Identification and optimization of triphenylmethane dyes removal by Streptomyces sp. from forest soil

Abstract

This study identified a common Streptomyces sp. (MN262194) from forest soil as an efficient decolorizer of triphenylmethane (TPM) dyes. Partial 16S rRNA sequencing identified the isolate as possibly Streptomyces bacillaris (similarity 99.32%). Live and dead cells of Streptomyces sp. were applied to decolorize Malachite Green (MG), Methyl Violet (MV), Crystal Violet (CV), and Cotton Blue (CB). The decolorization efficacy for both cell types was further optimized based on One-Factor-At-A-Time (OFAT) method to determine the influence of pH, agitation speed (rpm), biomass (g), initial dye concentration (mg L− 1), and oxygen. Removal of TPM dyes was repeated for both live and dead cells using combined optimal conditions determined for each biomass type. Results revealed that optimum conditions for live cells were pH 7, 100 rpm agitation, 0.5 g cell biomass, initial dye concentration of 100 mg L− 1 (50 mg L− 1 for CB), and with the presence of oxygen. In contrast, pH 9 (MG, MV, CV) and pH 3 (CB), with 100 rpm agitation, 0.75 g cell biomass, and initial dye concentrations of 100 mg L− 1 (50 mg L− 1 for CB), were the optimum conditions for dead cells. At optimal conditions, live cells showed significantly higher decolorization activities for all dyes (MG 95%, MV 92%, CV 87%, CB 68%). Removal of TPM dyes was via biosorption and biodegradation, detected with changes of ultraviolet-visible spectra between the untreated dye and treated dye. Sorption by Streptomyces sp. conforms to the Langmuir isotherm model. Streptomyces sp. was established as an effective decolorizer for most TPM dyes with > 85% decolorization (with the exception for CB).