Abstract:Several Fe(II)-oxidizing denitrifying bacteria (FODBs) were isolated from iron-rich anaerobic river sediments using the conventional cultivation method, and one of the FODBs named strain FX-Fe5was selected for further study. Based on the observation of gram staining, optical microscope and scanning electron microscope, and identification by 16s rRNA sequencing, strain FX-Fe5 was as gram-negative bacillus and was most closely related to Raoultella sp., which was the first time to be reported as FODBs. Strain FX-Fe5could efficiently oxide ferrous iron within 24h, when ferrous and acetic acid were supplied as electron donor separately or jointly. The oxidation rates of Fe(II) (%) in different electron donor systems were 89.77±0.47(ratio of ferrous to acetate was 1:1), 87.01±0.22 (ratio of ferrous to acetate was 3: 1), 86.96±0.07 (ferrous only) and 72.97±0.53(ratio of ferrous to acetate was 1:3), respectively. The oxidation rates of Fe(II) were all higher than those of pure isolates reported by other studies. In addition, the concentration of ferrous and acetic acid decreased simultaneously, when both of them were supplied as electron donor during the process of denitrification. However, the Fe oxidation process was limited when ferrous was used as a single electron. Furthermore, during the denitrification process driven by strain FX-Fe5, only N2O gas was observed, without nitrite and ammonium accumulation in the reaction system. Otherwise, the highest content of N2O gas was less than 0.5% (5000×10-6), and varied largely with different electron donor systems. Carbon source metabolism analysis using Biolog EcoplateTM confirmed that strain FX-Fe5 had a higher preference to use monosaccharide, indican and polymerization sugars as carbon source.