Improved decolorization of triphenylmethane dyes by halo-thermotolerant bacteria isolated from hypersaline environments

Industrial effluents carrying dyes are prominent environmental threats to receiving water bodies. Present study related with decolorization of two triphenylmethane (TPM) dyes, i.e., malachite green (MG) and crystal violet (CV), under laboratory settings. Primary screening experiments for dye decolorizing bacteria were performed with ten distinct bacterial isolates on MSM agar supplemented with different conc. of TPM dyes. For secondary screening, decolorization experiments were achieved under submerged fermentative conditions using two halo-thermotolerant bacterial isolates viz. Bacillus subtilis B2d and B. licheniformis B3e strains. Plackett–Burman design for 11 factors (10 numerical plus one categorical) and five internal replicates comprising total 18 experiments was used to screen the most influential parameter affecting decolorization of MG and CV by either bacterial strains. Under optimal fermentation conditions, the bacterial isolate B2d showed significantly higher decolorization than B3e isolate achieving maximum decolorization of MG (72%) and CV (57%). The maximum limits set for the variables like pH, agitation speed, KH2PO4, NaNO3 and yeast extract were found to increase the decolorization rates, whereas the increasing glucose and urea levels negatively affected dye decolorization efficiency of the bacterial isolates. Conclusively, halo-thermotolerant bacterial isolates of present study offer substantial potential for future environmental applications, if favorable conditions provided.