BIOLOGICAL EFFECTS OF A MERCURY FUNGICIDE ON A N -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 N , i.e. molecular nitrogen, and 5 mM KNO media) and heterocyst formation (in N medium) in the blue-green alga Nostoc muscorum at a concentration of 0.3 μg ml 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 N medium. It is suggested that a Hg-inducible protein/enzyme system is responsible for the intracellular mercury-resistance of this mutant.