| Summary: | Memoria de tesis doctoral presentada por Beatriz Fernández Gómez para optar al grado de Doctora en Oceanografía por la Universidad de las Palmas de Gran Canaria, Departamento de Biología, realizada bajo la dirección del Dr. Carlos Pedrós Alió del Institut de Ciències del Mar (ICM-CSIC) y el Dr. José M. González.-- 328 pages The Bacteroidetes phylum is one of the most abundant groups of bacteria in the oceans. Its members account for a significant fraction of marine bacterioplankton especially in coastal areas, although they are globally distributed. Bacteroidetes are successful in the degradation of particulate organic matter; they are claimed to prefer polymeric substances rather than small molecules. Contrary to most other groups of marine of bacteria, many representatives possess gliding motility and they tend to be more abundant attached to particles than free-living in the water column. Thus, they likely present a different strategy to that of Proteobacteria or Cyanobacteria and, therefore, they will fill different niches. Altogether, the Bacteroidetes are thought to have a unique and important role in the marine carbon cycle. The present dissertation uses a variety of approaches to understand the ecology of some members of this group of bacteria. First, a complete genome analysis of a representative of the Bacteroidetes (Polaribacter sp. MED152) was conducted. This suggested a strategy for survival different from those of other groups. Then, a comparative in silico analysis (using bioinformatics tools) of four marine Bacteroidetes whose genomes had been completely sequenced was carried out. We found that these bacteria had a large number of genes involved in polymer degradation and adhesion to surfaces. From the analyzed representatives, an average of 1.5% of the whole genome corresponded to genes acquired by means of horizontal gene transfer, providing new adaptations and metabolic capabilities. This finding lead to the analysis of genomic islands in marine bacteria, trying to discern possible patterns characteristic of Bacteroidetes. Some of the bacteria analyzed had the proteorhodopsin gene (PR), allowing them to obtain extra energy in the presence of light. Since the use of light by PR-containing bacteria could affect the way DOC is processed in the ocean, the experimental part of the work focused on the responses of two whole genome-sequenced, PR-containing bacteria, Polaribacter sp. MED152 and Dokdonia sp. MED134, to different growth conditions. Finally, an attempt was made to determine the degradation of polymers in a natural environment: the Arctic Ocean from winter to spring, when the Bacteroidetes, among other groups, were becoming progressively more active in the use of organic matter Peer Reviewed
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