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Étude de la faune microbienne et des paramètres physico-chimiques du tractus digestif d’annélides oligochètes, récoltés à Ebebda et à Nkolbikogo (région du Centre Cameroun)

Abstract : The study focuses firstly on the morphological analysis of ciliates and secondly the variation in abundance of acaryotes and prokaryotes of the digestive tract of annelids Oligochaetes collected in the Center Region of Cameroon. In addition, the physicochemical parameters that influence the seriation of these microorganisms along the digestive tract of their hosts were analysed. The morphological study is based on the techniques of impregnation of specimens with the ammoniacal silver carbonate, the DAPI and the Feulgen nuclear staining. The surveys carried out on the annelid oligochaetes of the family of Glossoscolecidae have anabled the description of twenty species of ciliates belonging to Heterotrichs, Hysterocinetidae and Astomes. Amoung Heterotrichs, have been described three species of the genus Nyctotherus characterized by the presence of an apical secant system on their right side and a species of the genus Nyctotheroïdes characterized by the existence of three secant systems on their two sides: one on the right side and two on the left. Up to now, the presence of Heterotrichs was unsuspected in Glossoscolecidae. In Hysterocinetidae, the description of nine new species demonstrates the existence of four different types of skeletal pattern. The first type, present four superimposed and antagonistic skeletal fibre layers, corresponds to that of the genus Ptychostomum. The second type is characterized by the existence of an unorganized field of fibrillary structures forming a dense and undivided mass in the central part of the suction cup, for which a new genus is created: Ptychostomoïdes. The third type, present in the genus Proptychotomoïdes, is characterized by the existence of a glabrous surface in the central area of the adhesive apparatus. In the genus Thurstonia, an uncialiated kidney shape surface bordered subsequently by two mobile lips deprived of skeletal fibers was observed. This morphological diversity within Hysterocinetidae requires a new approach of the systematic in this group. In some Astomes (Almophrya bivacuolata and A. mediovacuolata), the analysis of the morphological variations of the nuclear apparatus allowed us to highlight important digitations and the presence of dark bands in the H macro-nucleus structure of the small cellular types, as well as the presence of intermediate forms between H and X macronucleus in these two species. In Almophrya laterovacuolata, the disposition of the vacuolar apparatus is variable: either two longitudinal lines are arranged among branches of the H macronucleus, or two longitudinal lines are out of the H macronucleus branches. These longitudinal lines may also be arranged without obvious order among the H macronucleus branches. Given that the identification within the genus Almophrya is specifically based on the number and the arrangement of vacuoles, a revision of these criteria is required. Four new species belonging to genera Anoplophrya, Hoplitophrya and Dicontophrya were also described in Astomes. In addition to the description of two new genera in Hysterocinetidae, four species in Heterotrichs, and seven species in Astomes, the technique of the cytometry in flow enabled us to highlight an unsuspected population of viruses in the digestive tract of the Glossoscolecidae as well as a population of bacteria not less important. The technique of aspiration under a vacuum pump allowed us to isolate and collect the intestinal liquid in three portions of the digestive tract of Alma emini. The correlations carried out between physico-chemical parameters and ciliates biomass held our attention. These results suggest that each portion of the digestive tract of Alma emini is a set of biotope niches, and microhabitats in which a large number of physical and chemical factors create ecological niches more suitable to a species or a group of species. This might explain the striation and the variation of abundance of the microfauna along the digestive tract of oligochaetes annelids.
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Paul Alain Nana. Étude de la faune microbienne et des paramètres physico-chimiques du tractus digestif d’annélides oligochètes, récoltés à Ebebda et à Nkolbikogo (région du Centre Cameroun) . Sciences du Vivant [q-bio]. University of Yaounde I, Cameroon, 2015. Français. ⟨tel-01251323⟩

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