The Mannitol Utilization System of the Marine Bacterium Zobellia galactanivorans
Résumé
Mannitol is a polyol which occurs in a wide range of living organisms where it fulfills different physiological roles. Particularly, mannitol can account up to 20-30% of the dry weight of brown algae, and is likely to be an important source of carbon for marine heterotrophic bacteria. Zobellia galactanivorans (Flavobacteria) is a model to study pathways involved in degradation of seaweed carbohydrates. Annotation of its genome revealed the presence of genes potentially involved in mannitol catabolism, and we describe here the biochemical characterization of a recombinant mannitol-2-dehydrogenase (M2DH) and of a fructokinase (FK). Among the observations, the M2DH of Z. galactanivorans was active as a monomer, did not require metal ions for catalysis, and features narrow substrate specificity. The characterized FK was active on fructose and mannose in presence of a monocation, preferentially K+. Furthermore, genes coding for both proteins were adjacent in the genome, and located directly downstream three loci likely to encode an ATP binding cassette (ABC) transporter complex, suggesting organization into an operon. Gene expression analysis supported this hypothesis, and showed the induction of these five genes after culturing Z. galactanivorans in presence of mannitol as sole source of carbon. This operon for mannitol catabolism was identified in only six genomes of Flavobacteriaceae among the 76 publicly available at the time of the analysis. It is not conserved in all Bacteroidetes because some species contained a predicted mannitol permease instead of a putative ABC transporter complex upstream M2DH and FK ortholog genes.
Domaines
Sciences du Vivant [q-bio]
Origine : Fichiers produits par l'(les) auteur(s)
Loading...