- Volume 70, Issue 7, 2020

We here present annotated lists of names of Candidatus taxa of prokaryotes with ranks between subspecies and class, proposed between the mid-1990s, when the provisional status of Candidatus taxa was first established, and the end of 2018. Where necessary, corrected names are proposed that comply with the current provisions of the International Code of Nomenclature of Prokaryotes and its Orthography appendix. These lists, as well as updated lists of newly published names of Candidatus taxa with additions and corrections to the current lists to be published periodically in the International Journal of Systematic and Evolutionary Microbiology, may serve as the basis for the valid publication of the Candidatus names if and when the current proposals to expand the type material for naming of prokaryotes to also include gene sequences of yet-uncultivated taxa is accepted by the International Committee on Systematics of Prokaryotes.

A polyphasic taxonomic study was performed on an unidentified Arcanobacterium -like Gram-stain-positive bacterium designated strain C605018/01/1T isolated from a milk sample collected from the udder of a cow at post mortem. Comparative 16S rRNA gene sequencing showed that the bacterium belonged to the genus Arcanobacterium and was most closely related to the type strain of Arcanobacterium pluranimalium (99.76 %); sequence similarities to all other Arcanobacterium species were below 97 %. The wet-lab DNA–DNA hybridization values among strain C605018/01/1T and A. pluranimalium DSM 13483ᵀ were low, 16.9 % (reciprocal, 49.8 %). Pertaining to the whole genome sequence with a total length of 2.02 Mb and 1654 protein counts, the novel strain C605018/01/01T displayed a G+C content of 51.6 % mol%. The presence of the major menaquinone MK-9(H4) supported the affiliation of this strain to the genus Arcanobacterium . The polar lipid profile consisted of the major components diphosphatidylglycerol, phosphatidylcholine, phosphatidylinositol, phosphatidylinositol-mannoside and unidentified glycolipid and aminophospholipids. Based on these results it is proposed that strain C605018/01/1T should be classified as representing a novel species, Arcanbacterium bovis sp. nov. The type strain C605018/01/1T (CCUG 45425T=DSM 107286T=BCCM/LMG 30783T)

A novel moderately halophilic, filamentous actinobacterium, designated as XMNu-373T, was isolated from a saline–alkaline soil sample collected from the Mongolia Plateau, Dongwu County, Inner Mongolia Autonomous Region, PR China. The isolate grew optimally at 28‒37 °C, pH 7.0‒8.0 and with 2–5 % (w/v) NaCl. The substrate mycelia fragmented into rod-like elements, and the white aerial mycelia formed spore chains at maturity. The predominant menaquinone was MK-9(H4). The polar lipids were diphosphatidylglycerol, three unidentified phosphoglycolipids, an unidentified aminophospholipid, two phosphatidylinositol mannosides, four unidentified phospholipids, phosphatidylglycerol and two unidentified lipids. The major cellular fatty acids were iso-C16 : 0, anteiso-C17 : 0 and anteiso-C15 : 0. The genomic DNA G+C content was 66.2 mol%. It shared high 16S rRNA gene sequence similarities to Phytoactinopolyspora halotolerans YIM 96448T (96.1 %) and Phytoactinopolyspora endophytica EGI 60009T (96.0 %). Phylogenetic trees based on 16S rRNA gene sequences revealed that strain XMNu-373T resided in the clade of family Jiangellaceae , and it formed a monophyletic branch distinct from four other recognized type species in the subclade of the genus Phytoactinopolyspora . On the basis of polyphasic taxonomic evidence, strain XMNu-373T represents a novel species of the genus Phytoactinopolyspora , for which the name Phytoactinopolyspora mesophila sp. nov. is proposed. The type strain is XMNu-373T (=JCM 33740T=CGMCC 4.7654T).

