Nocardiopsis sp. for the removal of triphenylmethane dyes: Decolorization and optimization studies

This study demonstrated the dye removal potential of a lesser studied Actinobacteria, Nocardiopsis sp., on triphenylmethane (TPM) dyes. The actinobacterium was sampled from forest soil and identified as Nocardiopsis alba (99.24% similarity) via partial 16S rRNA sequencing. Both live and dead cells were used to decolorize TPM dyes (i.e., malachite green (MG), methyl violet (MV), crystal violet (CV), and cotton blue (CB)). The influence of pH, agitation speed, biomass, initial dye concentration, and oxygen was determined via one-factor-at-a-time (OFAT) approach. Results revealed that live cells showed higher dye removal potential following treatment under optimized conditions, i.e., pH 7, 100 rpm agitation, 0.75 g cell biomass, 100 mg L⁻¹ initial dye concentration (50 mg L⁻¹ for CB), and oxygen availability, with 96.8 (MG), 95.9 (MV), 48.8 (CV), and 80.6% (CB) of decolorization efficacy (DE). On the contrary, dead cells were less effective in decolorizing MG (91.1%), MV (68.9%), CV (46.6%), and CB (63.7%), although decolorization was performed at optimum conditions (pH 9 for MG, MV, CV; pH 3 for CB, 100 rpm agitation, 0.75 g cell biomass, and 100 mg L⁻¹ initial dye concentration (50 mg L⁻¹ for CB)). UV–Vis analysis revealed that the removal of TPM dyes occurred primarily via biodegradation (live cells) and biosorption (dead cells). The sorption data complied with Langmuir model (R² = 0.984–0.999), confirming the monolayer sorption of TPM dyes by cells of Nocardiopsis. This study established Nocardiopsis sp., particularly live cells, as an effective biological agent for the remediation of TPM dyes.