Isolation of hexavalent chromium (VI) tolerant fungi from tannery effluent and their growth responses to different concentrations of chromium (VI)

The main objective of this study was to isolate, characterize, and determine chromium (VI) tolerance capacities of fungal strains from tannery effluent of the Kolkata Leather Complex area. Chromium (VI) is a heavy metal that is known to be toxic as well as carcinogenic. It is an important heavy metal widely used in various industries of which the tanning industry deserves special mention. The majority of Cr (VI) waste is discharged into the environment annually as a consequence of industrial and manufacturing activities. Kolkata Leather Complex is an industrial complex intended to serve as a central leather-tanning complex for Kolkata located at Bantala, near East Kolkata, India. Samples (tannery effluent) were collected in sterile capped tubes from Kolkata Leather Complex Area and brought to the laboratory for analysis. The samples were serially diluted and were plated on Czapekdox agar plates and incubated at 300C. After a few days, a number of morphologically different colonies were selected and sequentially subcultured for pure colony isolation on the same medium. They were preserved in the refrigerator at 40 C. Lactophenol cotton blue staining was done to observe and record the fungal morphological characteristics. They were further assessed for their hexavalent chromium tolerance capacities and subsequently the metal tolerance index was derived for each strain respectively. All 16 fungal strains isolated from the Kolkata Leather Complex tannery area were found to be chromium (VI) tolerant starting at 0.1mg/ml Cr (VI) concentration. Maximum chromium (VI) tolerance was displayed by sample S12 (2mg/ml) which was later identified as having 99.82% similarity with Aspergillus nomius strain.Keywords: effluent, fungi, heavy metal, isolation, hexavalent chromium, tannery, tolerance