Effect of Methionine Sulfoximine on Heterocyst Differentiation in Nostoc muscorum in Presence of Amino Acids and Metabolic Inhibitors

Abstract

Summary Differentiation of heteroeysts in N. muscorum was completely suppressed by addition of ammonia (2 mM), alanine, glutamine, glutamate, histidine, lysine, methionine and serine (0.5–1 mM). Addition of methionine-sulfoximine, an analog of glutamate, induced heterocyst differentiation in ammonia grown cultures and also enhanced their number to 2a3 fold under N2-fixing conditions with release of newly fixed ammonia into the medium. Derepression of heterorysts in ammonia by MSO treatment was repressed by addition of glutamine, glutamate, lysine, methionine and serine while alanine, arginine, aspartate, histidine and leucine showed partial repression. Periodic administration of glutamine or glutamate upto 8–10 h after nutrient-shift repressed the MSO induced heterocysts completely, but their addition between 10–15 h showed partial suppression. Treatment of mitomycin (5 mM), chloramphenicol (10 μg) and rifampicin (20 μg) blocked the derepression of heterocysts in ammonia by MSO and also their differentiation in N2-fixing cultures. Treatment of MSO failed to induce heterocyst development in cultures pretreated with these drugs. Results indicate that ammonia or glutamine synthetase are not the only key factors for regulation and spacing of heterocysts.