The ABC Transporter Components HgdB and HgdC are Important for Glycolipid Layer Composition and Function of Heterocysts in Anabaena sp. PCC 7120

Abstract

Anabaena sp. PCC 7120 is a filamentous cyanobacterium able to fix atmospheric nitrogen in semi-regularly spaced heterocysts. For correct heterocyst function, a special cell envelope consisting of a glycolipid layer and a polysaccharide layer is essential. We investigated the role of the genes hgdB and hgdC, encoding domains of a putative ABC transporter, in heterocyst maturation. We investigated the subcellular localization of the fusion protein HgdC-GFP and followed the differential expression of the hgdB and hgdC genes during heterocyst maturation. Using a single recombination approach, we created a mutant in hgdB gene and studied its phenotype by microscopy and analytical chromatography. Although heterocysts are formed in the mutant, the structure of the glycolipid layer is aberrant and also contains an atypical ratio of the two major glycolipids. As shown by a pull-down assay, HgdB interacts with the outer membrane protein TolC, which indicates a function as a type 1 secretion system. We show that the hgdB-hgdC genes are essential for the creation of micro-oxic conditions by influencing the correct composition of the glycolipid layer for heterocyst function. Our observations confirm the significance of the hgdB-hgdC gene cluster and shed light on a novel mode of regulation of heterocyst envelope formation.

Glycolipid composition of the heterocyst envelope of Anabaena sp. PCC 7120 is crucial for diazotrophic growth and relies on the UDP-galactose 4-epimerase HgdA

“…At these time points, the heterocysts were already visible by light microscopy. The up-regulation of hgdA was notably later than the previously reported up-regulation of devB (18), and the expression pattern of hgdA was almost identical to that of hgdB (23).…”

“…The hgdA gene is the third gene in the previously described cluster involved in heterocyst formation, all5347/all5346/all5345 ( hgdB/hgdC/hgdA ) [Fig. 1A; (22, 23)]. It encodes a protein of 333 amino acids with a predicted molecular mass of 36.7 kDa.…”

“…have been identified (19, 20). Some are important for diazotrophic growth and heterocyst maturation (21– 23). The cluster all5347/all5346/all5345 ( hgdB/hgdC/hgdA ) is of particular interest because the ATPase-coding gene devA is replaced by the hgdA gene coding for a putative epimerase.…”

“…This gene cluster is essential for proper hgl layer deposition and growth of Anabaena sp. without combined nitrogen source (22, 23), but the functions of the protein HgdA (All5345) remain unknown.…”

Two DevBCA‐like ABC transporters are involved in the multidrug resistance of the cyanobacterium Anabaena sp. PCC 7120

“…carries several gene clusters whose products are homologous to DevBCA. They include the open reading frames of all5347/all5346 ( hgdB/hgdC ) , alr3647/alr3648/alr3649 , all2652/all2651/all2650 , alr4280/alr4281/alr4282 , alr4973/alr4974/alr4975 , and all0809/all0808/all0807 . All of them except for hgdB/hgdC , which is devoid of an ATPase gene, contain genes coding for MFPs and ABC transporters (see alignments of MFPs and transmembrane domains in Fig.…”