Genomic-based taxonomic classification of the order Sphingomonadales

The order Sphingomonadales strains are globally distributed in various biomes and are renowned for their biodegradable and biosynthesis capabilities. At present, it consists of 4 families and 49 genera making it the third largest order within the class Alphaproteobacteria. However, their taxonomy remains complex, especially due to polyphyly in the family Sphingomonadaceae. In this study, we collected 429 Sphingomonadales type strain genomes, reconstructed robust phylogenomic relationships, and proposed delineation thresholds at the genus and family levels based on average amino acid identities (AAI) and evolutionary distances (ED). Based on the maximum-likelihood and Bayesian phylogenomic trees reconstructed by two molecular sets determined by orthologous sequence identity and the Genome Taxonomy Database, the consensus degree values were all higher than 90%, revealing that those phylogenomic trees had similar topological structures. By confirming monophyletic taxa and determining stable nodes, we reclassified the order Sphingomonadales into thirteen families including nine novel ones. AAI calculations indicated that the average intra-family AAI values ranged from 0.62 to 0.84, while inter-family ones were 0.51 to 0.60. ED summaries demonstrated that the average and median intra-family ED values were 0.16 to 0.57, and inter-family ones ranged from 0.50 to 1.22. Comparisons of AAI and ED values calculated by using genomic and phylogenetic analyses supported that those 13 families were significantly separated with p values < 2.2×10-16. Thus, it was speculated that the AAI and ED thresholds for distinguishing different families were <0.6 and >0.5, respectively. Additionally, we reclassified 163 species into new genera with their phylogenetic topologies, according to the previous genus AAI and ED boundaries of 0.7 and 0.4. Our study is the first genomic-based study of the order Sphingomonadales and will promote further insights into the evolution of this order.

Novosphingobium percolationis sp. nov. and Novosphingobium huizhouense sp. nov., isolated from landfill leachate of a domestic waste treatment plant

Two strains designated as c1T and c7T, were isolated from the landfill leachate of a domestic waste treatment plant in Huizhou City, Guangdong Province, PR China. The cells of both strains were aerobic, rod-shaped, non-motile and formed yellow colonies on Reasoner’s 2A agar plates. Strain c1T grew at 10–42 °C (optimum, 30 °C), pH 4.5–10.5 (optimum, pH 7.0) and 0–2.0 % (w/v) NaCl (optimum, 0–0.5 %). Strain c7T grew at 10–42 °C (optimum, 30 °C), pH 4.5–10.5 (optimum, pH 6.0) and 0–2.0 % (w/v) NaCl (optimum, 0–0.5 %). Phylogenetic analyses revealed that strains c1T and c7T belong to the genus Novosphingobium . The 16S rRNA gene sequence similarities of strains c1T and c7T to the type strains of Novosphingobium species were 94.5–98.2 % and 94.3–99.1 %, respectively. The calculated pairwise average nucleotide identity values among strains c1T, c7T and the reference strains were in the range of 75.2–85.9 % and the calculated pairwise average amino acid identity values among strains c1T, c7T and reference strains were in the range of 72.0–88.3 %. Their major respiratory quinone was Q-10, and the major cellular fatty acids were C18 : 1  ω7c, C18 : 0, C16 : 1  ω7c, C16 : 0 and C14 : 0 2OH. The major polar lipids of strains c1T and c7T were phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylglycerol, sphingoglycolipid, unidentified lipids and unidentified phospholipid. Based on phenotypic, chemotaxonomic, phylogenetic and genomic results from this study, strains c1T and c7T should represent two independent novel species of Novosphingobium , for which the names Novosphingobium percolationis sp. nov. (type strain c1T=GDMCC 1.2555T=KCTC 82826T) and Novosphingobium huizhouense sp. nov. (type strain c7T=GDMCC 1.2556T=KCTC 82827T) are proposed. The gene function annotation results of strains c1T and c7T suggest that they could play an important role in the degradation of organic pollutants.

