Dye degradation potential of Acinetobacter baumannii strain VITVB against commercial azo dyes

Abstract

The textile industry is an age-old industry in human civilization and to date, it contributes to a major portion of the economy in several nations. However, the generation of a huge volume of toxic colored effluent is a major environmental concern. Azo dyes are extensively used for textile dyeing and are thus found in the wastewater. In this article, bacterial bioremediation of azo dyes was studied. Acinetobacter baumannii strain VITVB, a gram-negative bacterium aerobically decolorized 500 mg L−1 of two textile azo dyes Reactive Blue 221 (RB-221) and Reactive Black 5 (RB-5) with 90% and 87% efficiency after 48 h under static condition. Dye degradation was further maximized by optimization studies. A. baumanii VITVB exerted maximum dye degradation within 24 h under optimized conditions of pH 9, temperature at 45 °C, 5% NaCl concentration, and supplementation of 1% starch (Carbon source) and 1% peptone (Nitrogen source) in growth media. Dye Degradation was then analyzed. Fourier transform infrared spectra of pure and degraded dyes revealed that the potential bacterial strain targeted the characteristic chromophore group (N = N) during the break down of dyes. High-performance liquid chromatography of pure and degraded dyes presented the emergence of different peaks at altered retention times, which also indicates the degradation of dyes. Gas Chromatography–Mass Spectrometry chromatogram revealed probable end products as diphenylmethane from RB-221 degradation and benzene,1,1'-Pentylidenebis from RB-5 degradation. Finally, phytotoxicity and biotoxicity assays implied the nontoxicity of the degraded metabolites of RB-221 and RB-5. Pure dyes inhibited seed germination, showed marked phenotypic changes and cellular damages in plants (Cicer arietinum and Tagetes erecta) while the degraded metabolites promoted a healthy seed germination rate and no marked cellular damages or phenotypic changes in plants. Artemia salina cysts also showed a similar pattern as major hatchability inhibition occurred with pure dyes compared to degraded dye metabolites.