Catabolic function of compartmentalized alanine dehydrogenase in the heterocyst-forming cyanobacterium Anabaena sp. strain PCC 7120

In the diazotrophic filaments of heterocyst-forming cyanobacteria, an exchange of metabolites takes place between vegetative cells and heterocysts that results in a net transfer of reduced carbon to the heterocysts and of fixed nitrogen to the vegetative cells. Open reading frame alr2355 of the genome of Anabaena sp. strain PCC 7120 is the ald gene encoding alanine dehydrogenase. A strain carrying a green fluorescent protein (GFP) fusion to the N terminus of Ald (Ald-N-GFP) showed that the ald gene is expressed in differentiating and mature heterocysts. Inactivation of ald resulted in a lack of alanine dehydrogenase activity, a substantially decreased nitrogenase activity, and a 50% reduction in the rate of diazotrophic growth. Whereas production of alanine was not affected in the ald mutant, in vivo labeling with [14C]alanine (in whole filaments and isolated heterocysts) or [14C]pyruvate (in whole filaments) showed that alanine catabolism was hampered. Thus, alanine catabolism in the heterocysts is needed for normal diazotrophic growth. Our results extend the significance of a previous work that suggested that alanine is transported from vegetative cells into heterocysts in the diazotrophic Anabaena filament.Ministerio de Ciencia y Tecnología y FEDER BFU2008-0381

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

Tissue Simulator: A Graphical Tool for Tissue P Systems

Recently, different new models of tissue-like P systems have received important attention from the scientific community. This paper is focused in a concrete model: recognizing tissue P system with cell division. A software application allowing to understand better this model is presented. A linear-time solution to an NP-complete problem from graph theory, the 3–coloring problem is considered as a case study with this tool.Ministerio de Educación y Ciencia TIN2006-13425Junta de Andalucía TIC-58

The Peptidoglycan-Binding Protein SjcF1 Influences Septal Junction Function and Channel Formation in the Filamentous Cyanobacterium Anabaena

Filamentous, heterocyst-forming cyanobacteria exchange nutrients and regulators between cells for diazotrophic growth. Two alternative modes of exchange have been discussed involving transport either through the periplasm or through septal junctions linking adjacent cells. Septal junctions and channels in the septal peptidoglycan are likely filled with septal junction complexes. While possible proteinaceous factors involved in septal junction formation, SepJ (FraG), FraC, and FraD, have been identified, little is known about peptidoglycan channel formation and septal junction complex anchoring to the peptidoglycan. We describe a factor, SjcF1, involved in regulation of septal junction channel formation in the heterocyst-forming cyanobacterium Anabaena sp. strain PCC 7120. SjcF1 interacts with the peptidoglycan layer through two peptidoglycan-binding domains and is localized throughout the cell periphery but at higher levels in the intercellular septa. A strain with an insertion in sjcF1 was not affected in peptidoglycan synthesis but showed an altered morphology of the septal peptidoglycan channels, which were significantly wider in the mutant than in the wild type. The mutant was impaired in intercellular exchange of a fluorescent probe to a similar extent as a sepJ deletion mutant. SjcF1 additionally bears an SH3 domain for protein-protein interactions. SH3 binding domains were identified in SepJ and FraC, and evidence for interaction of SjcF1 with both SepJ and FraC was obtained. SjcF1 represents a novel protein involved in structuring the peptidoglycan layer, which links peptidoglycan channel formation to septal junction complex function in multicellular cyanobacteria. Nonetheless, based on its subcellular distribution, this might not be the only function of SjcF1.Peer reviewe

Transporte de aminoácidos y relaciones intercelulares en la cianobacteria formadora de heterocistos Anabaena sp