Novosphingobium olei sp. nov., with the ability to degrade diesel oil, isolated from oil-contaminated soil and proposal to reclassify Novosphingobium stygium as a later heterotypic synonym of Novosphingobium aromaticivorans

Two yellow-pigmented, non-motile, Gram-stain-negative, and rod-shaped bacteria, designated TW-4^T and TNP-2 were obtained from oil-contaminated soil. Both strains degrade diesel oil, hydrolyse aesculin, DNA, Tween 40 and Tween 60. A phylogenetic analysis based on its 16S rRNA gene sequence revealed that strain TW-4^T formed a lineage within the family Erythrobacteraceae and clustered as members of the genus Novosphingobium. The closest members of strain TW-4^T were Novosphingobium subterraneum DSM 12447^T (97.9 %, sequence similarity), Novosphingobium lubricantis KSS165-70^T (97.8 %), Novosphingobium taihuense T3-B9^T (97.8 %), Novosphingobium aromaticivorans DSM 12444^T (97.7 %), Novosphingobium flavum UCT-28^T (97.7 %), and Novosphingobium bradum STM-24^T (97.6 %). The sequence similarity for other members was ≤97.6 %. The genome of strain TW-4^T was 4 683 467 bp long with 44 scaffolds and 4280 protein-coding genes. The sole respiratory quinone was Q-10. The major cellular fatty acids were summed feature 8 (C_18 : 1  ω7c and/or C_18 : 1  ω6c), summed feature 3 (C_16 : 1  ω7c and/or C_16 : 1  ω6c), C_16 : 0 and C_14 : 0 2-OH. The major polar lipids were phosphatidylethanolamine (PE), phosphatidylglycerol (PG), diphosphatidylglycerol (DPG), phosphatidylcholine (PC), phosphatidyl-n-methylethanolamine (PME) and sphingoglycolipid (SGL). The DNA G+C content of the type strain was 65.0 %. The average nucleotide identity (ANIu) and in silico DNA-DNA hybridization (dDDH) relatedness values between strain TW-4^T and closest members were below the threshold value for species delineation. Based on polyphasic taxonomic analyses, strain TW-4^T represents novel species in the genus Novosphingobium, for which the name Novosphingobium olei sp. nov. is proposed. The type strain is TW-4^T (=KACC 21628^T=NBRC 114364^T) and strain TNP-2 (=KACC 21629=NBRC 114365) represents an additional strain. Based on new data obtained in this study, it is also proposed to reclassify Novosphingobium stygium as a later heterotypic synonym of Novosphingobium aromaticivorans.

Novosphingobium fontis sp. nov., isolated from a spring

A bacterial strain designated STM-14T was isolated from a spring in Taiwan and characterized using a polyphasic taxonomic approach. Strain STM-14T was a Gram-stain-negative, aerobic, poly-β-hydroxybutyrate-accumulating, non-motile, rod-shaped bacterium and formed cream-coloured colonies. Strain STM-14T grew at 15-37 °C (optimum, 30 °C), at pH 5.0-9.0 (optimum, pH 6.0) and with 0-0.5 % (w/v) NaCl (optimum, 0 %). Phylogenetic analyses based on 16S rRNA gene sequences showed that strain STM-14T belonged to the genus Novosphingobium and showed the highest levels of sequence similarity to Novosphingobium naphthae D39T (98.5 %) and Novosphingobium mathurense SM117T (97.6 %). The major fatty acids (>10 %) of strain STM-14T were C17 : 1ω6c, summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c), C18 : 1ω7c, C15 : 0 2-OH and C17 : 1ω8c. The polar lipid profile consisted of phosphatidylglycerol, phosphatidylethanolamine, diphosphatidylglycerol, phosphatidyldimethylethanolamine, sphingoglycolipid, phosphatidylcholine and several uncharacterized lipids. The major polyamine was spermidine. The major isoprenoid quinone was Q-10. The DNA G+C content was 66.6 mol%. The DNA-DNA hybridization value for strain STM-14T with N. naphthae JCM 31158T and N. mathurense DSM 23374T was less than 49 %. Differential phenotypic properties, together with the phylogenetic inference, demonstrate that strain STM-14T should be classified as representing a novel species of the genus Novosphingobium, for which the name Novosphingobium fontis sp. nov. is proposed. The type strain is STM-14T (=BCRC 80924T=LMG 29290T=KCTC 42983T).

