Biomedical subjects

Margaret C Henk

Publications and source records attributed to Margaret C Henk.

5 recordsLinked to original sources

PubMed2006

Fixation methods can produce misleading artifacts in sperm cell ultrastructure of diploid and tetraploid Pacific oysters, Crassostrea gigas.

Spermatozoa from diploid and tetraploid Pacific oysters (Crassostrea gigas) were examined after anisotonic fixation. Morphological anomalies, such as membrane rupture, detached tails, and the formation of tail vesicles (typically associated with damage attributable to procedures such as cryopreservation) were observed; the Mantel-Haenszel Chi-square test indicated a strong association between the anomalies and fixative osmolality (P<0.001). The present study also indicated that media in a range of 800 to 1,086 mOsm/kg could be assumed to be functionally isotonic to Pacific oysters, and osmolalities below or above this caused severe cell damage. For example, the maximum volume of flagella obtained after hypotonic fixation was approximately twice the volume of the flagella in isotonic fixation. Sperm cell flagellar volumes after hypertonic fixation (1,110 mOsm/kg) were 32% smaller than those in isotonic fixation, and sperm heads were 25% smaller. Although the damage associated with anisotonic fixation was evident in all parts of the sperm cells, the most vulnerable locations were the plasma membrane and flagellum motor apparatus. The formation of tail vesicles after hypotonic fixation was also examined. Because of water uptake, oyster sperm became swollen in hypotonic fixative, and bending or coiling of the axoneme within the tail vesicles led to the appearance of multiple axonemal structures in cross sections when observed by transmission electron microscopy. This phenomenon might be generally misinterpreted as the presence of double tails. This and other fixation artifacts can lead to the misinterpretation of damage caused by cryopreservation in ultrastructure studies of sperm of aquatic species, especially those in marine species.

Animals↗

PubMed2005

Extensive diversity of ionizing-radiation-resistant bacteria recovered from Sonoran Desert soil and description of nine new species of the genus Deinococcus obtained from a single soil sample.

The ionizing-radiation-resistant fractions of two soil bacterial communities were investigated by exposing an arid soil from the Sonoran Desert and a nonarid soil from a Louisiana forest to various doses of ionizing radiation using a (60)Co source. The numbers of surviving bacteria decreased as the dose of gamma radiation to which the soils were exposed increased. Bacterial isolates surviving doses of 30 kGy were recovered from the Sonoran Desert soil, while no isolates were recovered from the nonarid forest soil after exposure to doses greater than 13 kGy. The phylogenetic diversities of the surviving culturable bacteria were compared for the two soils using 16S rRNA gene sequence analysis. In addition to a bacterial population that was more resistant to higher doses of ionizing radiation, the diversity of the isolates was greater in the arid soil. The taxonomic diversity of the isolates recovered was found to decrease as the level of ionizing-radiation exposure increased. Bacterial isolates of the genera Deinococcus, Geodermatophilus, and Hymenobacter were still recovered from the arid soil after exposure to doses of 17 to 30 kGy. The recovery of large numbers of extremely ionizing-radiation-resistant bacteria from an arid soil and not from a nonarid soil provides further ecological support for the hypothesis that the ionizing-radiation resistance phenotype is a consequence of the evolution of other DNA repair systems that protect cells against commonly encountered environmental stressors, such as desiccation. The diverse group of bacterial strains isolated from the arid soil sample included 60 Deinococcus strains, the characterization of which revealed nine novel species of this genus.

DNA, Bacterial↗

PubMed2005

High-frequency phase variation of Vibrio vulnificus 1003: isolation and characterization of a rugose phenotypic variant.

The marine bacterium Vibrio vulnificus is a human pathogen that can spontaneously switch between virulent opaque and avirulent translucent phenotypes. Here, we document an additional form, the rugose variant, which produces copious biofilms and which may contribute both to pathogenicity of V. vulnificus and to its survival under adverse environmental conditions.

Biofilms↗

PubMed2004

Method for collecting air-water interface microbes suitable for subsequent microscopy and molecular analysis in both research and teaching laboratories.

A method has been developed for collecting air-water interface (AWI) microbes and biofilms that enables analysis of the same sample with various combinations of bright-field and fluorescence light microscopy optics, scanning and transmission electron microscopy (TEM), and atomic force microscopy. The identical sample is then subjected to molecular analysis. The sampling tool consists of a microscope slide supporting appropriate substrates, TEM grids, for example, that are removable for the desired protocols. The slide with its substrates is then coated with a collodion polymer membrane to which in situ AWI organisms adhere upon contact. This sampling device effectively separates the captured AWI bacterial community from the bulk water community immediately subtending. Preliminary data indicate that the AWI community differs significantly from the water column community from the same sample site when both are evaluated with microscopy and with 16S ribosomal DNA sequence-based culture-independent comparisons. This microbe collection method can be used at many levels in research and teaching.

Adhesives↗

PubMed2003

Evidence that acetyl phosphate functions as a global signal during biofilm development.

We used DNA macroarray analysis to identify genes that respond to the status of the intracellular acetyl phosphate (acP) pool. Genes whose expression correlated negatively with the ability to synthesize acP (i.e. negatively regulated genes) function primarily in flagella biosynthesis, a result consistent with observations that we published previously (Prüss and Wolfe, 1994, Mol Microbiol 12: 973-984). In contrast, genes whose expression correlated positively with the ability to synthesize acP (i.e. positively regulated genes) include those for type 1 pilus assembly, colanic acid (capsule) biosynthesis and certain stress effectors. To our knowledge, this constitutes the first report that these genes may respond to the status of the intracellular acP pool. Previously, other researchers have implicated flagella, type 1 pili, capsule and diverse stress effectors in the formation of biofilms. We therefore tested whether cells altered in their ability to metabolize acP could construct normal biofilms, and found that they could not. Cells defective for the production of acP and cells defective for the degradation of acP could both form biofilms, but these biofilms exhibited characteristics substantially different from each other and from biofilms formed by their wild-type parent. We confirmed the role of individual cell surface structures, the expression of which appears to correlate with acP levels, in fim or fli mutants that cannot assemble type 1 pili or flagella respectively. Thus, the information gained by expression profiling of cells with altered acP metabolism indicates that acP may help to co-ordinate the expression of surface structures and cellular processes involved in the initial stages of wild-type biofilm development.

Bacterial Adhesion↗