Biomedical subjects

D Gurian-Sherman

Publications and source records attributed to D Gurian-Sherman.

4 recordsLinked to original sources

PubMed2001

Diversity of the Burkholderia cepacia complex and implications for risk assessment of biological control strains.

The Burkholderia cepacia complex (Bcc) consists of several species of closely related and extremely versatile gram-negative bacteria found naturally in soil, water, and the rhizosphere of plants. Strains of Bcc have been used in biological control of plant diseases and bioremediation, while some strains are plant pathogens or opportunistic pathogens of humans with cystic fibrosis. The ecological versatility of these bacteria is likely due to their unusually large genomes, which are often comprised of several (typically two or three) large replicons, as well as their ability to use a large array of compounds as sole carbon sources. The original species B. cepacia has been split into eight genetic species (genomovars), including five named species, but taxonomic distinctions have not enabled biological control strains to be clearly distinguished from human pathogenic strains. This has led to a reassessment of the risk of several strains registered by the U.S. Environmental Protection Agency for biological control. We review the biology of Bcc bacteria, especially how our growing knowledge of Bcc ecology and pathogenicity might be used in risk assessment. The capability of this bacterial complex to cause disease in plants and humans, as well as to control plant diseases, affords a rare opportunity to explore traits that may function in all three environments.

Biodegradation, Environmental↗

PubMed1995

Differential effects of growth temperature on ice nuclei active at different temperatures that are produced by cells of Pseudomonas syringae.

The temperature at which ice-nucleating bacteria are grown causes differences of 100- to 10,000-fold in the fraction of cells that nucleate ice at a given temperature (ice nucleation frequency). Ice nucleation frequencies of cells of Pseudomonas syringae grown at temperatures that ranged from 9 to 33 degrees C were examined in order to more accurately characterize physiological effects on ice nuclei active at temperatures of from about -2 to -10 degrees C, the temperature range for this phenotype. Large differences in ice nucleation frequency occurred at all but the lowest assay temperatures in cells of P. syringae grown in the temperature range of 15 to 33 degrees C. These differences in ice nucleation frequency may be attributed, at least in part, to post-translational factors. Because other studies have indicated that ice nuclei active at the lowest assay temperatures may reflect the amount of ice nucleation protein produced, while higher nucleation temperatures reflect aggregates of this ice nucleation protein, data was normalized to the frequency of ice nuclei active at the lowest ice nucleation temperatures (which also correspond to the most abundant nuclei). This was done in order to develop a baseline of comparison for cells grown at different temperatures that more clearly shows possible post-translational effects such as aggregation of the nucleation protein. After this normalization was performed, and in contrast to the results noted above, the number of ice nuclei in cells grown at 9, 15, and 20 degrees C that were active at different assay temperatures was very similar. Differences in ice nucleation frequency that occurred over all assay temperatures in cells grown between 9 and 20 degrees C may be attributed to differences in the total number of nuclei present in the population of cells. The large effects of growth temperature on nucleation frequency have important implications for estimating numbers of ice nucleating bacteria in environmental samples by determining the number of bacterial ice nuclei in such samples.

Bacterial Outer Membrane Proteins↗

PubMed1993

Bacterial ice nucleation: significance and molecular basis.

Several bacterial species are able to catalyze ice formation at temperatures as warm as -2 degrees C. These microorganisms efficiently catalyze ice formation at temperatures much higher than most organic or inorganic substances. Because of their ubiquity on the surfaces of frost-sensitive plants, they are responsible for initiating ice formation, which results in frost injury. The high temperature of ice catalysis conferred by bacterial ice nuclei makes them useful in ice nucleation-limited processes such as artificial snow production, the freezing of some food products, and possibly in future whether modification schemes. The rarity of other ice nuclei active at high subfreezing temperature, and the ease and sensitivity with which ice nuclei can be quantified, have made the use of a promoterless bacterial ice nucleation gene valuable as a reporter of transcription. Target genes to which this promoter is fused can be used in cells in natural habitats. Warm-temperature ice nucleation sites have also been extensively studied at a molecular level. Nucleation sites active at high temperatures (above -5 degrees C) are probably composed of bacterial ice nucleation protein molecules that form functionally aligned aggregates. Models of ice nucleation proteins predict that they form a planar array of hydrogen binding groups that closely complement that of an ice crystal face. Moreover, interdigitation of these molecules may produce a large contiguous template for ice formation.

Bacteria↗

PubMed1993

Isolation and characterization of hydroxylamine-induced mutations in the Erwinia herbicola ice nucleation gene that selectively reduce warm temperature ice nucleation activity.

Cells of ice nucleation active bacterial species catalyse ice formation over the temperature range of -2 to -12 degrees C. Current models of ice nucleus structure associate the size of ice nucleation protein aggregates with the temperature at which they catalyse ice formation. To better define the structural features of ice nucleation proteins responsible for the functional heterogeneity of ice nuclei within a genetically homogeneous collection of cells we used in vitro chemical mutagenesis to isolate mutants with reduced ability to nucleate ice at warm assay temperatures but which retain normal or near normal nucleation activity at cold temperatures (WIND, i.e. warm ice nucleus-deficient mutants). Nearly half of the mutants obtained after hydroxylamine mutagenesis of the iceE gene from Erwinia herbicola had this phenotype. The phenotypes and location of lesions on the genetic map of iceE were determined for a number of mutants. All WIND mutations were restricted to the portion of iceE encoding the repetitive region of the polypeptide. DNA sequencing of two WIND mutants revealed single nucleotide substitutions changing a conserved serine or glycine residue to phenylalanine and serine, respectively. The implications of these findings in structure/function models for the ice nucleation protein are discussed.

Amino Acid Sequence↗