El transporte de sustancias a través de membranas es un aspecto esencial de los procesos que se llevan a cabo en los organismos vivos. Por una parte, permite la entrada a la célula de nutrientes esenciales y mantiene concentraciones fisiológicas de iones en el interior celular que pueden diferir en órdenes de magnitud de las presentes en el medio externo. Por otra parte, regula la concentración de metabolitos en el citoplasma mediante mecanismos de excreción y evita los efectos nocivos de toxinas y drogas mediante su exportación activa. Por último, exporta macromoléculas, cataliza la importación y exportación de moléculas de señalización que median la comunicación de la célula con el medio externo, así como la comunicación intercelular, y participa en procesos de defensa y ataque mediante la exportación de agentes biológico activos, que atraviesan las membranas de las células diana.En las bacterias Gram-negativas, que para entrar en la célula, los sustratos deben superar en primer lugar la barrera de permeabilidad que supone la membrana externa y, una vez en el espacio periplásmico, atravesar la membrana plasmática. La membrana externa es muy impermeable a compuestos tóxicos como antibióticos, toxinas y enzimas líticas, siendo una de sus principales funciones la protección de la célula frente a este tipo de compuestos. Esta membrana presenta una escritura asimétrica, al estar constituida por una monocapa externa rica en lipopolisacáridos y otra interna de fosfolípidos. Esta asimetría y algunas características de los lipopolisacáridos, como la presencia de 6 ó 7 cadenas de ácidos grasos saturados por molécula en lugar de las 2 presentes por molécula de fosfolípido, explican las propiedades de Impermeabilidad de esta envuelta (Nikaido, 2003). Sin embargo, en la membrana externa existen canales proteicos hidrofílicos, conocidos como porinas, que permiten la difusión, generalmente inespecífica o con baja especificidad, de moléculas pequeñas. En aquellas bacterias que carecen prácticamente de porinas inespecíficas, la presencia de porinas específicas tiene una gran importancia en los procesos de transporte. Además de las porinas, en la membrana externa también hay canales con sitios de unión específicos que facilitan la difusión de determinados compuestos que son demasiado grandes para penetrar rápidamente a través de los canales de las porinas clásicas (Nikaido, 2003). Una vez superada la membrana externa y el espacio periplásmico, la estructura que rodea a la célula es la membrana plasmática, que representa la barrera principal de las células para la difusión de solutos. Esta membrana presenta un elevado número de sistemas de transporte específicos para distintos sustratos, destacando en bacterias por su importancia fisiológica los sistemas de transporte activo secundario y los primarios de tipo ABC (del inglés ATP-binding Cassette superfamily).De forma general, mientras que el transporte pasivo ocurre a favor del gradiente electroquímico del sustrato hasta que se alcanza el equilibrio, como en el caso del mediado por las porinas de la membrana externa, el transporte activo requiere un aporte de energía, como ocurre en el caso de los sistemas de transporte activo primario y secundario de la membrana plasmática, y permite la concentración de los sustratos en contra de su gradiente electroquímico. El objetivo que nos planteamos al comienzo de este trabajo fue la caracterización de los sistemas de transporte de aminoácidos en la cianobacteria Anabaena sp. PCC 7120, así como el estudio de la implicación de los mismos en la transferencia de nitrógeno entre las células vegetativas y los heterocistos y la identificación de metabolitos utilizados como portadores de nitrógeno en dicha transferencia

Metalloproteins in the Biology of Heterocysts

Cyanobacteria are photoautotrophic microorganisms present in almost all ecologically niches on Earth. They exist as single-cell or filamentous forms and the latter often contain specialized cells for N2 fixation known as heterocysts. Heterocysts arise from photosynthetic active vegetative cells by multiple morphological and physiological rearrangements including the absence of O2 evolution and CO2 fixation. The key function of this cell type is carried out by the metalloprotein complex known as nitrogenase. Additionally, many other important processes in heterocysts also depend on metalloproteins. This leads to a high metal demand exceeding the one of other bacteria in content and concentration during heterocyst development and in mature heterocysts. This review provides an overview on the current knowledge of the transition metals and metalloproteins required by heterocysts in heterocyst-forming cyanobacteria. It discusses the molecular, physiological, and physicochemical properties of metalloproteins involved in N2 fixation, H2 metabolism, electron transport chains, oxidative stress management, storage, energy metabolism, and metabolic networks in the diazotrophic filament. This provides a detailed and comprehensive picture on the heterocyst demands for Fe, Cu, Mo, Ni, Mn, V, and Zn as cofactors for metalloproteins and highlights the importance of such metalloproteins for the biology of cyanobacterial heterocysts

