Homogenization of Pseudomonas aeruginosa PAO1 biofilms visualized by freeze-substitution electron microscopy.

A knowledge of the mechanical properties of bacterial biofilms is required to more fully understand the processes of biofilm formation such as initial adhesion or detachment. The main contribution of this article is to demonstrate the use of homogenization techniques to compute mechanical parameters of Pseudomonas aeruginosa PAO1 biofilms. For this purpose, homogenization techniques are used to analyze freeze substitution electron micrographs of the biofilm cross-sections. The concept of a representative volume element and the study about his representativeness allows us to determine the optimal size in order to analyze these biofilm images. Results demonstrate significant heterogeneities with respect to stiffness and these can be explained by varying cell density distribution throughout the bacterial biofilms. These stiffness variations lead to different mechanical properties along the height of the biofilm. Moreover, a numerical shear stress test shows the impact of these heterogeneities on the detachment process. Several modes of detachment are highlighted according to the local strain energy in the different parts of the biofilm. Knowing where, and how, a biofilm may detach will allow better prediction of accumulation and biomass detachment.

2-Methylhopanoids are maximally produced in akinetes of Nostoc punctiforme: geobiological implications.

2-Methylhopanes, molecular fossils of 2-methylbacteriohopanepolyol (2-MeBHP) lipids, have been proposed as biomarkers for cyanobacteria, and by extension, oxygenic photosynthesis. However, the robustness of this interpretation is unclear, as 2-methylhopanoids occur in organisms besides cyanobacteria and their physiological functions are unknown. As a first step toward understanding the role of 2-MeBHP in cyanobacteria, we examined the expression and intercellular localization of hopanoids in the three cell types of Nostoc punctiforme: vegetative cells, akinetes, and heterocysts. Cultures in which N. punctiforme had differentiated into akinetes contained approximately 10-fold higher concentrations of 2-methylhopanoids than did cultures that contained only vegetative cells. In contrast, 2-methylhopanoids were only present at very low concentrations in heterocysts. Hopanoid production initially increased threefold in cells starved of nitrogen but returned to levels consistent with vegetative cells within 2 weeks. Vegetative and akinete cell types were separated into cytoplasmic, thylakoid, and outer membrane fractions; the increase in hopanoid expression observed in akinetes was due to a 34-fold enrichment of hopanoid content in their outer membrane relative to vegetative cells. Akinetes formed in response either to low light or phosphorus limitation, exhibited the same 2-methylhopanoid localization and concentration, demonstrating that 2-methylhopanoids are associated with the akinete cell type per se. Because akinetes are resting cells that are not photosynthetically active, 2-methylhopanoids cannot be functionally linked to oxygenic photosynthesis in N. punctiforme.

The teaching of consultation-liaison psychiatry in the undergraduate curriculum of Canadian medical schools.

The teaching of consultation liaison psychiatry in the undergraduate curriculum of the 16 Canadian medical schools and the views of the directors of undergraduate psychiatric education were surveyed with a 25-item questionnaire. Some teaching in consultation liaison psychiatry is provided by 14 medical schools. The predominant format of teaching is that of supervised experience, and systematic evaluation of this teaching is uniformly absent. The amount of consultation liaison teaching was small. More than 90% of the students were assigned primarily or exclusively to an inpatient service during their psychiatric clerkship. The majority of the respondents thought that the response of staff and students to the teaching of consultation liaison was good or excellent, that this teaching should be an obligatory part of the curriculum, that it would increase in the next five years, that insufficient staff was a factor impeding it, and that an increase in staff psychiatrists specializing in consultation liaison psychiatry would facilitate this teaching in their department. It is suggested that the consultation liaison psychiatry teaching of medical students should be increased, in the short term by making greater use of services and resources. In the longer term, however, such increase would be dependent on the growth and development of consultation liaison services in the teaching hospitals across the country.

Psychosomatic disorders in the elderly.

There is no agreement on the incidence or prevalence of psychosomatic disorders in the elderly. This is due in large part to the methodological difficulties of the epidemiological studies which have not employed the same diagnostic criteria and classification. Drawing on the literature and on clinical experience, a classification is offered, and using the diagnostic criteria explicit in this classification, probable trends are identified. Pseudodementia may well be the only stress-related disorder that is peculiar to the elderly.

Euthanasia--a paper for discussion by psychiatrists.

There are two factors that are focusing attention, both public and professional, on euthanasia. These are: (i) the increasing ability of medicine to maintain life; (ii) the activity of the Law Reform Commission of Canada which might result in new legislation. Euthanasia raises problems medically, legally, morally and ethically. These difficulties are placed in context and discussed. The author offers a personal opinion on euthanasia in an attempt to mobilize Canadian psychiatric opinion.

Forgiveness, retaliation and paranoid reactions.

It has been suggested that clinical states from grudgingness and habitual bitterness through to delusions of persecution are best resolved by forgiving. The process of forgiving requires that previously unacknowledged impulses, particularly aggressive ones, are accepted in oneself and others. If the therapist is aware of this, he can, in the transference, reinforce the patient's good introjects by providing a non-judgemental, acceptant model for the patient and thereby facilitate the adoption of the forgiving attitude. Sometimes habitual forgiving can occur as a reaction formation, and should be dealt with as such.

Organotin compounds and their use for insect and mite control.

A brief overview of biological activity of organotin compounds is given, with emphasis on activity against plant-feeding arthropods. Plictran miticide, containing cyhexatin (tricyclohexylhydroxystannane), the first product to be fully commercialized for control of plant-feeding mites on a broad range of agricultural crops, is used as a model to indicate the chemistry and potential performance, phytotoxicity, residues, limitations on usage, environmental acceptability, and use patterns for products containing similar organotin compounds.