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- Bauer, Karolina, 1975-
(författare)
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Diazotrophy and diversity of benthic cyanobacteria in tropical coastal zones
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Discoveries in recent years have disclosed the importance of marine cyano-bacteria in the context of primary production and global nitrogen cycling. It is hypothesized here that microbial mats in tropical coastal habitats harbour a rich diversity of previously uncharacterized cyanobacteria and that benthic marine nitrogen fixation in coastal zones is substantial.A polyphasic approach was used to investigate cyanobacterial diversity in three tropical benthic marine habitats of different characters; an intertidal sand flat and a mangrove forest floor in the Indian Ocean, and a beach rock in the Pacific Ocean. In addition, nitrogenase activity was measured over diel cycles at all sites. The results revealed high cyanobacterial diversity, both morphologically and genetically. Substantial nitrogenase activity was observed, with highest rates at daytime where heterocystous species were present. However, the three habitats were dominated by non-heterocystous and unicellular genera such as Microcoleus, Lyngbya, Cyanothece and a large group of thin filamentous species, identified as members of the Pseudanabaenaceae family. In these consortia nocturnal nitrogenase activities were highest and nifH sequencing also revealed presence of non-cyanobacterial potential diazotrophs. A conclusive phylogenetic analysis of partial nifH sequences from the three sites and sequences from geographi-cally distant microbial mats revealed new clusters of benthic potentially ni-trogen-fixing cyanobacteria. Further, the non-heterocystous cyanobacterium Lyngbya majuscula was subjected to a physiological characterization to gain insights into regulatory aspects of its nitrogen fixation. The data demon-strated that nitrogenase activity is restricted to darkness, which called upon a re-evaluation of its diazotrophic behaviour.
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| 2. |
- Ran, Liang, 1974-
(författare)
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Proteomic profiles and gene expressions in the symbiotically competent cyanobacterium Nostoc sp. PCC 73102
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nostoc PCC 73102 is an evolutionary important cyanobacterium with multiple phenotypic traits and symbiotic capacities. Based on two-dimensional gel electrophoresis (2-DE) and MALDI-TOF mass spectrometry, a proteomic approach was developed in order to obtain protein profiles of this symbiotically competent cyanobacterium during three trophic types/life stages: free-living photo-autotrophic and diazotrophic growth conditions, dark heterotrophic conditions and hormogonium formation. The proteomic data obtained revealed a total of 82 proteins that could be organized into 12 functional categories. The majority of proteins identified were involved in carbon, nitrogen and energy metabolism. The analysis also indicates that a thioredoxin-dependent redox regulation is vital under photo-autotrophic and diazotrophic growth conditions. The differentiation of vegetative filaments into hormogonia led to distinct morphological as well as drastic changes in C and N metabolism, with levels of Rubisco large subunit and glutamine synthetase clearly down-regulated, while glycogen synthesis (C storage) was enhanced, a metabolic specialisation maintained in symbiosis. RT-PCR and quantitative real-time PCR showed that gene transcription related to surface structures and hormogonium function was affected early during the developmental process: genes encoding proteins involved in motility (pil genes) and gas vesicle formation (gvp genes) were up-regulated, but also genes encoding proteins involved in DNA replication (dnaA) and cell division (ftsZ, ftsA and ftn2) and proteolysis (hetR). Dark heterotrophy, mimicking symbiosis, led to a repression of CO2 fixation, while sugar uptake, the glycolysis pathway and N2-fixation were stimulated. In addition, three proteins involved in light adaptation processes were upregulated. Collectively, these data contribute to our understanding and the definition of ‘symbiotic competence’ and suggest that the cyanobacterium behaves like a cyanobiont even before getting into physical contact with host plants if subject to the appropriate signals.
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