No description available.

The Tardigrada are hydrophilous, segmented, molting micrometazoans that occupy a diversity of niches in freshwater, marine, and terrestrial habitats. A sister group of the arthropods, this phylum of bilaterally symmetrical lobopods, most less than 1 mm in length, have a hemocoel, a complete digestive tract, a dorsal gonad with one or two gonoducts, and a dorsal lobed brain with a ventral nerve cord and five ganglia. About 1000 species have been described based on the morphology of sclerified structures, especially the claws and buccal-pharyngeal apparatus. Reproduction occurs through fertilized or unfertilized eggs, with individuals being either gonochoric, unisexual, or hermaphroditic, and eggs are deposited either freely or within the shed exuvium. Parthenogenesis, very frequent in limnic and terrestrial tardigrades, allows them to colonize new territories by passive dispersal of a single individual. Quiescence (cryptobiosis: anhydrobiosis, anoxybiosis, cryobiosis, and osmobiosis) and diapause (encystment and resting eggs) occur during the tardigrade life history. Ecological parameters and global distribution patterns are poorly known or understood. Methods for collection, microscopy, and culturing have been developed.

V. vermiformis est une amibe libre répandue dans l'environnement et les milieux artificiels comme les réseaux d'eau chaude sanitaire (RECS). Il est maintenant bien établi qu'elle joue un rôle de réservoir pour des bactéries pathogènes, comme L. pneumophila. Le contrôle de V. vermiformis dans les RECS représente donc un enjeu sanitaire important. Les amibes libres peuvent passer d'une forme métaboliquement active (trophozoïte) à une forme de résistance, le kyste, lorsque les conditions sont défavorables ce qui leur confère une résistance aux traitements. Malgré la haute prévalence de V. vermiformis dans les RECS, les processus de différenciation et la résistance de ses kystes aux traitements n'ont été que peu étudiés. Nous avons donc investigué les changements morphologiques et ultrastructuraux qui s'opèrent lors de l'enkystement et désenkystement de V. vermiformis. Il en ressort que l'enkystement est un phénomène rapide (9 h) qui conduit à la formation de kystes entourés d'une paroi double couche. Lors du désenkystement, les trophozoïtes n'émergent pas à travers un ostiole comme c'est le cas chez Acanthamoeba. Puis, nous avons étudié l'effet des conditions environnementales et de la concentration cellulaire sur l'enkystement. Nous avons observé que plus la concentration cellulaire est élevée plus l'enkystement est rapide, ce qui suggère l'existence de mécanismes de communication intercellulaire. Enfin, nous avons étudié la résistance des kystes aux traitements utilisés dans les RECS et aux protéases. Ces traitements étaient efficaces, in vitro, pour inactiver les kystes de V. vermiformis. Ces travaux ont permis d'apporter des connaissances de bases sur les processus de d / Vermamoeba vermiformis is a free-living amoeba (FLA) widespread in the environment and artificial environments such as hot water networks. It is now well established that it acts as a reservoir for many pathogenic bacteria, such as Legionella pneumophila. The control of V. vermiformis in artificial environments represents an important health issue. FLA can turn from a metabolic active form (trophozoite) to a resistance form, called cyst, when conditions are unfavorable. Cysts are more resistant to treatments. Despite the high prevalence of V. vermiformis in hot water networks, the processes of differentiation and the resistance of cysts to disinfection treatments have been poorly studied. Therefore we investigated morphological and ultrastructural changes occurring during encystment and excystment of V. vermiformis. It appears that encystment is a fast process (9 h) which leads to the formation of cysts surrounded by a double-layered wall. During excystment, trophozoites do not emerge through an ostiole as is the case with Acanthamoeba. Then, we studied the effect of environmental conditions and cell concentration on encystment. We observed that the higher cell concentration was, the faster the encystment was, which suggests the existence of intercellular communication. Finally, we studied the resistance of cysts to conventional disinfection treatments used in hot water networks and to innovative treatment with proteases. These treatments were effective, in vitro, to inactivate V. vermiformis cysts. This work provides new finding regarding differentiation processes and cysts resistance of V. vermiformis, a free-living amoeba poorly studied.

A sister group of the Arthropoda, the Tardigrada are micrometazoans that occupy a diversity of niches in freshwater, marine, and terrestrial habitats. Commonly called water bears because of their slow, lumbering gait, these molting lobopods have four pairs of legs, usually terminating in claws. Most are less than 1 mm in length, with a complete digestive tract, a dorsal gonad with one or two gonoducts, and a dorsal lobed brain with a ventral nerve cord and four bilobed ganglia, one per leg-bearing metamere. The body cavity (hemocoel) functions in respiration and circulation. Over 1200 species have been described based primarily on the morphology of the claws and buccal-pharyngeal apparatus. Individuals may be either gonochoric, unisexual, or hermaphroditic, with fertilized or unfertilized eggs deposited either freely or within the shed exuvium. Parthenogenesis occurs frequently in limnic and terrestrial tardigrades, allowing them to colonize new territories by passive dispersal of a single individual. Cryptobiosis (anhydrobiosis, anoxybiosis, cryobiosis, and osmobiosis) and diapause (encystment and resting eggs) occur during the life history. Active adults (surrounded by water) and cryptobiotic adults and eggs are primarily dispersed passively, but some active dispersal can also occur. Due to the characteristic patchy distributions of tardigrade populations, little is known about their population dynamics and trophic relationships. Improved methods for collection, microscopy, culturing, and molecular analyses have been have contributed much to our knowledge of tardigrades.