PhD thesis: Evaluation of the OPU approach in hypersaline environments



Photo: Merit Mora and her thesis directors, Dr. Alejandro Orfila (left) and Dr. Ramón Rosselló-Móra (right) (Author: Mercedes Urdiain)



Esporles, September 19, 2017. Merit del Rocío Mora Ruiz will defend her doctoral thesis led by Dr. Ramon Rosselló-Móra and Dr. Alejandro Orfila Förster, from IMEDEA (CSIC-UIB). The event will take place today, September 19, 2017 at the University of the Balearic Islands.


Microorganisms comprise the majority of the richness in the planet and their current analyses have dramatically expanded our understanding of biodiversity. Particularly, microbiology of extreme environments such as acidic or hypersaline habitats has been a hot scientific topic of research since it resembles the hypothesized conditions of the origin of life. Hypersaline habitats are considered extreme environments due to their extreme conditions: high salinity, UV radiation and temperature. However, life finds its way and organisms from the three domains on life: Bacteria, Archaea and Eukarya are present in high numbers in these habitats. In this Thesis, we analyze the microbial communities inhabiting different environments including brines and sediments of different salterns around the world as well as associated to plants and animals using the Operational Phylogenetic Unit (OPU) as biological entity. The OPU approach is the central core of this Thesis, and therefore we have used it as a base to elucidate biodiversity, connectivity between communities and the influence of the environmental parameters on the microbial assemblage.



Throughout this Thesis we have used different techniques combining culture-depending (e.g. the tandem MALDI-TOF/MS – 16S rRNA gene sequencing) and culture-independent (454 amplicon pyrosequencing) methods. Furthermore, we used different statistical tools such as multivariate techniques and co-occurrence networks in to unravel the spatial and temporal variations among microbial communities.



Firstly we focused on the microbial communities associated with euhalophytes due to their capacity to concentrate salt in their internal tissues. Our results confirmed that most of the epiphytic and endophytic communities were putatively moderate halophiles and few mesophiles probably because the internal compartmentalization of the plant. We also evidenced a geographical distance effect on the microbial communities and furthermore the influence of the physicochemical parameters of the rhizospheric soils. Additionally, this Thesis includes the first report of endophytic Archaea by 16S rRNA amplicon sequencing (principally Halocuccus, Halorubrum, and Haloquadratum), presenting also microscopy evidences and cultures.



Our results showed a strong predominance of Euryarchaeota, Proteobacteria, Bacteroidetes and Firmicutes in the different hypersaline habitats analyzed. Nonetheless, variations on specific taxa, both in Archaea and Bacteria were detected at different spatial scales (e.g. or the spatial differentiation of communities in distant salterns). Additionally we found novel diversity in the analyzed environments. We also used OPUs to analyze the diversity in the gastric cavity of the jellyfish Cotylorhiza tuberculata, finding that major key organisms were related to the genera Spiroplasma, Thalassospira, Tenacibaculum and Vibrio. Some of these OPUs could be potential pathogens and therefore the host may serve as dispersal mechanism.



Some biotechnological applications derived from this Thesis include the identification of certain strains with plant growth promoting activity on a plant model species, which could be used as biofertilizers. Additionally, the databases here obtained were used in a global analysis on the suitability of OPU over traditional OTU approach. The tools used in this work produced a wide landscape of microbial diversity from mostly, but not only, hypersaline environments. Finally, the results of this Thesis are a step forward in the understanding of the diversity and the biological patterns of microbial communities based on a more detailed phylogenetic approach.



Date: September 19, 2017

Place: Degree Hall of the "A" block of the Jovellanos building (UIB)

Time: 11:00h