Department of Microbiology and Parasitology, Faculty of Pharmacy. Sevilla University.
Responsable: Antonio Ventosa
Our group has been working on studies related to different aspects of halophilic microorganisms and hypersaline environments in which they are, from their biodiversity, evolutionary relationships, phylogenomics and taxonomy, etc. In recent years we have conducted a series of metagenomic studies in salt ponds located on the Mediterranean coast (Salinas de Santa Pola, Alicante) as well as atlantic (Salinas de Isla Cristina, Huelva). These studies have allowed to know in more detail the taxonomic and metabolic diversity of the ponds with intermediate salinities, from 13 to 33% of total salts, in comparison with the crystallizing ponds that had already been the subject of more detailed studies using both traditional culture techniques and Molecular independent cultures. One of the best-studied hypersaline environments from a microbiological point of view is the "Bras del Port" saltworks in Santa Pola, of which a review article has recently been published (Ventosa et al., 2014). Unlike the crystallizing ponds, where there is a predominance of the square archaea Haloquadratum walsbyi and the halophilic bacterium Salinibacter ruber, in the concentration ponds with intermediate salinities there is a greater diversity of species belonging to nine higher taxa. The assembly of contigs from the metagenomic sequences has allowed us to detect the abundant presence of new representatives of the Archaea and Bacteria domains in intermediate concentrator ponds, such as the nanohaloarquea "Candidatus Haloredivivus", new haloarchaeas related to the genus Halorubrum and a new Gammaproteobacteria , phylogenetically related to the genus Alkalilimnicola.
The metagenomic studies carried out in the salinas have allowed us to develop different strategies focused on the isolation and characterization of new abundant representatives in the salinas, among them the bacteria belonging to the Gammaproteobacteria class, which we have designated as Spiribacter salinus (León et al., 2014). The analysis of the complete genome of this bacterium has allowed to determine that it is a microorganism that has a very simple genome, with a size of 1.74 MB (the smallest described for a representative of the Ectothiorhodospiraceae family to which it belongs), a G + C content of 62.7% and a single rRNA operon. Spiribacter salinus has a very simplified metabolic versatility, showing characteristics typical of other oligotrophic microorganisms that reach high densities in aquatic environments (López-Pérez et al., 2013). One of the peculiarities of this bacterium is its cellular morphology: it is a Gram-negative bacillus curved in young cultures that later form spirals; in stationary phase they tend to condense into a compact spiral. Some of these cells are surrounded by an outer envelope similar to that described in Thermus or Oceanothermus. Some aspects that we have studied in detail about this new bacterium are the composition of the polar lipids of its membranes, the structure of the cell wall murein or its mechanism of osmoregulation (it has a "salt-out" strategy). Undoubtedly, recent metagenomic studies will advance knowledge of the biodiversity of hypersaline environments and the mechanisms of adaptation of microorganisms to these extreme environments, as well as the isolation and characterization of the most abundant microorganisms in these habitats.
Another aspect that our group is currently studying is the application of genomic techniques in microbial systematics. At present, the main phylogenetic marker used in the taxonomy of prokaryotes is the 16S rRNA gene, although it has certain limitations such as its high degree of conservation that does not allow to distinguish in many cases between closely related species, its high frequency of recombination between nearby strains or the presence of multiple divergent copies. For this reason, we have carried out several studies based on alternative phylogenetic markers, to carry out an analysis by multilocic sequencing (MLSA), studying both the individual sequences of housekeeping genes and the concatenated sequences. Among the groups studied are bacteria belonging to the family Halomonadaceae or archaea of %u200B%u200Bthe genus Halorubrum.
In this last group we have performed a comparative analysis of the MLSA scheme with respect to DNA-DNA hybridization (which has allowed us to validate this scheme), as well as with respect to the composition of polar lipids by high-resolution thin-layer chromatography ( widely used in this group of archaea as a chemotaxonomic marker) and the sequencing and comparative analysis of some complete genomes.
Universidad de Alicante
Carretera de San Vicente del Raspeig s/n
03690 San Vicente del Raspeig
Tel: (+34) 96 590 3400Fax: (+34) 96 590 3464