BIOLOGICAL EFFECTS OF A MERCURY FUNGICIDE ON A N2 -FIXING BLUE-GREEN ALGA NOSTOC MUSCORUM: ISOLATION AND PRELIMINARY CHARACTERIZATION OF A Hg-RESISTANT MUTANT.

Mercuric chloride, which is used as a fungicide in tropical paddy-fields, inhibits growth (in N2 , i.e. molecular nitrogen, and 5 mM KNO3 media) and heterocyst formation (in N8 medium) in the blue-green alga Nostoc muscorum at a concentration of 0.3 µg ml-1 and above. These inhibitory effects were reversed on supplementation with 3 mM exogenous glucose. A mercury resistant mutant of this alga has been obtained, which is stable through repeated cell transfers in N2 medium. It is suggested that a Hg-inducible protein/enzyme system is responsible for the intracellular mercury-resistance of this mutant.