L' Annee biologique最新文献

The hydrolysis of proteins in the rumen is a process brought about mainly by bacteria, of which many species produce proteases. The majority of endopeptidases are cysteine proteases, whereas exopeptidases are mainly aminopeptidases. Prevotella ruminicola is distinguished from other bacterial species by its capacity to produce dipeptidases such as type I dipeptidyl aminopeptidase. The mechanisms controlling the synthesis of endo- and exopeptidases have been little studied. Enzyme production seems to depend on the concentrations of peptides, amino acids and carbohydrates. Proteolytic activity varies in relation to pH, and the concentrations of ions and phenolic compounds. Various works have shown that hydrolysis of a protein by enzymes depends on its three-dimensional structure and possible bonding to non-protein structures. These properties determine the peptide and amino acid concentrations that occur in the rumen. The molecular weight, hydrophobic property and primary structure of the peptides are the main factors that affect the hydrolysis and/or uptake of these compounds by rumen bacteria. The methodological problems inherent to assaying these compounds do however lead to current divergences of opinion concerning the physico-chemical characteristics of the peptides that escape rumen fermentation.

Within the framework of the increasing development of techniques and technology, Humankind is often considered and used as an instrument. Because power from the industry can generate bad consequences that are unforeseeable and thus out of a comprehensive control, new thoughts on Mankind and its values are needed. The moral code gives the practical distinction between good and evil. Ethics calls to a reflection from free, reasonable and responsible beings. Numerous groups of thoughts working for a progressive emergence of universally admitted ethic rules that should allow the offer of an international right of ‘Human rights’ are now available at different levels, i.e. professional, national, international. From the biomedical ethic, it appears that Human beings, considered as biological entities, have the right to live, that the embryo must not be used as an usual research material and that the diagnostic of embryos before implantation must be exceptional. Human being has a right to dignity. This means that one must not be submitted to degrading treatments (torture, slavery, …), must have access to health care, must not constitute an experimental object, the germinal cells must not be manipulated and neither his body or its constituting elements must ever be commercialised or patented. Corpses need respect and any attack to their integrity (in order to extract profits for public health, science, justice…) must be justified. A person, defined here as a self-awa-reness constructed in function of other persons, must be free (i.e. his consent is absolutely needed for a diagnostic or experimental treatment) and has economical, social and cultural rights. French laws do not permit a person to choose his death The international law progressively refines a definition of crime against humanity (ethnic extinction, torture, rape…). In the ethics for environment, the respect of men towards animals considered as individuals and species in the framework of the conservation of the nature and genetics resources, is taken into account rather than the rights of animals per se. Finally, an arsenal of agreements, directives and legislation at local, national and international levels attempts to harmonise the practices of the technoscience with the concept of long lasting development, in order to maintain the higher-order balances within ecosystems. Mankind felt itself responsible of the environment for the future generations. Nevertheless, any regulation in the matter of ethic remains a compromise within contradictory views. The only general rule for every one, remains not to harm others, and to give oneself to others. This is, for long time, the traditional basis of religious preachments, although its success remains relatively controversial.

Toxoplasma gondii is an intracellular obligate protozoan parasite. Human infection is generally subclinical but hosts with defective cellular immunity are at risk of severe disease. In many countries, congenital toxoplasmosis and toxoplasmic encephalitis in HIV-infected individuals are significant causes of morbidity and mortality. We review here the role of the members of phospholipases A₂ (PLA₂) family and how they participate in the invasion process of T. gondii. PLA₂ have been described in mammals cells as a family composed of nine groups of enzymes that specifically hydrolyse sn-2 bonds of phospholipids. Each PLA₂ group have a distinctive substrate preference, localization and way of activation indicating different physiological roles. We describe the existence of three PLA₂ isoforms in T. gondii. Inhibitors of secretory PLA₂ isoforms (sPLA₂) and cytosolic PLA₂ (cPLA₂), showed that cell and parasite sPLA₂ and parasite cPLA₂, but not cell cPLA₂, favours T. gondii invasion. The addition of IFNγ to cultured infected THP1 cells protected against T. gondii infection by an early mechanism involving a reduction in the number of parasitized cells. The reduction in the percentage of parasitized cells obtained by treatment with IFN γ is linked with a decrease in parasite and cellular PLA₂ activity. This is a new effector mechanism of IFN γ against T. gondii infection. The inhibitors of sPLA₂ type II have a pharmacological potential against T. gondii infection that remain to be tested in vivo.

The maintenance of the quality of water from the outlet of the treatment plant to the consumer tap is a major concern of water distributors. From a biological point of view, this maintenance must be characterized by a stability of biological features, namely bacterial growth from biodegradable organic matter, and protozoan bacterivory which must be not detectable. However, drinking water distribution systems are continuously exposed to a flow of biodegradable organic matter, which can represent around 20–30 % of the total dissolved organic carbon, and a flow of allochthonous microorganisms (bacteria, fungi, protozoa…), coming from the water treatment plant but also from incidents (breaks/repairs) on the distribution network itself. Apart from these microorganisms (heterotrophic bacteria in particular) can grow in this ultra-oligotrophic environment and colonize the all drinking water distribution system. The highest density of microorganisms occurs on the surface of pipewalls where they are organized in microcolonies (biofilm) that are mixed with corrosion products and inorganic precipitates. Five groups of organisms have been identified in distribution networks, in both the water phase and the biofilm: bacterial cells, protozoa, yeast, fungi and algae. The majority of these organisms are not pathogens, nevertheless potentially pathogen bacteria (Legionella…), fecal bacteria (coliforms, E. coli…), and pathogen protozoan cysts (Giardia intestinalis, Cryptosporidium parvum…) can transitorily find favorable conditions for their proliferation in the networks. Bacteria grow from the biodegradable fraction of dissolved organic matter while protozoa grow from dissolved organic matter, other protozoa but especially from bacterial prey items. The protozoan bacterivory was extensively studied in marine aquatic environments and in rivers, lakes,… but very rarely in drinking water distribution networks. Actually, proofs of the protozoan grazing on fixed and free-living bacterial cells were given by photography or film of biofilms accumulation on coupons that were previously immersed in potable water or by direct microscopic observation of bacteria in food vacuole of protozoa from potable water. A single and recent study has estimated protozoan bacterivory rate from laboratory experiences using fluorescent markers. It appears that in an experimental distribution system fed with biologically treated water (ozone/filtration through granular activated carbon), only ciliates present in the biofilm have a measurable grazing activity, estimated at 2 bacteria·ciliate⁻¹·h⁻¹ on average.

Bacterial dynamics in drinking water distribution systems is complex and related to different parameters, like the biodegradable fraction of dissolved organic carbon, the presence of a residual of disinfectant, the nature and the state of pipewalls, the relative biomass of free and fixed bacterial, and grazing impact.