Whole-genome optical mapping and finished genome sequence of Sphingobacterium deserti sp. nov., a new species isolated from the Western Desert of China

Comparative genomic analysis provides insight into the phylogeny and potential mechanisms of adaptive evolution of Sphingobacterium sp. CZ-2

Sphingobacterium is a class of Gram-negative, non-fermentative bacilli that have received widespread attention due to their broad ecological distribution and oil degradation ability, but are rarely involved in infections. In this manuscript, a novel Sphingobacterium strain isolated from wildfire-infected tobacco leaves was named Sphingobacterium sp. CZ-2. NGS and TGS sequencing results showed a whole genome of 3.92 Mb with 40.68 mol% GC content and containing 3,462 protein-coding genes, 9 rRNA-coding genes and 50 tRNA-coding genes. Phylogenetic analysis, ANI and dDDH calculations all supported that Sphingobacterium sp. CZ-2 represented a novel species of the genus Sphingobacterium. Analysis of the specific genes of Sphingobacterium sp. CZ-2 by comparative genomics revealed that metal transport proteins encoded by the troD and cusA genes could maintain the balance of heavy metal ion concentrations in the internal environment of bacteria and avoid heavy metal toxicity while meeting the needs of growth and reproduction, and transport proteins encoded by the malG gene could keep nutrients required for the survival of bacteria. Synteny and genome evolutionary analyses of Sphingobacterium strains implicated that the gene family contraction as a major process in genome evolution, with insertional sequences leading to mutations, deletions and reversals of genes that help bacteria to withstand complex environmental changes. Complete genome sequencing and systematic comparative genomic analysis will contribute new insights into the adaptive evolution of this novel species and the genus Sphingobacterium.

Sphingobacterium micropteri sp. nov. and Sphingobacterium litopenaei sp. nov., isolated from aquaculture water

Two novel bacterial strains, designated as DN00404^T and DN04309^T, were isolated from aquaculture water and characterized by using a polyphasic taxonomic approach. Cells of strains DN00404^T and DN04309^T were Gram-stain-negative, aerobic, non-motile, oxidase-positive and catalase-positive. Cells of DN00404^T were short rod-shaped and those of DN04309^T were long rod-shaped. Strain DN00404^T was found to grow at 15-37 °C (optimum, 25-30 °C), at pH 6.0-11.0 (optimum, pH 7.5) and in 0-2.0 % (w/v) NaCl (optimum, 1.0 %). Strain DN04309^T was found to grow at 15-45 °C (optimum, 20-37 °C), at pH 5.5-11.0 (optimum, 7.5) and in 0-4.0 % (w/v) NaCl (optimum, 0.5 %). Phylogenetic analyses based on 16S rRNA gene and genome sequences revealed that the two strains belonged to the genus Sphingobacterium and were distinct from all known species of this genus. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between the two strains and between each of the two strains and related type strains of this genus were well below the recognized thresholds of 95.0-96.0 % ANI and 70.0 % dDDH for species delineation. The genomic DNA G+C contents of strains DN00404^T and DN04309^T were 41.6 and 36.0 mol%, respectively. The respiratory quinone in both strains was identified as MK-7, and their major fatty acids were iso-C_15 : 0 and summed feature 3 (C_16 : 1  ω6c and/or C_16 : 1  ω7c), which were similar to those of other species of this genus. The two major fatty acids C_16 : 0 and iso-C_17 : 0 3-OH were also found in strain DN00404^T. Based on genotypic and phenotypic characteristics, two novel species of the genus Sphingobacterium are proposed: Sphingobacterium micropteri sp. nov. with DN00404^T (=GDMCC 1.1865^T=KACC 21924^T) as the type strain and Sphingobacterium litopenaei sp. nov. with DN04309^T (=GDMCC 1.1984^T=KCTC 82348^T) as the type strain.

Sphingobacterium puteale sp. nov., isolated from a deep subsurface aquifer

A bacterial strain M05W1-28^T was isolated from a well that collected water for irrigation from a deep aquifer at a depth of 400 m. Cells were observed to be rod-shaped, non-motile, aerobic, stained Gram-negative. Optimal growth was obtained at pH 7.0 (range: 6.0-9.0), 28 °C (range: 15-37 °C) and 0 % NaCl (range: 0-1.5 %, w/v) in modified tryptic soy broth (mTSB) without added NaCl and R2A. The cells were found to be positive for catalase and oxidase activities. The major fatty acids (>10 %) were identified as summed feature 3 (C_16 : 1  ω7c / C_16 : 1  ω6c) and iso-C_15 : 0. The major polar lipids were phosphatidylethanolamine, glycolipid, phosphoglycolipids, phospholipids, and unidentified lipids. The major respiratory quinone was menaquinone-7 (MK-7). The genomic G+C content of strain M05W1-28^T was 40.7 %. Based on similarities of 16S rRNA gene sequences, strain M05W1-28^T was affiliated with the genus Sphingobacterium, exhibiting the highest sequence similarities with S. multivorum LMG 8342^T (97.5 %), S. ginsenosidimutans THG07^T (97.1 %) and less than 97.0 % to other members of the genus. The average nucleotide identity (ANI) and digital DNA-DNA hybridisation values (dDDH) between M05W1-28^T and S. multivorum LMG 8342^T were 78.1 and 22.5 %, respectively. Phenotypic characteristics including enzyme activities and carbon source utilisation differentiated the strain from other Sphingobacterium species. The phenotypic, chemotaxonomic and phylogenetic properties suggested that strain M05W1-28^T represented a novel species within the genus Sphingobacterium, for which the name Sphingobacterium puteale sp. nov. is proposed. The type strain is M05W1-28^T (=CGMCC 1.13711^T=KCTC 72027^T).

Sphingobacterium alkalisoli sp. nov., isolated from a saline-alkaline soil

A Gram-staining-negative, non-motile, non-spore-forming bacterium designated Y3L14T was isolated from the saline-alkaline soil of a farmland, Inner Mongolia, northern China. Strain Y3L14T could grow at 10-40 °C (optimally at 30 °C), pH 6.0-10.0 (optimally at pH 8.0), and in the presence of 0-6.0 % (w/v) NaCl (optimally with 0-2.0 %). Phylogenetic analysis based on the 16S rRNA gene and DNA gyrase subunit B (gyrB) gene sequences revealed that strain Y3L14T clustered with strains belonging to the genus Sphingobacterium, sharing the highest 16S rRNA gene sequence similarity with Sphingobacterium lactis WCC 4512T (94.99 %). Its major cellular fatty acids contained iso-C15 : 0, C16 : 0, iso-C17 : 0 3-OH and summed feature 3 (iso-C15 : 0 2-OH and/or C16 : 1ω7c). Menaquinone-7 (MK-7) was the only isoprenoid quinone. Strain Y3L14T contained phosphatidylethanolamine, sphingophospholipid, two unknown phospholipids and three unknown lipids as the major polar lipids. The genomic DNA G+C content of strain Y3L14T was 36.0 mol%. Based on the phenotypic, phylogenetic and genotypic characteristics, strain Y3L14T represents a novel species within the genus Sphingobacterium, for which Sphingobacterium alkalisoli sp. nov. is proposed; the type strain is Y3L14T (=CGMCC 1.15782T=KCTC 52379T).