We investigated the taxonomic relationships among Streptomyces diastaticus subsp. ardesiacus , Streptomyces diastaticus subsp. diastaticus , Streptomyces gougerotii and Streptomyces rutgersensis . The 16S rRNA gene sequence similarity between S. diastaticus subsp. ardesiacus and S. diastaticus subsp. diastaticus was 97.7 %, whereas S. diastaticus subsp. diastaticus , S. gougerotii and S. rutgersensis showed 100 % nucleotide sequence identity. In addition, S. diastaticus subsp. diastaticus, S. gougerotii and S. rutgersensis formed a single clade in the phylogenetic tree. Digital DNA–DNA relatedness between S. diastaticus subsp. diastaticus and S. diastaticus subsp. ardesiacus was only 22.8%, indicative of different species. In comparison, DNA–DNA relatedness values for S. diastaticus subsp. diastaticus , S. gougerotii and S. rutgersensis ranged from 95.8 to 97.2 %, suggesting the three taxa belong to the same genomospecies. Previously reported phenotypic data also supported synonymy. Therefore, we propose that S. diastaticus subsp. ardesiacus should be classified as an independent species, Streptomyces ardesiacus sp. nov. The type strain is NBRC 13412T (=ATCC 3315T=CBS 713.72T=DSM 40496T=ISP 5496T=JCM 4745T=NBRC 3714T=NRRL B-1241T=RIA 1373T). Our data also suggests that S. rutgersensis and S. gougerotii should be reclassified as later heterotypic synonyms of S. diastaticus .

A novel Gram-positive, aerobic and motile endophytic actinomycete, designated TRM 65233T, was isolated from the root of Peganum harmala L. collected from Xinjiang Uygur Autonomous Region of China. The isolate had white aerial mycelium and brown substrate mycelium on Gause’s synthetic agar. Growth occurred at 10–40 °C, pH 6–9 with NaCl concentration of 0–6 % (w/v). Strain TRM 65233T contained meso-diaminopimelic acid as the diagnostic diamino acid in the cell-wall peptidoglycan. The whole-cell hydrolysates included glucose and galactose as the major whole-cell sugars. The menaquinones were MK-9 (H4) and MK-7. The major cellular fatty acids were iso-C16 : 0, iso-C15 : 0 and anteiso-C17 : 0. The polar lipid profile consisted of diphosphatidylglycerol, phosphatidylglycerol, phospholipids, phosphatidylinositol and one unidentified lipid. Strain TRM 65233T showed the highest 16S rRNA gene sequence similarity to Actinokineospora cianjurensis BTCC B-558T (98.13 %), Actinokineospora auranticolor IFO 16518T (98.06 %), Actinokineospora spheciospongiae EG49T (97.99 %), Actinokineospora baliensis ID03-0561T (97.97 %), Actinokineospora mzabensis PAL84T (97.95 %) and Actinokineospora bangkokensis 44EHWT (97.06 %). The isolate was distinguished from these phylogenetically related strains by digital DNA–DNA hybridization and average nucleotide identity analyses and by a range of physiological and biochemical characteristics. The G+C content of the genomic DNA was 72.6 mol%. On the basis of polyphasic taxonomic data, strain TRM 65233T represents a novel species of the genus Actinokineospora , for which the name Actinokineospora pegani sp. nov. is proposed. The type strain is TRM 65233T (KCTC 49342=CCTCC AA 2019050).

Three novel carbon monoxide-oxidizing Halobacteria were isolated from Bonneville Salt Flats (Utah, USA) salt crusts and nearby saline soils. Phylogenetic analysis of 16S rRNA gene sequences revealed that strains PCN9T, WSA2T and WSH3T belong to the genera Halobacterium , Halobaculum and Halovenus , respectively. Strains PCN9T, WSA2T and WSH3T grew optimally at 40 °C (PCN9T) or 50 °C (WSA2T, WSH3T). NaCl optima were 3 M (PCN9T, WSA2T) or 4 M NaCl (WSH3T). Carbon monoxide was oxidized by all isolates, each of which contained a molybdenum-dependent CO dehydrogenase. G+C contents for the three respective isolates were 66.75, 67.62, and 63.97 mol% as derived from genome analyses. The closest phylogenetic relatives for PCN9T, WSA2T and WSH3T were Halobacterium noricense A1T, Halobaculum roseum D90T and Halovenus aranensis EB27T with 98.71, 98.19 and 95.95 % 16S rRNA gene sequence similarities, respectively. Genome comparisons of PCN9T with Halobacterium noricense A1T yielded an average nucleotide identity (ANI) of 82.0% and a digital DNA–DNA hybridization (dDDH) value of 25.7 %; comparisons of WSA2T with Halobaculum roseum D90T yielded ANI and dDDH values of 86.34 and 31.1 %, respectively. The ANI value for a comparison of WSH3T with Halovenus aranensis EB27T was 75.2 %. Physiological, biochemical, genetic and genomic characteristics of PCN9T, WSA2T and WSH3T differentiated them from their closest phylogenetic neighbours and indicated that they represent novel species for which the names Halobaculum bonnevillei, Halobaculum saliterrae and Halovenus carboxidivorans are proposed, respectively. The type strains are PCN9T (=JCM 32472=LMG 31022=ATCC TSD-126), WSA2T (=JCM 32473=ATCC TSD-127) and WSH3T (=JCM 32474=ATCC TSD-128).

