Azo dyes are xenobiotic pose a long-term effect on human life. The capability of Acinetobacter baumannii SM01 and Klebsiella pneumoniae SM27 isolated from petroleum oil contaminated soil sites in Egypt for degradation of methyl red (MR) was investigated. The physicochemical parameters which affect MR degradation were examined. The maximum degradation of MR by both isolates was attained when 1.0 % (w/v) of glucose, 0.1 % (w/v) of yeast extract and 1.0 mM of CaCl₂ were added to the culture media, and incubated for 6.0 h at 35℃ with the highest speed of shaking (150 rpm).
The mechanism of degradation of MR by Acinetobacter baumannii SM01 and Klebsiella pneumoniae SM27 isolates was studied through analysis of MR degradation products by FT-IR and double beam UV-visible spectrophotometer. Their results confirmed that MR underwent azo reduction and further degradation. The enzymes responsible for biodegradation of MR by Acinetobacter baumannii SM01 isolate were investigated, in the cell free medium obtained after 6.0 h of incubation and a control. The results showed a significant increase in the activities of laccase, tyrosinase, azoreductase and NADH-DCIP reductase enzymes. The outcomes of phytotoxicity studies on seeds of Triticum aestivum illustrated that MR degradation metabolites produced by Acinetobacter baumannii SM01 inhibited the germination rate by only 10 % and decreased root and shoot length by 27.8 % and 23.9 % respectively correlated to the inhibition exhibited by the intact MR. Consequently, the high efficiency of MR degradation enables Acinetobacter baumannii SM01 to be a potential candidate for bioremediation of MR containing wastewater.