Altererythrobacter aquimixticola sp. nov., isolated from sediment sampled at the junction between the ocean and a freshwater spring

Actirhodobacter atriluteus gen. nov., sp. nov., isolated from the surface water of the Yellow Sea

A Gram-stain-negative, aerobic, orange-pigmented bacterial strain, designated HHU K3-1 ^T, was isolated from the surface water of the Yellow Sea. The strain was observed to grow on 2216E agar medium, and growth occurred at pH 6.0-8.0 (optimum 7.0), 28-37 °C (optimum 28 °C), and in the presence of 0.5-5% (w/v) NaCl (optimum 1-3%). The major fatty acids (> 10%) were summed feature 3 (C_16:1ω6c/C_16:1ω7c), C_17:1ω6c and summed feature 8 (C_18:1ω6c/C_18:1ω7c). Strain HHU K3-1 ^T was found to contain ubiquinone-10 as the predominant quinone and the major polar lipids were diphosphatidylglycerol (DPG), phosphatidylethanolamine (PE), phosphatidylglycerol (PG) and sphingoglycolipid (SGL). The 16S rRNA gene sequence analysis indicated that strain HHU K3-1 ^T shared highest similarities with Pelagerythrobacter marensis KCTC 22370 ^T (97.7%) and Qipengyuania oceanensis MCCC 1A09965^T (96.9%). However, a phylogenetic tree based on 288 orthologous clusters (OCs) indicated that HHU K3-1 ^T was close related to Parapontixanthobacter aurantiacus MCCC 1A09962^T. The pairwise AAI and evolutionary distance between HHU K3-1 ^T and Parapontixanthobacter aurantiacus MCCC 1A09962^T are 67.1% and 0.43, respectively, which meet the recently proposed standard to differentiate genera in the family Erythrobacteraceae. On the basis of the result obtained by the polyphasic taxonomic study, strain HHU K3-1 ^T can be considered to represent a novel genus in the family Erythrobacteraceae, for which the name Actirhodobacter atriluteus gen. nov., sp. nov. is proposed. The type strain is HHU K3-1 ^T (= MCCC 1K04225^T = KCTC 72834 ^T = CGMCC 1.17395 ^T).

Genomic-based taxonomic classification of the family Erythrobacteraceae

The family Erythrobacteraceae, belonging to the order Sphingomonadales, class Alphaproteobacteria, is globally distributed in various environments. Currently, this family consist of seven genera: Altererythrobacter, Croceibacterium, Croceicoccus, Erythrobacter, Erythromicrobium, Porphyrobacter and Qipengyuania. As more species are identified, the taxonomic status of the family Erythrobacteraceae should be revised at the genomic level because of its polyphyletic nature evident from 16S rRNA gene sequence analysis. Phylogenomic reconstruction based on 288 single-copy orthologous clusters led to the identification of three separate clades. Pairwise comparisons of average nucleotide identity, average amino acid identity (AAI), percentage of conserved protein and evolutionary distance indicated that AAI and evolutionary distance had the highest correlation. Thresholds for genera boundaries were proposed as 70 % and 0.4 for AAI and evolutionary distance, respectively. Based on the phylo-genomic and genomic similarity analysis, the three clades were classified into 16 genera, including 11 novel ones, for which the names Alteraurantiacibacter, Altericroceibacterium, Alteriqipengyuania, Alteripontixanthobacter, Aurantiacibacter, Paraurantiacibacter, Parerythrobacter, Parapontixanthobacter, Pelagerythrobacter, Tsuneonella and Pontixanthobacter are proposed. We reclassified all species of Erythromicrobium and Porphyrobacter as species of Erythrobacter. This study is the first genomic-based study of the family Erythrobacteraceae, and will contribute to further insights into the evolution of this family.