Assessment of Biodegradation and Phytotoxicity of Azo Dyes Methyl Orange and Crystal Violet by Escherichia coli and Bacillus subtilis

Azo dyes are widely used colourants, possess array of colours and are generally recalcitrant to microbial degradation. This study aimed to isolate azo dyes degrading bacteria from soil; treat methyl red and crystal violet dyes using the isolates, and assess the phytotoxicity of the treated and untreated dyes on sorghum. Ten bacteria were isolated from the soil, of which two were identified as efficient azo dyes degrading bacteria by efficiency in dye decolouration. The isolates were identified as Escherichia coli and Bacillus subtilis based on their biochemical characteristics. The isolates were able to degrade methyl orange dye by 16-75 % and crystal violet by 16-78%, depending on the concentration of the dye. The isolates were more efficient at degrading the dyes at a low concentration of 0.00025 mg/ml, as indicated by a higher percentage of decolourization (53-79%). The percentage phytotoxicity of the untreated methyl red ranged from 33-59%, while the toxicity of the untreated crystal violet ranged from 62-91%. The toxicity of the treated methyl red ranged from 9-34%, while the toxicity of the treated crystal violet ranged from 12-32%. The results revealed that the isolates were capable of degrading methyl red and crystal violet dyes, and could be useful in the bioremediation of azo dyes polluted soil.