A marine strain, designated KK4T, was isolated from the surface of a starfish, Patiria pectinifera, which was collected from seawater off the coast of Hokkaido, Japan. Strain KK4T is a Gram-stain-negative, non-spore-forming, rod-shaped, aerobic bacterium that forms yellow-pigmented colonies. A phylogenetic relationship analysis, based on 16S rRNA gene sequences, revealed that strain KK4T was closely related to Ulvibacter marinus IMCC12008T, Ulvibacter antarcticus IMCC3101T and Ulvibacter litoralis KMM 3912T, with similarities of 96.9, 95.8 and 95.6 %, respectively, but low sequence similarities (<94 %) among other genera in the family Flavobacteriaceae . Genomic similarities between strain KK4T and the three Ulvibacter type strains based on average nucleotide identity and digital DNA–DNA hybridization values were lower than the species delineation thresholds. Moreover, phylogenetic tree based on genome sequences showed that strain KK4T was clustered with U. marinus IMCC12008T and formed a branch independent from the cluster including type species of the genera Ulvibacter , Marixanthomonas , Marinirhabdus , Aureitalea and Aequorivita . Amino acid identity values between strain KK4T/ U. marinus IMCC12008T and the neighbour type species/strains were 61.9–68.2% and 61.5–67.4 %, which were lower than the genus delineation threshold, implying the novel genus status of strain KK4T. Strain KK4T growth occurred at pH 6.0–9.0, 4–30 °C and in NaCl concentrations of 0.5–5.0 %, and optimally at pH 7.0, 25 °C and 3.0 %, respectively. Unlike Ulvibacter strains, strain KK4T could assimilate glucose, mannose, galactose and acetate. The major quinone and fatty acids were menaquinone-6 and iso-C15 : 0 (27.5 %), iso-C15 : 1 G (22.5 %) and iso-C17 : 0 3-OH (12.8 %), respectively. Based on genetic, phylogenetic and phenotypic properties, strain KK4T represents a novel species of the genus Patiriisocius, for which the name Patiriisocius marinistellae gen. nov., sp. nov. is proposed. The type strain is KK4T (=JCM 33344T=KCTC 72225T). In addition, based on the current data, Ulvibacter marinus should be reclassified as Patiriisocius marinus comb. nov.

Strains of Echinicola , thought to play vital roles in the environment for their high enzyme production capacity during decomposition of polysaccharides, are ubiquitous in hypersaline environments. A Gram-negative, non-spore forming, gliding, aerobic bacterial strain, designated LN3S3T, was isolated from alkaline saline soil sampled in Tumd Right Banner, Inner Mongolia, northern PR China. Strain LN3S3T grew at 10–40 °C (optimum, 30 °C), pH 5.0–9.0 (optimum, pH 8.0) and with 0–12.5 % NaCl (optimum, 2.0 %). A phylogenetic tree based on the 16S rRNA gene sequences showed that strain LN3S3T clustered with Echinicola rosea JL3085T and Echinicola strongylocentroti MEBiC08714T, sharing 97.0, 96.7 and <96.50 % of 16S rRNA gene sequence similarities to E. rosea JL3085T, E. strongylocentroti MEBiC08714T and all other type strains. MK-7 was the major respiratory quinone, while phosphatidylethanolamine, two unidentified phospholipids, an unidentified aminophospholipid, an unidentified lipid and two unidentified aminolipids were the major polar lipids. Its major cellular fatty acids were iso-C15 : 0, anteiso-C15 : 0 and summed feature 3 (C16 : 1  ω7c and/or C16 : 1  ω6c). The genome consisted of a circular 5 550 304 bp long chromosome with a DNA G+C content of 44.0 mol%. The average nucleotide identity (ANI), average amino acid identity (AAI) and digital DNA–DNA hybridization (dDDH) values of strain LN3S3T to E. rosea JL3085T and E. strongylocentroti MEBiC08714T were 82.5 and 81.5 %, 87.5 and 86.0 %, and 39.1 and 35.1 %, respectively. Based on physiological, genotypic and phylogenetic analyses, strain LN3S3T could be discriminated from its phylogenetic relatives. Echinicola soli sp. nov. is therefore proposed with strain LN3S3T (=CGMCC 1.17081T=KCTC 72458T) as the type strain.

