Congo red, a dye used in biological research as well as in diagnostics, is highly carcinogenic. As a constituent of textile dyes, it is a major pollutant in industrial wastewater and is detrimental to organisms in water bodies where it is released.
A team of microbiologists from the G B Pant University of Agriculture and Technology recently devised a way to remediate waste dyes. They took soil from near a drain, washed the soil with distilled water and used that water to seed culture plates containing the dye. Thirty-one microbes could grow even in the presence of the dye.
The team isolated the best strain from the culture plate – the one with maximum diameter of clearance of the dye. By matching the DNA sequences of the strain against known sequences in DNA databases, they identified it as Penicillium crustosum.
They cultured the chosen fungus, and immobilised the fungal mycelia in agar plugs. They tested the activity of these agar plugs against water containing Congo red at levels mimicking wastewater. The water was decolourised by more than eighty per cent within a day!
Now the problem was the actual mechanism: how is the fungus able to do it?
The researchers thought of identifying enzymes that are liberated by the fungus in larger quantities in the presence of Congo red. To obtain the fungal enzymes, they centrifuged the culture media and separated the liquid for assessment. Four enzymes were seen to be overexpressed in response to the dye.
“This strain of the fungus, Penicillium crustosum, seems to derive energy from metabolizing Congo red dye”, says Barkha Sharma, G B Pant University of Agriculture and Technology.
The team optimised the system and the growth conditions for the strain in terms of best temperature, pH, the inoculum and the number and size of agar plugs and found that the system can decolourise by 99.85 per cent within 16 hours!
And, what is more, the system can tolerate the higher concentrations of Congo red usually found in wastewater.
The next issue was whether the treated water was safe for irrigation. The team tested, using tap water, Congo red-contaminated water and treated water to grow seeds of barley and black gram. Seeds grown with treated water fared better than those grown with tap water.
“Industries that pollute water now need to come forward to help us upscale and test the system on a larger scale”, says Lakshmi Tewari, the team leader
Freelance science writer, Mumbai
STEAMindiaReports: Science news from India free for Indian media to use