Biodegradation of Methylene Blue as an Evidence of Synthetic Dyes Mineralization during Textile Effluent Biotreatment by Acinetobacter pittii

We investigated the textile effluent decolorization potential of Acinetobacter pittii isolated from dye house effluent (DHE), its ability to degrade methylene blue (MB) and to detoxify the DHE. The organism demonstrated 73% decolorization of the effluent within 5 d and MB degradation at 76% and 84% in 5 and 24 h, respectively. The organism preferred peptone water and nutrient broth to other media and had an optimum pH and temperature of 7.5 and 38 ºC, respectively. Fourier transform infrared spectrometry (FTIR) analysis of the MB when compared to that of its metabolites revealed the reduction in intensity and disappearance of specific peaks, particularly those corresponding to the aromatic C–H bending around 600–800 cm − 1 . Gas chromatography-mass spectrophotometry (GCMS) results of the degraded MB dye revealed several metabolites. Prominent among these is 6-methyl-2,3-dihydro-1,4-thiazin-1-ium, with m/z value of 114 that is less than half of the MB molecular mass, thus suggesting biodegradation of MB. The pathway of the MB biodegradation was proposed based on identified metabolites from the GCMS results. Phytotoxicity studies revealed that the metabolites of the DHE biotreatment were not toxic to the germination and growth of Zea mays and Vigna unguiculata , unlike the DHE itself, thus proving that this strain of Acinetobacter pittii has the potential to decolorize, degrade and detoxify dyes in textile effluent.