A Gram-stain-negative, facultative anaerobic, red-pigmented, rod-shaped and non-motile strain (RC1_OXG_1FT) was isolated from deep sea water of the Indian Ocean. It was able to grow at pH 5–8 (optimum, pH 7), at 5–37 °C (optimum, 30 °C), and at salinity (% NaCl, w/v) of 0.5–5 % (optimum, 1–2 %). Catalase- and oxidase-positive. It had highest 16S rRNA gene similarity (96.7 %) to ‘ Sunxiuqinia dokdonensis ’ DH1T, followed by Sunxiuqinia faeciviva JAM-BA0302T (96.6 %), Sunxiuqinia elliptica CGMCC 1.9156T (96.2 %), Sunxiuqinia rutila HG677T (96.0 %) and species (less than 92.3 %) of other genera. It belongs to the genus Sunxiuqinia within the phylum Bacteroidetes , based on the phylogenetic analysis. The results of digital DNA–DNA hybridization and average nucleotide identity analyses indicated that the strain belonged to a novel species. Its genome size is 5,250, 885 bp, with DNA G+C content of 40.5 mol%. Genome analysis revealed that the strain possessed many genes involved in polysaccharide degradation, especially hemicellulose degradation, indicating that the strain could maintain its normal metabolism by using recalcitrant organic matter in the oligotrophic deep sea environment. Its principal fatty acids were anteiso-C15 : 0 and iso-C15 : 0 and the major polar lipids were phosphatidylethanolamine, two unidentified glycolipids, three unidentified phospholipids and two unidentified polar lipids. The isoprenoid quinone was MK-7. Based on the phenotypic, chemotaxonomic and genotypic data, the strain represents a novel species within the genus Sunxiuqinia , for which the name Sunxiuqinia indica sp. nov. is proposed. The type strain is RC1_OXG_1FT (=MCCC 1A13858T=KCTC 62805T).

A Gram-stain-negative, short-rod-shaped and pink-pigmented bacterial strain (HB172049T) was isolated from mangrove sediment. Cells grew at 10–45 °C (optimum, 30 °C), pH 6.0–9.0 (optimum, pH 7.0) and with 0.5–9.0 % (w/v) NaCl (optimum, 2–5 %). Analysis of the 16S rRNA gene sequence revealed that the isolate had highest sequence similarities to Pontibacter mucosus DSM 100162T (96.5 %) and Pontibacter korlensis X14-1T (96.5 %). The values of average nucleotide identity, average amino acid identity and digital DNA–DNA hybridization between the isolate and its close neighbours were, respectively, less than 80.1, 81.7 and 23.2 %. Chemotaxonomic analysis indicated that the sole respiratory quinone was MK-7 and the predominant cellular fatty acids were summed feature 4 and iso-C15 : 0 (42.2 and 24.6 %, respectively). The major polar lipids consisted of phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylglycerol, one unidentified glycolipid, one unidentified phospholipid, one unidentified aminophospholipid and two unidentified polar lipids. The genomic DNA G+C content was 52.6 mol%. Based on polyphasic taxonomic characterization, it is proposed that strain HB172049T belongs to the genus Pontibacter and represents a novel species, for which the name Pontibacter mangrovi sp. nov. is proposed. The type strain is HB172049T (=CGMCC 1.16729T=JCM 33333T).

