Sequence and mutational analysis of the devBCA gene cluster encoding a putative ABC transporter in the cyanobacterium Anabaena variabilis ATCC 29413

AbstractThe devBCA gene cluster (dev for development), shown to be essential for envelope formation in heterocysts of Anabaena sp. strain PCC 7120, was identified in the gene bank of a second heterocyst-forming strain, Anabaena variabilis ATCC 29413. Sequence and structural organization of the three genes, encoding subunits of a presumptive ABC transporter, were nearly identical in both strains. Mutants of A. variabilis defective in the devA gene were constructed. As devA mutants of Anabaena 7120, A. variabilis mutants were unable to grow on N2 as sole nitrogen source due to incomplete differentiation of heterocysts

Septal Junctions in Filamentous Heterocyst-Forming Cyanobacteria

In the filaments of heterocyst-forming cyanobacteria, septal junctions that traverse the septal peptidoglycan join adjacent cells, allowing intercellular communication. Perforations in the septal peptidoglycan have been observed, and proteins involved in the formation of such perforations and putative protein components of the septal junctions have been identified, but their relationships are debatedEspaña, Plan Nacional de Investigaci´601027022on BFU2014 - 56757 - P (EF) and BFU2013 - 157 44686 -

Approximate Hermitian-Yang-Mills structures and semistability for Higgs bundles. II: Higgs sheaves and admissible structures

We study the basic properties of Higgs sheaves over compact K\"ahler manifolds and we establish some results concerning the notion of semistability; in particular, we show that any extension of semistable Higgs sheaves with equal slopes is semistable. Then, we use the flattening theorem to construct a regularization of any torsion-free Higgs sheaf and we show that it is in fact a Higgs bundle. Using this, we prove that any Hermitian metric on a regularization of a torsion-free Higgs sheaf induces an admissible structure on the Higgs sheaf. Finally, using admissible structures we proved some properties of semistable Higgs sheaves.Comment: 18 pages; some typos correcte

Two novel heteropolymer‐forming proteins maintain the multicellular shape of the cyanobacterium Anabaena sp. PCC 7120

Polymerizing and filament-forming proteins are instrumental for numerous cellular processes such as cell division and growth. Their function in stabilization and localization of protein complexes and replicons is achieved by a filamentous structure. Known filamentous proteins assemble into homopolymers consisting of single subunits – for example, MreB and FtsZ in bacteria – or heteropolymers that are composed of two subunits, for example, keratin and α/β tubulin in eukaryotes. Here, we describe two novel coiled-coil-rich proteins (CCRPs) in the filament-forming cyanobacterium Anabaena sp. PCC 7120 (hereafter Anabaena) that assemble into a heteropolymer and function in the maintenance of the Anabaena multicellular shape (termed trichome). The two CCRPs – Alr4504 and Alr4505 (named ZicK and ZacK) – are strictly interdependent for the assembly of protein filaments in vivo and polymerize nucleotide independently in vitro, similar to known intermediate filament (IF) proteins. A ΔzicKΔzacK double mutant is characterized by a zigzagged cell arrangement and hence a loss of the typical linear Anabaena trichome shape. ZicK and ZacK interact with themselves, with each other, with the elongasome protein MreB, the septal junction protein SepJ and the divisome associate septal protein SepI. Our results suggest that ZicK and ZacK function in cooperation with SepJ and MreB to stabilize the Anabaena trichome and are likely essential for the manifestation of the multicellular shape in Anabaena. Our study reveals the presence of filament-forming IF-like proteins whose function is achieved through the formation of heteropolymers in cyanobacteria

Cyanobacterial Heterocysts

10 páginas, 4 figuras.Cyanobacteria are phototrophic bacteria carrying out oxygen-producing photosynthesis. Indeed, cyanobacteria were the inventors of oxygenic photosynthesis carried out by eukaryotic algae and plants. Besides showing the capability of building their cellular carbon from carbon dioxide, available in the atmosphere, several strains of cyanobacteria have also acquired the ability to fix molecular dinitrogen (N2). As the enzyme responsible for nitrogen fixation (nitrogenase) is highly sensitive towards oxygen, nitrogen fixation and oxygenic photosynthesis cannot take place simultaneously in cyanobacterial cells. To solve this problem, some filamentous strains are able to restrict N2 fixation to a special cell type, the heterocyst. Heterocysts are specialised, morphologically distinct, terminally differentiated cells that develop, in the absence of alternative sources of combined nitrogen, mostly in a semiregular pattern along the filament. Thus, a filament containing heterocysts provides division of labour between photosynthetic carbon dioxide fixation (in vegetative cells) and anaerobic N2 fixation (in heterocysts). These cyanobacteria represent true multicellular organisms with profound morphological cell differentiation and sophisticated intercellular communication systems.The support to I.M. by Deutsche Forschungsgemeinschaft at the University of Regensburg and Tübingen is gratefully acknowledged.Peer reviewe