Seasonal occurrence of Campylobacter spp. in surface waters and their correlation with standard indicator bacteria.

Campylobacter jejuni, Campylobacter coli, and a Campylobacter-like organism were isolated from a number of natural water sources in central Washington, including ponds, lakes, and small mountain streams at elevations ranging from 1,460 to 5,400 feet (ca. 445 to 1,646 m) above sea level. At the two sites where extensive sampling was done, the bacteria were recovered throughout the year. Generally, the recovery rates were highest in the fall and winter months and lowest during the spring and summer months. Campylobacter density did not show significant correlation with microbiological (plate counts of fecal and total coliforms, fecal streptococci, and heterotrophic bacteria) or physical (water temperature, pH, and conductivity) parameters.     

A highly sensitive chromogenic microtiter plate assay for plasminogen activators which quantitatively discriminates between the urokinase and tissue-type activators

A simple and highly sensitive chromogenic microtiter plate assay for plasminogen activators is described. The assay is based on plasmin cleavage of the synthetic tripeptide plasmin substrate H-D-norleucyl-hexahydrotyrosyl-lysine p-nitroaniline, which yields the yellow chromophore p-nitroanilide. Production of the latter compound is then quantitated spectrophotometrically at 405 nm on an ELISA plate reader. Linearity of the assay can be achieved over at least four orders of magnitude in a single experiment (0.01-100 milliPloug units) with appropriate incubation times. Capitalizing on tissue-type plasminogen activator's dependence on fibrin for enzymatic activity, the selective use of soluble fibrin products allows discrimination between urokinase and tissue-type activator. The utility of this aspect of the assay for the analysis of complex samples containing both types of plasminogen activators is demonstrated.     

Magnesium ion effects on microtubule nucleation in vitro

Much interest has currently been attached to the length distribution of microtubules polymerized in vitro and the related question of their possible 'dynamic instability'. Fundamental to this question is the mechanism of microtubule nucleation, which controls the rates of assembly and disassembly of microtubule protein in vitro. These kinetics are affected by a number of factors, including both the guanine nucleotides, GTP and GDP, and magnesium ion. Mg2+ exerts complex effects, as indicated by the existence of an optimal Mg2+ concentration for the maximum assembly rate of microtubule protein, and we investigate these effects in this report. At [Mg2+] greater than 0.5 mM, the characteristic lag-phase is substantially increased and the rate of assembly is greatly reduced without affecting the critical concentration significantly. We show that increasing [Mg2+] has two effects on the assembly process: nucleation is less efficient and the intrinsic rate constant for the elongation reaction is reduced. Lowering [Mg2+] (less than 0.5 mM) also inhibits nucleation. These effects of varying [Mg2+] can be explained predominantly in terms of enhanced stability of the microtubule-associated protein-containing oligomeric species present in the microtubule protein preparation. [Mg2+] is thus found to be a further important factor in microtubule nucleation, and hence, in determining length distributions in assembling microtubules.     

Natural Selection and Y-Linked Polymorphism

Several population genetic models allowing natural selection to act on Y-linked polymorphism are examined. The first incorporates pleiotropic effects of a Y-linked locus, such that viability, segregation distortion, fecundity and sexual selection can all be determined by one locus. It is shown that no set of selection parameters can maintain a stable Y-linked polymorphism. Interaction with the X chromosome is allowed in the next model, with viabilities determined by both X- and Y-linked factors. This model allows four fixation equilibria, two equilibria with X polymorphism and a unique point with both X- and Y-linked polymorphism. Stability analysis shows that the complete polymorphism is never stable. When X- and Y-linked loci influence meiotic drive, it is possible to have all fixation equilibria simultaneously unstable, and yet there is no stable interior equilibrium. Only when viability and meiotic drive are jointly affected by both X- and Y-linked genes can a Y-linked polymorphism be maintained. Unusual dynamics, including stable limit cycles, are generated by this model. Numerical simulations show that only a very small portion of the parameter space admits Y polymorphism, a result that is relevant to the interpretation of levels of Y-DNA sequence variation in natural populations.     

A reply to Holmes on Gendercide

Warren's book, Gendercide: The Implications of Sex Selection (Totowa, N.J.: Rowman and Allanheld; 1985), was reviewed by Helen Bequaert Holmes in the January 1987 issue of Bioethics. Here, Warren responds to the review by clarifying some of her moral arguments and continuing to defend the point of view that selecting the sex of children before conception or before birth is not always sexist, socially harmful, or disrespectful of the child as an end in itself.     

