Antibiotic effects on growth and heterocyst differentiation of the cyanobacterium Nostoc muscorum.

In a medium free of combined nitrogen, 1.0-6.0 micrograms/ml chloramphenicol gradually decreased the growth of the nitrogen-fixing cyanobacterium Nostoc muscorum; at 2.0 micrograms/ml the culture appeared yellowish, heterocyst frequency was not evident up to 3.0 micrograms/ml, whereas 4.0 micrograms/ml suppressed heterocyst differentiation. Lower concentrations (0.0125-0.75 microgram/ml) of rifampicin suppressed the growth but had no significant effect on heterocyst frequency in liquid medium, whereas on solid medium 0.02 micrograms/ml produced chains of heterocysts in filaments. The growth and heterocyst frequency declined gradually with increasing doses of puromycin and 6.0 micrograms/ml suppressed the heterocyst differentiation. Actinomycin-D did not affect significantly growth and heterocyst frequency even at 10.0 and 20.0 micrograms/ml.