Effect of controlled expression of the hetR gene on heterocyst formation in the filamentous cyanobacterium Anabaena sp. PCC 7120 |
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Authors: | Rehab M El-Shehawy Diethelm Kleiner |
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Institution: | Universität Bayreuth, Mikrobiologie, D-95440 Bayreuth, Germany;1 Present address: Stockholm University, Botaniska Institutionen, Lilla Frescativägen, 5, S-10691 Stockholm, Sweden |
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Abstract: | hetR is a central regulatory gene inducing and possibly maintaining irreversible heterocyst differentiation in filamentous cyanobacteria. A plasmid was constructed which enabled IPTG-mediated, controlled expression of hetR from a p tac promoter in Anabaena . When introduced into a heterocyst-deficient hetR mutant, induction led to massive formation of heterocysts in a medium free of combined nitrogen. In nitrate-containing cultures, induction elicited formation of only a few heterocysts, but led to nitrogen chlorosis in vegetative cells as evidenced from degradation of phycobiliproteins. Removal of the inducer IPTG caused chlorosis and death of the organisms in nitrate-free medium, but no reversal of heterocyst formation. This indicates that constant synthesis of HetR is not the (sole) reason for irreversibility of heterocyst formation. |
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