Two yellow-pigmented, Gram-stain-negative, aerobic, rod-shaped bacteria were isolated from the water of the hypersaline Chaka Salt Lake (strain SaA2.12T) and sediment of Qinghai Lake (strain LaA7.5T), PR China. According to the 16S rRNA phylogeny, the isolates belong to the genus Flavobacterium , showing the highest 16S rRNA sequence similarities to Flavobacterium arcticum SM1502T(97.6–97.7 %) and Flavobacterium suzhouense XIN-1T(96.5–96.6 %). Moreover, strains SaA2.12T and LaA7.5T showed 99.73 % 16S rRNA sequence similarity to each other. Major fatty acids, respiratory quinones and polar lipids detected in these isolates were iso-C15 : 0, menaquinone-6 and phosphatidylethanolamine, respectively. Strains SaA2.12T and LaA7.5T showed significant unique characteristics between them as well as between the closest phylogenetic members. The highest digital DNA–DNA hybridization (dDDH) and average nucleotide identity (ANI) values between SaA2.12T and its closest neighbours were 25.3 and 82.8 %, respectively; whereas these values (highest) between LaA7.5T and its closest members were 25.2 and 82.8 %, respectively. The dDDH and ANI values between strains SaA2.12T and LaA7.5T were calculated as 75.9 and 97.2 %, respectively. Therefore, based on polyphasic data, we propose that strain SaA2.12T represents a novel species with the name Flavobacterium salilacus sp. nov., with the type strain SaA2.12T (=KCTC 72220T=MCCC 1K03618T) and strain LaA7.5T as a subspecies within novel Flavobacterium salilacus with the name Flavobacterium salilacus subsp. altitudinum subsp. nov., with the type strain LaA7.5T (=KCTC 72806T=MCCC 1K04372T). These propositions automatically create Flavobacterium salilacus subsp. salilacus subsp. nov. with SaA2.12T (=KCTC 72220T=MCCC 1K03618T) as the type strain.

A novel, facultatively anaerobic actinobacterium, designated strain CBA3103T, was isolated from sediment of the Geum River in South Korea. Phylogenetic analysis indicated that strain CBA3103T is most closely related to Raineyella antarctica LZ-22T (98.47 % 16S rRNA gene sequence similarity). The genome of strain CBA3103T was 3 649 865 bp with a DNA G+C content of 69.6 mol%. The average nucleotide identity value between strain CBA3103T and R. antarctica LZ-22T was 79.22 %. Cells of strain CBA3103T were Gram-positive, rod-shaped, 0.6–0.9 µm wide and 1.4–2.4 µm long. Growth occurred at 15–40 °C (optimum, 35 °C), at pH 6.0–7.0 (optimum, pH 7.0) and with 0–2 % NaCl (w/v) (optimum, 0–1 %, w/v). The major cellular fatty acids in strain CBA3103T were anteiso-C15 : 0, anteiso-C15 : 1 A and iso-C14 : 0. The major respiratory quinone was menaquinone-9(H4). The polar lipids of strain CBA3103T were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, five unidentified glycolipids and three unidentified phospholipids. Based on the genotypic, phenotypic and chemotaxonomic analyses, strain CBA3103T represents a novel species of the genus Raineyella , for which the name Raineyella fluvialis sp. nov. (type strain CBA3103T=KACC 21446T=DSM 110288T) is proposed.

