Activity of heterotrophic bacteria is recognized as an important process governing the biochemical functioning of many aquatic ecosystems. The aim of this study is to compare bacterial isolates of pelagic heterotrophic bacteria from two sites, each with a different trophic status (4 microg/l at Kpass and 23 microg/l at Layo for chlorophyll index) located in the Ebrié lagoon, and the bacteria associated with periphyton growing on an artificial reef of bamboos stuck into the sediment of the two sites. Hierarchical classifications were performed from morphological and biochemical tests of 343 heterotrophic bacterial strains isolated from the two sites and for each habitat. Despite differences in trophic status, numerical taxonomic analysis of the pelagic bacterial strains (n = 165) showed a dominant cluster (72% of strains) of mixed origin (close to 50% of isolates from each site). The majority of these strains were non-fermentative rods producing neither amino-acids decarboxylases, nor acid from any carbohydrates. In the more eutrophic site (Layo), few differences of properties were observed between pelagic and periphyton-associated bacteria. On the contrary, a large part of bacteria isolated from bamboo at Kpass was characterized by specific particularities such as the degradation of arginine, tryptophan and citrate. Numerical taxonomic analysis allowed the distinguishing of specific characteristics of bacteria according to the habitat. Our results suggest that hydrological and biological conditions (especially photosynthetic exudates from periphyton) may induce an obvious specialization of the periphytic bacteria in the less eutrophic ecosystem (Kpass) compared to the bacteria isolated from the more eutrophic environment (Layo). (Résumé d'auteur
