Detection of Mannitol Formation by Bacteria

A test is described by means of which formation of mannitol from fructose by lactic acid bacteria can be readily detected. The test is based on removal of interference of residual fructose by dehydration with hydrochloric acid followed by thin-layer chromatography.     

Stoichiometric relationships in vernal pond plankton communities

1. The light-nutrient hypothesis (LNH) predicts that changes in light supply can alter the balance of nutrient and energy limitation in primary producers. We tested this prediction by examining temporal changes in vernal forest ponds, which are highly dynamic systems with respect to seasonal change in light and nutrient supply. In three vernal ponds that differ in productivity, we measured changes in light, total and seston nitrogen and phosphorus, and seston carbon and chlorophyll during the spring, before and after tree leaf-out. We also quantified changes in the population dynamics of the major zooplankton grazers in these systems.
2. In each pond, nutrient levels increased and light levels declined, creating a temporal shift in light-nutrient supply to the plankton. Results generally supported predictions of stoichiometric theory and the LNH, but there were notable exceptions.
3. Seston C : N : P ratios rapidly changed in response to dramatic increases in N and P supply rates. However, seston N : P was typically lower than values for total N : P in the water. Furthermore, as predicted, we observed a decline in seston C : P as the light : nutrient ratio declined, but seston C : N simultaneously increased. These results suggest an unexpected shift towards potential nitrogen limitation. Alternatively, this change in nutrient ratios may be driven by a seasonal change in phytoplankton composition or nutritional mode.
4. Seston carbon concentrations remained stable despite seasonal changes in grazing intensity associated with the phenology of large-bodied Daphnia grazers. However, chlorophyll concentrations declined dramatically as the season progressed, resulting in a simultaneous decline in the C : Chlorophyll ratio of seston. Both pond shading and increased grazing probably contributed to the decline in chlorophyll.     

Growth of Mixed Cultures on Mixed Substrates: I. Continuous Culture

Continuous culture on mixed glucose-lactose or glucose-butyrate media inoculated with river water led to a population composed of a pseudomonad and a coliform. The glucose was used preferentially to the other carbon source, and the utilization of the secondary carbon source was greatly reduced at high growth rates. Significant amounts of acetate were excreted even though the cultures were limited by the carbon source, rather than by oxygen or other nutrients. At high growth rates, the pseudomonad dominated the population, whereas at low and moderate growth rates the coliform was dominant. A syntrophic relationship was shown by the fact that the pseudomonad could not grow alone on the glucose-butyrate medium.     

Enrichment of auxotrophic mutants of Aspergillus flavus by tritium suicide

A method based on tritium suicide was developed to enrich auxotrophic mutants of Aspergillus flavus. N-methyl-N'-nitro-N-nitrosoguanidine (NG) was chosen as a mutagen, since a wide variety of mutations were induced by the action of 0.1% NG on A. flavus conidia suspended in phosphate buffer (pH 7.0). The decimal reduction time under these conditions was about 30 min, and the surviving population contained 4 to 6% auxotrophs after 1 hr of mutagenesis. This proportion was then increased by tritium suicide of wild-type cells. At a concentration of 1.3 mum, (3)H-leucine was incorporated better than (3)H-proline or (3)H-thymidine into the germinating conidia. With about 20 hr of incubation and a short treatment in a high-speed mixer to disentangle mycelia and conidia, a 5- to 20-fold decrease in the number of survivors resulted from the incorporated (3)H-leucine (5 c/mmole) after 1 week of storage at 5 C. At a 10-fold lower concentration, the uptake of radioactivity and the subsequent suicide rate were much lower. With (3)H-leucine, the proportion of auxotrophs in the surviving population rose from 5 to about 20% during 2 weeks of storage at 5 C. Mutants requiring various intermediates for protein or nucleic acid synthesis or requiring vitamins were isolated. Finally, it was noted that A. flavus shows a much higher resistance to tritium suicide than does Escherichia coli.     

Comparative cytotoxicity of fumonisin B1 in two cell lines derived from normal human bronchial epithelial cells using four distinct bioassay techniques

This study focuses on the cytotoxic effects of fumonisin B₁ (FB₁) on both immortalised and immortalised and subsequently transfected normal human bronchial epithelial (NHBE) cells of human origin using four bioassays. While the MTT, Neutral Red and hexosaminidase colorimetric assays showed little difference between the toxic effects on the two related cell lines, the clonogenic assay, measuring cell survival and proliferation, indicated that FB₁ had a more toxic effect on the nontransfected cells. This kind ofin vitro approach using cells which retain many characteristics of normal cell growth and differentiation can go some way to developing evaluation models for food safety in the case of mycotoxin contamination without resorting totally to whole animal testing. Nevertheless, one or two cytotoxicity tests may be inadequate for a complete appraisal of toxic potential: rather, as wide a range of methodologies as feasible should be employed initially before meaningful conclusions may be drawn.     

