Three chromium-resistant bacteria
Bacillus pumilus
-S4,
Pseudomonas doudoroffii
-S5 and
Exiguobacterium
-S8 were isolated from chromium-contaminated wastewater/soil and could resist very high concentrations of potassium chromate in Luria agar (up to 25 mg ml
-1) and acetate minimal medium (2 mg ml
-1). The strains showed growth at diverse pH and temperatures and could resist multiple heavy metals.
Pseudomonas doudoroffii-S5 reduced (8.27 mg hexavalent chromium 24 h
-1) at a lower initial potassium chromate concentration (100 μg ml
-1), but overall more chromate (28.4 mg hexavalent chromium 24 h
-1) was reduced at a higher initial concentration (1,000 μg ml
-1). The addition of various heavy metals (zinc sulphate, copper sulphate, and manganese sulphate at 50 μg ml
-1) in the chromium reduction media did not significantly affect the hexavalent chromium reduction potential of these isolates. The chromium removal/detoxification potential of these strains increased when used in conjunction with hydrophytes
Eichornia crassipes
and
Pistia stratiotes
. Interestingly, the whole process runs automatically with less energy input, that is, the bacterial strains support the growth of plant while in turn the plant releases exudates that help bacterial growth.
