Gessesse, Amare(PhD)Tilahun, Lulit2018-07-032023-11-182018-07-032023-11-182010-12http://etd.aau.edu.et/handle/12345678/5942Denitrifying bacteria (95 in number) were isolated from the four Soda Lakes of Ethiopia namely, Lake Abijata, Lake Arenguade, Lake Chitu and Lake Shalla. Similar species of denitrifying bacteria were identified from the four lakes. The sequence and phylogeny relation of the isolates show that Halomonas campisalis, Halomonas salina, Halomonas nitritophilus, Bacillus cohnii as well as Bacillus pseudofirmus exhibited high similarities with the isolates studied. In addition, 9 isolates from the four lakes show similarity with the novel bacterial group, Nitricola lacisaponesis. Fast denitrifyers were among the isolates that are capable of producing N2 gas only in 2 hours after inoculation. Molecular, morphological and some biochemical studies conducted on the DN-C18 isolate from L. Chitu, showed high similarity on all accounts with previously obtained isolate BACC180 from L. Chitu. These two isolates showed high denitrification activity and tolerance to high pH and salt concentration. Both isolates were found to be closely related the Halomonas sp. Key words: denitrification; alkaliphilic denitrifiers; soda lakes; Lake Abijata; Lake Arenguade; Lake Chitu; Lake Shalla; Halomonas; Bacillus; Nitricola lacisaponesisendenitrificationalkaliphilic denitrifierssoda lakesLake AbijataLake ArenguadeLake ChituLake ShallaHalomonasBacillusNitricola lacisaponesisThesis