Criteria for Species Delineation in the Ectothiorhodospiraceae
In a recent taxonomic revision of the family Ectothiorhodospiraceae , 16S rRNA analysis and coherent physiological properties were used to delineate two distinct genera, Ectothiorhodospira and Halorhodospira. Less halophilic species have been recognized as belonging to Ectothiorhodospira, while highly halophilic species have been assigned to Halorhodospira. Key features of the family Ectothiorhodospiraceae, and of the two genera belonging to it have been summarized in Table 1. Essentially on the basis of 16S rRNA sequence analysis, two new species of Ectothiorhodospira have been described and the existing species have been validated . The family Ectothiorhodospiraceae, as presently defined, thus houses the species Ect. mobilis, Ect. shaposhnikovii, Ect. marina, Ect. maris-mortui, Ect. haloalkaliphila and Ect. vacuolata; Hlr. halophila, Hlr. halochloris and Hlr. abdelmalekii. However, there is still incoherence between this species subdivision and some phenotypic and genotypic traits described for strains of Ectothiorhodospiraceae. Moreover, it is a common understanding that taxonomic relationships among highly correlated bacteria cannot be determined on the sole basis of 16S rRNA sequence similarities [2,3]. In the present contribution, the taxonomic status of the Ectothiorhodospiraceae have been thus reconsidered integrating phenotypic and genotypic data taken from the literature with new experimental results recently obtained in our laboratory. The following characters have been considered. Salt concentration for optimal growth [4,5]; quinone composition [6,7]; fatty acid composition ; lipopolysaccharide composition [8,9]; porins ; G+C% content [5,11-16]; DNA reassociation ; 16S+23S rDNA RFLP (ribotype) ; ARDRA (see the Results section below); 16S rRNA sequence .
KeywordsRestriction Profile Species Delineation Halophilic Species Salt Optimum Genotypic Trait
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