Taxonomic Comments

Although salt requirements are obviously important properties for the taxonomic characterization of Chromatiaceae species, the congruence between phylogenetic position and salt response requires further attention in a few species. Species such as Allo-chromatium vinosum have been reported to occur in freshwater, brackish water, and marine habitats. Large differences in the mol% G + C content of the DNA of strains assigned to this species (61.3-66.3) may indicate genetic heterogeneity. So far, clear proof of identity of various isolates from marine habitats tentatively assigned to Allochromatium vinosum is lacking, because of improper physiological and genetic (DNA-DNA hybridization, 16S rDNA sequences) characterization. Further studies are needed, to show whether differences in base composition are related to the marine or freshwater nature of these bacteria.

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