Metalloproteins in the biology of heterocysts

Cyanobacteria are photoautotrophic microorganisms present in almost all ecologically niches on Earth. They exist as single-cell or filamentous forms and the latter often contain specialized cells for N2 fixation known as heterocysts. Heterocysts arise from photosynthetic active vegetative cells by multiple morphological and physiological rearrangements including the absence of O2 evolution and CO2 fixation. The key function of this cell type is carried out by the metalloprotein complex known as nitrogenase. Additionally, many other important processes in heterocysts also depend on metalloproteins. This leads to a high metal demand exceeding the one of other bacteria in content and concentration during heterocyst development and in mature heterocysts. This review provides an overview on the current knowledge of the transition metals and metalloproteins required by heterocysts in heterocyst-forming cyanobacteria. It discusses the molecular, physiological, and physicochemical properties of metalloproteins involved in N2 fixation, H2 metabolism, electron transport chains, oxidative stress management, storage, energy metabolism, and metabolic networks in the diazotrophic filament. This provides a detailed and comprehensive picture on the heterocyst demands for Fe, Cu, Mo, Ni, Mn, V, and Zn as cofactors for metalloproteins and highlights the importance of such metalloproteins for the biology of cyanobacterial heterocysts

A TRAP Transporter for Pyruvate and Other Monocarboxylate 2-Oxoacids in the Cyanobacterium Anabaena sp. Strain PCC 7120▿

In the cyanobacterium Anabaena sp. strain PCC 7120, open reading frames (ORFs) alr3026, alr3027, and all3028 encode a tripartite ATP-independent periplasmic transporter (TRAP-T). Wild-type filaments showed significant uptake of [14C]pyruvate, which was impaired in the alr3027 and all3028 mutants and was inhibited by several monocarboxylate 2-oxoacids, identifying this TRAP-T system as a pyruvate/monocarboxylate 2-oxoacid transporter

VisualTissue: a friendly tool to study tissue P systems solutions for graph problems

Summary. P systems can be classified in two main groups: P systems with the membrane structure described by a tree, and tissue P systems with the membranes placed in the nodes of an arbitrary graph. NP-complete problems have been solved in linear time by trading space for time in the framework of recognizing tissue P systems with cell division. The design of this kind of systems is not an easy task to understand. In this paper we present a software application to help the design of solutions to NP-complete problems in the framework of recognizing tissue P systems with cell division. VisualTissue application can be downloaded from the web: www.visualtissue.es.kz.

A cobalt concentration sensitive Btu-like system facilitates cobalamin uptake in Anabaena sp. PCC 7120

Metal homeostasis is central to all forms of life, as metals are es-sential micronutrients with toxic effects at elevated levels. Macromolecular machines facilitate metal uptake into the cells and their intracellular level is regulated by multiple means, which can involve RNA elements and proteina-ceous components. While the general principles and components for uptake and cellular content regulation of, e.g., cobalt have been identified for prote-obacteria, the corresponding mechanism in other Gram-negative bacteria such as cyanobacteria remain to be established. Based on their photosynthet-ic activity, cyanobacteria are known to exhibit a special metal demand in comparison to other bacteria. Here, the regulation by cobalt and cobalamin as well as their uptake is described for Anabaena sp. PCC 7120, a model filamen-tous heterocyst-forming cyanobacterium. Anabaena contains at least three cobalamin riboswitches in its genome, for one of which the functionality is confirmed here. Moreover, two outer membrane-localized cobalamin TonB-dependent transporters, namely BtuB1 and BtuB2, were identified. BtuB2 is important for fast uptake of cobalamin under conditions with low external cobalt, whereas BtuB1 appears to function in cobalamin uptake under condi-tions of sufficient cobalt supply. While the general function is comparable, the specific function of the two genes differs and mutants thereof show distinct phenotypes. The uptake of cobalamin depends further on the TonB and a BtuFCD machinery, as mutants of tonB3 and btuD show reduced cobalamin uptake rates. Thus, our results provide novel information on the uptake of cobalamin and the regulation of the cellular cobalt content in cyanobacteria