Phenol-degrading strain P5 isolated by enrichment using phenol as a carbon and energy source under limited oxygen condition from contaminated environment. Through chemotaxanomy and molecularsystematics, strain P5 was included into Alcaligenes. Strain P5 had catechol 2,3-dioxygenase thereby was capable of degrading phenol only in the existence of oxygen. Under anoxic conditions, strain P5 was not able to utilize phenolic compounds. However very little levels of oxygen, even 0.05 ppm, induced cell growth and phenol degradation of strain P5. Also, strain P5 could respire with nitrate irrespective of the existence of oxygen. Co-respiration of oxygen and nitrate was superior to single respiration under limited oxygen condition. Under aerobic condition, nitrate reduction was not or partially inhibited by 0.1 mM of azide and 0.5 % Triton X-100. However anaerobic nitrate reductase was very sensitive to azide and Triton X-100. This suggests that strain P5 has two nitrate reduction systems. Strain P5-like bacteria, 39 isolates, were isolated from various environments including contaminated sites using phenol as a carbon and energy source under limited oxygen condition. All isolates had nitrate reductase and 24 isolates had azide (5mM) insensitive nitrate reductase by nitrite overlay technique. The chances that these bacteria are aerobic nitrate respiring bacteria are very high. By 16S rRNA sequence, Alcaligenes, Acidovorax, Lysobacter, Mesorhizobium, Stenotrophomonas, Ensifer, Methylobacterium, Staphyloccus, Brucella, Aquasprillu, and Ochrobacterim were identified.
