Identification of locally isolated reactive black 5 decolorizing bacteria

Abstract

Seven bacterial strains were successfully isolated from textile wastewater. They were screened for their ability to degrade azo dyes including Reactive Black 5 and Acid Orange 7. The screening showed that the decolourization of Reactive Black 5 was best performed under facultative anaerobic conditions with color removal ranging from 80% - 93% for the three bacterial strains (L1, L6 and L7) at 37°C after 96 hours incubation. However, no decolorization of Acid Orange 7 was observed in all of the isolated bacteria under facultative anaerobic condition. The L1, L6 and L7 were further tested for decolorization of Reactive Black 5 and Acid Orange 7 under aerobic conditions. No decolourization was observed in all sets of experiments. Inducibility studies showed Reactive Black 5 did not show an inducing effect on decolourization process. Two parameters (pH and temperature) were optimized for decolorization. The strains were incubated in medium with pH 4, 7 or 10 and it was found that the optimum pH for decolourization was 7 with 49%, 63% and 70% of decolourization by bacterial strains of L1, L6 and L7, respectively, after 48 hours of incubation. When the strains were incubated at 30°C, 37°C and 55°C, it was found that the optimum temperature was 37°C, which the highest decolourization percentage in the tested strains ranged from 53% - 71% after 48 hours of incubation. The 16S ribosomal ribonucleic acid (16S rRNA) sequences analysis revealed that strains L1 and L6 belonged to genus Bacillus with 99% identity to 16S rRNA gene of Bacillus thuringiensis. Strain L7 was found belong to genus Escherichia with 99% identity to 16S rRNA gene of Escherichia coli strain SCDC-1.