Reclassification of Angiococcus disciformis, Cystobacter minus and Cystobacter violaceus as Archangium disciforme comb. nov., Archangium minus comb. nov. and Archangium violaceum comb. nov., unification of the families Archangiaceae and Cystobacteraceae, and emended descriptions of the families Myxococcaceae and Archangiaceae

Abstract

The species Archangium gephyra, Angiococcus disciformis, Cystobacter minus and Cystobacter violaceus are currently classified in three different genera of the order Myxococcales. The 16S rRNA gene sequences of the respective type strains show a similarity higher than 98.4 % and form a tight phylogenetic group. A dendrogram calculating the similarity of MALDI-TOF spectra confirmed the close relatedness of the four species that grouped in a monophyletic cluster in the neighbourhood of other species of the genus Cystobacter. The type strains shared similar fatty acid patterns of high complexity with iso-C 15 : 0 , C 16 : 1 v5c and iso-C 14 : 0 3-OH as the major components. The vegetative cells of these species are uniformly long needle-shaped rods, and the myxospores are short rods, ovoid or irregularly spherical thus differing from the myxospores of species related to Cystobacter fuscus, the type species of this genus. Some enzymic and hydrolysing reactions of the type strains are described. As a result of the high relatedness and similarity of the four species, it is proposed to place them into one genus, and due to phylogenetic and morphological distinctness, the species should be classified in a genus distinct from the genus Cystobacter as Archangium gephyra (type strain M18 T 5DSM 2261 T 5ATCC 25201 T 5NBRC 100087 T), Archangium disciforme comb. nov. (type strain CMU 1 T 5DSM 52716 T 5ATCC 33172 T), Archangium minus comb. nov. (proposed neotype strain Cb m25DSM 147515JCM 12627) and Archangium violaceum comb. nov. (type strain Cb vi61 T 5DSM 14727 T 5CIP 109131 T 5JCM 12629 T). Since the family Archangiaceae Jahn 1924 AL has priority over the family Cystobacteraceae McCurdy 1970 AL, it is proposed to assign the genera Archangium, Anaeromyxobacter, Cystobacter, Hyalangium, Melittangium and Stigmatella to the family Archangiaceae. Emended descriptions of the families Myxococcaceae and Archangiaceae are also provided. At times when morphology was the most important feature in the taxonomy of myxobacteria, four species had been assigned to three different genera. Archangium gephyra, Angiococcus disciformis (listed as Myxococcus disciformis, see below for details) and Cystobacter minus are listed in the Approved Lists of Bacterial Names (AL) (Skerman et al., 1980) and Cystobacter violaceus was described in Abbreviations: AL, Approved Lists of Bacterial Names (Skerman et al., 1980); ECL, equivalent chain-length; MALDI-TOF, matrix-assisted laser desorption/ionization time-of-flight. Four supplementary tables are available with the online Supplementary Material.

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