Acinetobacter baumannii, Corynebacterium sp., Cytophaga columnaris, Escherichia coli,Pseudomonas fluorescence and Pseudomonas luteola were locally isolated bacteria from sewage Disposal Lake at Jeddah, Saudi Arabia and they can decolorize methyl orange (MO), except P. luteola. P. fluorescence was the most potent MO decolorizing and to a lesser extends A. baumannii. Five different media were tested to elucidate medium formulation in favor MO decolorization by P. fluorescence and A. baumannii. Ingredients of the basal medium favored the highest decolorization percentage of 50 µg MO/ml after 61 h of fermentation. P. fluorescence was satisfactory able to decolorize different levels of MO up to 150 µg/ml after 57 h of fermentation. Bacterial consortium of P. fluorescence and A. baumannii was highly efficient to decolorize MO than monoculture, where the decolorization period reduced by about 19% and increased decolorization rate (µg/h) by 19%. Statistical designs of two phase multifactorial optimization (Plackett-Burman and Box-Behnken) were carried out to optimize cultural conditions to increase the efficiency of mixed culture to decolorize 150 µg MO/ml. Under the optimized conditions the decolorization period was reduced by more than 31% and with increased decolorization rate by more than 45%. Methyl orange can be efficiently decolorized by P. fluorescenceand A. baumannii. The decolorization process was markedly influenced by the composition of the fermentation medium and concentration of MO. Mixed culture of P. fluorescence andA. baumannii was highly efficient to decolorize MO than monoculture technique. The cultural conditions were considerably optimized using statistical experimental designs of Plackett-Burman and Box-Behnken.
Key words: Methyl orange, Pseudomonas fluorescence and Acinetobacter baumannii, mixed culture, statistical optimization.
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