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A TolC-Like Protein Is Required for Heterocyst Development in Anabaena sp. Strain PCC 7120 ^,

LMU, Department of Biology I, VW-Research Group, Menzinger Str. 67, 80638 München, Germany,¹ Lehrstuhl für Zellbiologie und Pflanzenphysiologie, Universität Regensburg, 93040 Regensburg, Germany,² Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC, and Universidad de Sevilla, Américo Vespucio 49, E-41092 Seville, Spain³

Received 14 May 2007/ Accepted 10 August 2007

The filamentous cyanobacterium Anabaena sp. strain PCC 7120 forms heterocysts in a semiregular pattern when it is grown on N₂ as the sole nitrogen source. The transition from vegetative cells to heterocysts requires marked metabolic and morphological changes. We show that a trimeric pore-forming outer membrane ß-barrel protein belonging to the TolC family, Alr2887, is up-regulated in developing heterocysts and is essential for diazotrophic growth. Mutants defective in Alr2887 did not form the specific glycolipid layer of the heterocyst cell wall, which is necessary to protect nitrogenase from external oxygen. Comparison of the glycolipid contents of wild-type and mutant cells indicated that the protein is not involved in the synthesis of glycolipids but might instead serve as an exporter for the glycolipid moieties or enzymes involved in glycolipid attachment. We propose that Alr2887, together with an ABC transporter like DevBCA, is part of a protein export system essential for assembly of the heterocyst glycolipid layer. We designate the alr2887 gene hgdD (heterocyst glycolipid deposition protein).

Published ahead of print on 24 August 2007.

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