Effect of ammonia and sulfide on rifampicin-induced heterocyst formation inNostoc linckia

The effect of ammonia and sulfide on rifampicin-induced heterocyst differentiation was studied in the nitrogen-fixing cyanobacteriumNostoc linckia. Aerobic growth with nitrogen gas of the cyanobacterium was greatly affected by rifampicin with formation of multiple heterocysts in chains in the filaments whereas ammonia in the medium reversed the rifampicin inhibition of growth and prevented the induction of heterocysts. In a sulfide medium the suppression exerted by rifampicin on aerobic growth with nitrogen gas and heterocyst induction was found to be considerably reduced. The results suggest two interesting points,viz. that (i) rifampicin interferes with the nitrogen-fixing function of heterocysts, and (ii) it checks the synthesis of an unknown heterocyst, inhibitor and thus permits the adjacent vegetative cells to differentiate into heterocysts in chains.