Evaluation of biodecolorization of the textile azo dye by halophilic archaea

Azo dyes are the biggest group of colors. One of the special characteristic of this group of dye is the presence of double bonds of Nitrogen (N=N). Several studies reported biodecolorization using microorganisms, so far. However, it is for the first time to our knowledge that decolorization by halophilic archaea have been reported.
Among the 15 strains of archaea isolated from Qeshm saline cave and 7 type strains from Iranian biological resource center, 2 strains showed high ability in decolorization of azo dye. Effects of different factors including pH (5-9), temperature (30-50 °C), various salt concentrations (12.5-30%), different concentrations of dye (400-5000 mg/L), different carbon sources and several nitrogen sources and agitation have been measured after 4 days of incubation in static condition. Moreover, the toxicity tolerance of halo archaeal strains to dye, growth and decolorization rates were studied. Statistical significance was assessed by ANOVA Tukey’s multiple comparison test.
Strain A with 99.1 % similarity to Halogeometricum borinquense and strain B with 99.4 % similarity to Haloferax mediterranei were the best decolorizing strains. Both strains had their highest decolorization rate in the presence of NaCl (15-17.5 %), pH 7, microaerophilic condition and yeast extract as nitrogen source. Halogeometricum borinquense showed higher decolorization rate in the presence of saccharose and glucose as carbon sources at 45 oC temperature and for Haloferax mediterranei temperature of 40 oC and propionic acid as carbon source were best decolorizing conditions. These strains were able to decolorize dyes at 1000 mg/L concentration and tolerate dye concentrations to the highest level of 5000 mg/L.
Discussion and In conclusion, our results indicate that halophilic archaea have very high potential to decolorize azo dyes. Regarding high amounts of salts in textile wastewaters, using such microorganisms which can tolerate the harsh environment in order to decolorize azo dyes, could be a new approach in this field.