PubMed 72. Oesterhelt D, Krippahl G: Phototrophic growth of halobacteria and its use for isolation of photosynthetically-deficient mutants. Ann Microbiol (Paris) 1983, 134B:137–150. 73. Helgerson SL, Siemsen SL, Dratz EA: Enrichment of bacteriorhodopsin with isotopically labeled amino acids by biosynthetic incorporation in Halobacterium halobium. Canadian Journal of Microbiology 1992, 38:1181–1185.CrossRef 74. Cline SW, Lam WL, Charlebois RL, Schalkwyk LC, Doolittle WF: Transformation methods for halophilic archaebacteria. Can J Microbiol 1989, 35:148–152.CrossRefPubMed 75. Lorenz RJ: check details Grundbegriffe der
Biometrie. Gustav Fischer Verlag Stuttgart 1996, 338. 76. Thompson JD, Higgins DG, Gibson TJ: CLUSTAL W: improving the sensitivity of progressive multiple selleck screening library sequence
see more alignment through sequence weighting, position-specific gap penalties and weight matrix choice. Nucleic Acids Res 1994,22(22):4673–4680.CrossRefPubMed 77. Thompson JD, Gibson TJ, Plewniak F, Jeanmougin F, Higgins DG: The CLUSTAL_X windows interface: flexible strategies for multiple sequence alignment aided by quality analysis tools. Nucleic Acids Res 1997,25(24):4876–4882.CrossRefPubMed 78. Felsenstein J: PHYLIP (Phylogeny Inference Package) version 3.6. [http://evolution.genetics.washington.edu/phylip.html]Distributed by the author 2005. Authors’ contributions MS and DO conceived and designed the experiments. AM, JM, and MS performed the bait-fishing experiments. BS and FS performed the mass spectrometric measurements, MS and AM analyzed the MS data. AM created the deletion mutants, JM and AM the complementations. AM performed the swarm-plate assays, the cell-tracking experiments, and the dark-field microscopy with help from WS and SS. SS analyzed the cell-tracking data. AM performed the qRT-PCR experiments. MS performed the computational analysis. MS produced the figures 4-Aminobutyrate aminotransferase and wrote the manuscript. SS, WS, FS, and DO
revised the manuscript. All authors read and approved the final manuscript.”
“Background Cyanobacteria evolved more then 2.0 billion years ago and were the first organisms to perform oxygenic photosynthesis [1, 2]. They exist in many different shapes and forms e.g. unicellular, filamentous and colonial and can even form symbiosis with a variety of organisms [3]. Several cyanobacterial strains also have the ability to fix atmospheric nitrogen into ammonium, a process performed by the enzyme complex nitrogenase. Among filamentous cyanobacteria like Nostoc sp. strain PCC 7120 and Nostoc punctiforme ATCC 29133 (from now on referred to as Nostoc PCC 7120 and Nostoc punctiforme), both used in the present study, this process takes place in specialised cells called heterocysts in which a thick envelope and lack of photosystem II activity creates a nearly oxygen free environment for the nitrogenase [3, 4]. The same nitrogenase is also a key player in the hydrogen (H2) metabolism by producing H2 as a by-product during the fixing of atmospheric nitrogen (N2).