Novosphingobium guangzhouense sp. nov., with the ability to degrade 1-methylphenanthrene

A novel Gram-stain-negative, flagellated, rod-shaped, yellow-pigmented aerobic bacterium, strain SA925T, that is capable of degrading 1-methylphenanthrene was isolated from oil-polluted soil collected from a refinery located in Guangzhou, China. Phylogenetic analysis based on the 16S rRNA gene sequence demonstrated that strain SA925T belongs to the genus Novosphingobium and is evolutionarily close to the type strains of Novosphingobium gossypii (98.5 % similarity), Novosphingobium panipatense (98.2 %), Novosphingobium mathurense (98.0 %) and Novosphingobium pentaromativorans (96.5 %). The G+C content of the genomic DNA was 60.2 mol%. DNA-DNA hybridization experiments between strain SA925T and the closest strain, Novosphingobium gossypii JM-1396T, revealed a low level of relatedness (35.5 %). Strain SA925T grew at 10-35 °C, at pH 6.0-8.0 and in the presence of 0-4 % (w/v) NaCl. The major fatty acids were C18 : 1ω7c, C16 : 0 and summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c). The polar lipid profiles mainly consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidyldimethylethanolamine, phosphatidylethanolamine and sphingoglycolipid (the characteristic polar lipid). The predominant ubiquinone was Q-10. The major polyamine was spermidine. Based on the phylogenetic, phenotypic and physiological characteristics, strain SA925T was considered to represent a novel species of the genus Novosphingobium, for which the name Novosphingobium guangzhouense sp. nov. is proposed. The type strain is SA925T (=DSM 32207T=GDMCC 1.1110T).

Novosphingobium gossypii sp. nov., isolated from Gossypium hirsutum

A Gram-stain-negative, rod-shaped, non-spore-forming bacterium (strain JM-1396T) producing a yellow pigment, was isolated from the healthy internal stem tissue of post-harvest cotton (Gossypium hirsutum, cultivar ‘DES-119’) grown at the Plant Breeding Unit at the E. V. Smith Research Center in Tallassee (Macon county), AL, USA. 16S rRNA gene sequence analysis of strain JM-1396T showed high sequence similarity values to the type strains of Novosphingobium mathurense, Novosphingobium panipatense (both 98.6 %) and Novosphingobium barchaimii (98.5 %); sequence similarities to all other type strains of species of the genus Novosphingobium were below 98.3 %. DNA–DNA pairing experiments of the DNA of strain JM-1396T and N. mathurense SM117T, N. panipatense SM16T and N. barchaimii DSM 25411T showed low relatedness values of 8 % (reciprocal 7 %), 24 % (reciprocal 26 %) and 19 % (reciprocal 25 %), respectively. Ubiquinone Q-10 was detected as the dominant quinone; the fatty acids C18 : 1ω7c (71.0 %) and the typical 2-hydroxy fatty acid, C14 : 0 2-OH (11.7 %), were detected as typical components. The polar lipid profile contained the diagnostic lipids diphosphatidylglycerol, phosphatidylethanolamine, sphingoglycolipid and phosphatidylcholine. The polyamine pattern contained the major compound spermidine and only minor amounts of other polyamines. All these data revealed that strain JM-1396T represents a novel species of the genus Novosphingobium. For this reason we propose the name Novosphingobium gossypii sp. nov. with the type strain JM-1396T ( = LMG 28605T = CCM 8569T = CIP 110884T).

Proposal of Novosphingobium rhizosphaerae sp. nov., isolated from the rhizosphere

A yellow, Gram-stain-negative, rod-shaped, non-spore-forming bacterium (strain JM-1T) was isolated from the rhizosphere of a field-grown Zea mays plant in Auburn, AL, USA. 16S rRNA gene sequence analysis of strain JM-1T showed high sequence similarity to the type strains of Novosphingobium capsulatum (98.9 %), Novosphingobium aromaticivorans (97.4 %), Novosphingobium subterraneum (97.3 %) and Novosphingobium taihuense (97.1 %); sequence similarities to all other type strains of species of the genus Novosphingobium were below 97.0 %. DNA–DNA hybridizations of strain JM-1T and N. capsulatum DSM 30196T, N. aromaticivorans SMCC F199T and N. subterraneum SMCC B0478T showed low similarity values of 33 % (reciprocal: 21 %), 14 % (reciprocal 16 %) and 36 % (reciprocal 38 %), respectively. Ubiquinone Q-10 was detected as the major respiratory quinone. The predominant fatty acid was C18 : 1ω7c (71.0 %) and the typical 2-hydroxy fatty acid C14 : 0 2-OH (11.7 %) was detected. The polar lipid profile contained the diagnostic lipids diphosphatidylglycerol, phosphatidylethanolamine, sphingoglycolipid and phosphatidylcholine. Characterization by 16S rRNA gene sequence analysis, physiological parameters, pigment analysis, and ubiquinone, polar lipid and fatty acid composition revealed that strain JM-1T represents a novel species of the genus Novosphingobium . For this species we propose the name Novosphingobium rhizosphaerae sp. nov. with the type strain JM-1T ( = LMG 28479T = CCM 8547T).