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    STUDIA BIOLOGIA - Issue no. 1 / 2019  
         
  Article:   HALONOTIUS SPECIES GENOME-SCALE METABOLIC RECONSTRUCTIONS OF NEW DESIGNATED COBALAMIN SYNTHESIS AS A BLACK QUEEN (BQ) FUNCTION IN HALOARCHAEA.

Authors:  ANA DURÁN-VISERAS, ADRIAN-ȘTEFAN ANDREI, ROHIT GHAI, CRISTINA SÁNCHEZ-PORRO, ANTONIO VENTOSA.
 
       
         
  Abstract:  Hypersaline aquatic and terrestrial ecosystems display a cosmopolitan distribution. These environments teem with microbes and harbour a plethora of prokaryotic lineages that evaded ecological characterization due to the prior inability to cultivate them or to access their genomic information. In order to close the current knowledge gap, we performed two sampling and isolation campaigns in saline soils of the Odiel Saltmarshes and the salterns of Isla Cristina (Huelva, Spain). From the isolated haloarchaeal strains subjected to high-throughput phylogenetic screening, two were chosen (F9-27 and F15B) for physiological and genomic characterization because of their relatedness to the genus Halonotius. The topology of the phylogenomic tree based on 257 conserved protein sequences showed agreement with the phylogenetic ones based on 16S rRNA and rpoB´ genes, and together with average amino acid and nucleotide identities designated the two strains as novel species within the genus. We propose the names Halonotius roseus sp. nov. and Halonotius terrestris sp. nov. for the newly described strains. Comparative genomic analyses within the genus highlighted a typical ”salt-in” signature (characterised by acidic proteomes with low isoelectric points) and indicated heterotrophic aerobic lifestyles. Genome-scale metabolic reconstructions revealed that the newly proposed species, together with environmentally-recovered metagenome-assembled representatives, encode all the necessary enzymatic reactions involved in cobalamin (vitamin B12) biosynthesis. Based on the worldwide distribution of the genus and its high abundance in hypersaline habitats we postulate that its members perform a critical Black Queen function within the halophilic communities.

Keywords: Black Queen function, cobalamin, Halonotius, metabolic reconstruction, phylogenomics.
 
         
     
         
         
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