Riemerella anatipestifer gen. nov., comb. nov., the Causative Agent of Septicemia Anserum Exsudativa, and Its Phylogenetic Affiliation within the Flavobacterium-Cytophaga rRNA Homology Group

Abstract

The phylogenetic position of the causative agent of septicemia anserum exsudativa, now most often referred to as [Moraxella] anatipestifer (brackets indicate a generically misnamed taxon) or "[Pasteurella] anatipestifer," was established by performing rRNA cistron similarity studies.[Moraxella] anatipestifer belongs to rRNA superfamily V, together with the genera Flavobacterium, Cytophuga, Fkxibacter, Weeksella, Capnocytophaga, and Sphingobacterium. The detailed structure of rRNA superfamily V, which now contains five major rRNA homology groups, is described. An analysis of various phenotypic parameters, including new data (cellular proteins and fatty acids) and previously published data (respiratory quinones, enzyme activities, and classical phenotypic features), revealed that [Moraxella] anatipestifer differs in many aspects from its closest relatives, Flavobacterium indologenes, Flavobacterium gleum, Flavobacterium indoltheticum, Flavobacterium balustinum , Flavobacterium meningosepticum, and Weekseh zoohelcum. The combined genotypic and phenotypic data indicate that this organism should be placed in a separate genus; the name Riemerella anatipestifer gen. nov., comb. nov. is proposed for this bacterium. The specific epithet anatipestifer is kept in order to avoid nomenclatural confusion. However, it should be emphasized that the illness caused by this organism is a septicemic disease which is not restricted to ducks.The epizootic infectious disease of domestic birds known as septicemia anserum exsudativa was first described ,by Riemer in 1904 (30). The taxonomic status of few other bacteria has been changed as often as the taxonomic status of the organism causing this disease. The phylogenetic position of this organism remained unsettled (it was classified in various genera with several specific epithets) from 1904 until 1986, when Piechulla and coworkers described for the first time its correct affiliation with the FlavobacteriumCytophaga group (29). An overview of this nomenclatural odyssey was given by Floren et al. (14). At present, the organism is most often referred to as [Moraxella] anatipestifer (brackets indicate a generically misnamed taxon) or " [Pasteurella] anatipestifer," and it is considered a species incertae sedis in Be%ey s Manual of Systematic Bacteriology (5,24). The numerous similarities between this organism and members of the Flavobacterium-Cytophaga group (lack of flagellation, low DNA base ratio, presence of menaquinones as the sole respiratory quinones, presence of branchedchain fatty acids in high percentages, absence of carbohydrate fermentation, and similar hydrolytic enzyme patterns) were significant parameters used to determine genomic relatedness, as shown by Rossau and coworkers (31). Rossau et al. also showed by performing a DNA-rRNA hybridization analysis that [Moraxella] anatipestifer indeed is not a close relative of the Muraxella or Pasteurella rRNA homology clusters but belongs to the Flavobacten'urn-Cytophaga rRNA homology cluster (31).The phylogenetic relationships...

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