Lifestyle modifications to prevent and control hypertension. 2. Recommendations on obesity and weight loss. Canadian Hypertension Society,Canadian Coalition for High Blood Pressure Prevention and Control,Laboratory Centre for Disease Control at Health Canada,Heart and Stroke Foundation of Canada

OBJECTIVE: To provide updated, evidence-based recommendations concerning the effects of weight loss and maintenance of healthy weight on the prevention and control of hypertension in otherwise healthy adults (except pregnant women). OPTIONS: The main options are to attain and maintain a healthy body weight (body mass index [BMI] 20-25 kg/m2) or not to do so. For those at risk for hypertension, weight loss and maintenance of healthy weight may prevent the condition. For those who have hypertension, weight loss and maintenance of healthy weight may reduce or obviate the need for antihypertensive medications. OUTCOMES: The health outcome considered was change in blood pressure. Because of insufficient evidence, no economic outcomes were considered. EVIDENCE: A MEDLINE search was conducted for the years 1992-1996 with the terms hypertension and obesity in combination and antihypertensive therapy and obesity in combination. Other relevant evidence was obtained from the reference lists of the articles identified, from the personal files of the authors and through contacts with experts. The articles were reviewed, classified according to study design and graded according to level of evidence. VALUES: A high value was placed on the avoidance of cardiovascular morbidity and premature death caused by untreated hypertension. BENEFITS, HARMS AND COSTS: Weight loss and the maintenance of healthy body weight reduces the blood pressure of both hypertensive and normotensive people. The indirect benefits of a health body weight are well known. The negative effects of weight loss are primarily the frustrations associated with attaining and maintaining a healthy weight. The costs associated with weight loss programs were not measured in the studies reviewed. RECOMMENDATIONS: (1) It is recommended that health care professionals determine weight (in kilograms), height (in metres) and BMI for all adults. (2) To reduce blood pressure in the population at large, it is recommended that Canadians attain and maintain a healthy BMI (20-25). (3) All overweight hypertensive patients (BMI greater than 25) should be advised to reduce their weight. VALIDATION: These recommendations are similar to those of the World Hypertension League, the National High Blood Pressure Education Program Working Group on Primary Prevention of Hypertension, the Canadian Hypertension Society and the Canadian Coalition for High Blood Pressure Prevention and Control. They have not been clinically tested. SPONSORS: The Canadian Hypertension Society, the Canadian Coalition for High Blood Pressure Prevention and Control, the Laboratory Centre for Disease Control at Health Canada, and the Heart and Stroke Foundation of Canada.     

Life history predicts advancement of avian spring migration in response to climate change

An increasing number of studies demonstrate that plant and animal phenologies such as the timing of bird migration have been advancing over the globe, likely as a result of climate change. Even closely related species differ in their phenological responses, and the sources of this variation are poorly established. We used a large, standardized dataset of first arrival dates (FAD) of migratory birds to test the effects of phylogenetic relationships and various life-history and ecological traits on the degree to which different species adapt to climate change by earlier migration in spring. Using the phylogenetic comparative method, we found that the advancement of FAD was greater in species with more generalized diet, shorter migration distance, more broods per year, and less extensive prebreeding molt. In turn, we found little evidence that FAD trends were influenced by competition for mating (polygamy or extra-pair paternity) and breeding opportunities (cavity nests). Our findings were robust to several potentially confounding effects. These evolutionary correlations, coupled with the low levels of phylogenetic dependence we found, indicate that avian migration phenology adapts to climate change as a species-specific response. Our results suggest that the degree of this response is fundamentally shaped by constraints and selection pressures of the species' life history, and less so by the intensity of sexual selection.     

Bonafide,type-specific human papillomavirus persistence among HIV-positive pregnant women: predictive value for cytological abnormalities,a longitudinal cohort study

This study investigated the rate of human papillomavirus (HPV) persistence,associated risk factors, and predictors of cytological alteration outcomes in acohort of human immunodeficiency virus-infected pregnant women over an 18-monthperiod. HPV was typed through L1 gene sequencing in cervical smearscollected during gestation and at 12 months after delivery. Outcomes were defined asnonpersistence (clearance of the HPV in the 2nd sample), re-infection (detection ofdifferent types of HPV in the 2 samples), and type-specific HPV persistence (the sameHPV type found in both samples). An unfavourable cytological outcome was consideredwhen the second exam showed progression to squamous intraepithelial lesion or highsquamous intraepithelial lesion. Ninety patients were studied. HPV DNA persistenceoccurred in 50% of the cases composed of type-specific persistence (30%) orre-infection (20%). A low CD4⁺T-cell count at entry was a risk factor fortype-specific, re-infection, or HPV DNA persistence. The odds ratio (OR) was almostthree times higher in the type-specific group when compared with the re-infectiongroup (OR = 2.8; 95% confidence interval: 0.43-22.79). Our findings show thatbonafide (type-specific) HPV persistence is a stronger predictor for the developmentof cytological abnormalities, highlighting the need for HPV typing as opposed to HPVDNA testing in the clinical setting.     

Ultrastructure comparée de la spermiogenèse et du spermatozoïde de trois espèces de Paravortex (Rhabdocoela, "Dalyellioida", Graffillidae), Turbellariés parasites intestinaux de Mollusques

Three species of the genus Paravortex were studied. Spermiogenesis involves progressive lengthening of the spermatid. No centriole nor axoneme were found. Thc mature spermatozoon is threadlike, 30μm long and aflagellate. It contains a nucleus, two longitudinal parallel mitochondria, numerous dense bodies limited by a membrane, a row of cortical microtubules and granules. The spatial arrangement of the microtubules wah deduced from a statistical analysis of their number in transverse section. The microtubules are continuous along the length of the spermatozoon and are arranged along a long cone. The granules, not limited by a membrane, are about 25 nm in diameter. They are arranged in a semicircle and represent a new structure for sperm of Platyhclminthes. A statistical comparison demonstrated that two species may be distinguished by the number of their cortical sperm microtubules. This is the tirst ultrastructural study of an aflagellate spermatozoon in the Rhabdocoela. A rickettsia was found in P. cardii .     

Continuous Culture Used for Media Optimization

A technique is described in which continuous culture is used for the optimization of media in terms of growth-supporting ability. The technique consists of identifying growth-limiting nutrients by observing the reaction of the continuous system to injection of suspected growth-limiting nutrients into the growth vessel.