Abstract

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 methylene blue.E. coli was the most potent MB decolorizing and to a lesser extend P. luteola. Five different media were tested to elucidate medium formulation in favor of MB decolorization by E. coli and P. luteola. Ingredients of the basal medium favored the complete decolorization of 50 µ QUOTE  QUOTE   g MB/ml after 84 h of fermentation. Time course decolorization of MB by E. coli indicated that 75 h of fermentation was satisfactory to decolorize 50 µ QUOTE  QUOTE   g MB/ml. It was also able to decolorize different levels of MB up to 150 µ QUOTE  QUOTE   g MB/ml after 95 h of fermentation. Bacterial consortium of E. coli and P. luteola was highly efficient to decolorize MB than monoculture, where the decolorization period reduced by more than 37% and increased decolorization rate (µgMB/h) up to 58%. 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 MB/ml. Under the optimized conditions the decolorization period was reduced by about 31.7% and with increased decolorization rate by 46.4%. Methylene blue can be efficiently decolorized by facultative aerobic bacteria (E. coli and P. luteola). The decolorization process was markedly influenced by the composition of the fermentation medium and concentration of MB. Mixed culture of E. coli and P. luteola was highly efficient to decolorize MB than monoculture technique. The cultural conditions were considerably optimized using statistical experimental designs of Plackett-Burman and Box-Behnken.

Key words: Methylene blue, Escherichia coli, Pseudomonas luteola, mixed culture, statistical optimization.