Effects of three pesticides on MSX-induced ammonia photoproduction by the cyanobacterium Nostoc linckia

Abstract

Three pesticides (2,4-D, basalin, aldrin) inhibited L-methionine-DL-sulfoximine (MSX)-induced photoproduction of ammonia by the nitrogen-fixing cyanobacterium Nostoc linckia. Combinations of pesticides and MSX were inhibitory except at low concentrations (100 and 500 µg/ml) of 2,4-D which stimulated NH₄⁺ production. Similar results were obtained when pesticides were added 6 hr after the addition of MSX, but the inhibition was weaker. When MSX was added to the culture 6 hr after the addition of pesticides, the pesticides stimulated NH₄⁺ photoproduction. Similar results were obtained on nitrogenase activity of the organism.