Diazotroph

Nitrogen fixation

Heterocyst

Anabaena

Bacteria

Biology

Gene

Nitrogenase

Mutant

Phycoerythrin

Molecular biology

Phycobilisome

Operon

Cyanobacteria

Flow cytometry

Botany

Cell biology

Genetics

Biochemistry

Microbiology

In unicellular non-diazotrophic cyanobacteria, NblA is a small polypeptide required for phycobilisome degradation during macronutrient limitation. In the filamentous N2-fixing Tolypothrix sp., a nblA gene (nblAI) lies upstream of the cpeBA operon that encodes phycoerythrin apoproteins. Using a specific anti-NblAI antibody it was found that in strains of Tolypothrix sp. NblAI abundance increases under nitrogen-limiting conditions but the protein is also present in cells grown in nitrogen-replete medium. Gold immunolabelling experiments showed that, upon a nitrogen shift-down, NblAI is preferentially located in the differentiated heterocysts, where O2 evolution has to be shut off for nitrogenase to operate. The results lead to the proposal that NblAI is a necessary ‘cofactor’ but not the triggering factor that governs phycobilisome degradation in Tolypothrix sp.

Immunolocalization of NblA, a protein involved in phycobilisome turnover, during heterocyst differentiation in cyanobacteria