TRACE METALS AND METHYL MERCURY: ASSOCIATIONS AND TRANSFER IN HARP SEAL (PHOCA GROENLANDICA) MOTHERS AND THEIR PUPS

Milk samples from the stomachs of harp seal pups were analysed for Cu, Zn, Se, Cd and Hg, as were liver, kidney, and muscle from mother-pup pairs. Tissues were also analysed for MeHg. Milk contained, in addition to essential trace metals, Cd and Hg (57 ng/g and 6.5 ng/g respectively).
Pups had mercury in all three tissues. The percent methyl mercury in liver of pups was higher than in liver of mothers. Mercury in muscle was mostly methyl mercury in both mothers and pups. Total mercury in liver of mothers but not pups was correlated positively with selenium. Estimates of ingested mercury by pups indicated they had acquired most of their mercury during gestation.
Although mothers had cadmium in liver and kidney, it was not detected in tissues of pups. Cadmium did not transfer across the placenta, while mercury did. Tissue concentrations of Cu and Zn were higher in pups than mothers. The presence of metallothionein in pup tissues was postulated.
A strong positive correlation of copper and selenium between mothers and pups indicated transfer of these elements from mother to pup in direct proportion to their concentrations in maternal liver and kidney.     

Identification of the protein encoded by rodC, a cell division gene from Bacillus subtilis

The rodC1 mutation of Bacillus subtilis is a temperature-sensitive marker which affects the orientation of the plane of cell division. We have cloned the rodC gene and have localized the site of the rodC1 lesion. To identify the rodC gene product, we have subjected several plasmid clones containing B. subtilis chromosomal DNA from the rodC region to maxicell analysis in Escherichia coli. A 68 kiloDalton protein has been identified as the rodC gene product. This is the initial cloning of a cell division gene and the identification of its product from B. subtilis. The rodC gene has also been implicated as being directly associated with the synthesis of glycerol teichoic acid.     

Ultra sensitive detection of Listeria monocytogenes in milk by the polymerase chain reaction (PCR)

The polymerase chain reaction (PCR) has been used to detect Listeria monocytogenes in whole milk at a level of 0.1 cfu per 30 ml. This high degree of sensitivity has been achieved following enzymatic digestion, polysulphonone membrane filtration and amplification of a nucleotide sequence within the promoter region of hlyA. Key elements of the procedure are the absence of enrichment culture and a complete solubilization of the membrane filter, ensuring total nucleic acid recovery. The simplicity of the protocol coupled with high sample volumes and exquisite sensitivity extends the relevance of PCR within food and environmental microbiology.     

Changes in leaf,stem, and root anatomy of Chrysanthemum cv. Lillian Hoek following paclobutrazol application

Plants ofChrysanthemum cv. Lillian Hoek were treated with a paclobutrazol (PBZ) soil drench and histologically examined after 3 months. PBZ application resulted in thicker leaves, reduced stem diameter, and roots with an increased diameter and an unusual segmented appearance. Increased leaf thickness was partly due to an additional layer of palisade mesophyll, although individual palisade cells were shorter, of smaller diameter, and more tightly packed. Spongy mesophyll depth was also greater and the individual cells were more rounded and the volume of intercellular space was reduced. The narrower stems had an increased development of secondary xylem, but had a marked reduction in the number of sclerenchyma bundle caps. Increased root diameter was due to an increase in the number of rows and diameter of cortical cells. In PBZ-treated plants, root cortical cell length was 50–70% less than in untreated plants, and this reduction appeared to be associated with the segmentation of the roots. PBZ inhibited secondary vascular development in the roots. This study is similar to other relevant studies in recording thicker leaves and roots with PBZ application; however, many of the underlying anatomical changes described above have not been previously reported.     

