Genetic and functional diversity of Citrobacter spp. for their abilities to degrade aromatic compounds was evaluated to develop mixed cultures or a consortium for bioremediation technology. Thirty Citrobacter strains isolated from various effluent treatment plants were found to degrade a range of aromatic compounds: phenol, benzoate, hydroxy benzoic acid and biotransform mono-chlorophenols and di-chlorophenol within 24 to 48 h of incubation at 30 degrees C. Sequence similarity and phylogeny of the ARHD gene transcripts (730 nucleotides) depicted their diversity within 9 Citrobacter strains: HPC255, HPC369, HPC560, HPC570, HPC784, HPC1196, HPC1216, HPC1276 and HPC1299. Here, the degree of associations varied up to 84% with (i) ARHD alpha-sub unit (SU), (ii) LSU of Phenylpropionate dioxygenase (PDO), (iii) Phenol hydroxylase alpha-SU, (iv) Benzoate 1,2-dioxygenase, alpha-SU, (v) Naphthalene dioxygenase LSU, etc. This study has provided basic information, which can be used to develop a consortium of bacteria with mutually beneficial characteristics. (C) 2011 Elsevier Ltd. All rights reserved.