A new member of the family Flavobacteriaceae was isolated from the biofilm of a stone at Nordstrand, a peninsula at the German North Sea shore. Phylogenetic analysis of the 16S rRNA gene sequence showed that strain ANORD1T was most closely related to the validly described type strains Polaribacter porphyrae LNM-20T (97.0 %) and Polaribacter reichenbachii KMM 6386T (96.9 % 16S rRNA gene sequence similarity) and clustered with Polaribacter gangjinensis K17-16T (96.0 %). Strain ANORD1T was determined to be mesophilic, Gram-negative, non-motile and strictly aerobic. Optimal growth was observed at 20–30 °C, within a salinity range of 2–7 % sea salt and from pH 7–10. Like other type strains of the genus Polaribacter , ANORD1T was tested negative for flexirubin-type pigments, while carotenoid-type pigments were detected. The DNA G+C content of strain ANORD1T was 30.6 mol%. The sole respiratory quinone detected was menaquinone 6 (MK-6). The major fatty acids identified were C15 : 0, iso-C15 : 0, C15 : 1 ω6c and iso-C15 : 0 3-OH. Based on the polyphasic approach, strain ANORD1T represents a novel species in the genus Polaribacter , with the name Polaribacter septentrionalilitoris sp. nov. being proposed. The type strain is ANORD1T (=DSM 110039T=NCIMB 15081T=MTCC 12685T).

A novel marine Gram-stain-negative, non-motile, aerobic and rod-shaped bacterium, designated as strain MT-229T, was isolated from the deep seawater in the Mariana Trench and characterized phylogenetically and phenotypically. Bacterial optimal growth occurred at 30 °C (ranging 10–40 °C), pH 6 (ranging 3–11) and with 11 % (w/v) NaCl (ranging 0–17 %). Strain MT-229T was a piezophile, growing optimally at 20 MPa (range 0.1–70 MPa). The nearest phylogenetic neighbours were Muricauda antarctica CGMCC 1.2174T and Muricauda taeanensis JCM 17757T with 16S rRNA gene similarity of 98.7 %. The sole respiratory quinone was menaquinone-6 (MK-6). The major polar lipids were phosphatidylethanolamine (PE), two unidentified aminolipids (AL) and ten unidentified lipids. The major fatty acids of strain MT-229T were iso-C15 : 0, iso-C17 : 0 3-OH and iso-C15 : 1 G. The G+C content of the genomic DNA was 45.6 mol%. The combined genotypic and phenotypic data indicated that strain MT-229T represents a novel species of the genus Muricauda , for which the name Muricauda hadalis sp. nov. is proposed, with the type strain MT-229T (=DSM 109894T=MCCC 1K04201T). In addition, the whole-genome-based comparisons revealed that the type strains of Muricauda antarctica and Muricauda teanensis belong to a single species. It is, therefore, proposed that M. antarctica be recognized as a heterotypic synonym of M. teanensis.

Strain ISS653T, isolated from Atlantic seawater, is a yellow pigmented, non-motile, Gram-reaction-negative rod-shaped bacterium, strictly aerobic and chemoorganotrophic, slightly halophilic (1–15 % NaCl) and mesophilic (4–37 °C), oxidase- and catalase-positive and proteolytic. Its major cellular fatty acids are iso-C15 : 0, iso-C15 : 0 2-OH, and iso-C17 : 0 3-OH; the major identified phospholipid is phosphatidylethanolamine and the major respiratory quinone is MK6. Genome size is 4.28 Mbp and DNA G+C content is 34.9 mol%. 16S rRNA gene sequence similarity places the strain among members of the family Flavobacteriaceae, with the type strains of Mesonia phycicola (93.2 %), Salegentibacter mishustinae (93.1 %) and Mesonia mobilis (92.9 %) as closest relatives. Average amino acid identity (AAI) and average nucleotide identity (ANI) indices show highest values with M. mobilis (81 % AAI; 78.9 % ANI), M. phycicola (76 % AAI; 76.3 % ANI), Mesonia maritima (72 % AAI, 74.9 % ANI), Mesonia hippocampi (64 % AAI, 70.8 % ANI) and Mesonia algae (68 % AAI; 72.2 % ANI). Phylogenomic analysis using the Up-to-date-Bacterial Core Gene set (UBCG) merges strain ISS653T in a clade with species of the genus Mesonia . We conclude that strain ISS653T represents a novel species of the genus Mesonia for which we propose the name Mesonia oceanica sp. nov., and strain ISS653T (=CECT 9532T=LMG 31236T) as the type strain. A second strain of the species, ISS1889 (=CECT 30008) was isolated from Pacific Ocean seawater. Data obtained throughout the Tara oceans expedition indicate that the species is more abundant in the mesopelagic dark ocean than in the photic layer and it is more frequent in the South Pacific, Indian and North Atlantic oceans.