Most ultraviolet irradiation induced mutations in the nematode Caenorhabditis elegans are chromosomal rearrangements

In this study we have determined the utility of 254-nm ultraviolet light (UV) as a mutagenic tool in C. elegans. We have demonstrated that irradiation of adult hermaphrodites provides a simple method for the induction of heritable chromosomal rearrangements. A screening protocol was employed that identifies either recessive lethal mutations in the 40 map unit region balanced by the translocation eT1(III;V), or unc-36(III) duplications. Mutations were recovered in 3% of the chromosomes screened after a dose of 120 J/m2. This rate resembles that for 1500 R gamma-ray-induced mutations selected in a similar manner. The mutations were classified either as lethals [mapping to Linkage Group (LG)III or LGV] or as putative unc-36 duplications. In contrast to the majority of UV-induced mutations analysed in microorganisms, we found that a large fraction of the C. elegans UV-induced mutations are not simple intragenic lesions, but are deficiencies for more than one adjacent gene or more complex events. Preliminary evidence for this conclusion came from the high frequency of mutations that had a dominant effect causing reduced numbers of adult progeny. Subsequently 6 out of 9 analysed LGV mutations were found to be deficiencies. Other specific rearrangements also identified were: one translocation, sT5(II;III), and two unc-36 duplications, sDp8 and sDp9. It was concluded that UV irradiation can easily be used as an additional tool for the analysis of C. elegans chromosomes, and that C. elegans should prove to be a useful organism in which to study the mechanisms whereby UV acts as a mutagen in cells of complex eukaryotes.     

Fish size and habitat depth relationships in headwater streams

Summary Surveys of 262 pools in 3 small streams in eastern Tennessee demonstrated a strong positive relationship between pool depth and the size of the largest fish within a pool (P<0.001). Similarly, the largest colonizers of newly-created deep pools were larger than the colonizers of shallow pools. We explored the role of predation risk in contributing to the bigger fish — deeper habitat pattern, which has been noted by others, by conducting five manipulative field experiments in two streams. Three experiments used stoneroller minnows (Campostoma anomalum); one used creek chubs (Semotilus atromaculatus); and one used striped shiners (Notropis chrysocephalus). The stoneroller experiments showed that survival of fish approximately 100 mm in total length (TL) was much lower in shallow pools (10 cm deep) than in deep (40 cm maximum) pools (19% versus 80% survival over 12 d in one experiment) and added cover markedly increased stoneroller survival in shallow pools (from 49% to 96% in an 11-d experiment). The creek chub experiment showed that, as for stonerollers, pool depth markedly influenced survival: the chubs survived an average of 4.9 d in shallow pools and >10.8 d in deep pools. In the striped shiner experiment in shallow artificial streamside troughs, no individuals 75–100 mm TL survived as long as 13 d, where-as smaller (20–25 mm) fish had 100% survival over 13 d. The results of the experiments show that predation risk from wading/diving animals (e.g., herons and raccoons) is much higher for larger fishes in shallow water than for these fishes in deeper water or for smaller fish in shallow water. We discuss the role of predation risk from two sources (piscivorous fish, which are more effective in deeper habitats, and diving/wading predators, which are more effective in shallow habitats) in contributing to the bigger fish — deeper habitat pattern in streams.     

Use of a photolabeling technique to identify nonviable cells in fixed homologous or heterologous cell populations

Flow cytometric determination of viable versus nonviable cells in fixed samples can be accomplished by utilizing the irreversible binding of photoactivated ethidium monoazide (EMA). EMA is a positively charged molecule which is excluded by cells with intact membranes (viable cells), included by cells with damaged membranes, and can be photochemically crosslinked to nucleic acids using visible light. EMA fluorescence can be excited using a standard argon laser operating at 488 nm and is able to be distinguished from fluorescein and phycoerythrin. Fixation is important when analyzing cells from a potentially infectious origin. EMA is photochemically crosslinked and therefore unable to leak out of cells when removed from the extracellular media, unlike propidium iodide (PI) or other viability stains, which were heretofore commonly used. We demonstrate the usefulness of EMA in combination with fluoresceinated and phycoerythrin labeled monoclonal antibodies in immunophenotyping. The photoaffinity labeling technique allows for a quick and efficient means of identifying nonviable cells which cannot be distinguished on the basis of light-scattering properties.