Silver toxicity in a nitrogen-fixing Cyanobacterium

Abstract

Exposure ofNostoc muscorum to combinations of Ag + Cr, Ag + Ni, Ag + PB and Ag, Cr, Ni and Cr alone brought about a complex pattern of inhibition of growth, NO3, NH4 and14CO2 uptake and nitrogenase activity. The sensitivity hierarchy of different parameters to metal combinations may be given as: (a) inhibition of NH4 uptake and nitrogenase was almost identical for Ag + Ni, Ag + Cr and Ag + Pb; (b) the order of inhibition of growth and NO3 uptake was Ag + Cr > Ag + Ni > Ag + Pb; (c) the combination of Ag + Pb was least toxic for growth, nitrogenase, NO3 and NH4 uptake, but most toxic for14CO2 uptake; (d) the toxicity hierarchy for all parameters together was14C02 > nitrogenase > NH4 uPtake > NO3 uptake > growth. Hence, carbon fixation may be employed for biological monitoring of metal toxicity in a laboratory microcosm and possibly in aquatic ecosystems.