Abstract

Two cyanobacterial strains Synechocystis “AHZ-HB-MK” and “AHZ-HB-P2A” were isolated from tannery effluent form Lahore, Pakistan and their tolerance against K₂CrO₄was examined. Although growth was completely inhibited at 10 µg mL^-1 in AHZ-HB-P2Astrain, cell growth of AHZ-HB-MK strain was observed even at a concentration of 100 µg mL^-1. To show reasons for different tolerance between the two strains, we compared changes in nonprotein thiols, glutathione (GSH and GSSG), cysteine and cystine, after K₂CrO₄ treatment in both strains. After K₂CrO₄ treatment GSH completely disappeared in both strains, suggesting that GSH was involved in detoxification. GSSG content in former strain remarkably increased almost three and six times after 7-days treatment with 10 and 100 µg mL^-1 K₂CrO₄, respectively while it decreased in the later strain. Cysteine content in the former strain increased almost three and eleven times after 1 day and 7 days treatment with 100 µg mL^-1 K₂CrO₄, respectively, such increase in cysteine content was not observed in later strain. These data revealed that former strain could induce glutathione and cysteine but later strain could not. The difference in the ability to induce the nonprotein thiols between two strains must be responsible for differential tolerance in K₂CrO₄ observed in the growth inhibition.

Key words: Chromium, cysteine, cyanobacteria, glutathione, nonprotein thiol,Synechocystis.

Abbreviation

GSH, Glutathione reduced form; GSSG, glutathione oxidized form.