Novosphingobium ipomoeae sp. nov., isolated from a water convolvulus field

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.

Comparative Genomics of Degradative Novosphingobium Strains With Special Reference to Microcystin-Degrading Novosphingobium sp. THN1

Bacteria in genus Novosphingobium associated with biodegradation of substrates are prevalent in environments such as lakes, soil, sea, wood and sediments. To better understand the characteristics linked to their wide distribution and metabolic versatility, we report the whole genome sequence of Novosphingobium sp. THN1, a microcystin-degrading strain previously isolated by Jiang et al. (2011) from cyanobacteria-blooming water samples from Lake Taihu, China. We performed a genomic comparison analysis of Novosphingobium sp. THN1 with 21 other degradative Novosphingobium strains downloaded from GenBank. Phylogenetic trees were constructed using 16S rRNA genes, core genes, protein-coding sequences, and average nucleotide identity of whole genomes. Orthologous protein analysis showed that the 22 genomes contained 674 core genes and each strain contained a high proportion of distributed genes that are shared by a subset of strains. Inspection of their genomic plasticity revealed a high number of insertion sequence elements and genomic islands that were distributed on both chromosomes and plasmids. We also compared the predicted functional profiles of the Novosphingobium protein-coding genes. The flexible genes and all protein-coding genes produced the same heatmap clusters. The COG annotations were used to generate a dendrogram correlated with the compounds degraded. Furthermore, the metabolic profiles predicted from KEGG pathways showed that the majority of genes involved in central carbon metabolism, nitrogen, phosphate, sulfate metabolism, energy metabolism and cell mobility (above 62.5%) are located on chromosomes. Whereas, a great many of genes involved in degradation pathways (21-50%) are located on plasmids. The abundance and distribution of aromatics-degradative mono- and dioxygenases varied among 22 Novosphingoibum strains. Comparative analysis of the microcystin-degrading mlr gene cluster provided evidence for horizontal acquisition of this cluster. The Novosphingobium sp. THN1 genome sequence contained all the functional genes crucial for microcystin degradation and the mlr gene cluster shared high sequence similarity (≥85%) with the sequences of other microcystin-degrading genera isolated from cyanobacteria-blooming water. Our results indicate that Novosphingobium species have high genomic and functional plasticity, rearranging their genomes according to environment variations and shaping their metabolic profiles by the substrates they are exposed to, to better adapt to their environments.

Novosphingobium arvoryzae sp. nov., isolated from a flooded rice field

A bacterial strain, designated Jyi-02^T, was isolated from a flooded rice field in Taiwan and characterized using the polyphasic taxonomy approach. Cells of strain Jyi-02^T were aerobic, Gram-stain-negative, rod-shaped, non-motile and formed yellowish orange coloured colonies. Growth occurred at 10-40 °C (optimum, 20 °C) and pH 5.0-9.0 (optimum, pH 7.0) and in the presence of 0-1.0 % NaCl (optimum, 0 %, w/v). The major fatty acids (>10 %) of strain Jyi-02^T were C18 : 1ω7c, summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c) and C14 : 0 2-OH. The polar lipid profile consisted of a mixture of phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine, diphosphatidylglycerol, phosphatidyldimethylethanolamine, sphingoglycolipid, an uncharacterized phospholipid and an uncharacterized lipid. The major polyamine was spermidine. The major isoprenoid quinone was Q-10. The DNA G+C content was 64.8 mol%. Phylogenetic analyses based on 16S rRNA gene sequences showed that strain Jyi-02^T belonged to the genus Novosphingobium and had closest phylogenetic similarity to Novosphingobium soli CC-TPE-1^T (97.8 %). The DNA-DNA relatedness of strain Jyi-02^T with respect to valid published species of the genus Novosphingobium was less than 35 %. Phenotypic characteristics of the novel strain also differed from those of the closest related species of the genus Novosphingobium. On the basis of the genotypic, chemotaxonomic and phenotypic data, strain Jyi-02^T represents a novel species in the genus Novosphingobium, for which the name Novosphingobium arvoryzae sp. nov. is proposed. The type strain is Jyi-02^T (=BCRC 80537^T=KCTC 32422^T).