribosomal RNA cistrons from 16-S ribosomal RNA cistrons in Escherichia coli by the sequence complementarity test

Abstract It has been reported that the 16-S and 23-S components of Escherichia coli ribosomal RNA compete for common hybridization sites on homologous DNA. We here show that no such competition phenomenon occurs. Carefully purified preparations of the two major ribosomal RNA types do not competitively interact with one another during hybridization to Escherichia coli DNA. Consequently, as in all other organisms tested to date, genes coding for molecules of 23-S ribosomal RNA are entirely distinct from those giving rise to 16-S ribosomal RNA molecules. We also confirm that there are multiple gene copies responsible for the biogenesis of each ribosomal RNA component in Escherichia coli.

Studies on the interaction of a surface-bound ligand with a multi-valent high-molecular-weight ligate : The biotinycellulose—avidin system

Abstract Two types of biotinylated cellulose disks were examined: filter-paper disks to which biotin had been covalently attached directly to the paper surface (biotinylcellulose) and disks on which biotin was attached to polyacrylamide side-chains grafted onto the filter-paper surface (biotinylpolyacrylamide—cellulose). The amount of avidin taken up from solution by these disks was linearly related to the avidin input concentration and could be estimated by exposure to [ 14 C]biotin. The avidin-binding capacity of the disks depended on the surface density of covalently attached ligand and exhibited hyperbolic, Langmuir-type behaviour for both types of disks. The [ 14 C]biotin binding capacity of avidinylated disks, on the other hand, showed anomalous, biphasic behaviour: at higher ligand densities, a decrease in [ 14 C]biotin binding was observed. The largest anomalies were obtained with biotinylpolyacrylamide—cellulose disks. Calculated ratios of bound [ 14 C]biotin vs. amount of avidin tetramer (B/A 4 ) showed a similar biphasic behaviour. A constant value of B/A 4 = 3 was obtained at low ligand densities, whereas B/A 4 decreased monotonously with increasing ligand density and asymptotically approached B/A 4 = 1. The data could be explained by assuming that at high ligand densities tetrameric avidin interacts with more than one surface-bound biotin residue.