The pre-Columbian dog from Arica,Chile

Burials and mummies of dogs from the Arica, Chile, area are described. It is concluded that these dogs were brought to this area 2500 years ago by shepherds from the highlands and are still present, relatively unchanged.     

The cost of mutualism in a fly-fungus interaction

The movement ability of individuals has become increasingly important to a variety of ecological questions. In this study, I investigate how plant structure and changes in body size through development affect the movement ability of a predaceous stinkbug, Podisus maculiventris, on three species of goldenrod (Solidago spp.) representing a wide range of surface complexities. I adapt existing techniques for quantifying movement in two dimensions to the study of movement on natural plant structures in three dimensions. These experiments indicate that plant structure and insect size are significant factors affecting the movement ability of P. maculiventris. Changes in movement ability due to factors of ontogeny and different habitat structures suggest that the scale of an individual’s ambit or ecological sphere of influence may vary within its lifespan. Considering the influence of ontogeny and habitat structure on movement ability may be useful to investigations of population dynamics, foraging behavior, and pest management. Received: 14 July 1999 / Accepted: 23 March 2000     

Correlation of cell surface antigen expression on human thymocytes by multi-color flow cytometric analysis: implications for differentiation

Thymocytes undergo a complex series of phenotypic and genotypic changes during maturation in the thymus. This dynamic process involves qualitative and quantitative changes in the expression of certain cell surface differentiation antigens. In this study, we have directly examined the relationship of T cell differentiation antigen expression on normal human thymocytes by using multi-color immunofluorescence and multi-parameter flow cytometric analysis. The results from these studies have provided new insights into the complexity of antigen expression during thymic maturation and suggest that the CD3/T cell antigen receptor complex is expressed early in the development of thymocytes. Direct quantitative measurements of antigen expression by using multi-parameter flow cytometric analysis also suggest quantitative co-regulation of certain antigens (e.g., CD3 and CD5) during thymic maturation.     

Microbial degradation of oxalate in the gastrointestinal tracts of rats.

Rates of oxalate degradation by mixed bacterial populations in cecal contents from wild rats ranged from 2.5 to 20.6 mumol/g (dry weight) per h. The oxalate-degrading activity in cecal contents from three strains of laboratory rats (Long-Evans, Wistar, and Sprague-Dawley) from four commercial breeders was generally lower, ranging from 1.8 to 3.5 mumol/g (dry weight) of cecal contents per h. This activity did not increase when diets were supplemented with oxalate. When Sprague-Dawley rats from a fifth commercial breeder were fed an oxalate diet, rates of oxalate degradation in cecal contents increased from 2.0 to 23.1 mumol/g (dry weight) per h. Obligately anaerobic, oxalate-degrading bacteria, similar to ruminal strains of Oxalobacter formigenes, were isolated from the latter group of laboratory rats and from wild rats. Viable counts of these bacteria were as high as 10(8)/g (dry weight) of cecal contents, which was less than 0.1% of the total viable population. This report presents the first evidence for the presence of anaerobic oxalate-degrading bacteria in the cecal contents of rats and represents the first direct measurement of the concentration of these bacteria in the large bowel of monogastric animals. We propose that methods used for the maintenance of most commercial rat colonies often preclude the intestinal colonization of laboratory rats with anaerobic oxalate-degrading bacteria.     

Mutations in the signal sequence of prepro-alpha-factor inhibit both translocation into the endoplasmic reticulum and processing by signal peptidase in yeast cells.

The effects of five single-amino-acid substitution mutations within the signal sequence of yeast prepro-alpha-factor were tested in yeast cells. After short pulse-labelings, virtually all of the alpha-factor precursor proteins from a wild-type gene were glycosylated and processed by signal peptidase. In contrast, the signal sequence mutations resulted in the accumulation of mostly unglycosylated prepro-alpha-factor after a short labeling interval, indicating a defect in translocation of the protein into the endoplasmic reticulum. Confirming this interpretation, unglycosylated mutant prepro-alpha-factor in cell extracts was sensitive to proteinase K and therefore in a cytosolic location. The signal sequence mutations reduced the rate of translocation into the endoplasmic reticulum by as much as 25-fold or more. In at least one case, mutant prepro-alpha-factor molecules were translocated almost entirely posttranslationally. Four of the five mutations also reduced the rate of proteolytic processing by signal peptidase in vivo, even though the signal peptide alterations are not located near the cleavage site. This study demonstrates that a single-amino-acid substitution mutation within a eucaryotic signal peptide can affect both translocation and proteolytic processing in vivo and may indicate that the recognition sequences for translocation and processing overlap within the signal peptide.     

Influence of pH, nutrient availability, and growth rate on amine production by Bacteroides fragilis and Clostridium perfringens

Dimethylamine, methylamine, propylamine, and pyrrolidine were the major amines formed by Bacteroides fragilis NCDO 2217 during the active phase of growth in batch culture. Production of these metabolites was strongly pH dependent and was optimal under acidic conditions (pH 6.0). Low pH also favored the formation of pyrrolidine, cadaverine, and dimethylamine by Clostridium perfringens C523, but the reverse was the case with putrescine, butylamine, and propylamine, where production was maximal at neutral pH. B. fragilis was grown in continuous culture under either starch or casein limitation. Amine formation was influenced by carbohydrate availability and was greatest when the bacteria were grown at high growth rates (dilution rate, 0.20/h) under starch limitation, where they constituted about 18% of the total fermentation products measured. Amine production was optimal and increased concomitantly with growth rate when C. perfringens was grown in glucose-limited continuous culture. Under conditions of high growth rate and glucose limitation, amines accounted for approximately 27% of the fermentation products measured. When glucose in the feed medium was increased from 5 to 15 g/liter, amine production was repressed, and under these nutritional conditions the growth rate had little effect on the process.