Intercellular Diffusion of a Fluorescent Sucrose Analog via the Septal Junctions in a Filamentous Cyanobacterium

D.J.N. was supported by a Queen Mary University of London College studentship. M.N.M. was the recipient of an FPU (Formación del Personal Universitario) fellowship from the Spanish Government. Work in Seville was supported by grant BFU2011-22762 from Plan Nacional de Investigación, Spain, cofinanced by the European Regional Development Fund, and by Plan Andaluz de Investigación, Regional Government of Andalucía (grant P10-CVI-6665). Research in Tübingen was supported by the Deutsche Forschungsgemeinschaft (SFB766)

Changes in Envelope Structure and Cell-Cell Communication during Akinete Differentiation and Germination in Filamentous Cyanobacterium Trichormus variabilis ATCC 29413

Planktonic freshwater filamentous cyanobacterium Trichormus variabilis ATCC 29413 (previously known as Anabaena variabilis) can differentiate heterocysts and akinetes to survive under different stress conditions. Whilst heterocysts enable diazotrophic growth, akinetes are spore-like resting cells that make the survival of the species possible under adverse growth conditions. Under suitable environmental conditions, they germinate to produce new vegetative filaments. Several morphological and physiological changes occur during akinete formation and germination. Here, using scanning electron microscopy (SEM), we found that the mature akinetes had a wrinkled envelope, and the surface of the envelope smoothened as the cell size increased during germination. Thereupon, the akinete envelope ruptured to release the short emerging filament. Focused ion beam-scanning electron microscopy (FIB/SEM) tomography of immature akinetes revealed the presence of cytoplasmic granules, presumably consisting of cyanophycin or glycogen. In addition, the akinete envelope architecture of different layers, the exopolysaccharide and glycolipid layers, could be visualized. We found that this multilayered envelope helped to withstand osmotic stress and to maintain the structural integrity. Furthermore, by fluorescence recovery after photobleaching (FRAP) measurements, using the fluorescent tracer calcein, we found that intercellular communication decreased during akinete formation as compared with the vegetative cells. In contrast, freshly germinating filaments restored cell communication

A new chlorophyll d-containing cyanobacterium: Evidence for niche adaptation in the genus Acaryochloris

Chlorophyll d is a photosynthetic pigment that, based on chemical analyses, has only recently been recognized to be widespread in oceanic and lacustrine environments. However, the diversity of organisms harbouring this pigment is not known. Until now, the unicellular cyanobacterium Acaryochloris marina is the only characterized organism that uses chlorophyll d as a major photopigment. In this study we describe a new cyanobacterium possessing a high amount of chlorophyll d, which was isolated from waters around Heron Island, Great Barrier Reef (23° 26′ 31.2 S, 151° 54′ 50.4 E). The 16S ribosomal RNA is 2% divergent from the two previously described isolates of A. marina, which were isolated from waters around the Palau islands (Pacific Ocean) and the Salton Sea lake (California), suggesting that it belongs to a different clade within the genus Acaryochloris. An overview sequence analysis of its genome based on Illumina technology yielded 871 contigs with an accumulated length of 8 371 965 nt. Their analysis revealed typical features associated with Acaryochloris, such as an extended gene family for chlorophyll-binding proteins. However, compared with A. marina MBIC11017, distinct genetic, morphological and physiological differences were observed. Light saturation is reached at lower light intensities, Chl d/a ratios are less variable with light intensity and the phycobiliprotein phycocyanin is lacking, suggesting that cyanobacteria of the genus Acaryochloris occur in distinct ecotypes. These data characterize Acaryochloris as a niche-adapted cyanobacterium and show that more rigorous attempts are worthwhile to isolate, cultivate and analyse chlorophyll d-containing cyanobacteria for understanding the ecophysiology of these organisms. © 2010 International Society for Microbial Ecology All rights reserved

DevT (Alr4674), resembling a Ser/Thr protein phosphatase, is essential for heterocyst function in the cyanobacterium Anabaena sp. PCC 7120

Heterocyst-forming cyanobacteria are able to perform oxygenic photosynthesis and nitrogen fixation simultaneously in the same filament, by restricting the highly O2 sensitive nitrogenase to specialized cells, the heterocysts. A remarkable change in morphology and metabolism accompanies the differentiation of heterocysts, which only occurs when no source of combined nitrogen is available. In the present study, we characterized DevT (Alr4674), a putative protein phosphatase from Anabaena PCC 7120. Mutants defective in devT are able to form morphologically mature heterocysts, which however cannot fix N2 and the mutant cannot survive without a source of combined nitrogen. DevT shows homology to phosphatases of the PPP family and displays a Mn2+-dependent phosphatase activity that can be inhibited by phosphatase inhibitors and oxidizing conditions. DevT is constitutively expressed both in vegetative cells and heterocysts, and is not regulated by NtcA. Heterocyst regulator HetR may exert a certain inhibition on expression of devT. Under diazotrophic growth conditions, DevT protein accumulates specifically in mature heterocysts. Therefore DevT plays a still unknown role in a late essential step of heterocyst differentiation.This work was supported by a grant from the Deutsche Forschungsgemeinschaft, DFG (MA1359/2-3). J. E. received a grant from the Ministerio de Ciencia e Innovación, Spain