Microbial community present in contaminated sites are able to tolerate any adverse conditions, due to their adaptation to extreme circumstances. Hence, in this study the bacterium was isolated from tannery effluent for the purpose of AV90 dye decolourization. Based on 16S rRNA sequence analysis the isolate was identified as Bacillus species (KTSMBNL-16). Decolourization process by KTSMBNL-16 was optimized for different parameters such as pH and temperature under shaking condition. Maximum decolourization (82 %) of AV90 dye was observed at an initial pH 6.0 and temperature 40 °C using Bacillus species. To disclose the role of functional groups in dye decolourization, FTIR spectrum (4000–400 cm⁻¹) was carried out for control and the treated sample. The spectrum reveals the significant changes in the position of the peaks, when compared to the control and decolourization products. Hence, Bacillus sp. KTSMBNL-16 could be used a potential candidate for the treatment of textile dyes and industrial effluents. The finding in the present study can serve as an important base for the development of an economical as well as a simplified biological treatment system for dye decolouration.