# name
Ecology and evolution of microbial nitrifiers / Ecología y evolución de los microorganismos nitrificantes

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Universitat de Barcelona. Departament de Genètica

# metadata.dc.description.abstract[].value
[eng] Ammonia oxidation, the first and the rate-limiting step in nitrification, is one of the cornerstones of the cycle. Members from the bacterial and archaeal domains are key players in ammonia oxidation in many different environ- ments. Usually these organisms are found coexisting but the most recent studies suggests that archaeal ammonia oxidizers show an incredible ability to adapt and oxidize ammonia under different environmental conditions and have displaced their bacterial counterparts in terms of importance in the global biogeochemical cycle, providing an avalanche of AOA molecular data (16S rDNA and amoA gene sequences) from very diverse environments worldwide. As far as we don’t have enough genomic data to perform an holistic approach using population genomics and reverse ecology to unveil the ecological and evolutionary mechanisms driving the adaptation; we focused our experiments on the amoA gene sequence. Because ammonia monooxygenase is supposed to be the key enzyme in the ammonia oxidation, we applied a combination of community ecology and molecular evolution methods to understand the mechanisms of the diversification patterns observed in the amoA gene. Another unsolved question in the archaeal ammonia oxidation is the unusual biochemistry found in the genome sequences from cultured archaeal ammonia oxidizers. In archaea, all the elements of the bacterial ammonia oxidizing pathway are missing but the genes coding for the presumptive AMO. To unveil missing pathways in this process, we have developed a powerful approach based on graphical models to capture all the functional associations present in metagenomes based in their ecological co-ocurrence.

The results of the analyses revealed for the first time a global picture of the phylogenetic community structure of ammonia- oxidizing assemblages. Our study unveiled larger phylogenetic richness in AOA with more dissimilar communities and clear monophyletic groups for the different habitats. The rates of diversification in AOA were higher than in AOB and the archaeal diversification dynamics showed an unusual feature, with an initial diversification process followed by a long period of stasis and a final burst of diversification. The variations observed between AOB and AOA in terms of community structure, phylogenetic diversity, diversification patterns, and habitat dispersion were unexpected just a very few years ago, and the community phylogenetics approach has nicely captured these differences.
Understand the diversification processes observed in AOA and their successful performance under a myriad of different environmental conditions such as low pH, different ammonia concentrations, high hydrostatic pressures, high light exposure, low oxygen availability among others, needs however of a deeper insight adding the evolutionary processes. Individual changes at the level of nucleotides were translated to the global diversification patterns of archaeal ammonia oxidizers. Thus, this resulted in a step further from the results obtained after applying community phylogenetics methods providing precise evolutionary information behind the phylogenetic patterns observed within an ecological context. We will gain the full picture once the results can be integrated in a comparative genomics framework.
After applying methods of reverse engineering of regulatory the associations between the known and the unknown fraction were reconstructed offering a pioneering fresh view for microbial ecology. One especially relevant result obtained from this approach on AOA was the reconstruction of the association network of the different AMO subunits to the other proteins previously reported in the marine AOA Nitrosopumilus. The information recovered from metagenomics combined with available genomes fuels hypothesis for the particular and yet unknown biochemistry of ammonia oxidation in Archaea.

# metadata.dc.description.abstract[].value
[spa] La oxidación del amonio es una de las piezas clave del ciclo del Nitrógeno. Tanto las bacterias como las arqueas oxidadoras del amonio se pueden encontrar coexistiendo a lo largo de diferentes ambientes. Pero cuando la primera arquea oxidadora del amonio fue aislada, se puso en relevancia la importancia de estas en comparación con las bacterias en los ciclos biogeoquímicos globales. Desde entonces hemos sido inundados por una avalancha de secuencias génicas de estas arqueas, mostrando una gran capacidad de diversificación y adaptación a ambientes diferentes.
Al no disponer de suficientes datos para realizar una aproximación holistica utilizando genómica de poblaciones y de ecología inversa para poder discernir los mecanismos ecológicos y evolutivos relacionados con la adaptación; nos hemos centrado en estudiar la secuencia del amoA. La amonio monooxigenasa es la enzima responsable de la oxidación del amonio, para su estudio hemos aplicado una combinación de técnicas de ecología de comunidades y de evolución molecular con el objetivo de entender los mecanismos de los patrones de diversificación observados.
Por otra banda, otro de los misterios asociados a la oxidación del amonio por parte de las arqueas, es su inusual bioquímica para realizar la oxidación del amonio. En arqueas faltan todos los elementos necesarios para llevar a cabo la oxidación del amonio a excepción del AMO. Para poder aportar algo de luz a este misterio hemos desarrollado un potente método basado en modelos gráficos para capturar todas las asociaciones funcionales presentes en los metagenomas basado en sus co-ocurrencias ecológicas.

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Tesis Doctorals - Departament - Genètica

# metadata.dc.title[].value
Ecology and evolution of microbial nitrifiers / Ecología y evolución de los microorganismos nitrificantes