Farming,fishing, and fire in the history of the upper Río Negro region of Venezuela

Studies of Río Negro subsistence farming and fishing activities are used to estimate the human carrying capacity for the region and the likely pattern of human land-use during prehistory. Ceramic evidence suggests human presence in the region more than 3000 years ago. Traditional farming is labor intensive and relatively unproductive. Nevertheless, farmers achieve an energy return of 15.21, and produce 2600 kcal per work hour. Fish are the major protein source, but fish catch per unit of effort and fish yield per hectare of floodplain are very low; fishermen are probably exploiting local fish resources very close to their limit. The low human population density would suggest that the Río Negro forest has been relatively undisturbed. Nevertheless, charcoal is widespread and abundant in forest soils. This charcoal is probably from anthropogenic or natural wildfires. These results suggest a much more complex history for Amazonia than previously thought.K. Clark is a free-lance biologist residing in Lima, Peru     

Glomerular ultrastructure of the trout,Salmo gairdneri: Effects of angiotensin II and adaptation to seawater

Summary The effect of angiotensin infusion on the glomerular ultrastructure of freshwater- and seawater-adapted rainbow trout, Salmo gairdneri, has been examined by scanning and transmission electron microscopy. Adaptation of trout to seawater resulted in epithelial podocyte flattening, primary process broadening and apparent loss of foot processes in almost all glomeruli, features which were uncommon in freshwater-adapted trout. Similar changes were induced by infusion of freshwater-adapted animals with angiotensin, suggesting that the renin-angiotensin system plays a role in the modification of glomerular epithelial ultrastructure. Adaptation of trout to seawater also reduced glomerular diameter, but infusion of freshwater-adapted animals with angiotensin did not mirror this effect. Infusion of angiotensin into seawater-adapted animals increased the overall thickness of glomerular basement membrane by increasing the lamina rara interna and lamina densa. This did not occur when freshwater-adapted fish were either infused with angiotensin or adapted to seawater. These findings suggest that other humoral systems are involved in the control of glomerular diameter and basement membrane thickness as part of an integrated response to increased environmental salinity.     

A cellular protein binds to a conserved sequence in the adenovirus type 2 enhancer.

A sensitive gel retention assay has been utilized to detect proteins from uninfected Hela nuclei which interact with the adenovirus type 2 enhancer. This assay has been employed to monitor fractionation of nuclear extracts. Three enhancer binding factors were resolved by chromatography on DEAE-Sepharose and one of the factors was further purified by chromatography on heparin-Sepharose. DNase protection experiments have shown that the heparin-Sepharose fraction contains a factor which binds predominantly to the conserved sequence GTGGAAATTT present at position 160 in the adenovirus type 2 genome and found in many viral and cellular enhancers. Protection of this sequence from DNase I digestion was abolished by competition with a synthetic duplex oligonucleotide spanning bases 144-181. This region corresponds to the sequence defined by Hen et al. as possessing enhancer function. Competition experiments indicated that the enhancer binding factor also bound, albeit with reduced affinity, to multiple sites in the Ela upstream region located between positions 192 and 353. Within the sequences which compete are regions with homology to the high affinity site at position 160. The enhancer binding factor also binds with high affinity to sequences within the SV40 enhancer demonstrating that this factor interacts with sequences common to both the adenovirus and SV40 enhancers.     

Differential expression within a family of novel wound-induced genes in potato

Summary Wounding in higher plants leads to an increased synthesis of specific messenger RNAs. A cDNA clone complementary to a wound-induced message from potato tubers was used to isolate a lambda clone from a genomic library of Salanum tuberosum var. Maris Piper. DNA sequence analysis has shown that this single genomic clone contains two novel wound-induced genes, called win1 and win2, organised in close tandem array. The coding sequences of these two genes are highly homologous and are interrupted by a single intron. However, the sequences of the introns and flanking regions have diverged widely. Win1 and win2 encode cysteine-rich proteins of 200 and 211 amino-acids, respectively, which show striking homologies to several chitin-binding proteins. Southern analysis of genomic DNA has shown that win1 and win2 are members of a small multi-gene family which is estimated to have a minimum of five members per haploid genome of Maris Piper and appears to be conserved within the Solanaceae. We have shown by Northern analysis and S1 mapping that the two genes exhibit differential organ-specific expression after the wounding of a potato plant.