Strain NB1 was isolated from aerobic granular sludge capable of degrading nitrobenzene. Effects of several factors including pH, temperature, salinity, and second carbon/nitrogen source as co-substrate on the biodegradation of nitrobenzene by strain NB1 were investigated. Results showed that the optimal conditions for the biodegradation of nitrobenzene by strain NB1 were at pH 7.0 and 28-35 degrees C. Under these conditions, the biodegradation rate of nitrobenzene could reach 9.29 mg l(-1) h(-1) when the initial nitrobenzene concentration was 600 mg l(-1). The addition of 1840 mg l(-1) glucose or 500 mg l(-1) ammonium chloride could slightly enhance the biodegradation efficiency, but even more addition of glucose or ammonium chloride delayed the biodegradation. Strain NB1 could degrade nitrobenzene in the presence of less than 3% NaCl (w/v %). Based on morphological and physiological characteristics as well as the phylogenetic analysis of 16S rDNA sequences, strain NB1 was identified as Klebsiella ornithinolytica. (C) 2012 Published by Elsevier Ltd.