| タイトル |
Phylogenetic analyses of the genus Glaciecola: emended description of the genus Glaciecola, transfer of Glaciecola mesophila, G. agarilytica, G. aquimarina, G. arctica, G. chathamensis, G. polaris and G. psychrophila to the genus Paraglaciecola gen. nov. as Paraglaciecola mesophila comb. nov., P. agarilytica comb. nov., P. aquimarina comb. nov., P. arctica comb. nov., P. chathamensis comb. nov., P. polaris comb. nov. and P. psychrophila comb. nov., and description of Paraglaciecola oceanifecundans sp. nov., isolated from the Southern Ocean.
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| Abstract |
Phylogenetic analyses of the genus Glaciecola were performed using the sequences of the 16S rRNA gene and the GyrB protein to establish its taxonomic status. The results indicated a consistent clustering of the genus Glaciecola into two clades, with significant bootstrap values, with all the phylogenetic methods employed. Clade 1 was represented by seven species, Glaciecola agarilytica, G. aquimarina, G. arctica, G. chathamensis, G. mesophila, G. polaris and G. psychrophila, while clade 2 consisted of only three species, Glaciecola nitratireducens, G. pallidula and G. punicea. Evolutionary distances between species of clades 1 and 2, based on 16S rRNA gene and GyrB protein sequences, ranged from 93.0 to 95.0 % and 69.0 to 73.0 %, respectively. In addition, clades 1 and 2 possessed 18 unique signature nucleotides, at positions 132, 184 : 193, 185 : 192, 230, 616 : 624, 631, 632, 633, 738, 829, 1257, 1265, 1281, 1356 and 1366, in the 16S rRNA gene sequence and can be differentiated by the occurrence of a 15 nt signature motif 5'-CAAATCAGAATGTTG at positions 1354-1368 in members of clade 2. Robust clustering of the genus Glaciecola into two clades based on analysis of 16S rRNA gene and GyrB protein sequences, 16S rRNA gene sequence similarity of ≤95.0 % and the occurrence of signature nucleotides and signature motifs in the 16S rRNA gene suggested that the genus should be split into two genera. The genus Paraglaciecola gen. nov. is therefore created to accommodate the seven species of clade 1, while the name Glaciecola sensu stricto is retained to represent species of clade 2. The species of clade 1 are transferred to the genus Paraglaciecola as Paraglaciecola mesophila comb. nov. (type strain DSM 15026(T) = KMM 241(T)), P. agarilytica comb. nov. (type strain NO2(T) = KCTC 12755(T) = LMG 23762(T)), P. aquimarina comb. nov. (type strain GGW-M5(T) = KCTC 32108(T) = CCUG 62918(T)), P. arctica comb. nov. (type strain BSs20135(T) = CCTCC AB 209161(T) = KACC 14537(T)), P. chathamensis comb. nov. (type strain E3(T) = CGMCC 1.7001(T) = JCM 15139(T)), P. polaris comb. nov. (type strain ARK 150(T) = CIP 108324(T) = LMG 21857(T)) and P. psychrophila comb. nov. (type strain 170(T) = CGMCC1.6130(T) = JCM 13954(T)). The type species of the genus Paraglaciecola is Paraglaciecola mesophila. An emended description of the genus Glaciecola is provided. In addition, a novel strain, 162Z-12(T), was isolated from seawater collected as part of an iron fertilization experiment (LOHAFEX) conducted in the Southern Ocean in 2009 and was subjected to polyphasic taxonomic characterization. Cells of 162Z-12(T) were Gram-negative, aerobic, motile, ovoid to short rod-shaped, obligatorily halophilic and possessed all the characteristics of the genus Paraglaciecola. Strain 162Z-12(T) shared the highest 16S rRNA gene sequence similarity with the type strains of P. agarilytica (99.7 %), P. chathamensis (99.7 %), P. mesophila (98.5 %) and P. polaris (98.3 %). However, it exhibited DNA-DNA relatedness of less than 70.0 % with its nearest phylogenetic relatives, well below the threshold value for species delineation. Further, strain 162Z-12(T) differed from the nearest species in several phenotypic characteristics, in addition to the occurrence of unique nucleotides G, T, T and T at positions 1194, 1269, 1270 and 1271 of the 16S rRNA gene. Based on the cumulative differences it exhibited from its nearest phylogenetic neighbours, strain 162Z-12(T) was identified as a novel member of the genus Paraglaciecola and assigned to the novel species Paraglaciecola oceanifecundans sp. nov. The type strain of Paraglaciecola oceanifecundans is 162Z-12(T) ( = KCTC 32337(T) = LMG 27453(T)).
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