Aurantiacibacter rhizosphaerae sp. nov., isolated from a rhizosphere mudflat of a halophyte and proposal to reclassify Erythrobacter suaedae Lee et al. 2019. and Erythrobacter flavus Yoon et al. 2003 as Aurantiacibacter suaedae comb. nov. and Qipengyuania flava comb. nov., respectively

Aurantiacibacter hainanensis sp. nov. and Qipengyuania zhejiangensis sp. nov., two novel Erythrobacteraceae species isolated from tidal flat sediments

Two Gram-stain-negative, rod-shaped, non-motile, aerobic and carotenoid-producing strains, belonging to the family Erythrobacteraceae, designated as H149T and Z2T, were isolated from tidal flat sediment samples collected in Hainan and Zhejiang, PR China, respectively. Growth of strain H149T occurred at 15-42 °C, 0-10.0 % (w/v) NaCl, and pH 6.0-8.5, with the optima at 35-37 °C, 3.0-3.5 % (w/v) NaCl and pH 7.0. Strain Z2T grew at 15-37 °C, 0-6.0 % (w/v) NaCl, and pH 6.0-9.5, with the optima at 25-30 °C, 0.5-1.0 % (w/v) NaCl and pH 6.0-6.5. Ubiquinone-10 was the sole ubiquinone in two strains. The predominant cellular fatty acids of strain H149T were C16 : 0, summed feature 3 and summed feature 8, while those of strain Z2T were C17 : 1  ω6c, summed feature 3 and summed feature 8. Strains H149T and Z2T shared diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine and sphingoglycolipid as major polar lipids. The 16S rRNA gene sequence identity analysis indicated that strain H149T had the highest sequence identity of 98.4 % with Aurantiacibacter odishensis KCTC 23981T, and strain Z2T had that of 98.2 % with Qipengyuania pacifica NZ-96T. Phylogenetic trees based on 16S rRNA gene and core-genome sequences revealed that strains H149T and Z2T formed two independent clades in the genera Aurantiacibacter and Qipengyuania, respectively. Strain H149T had average nucleotide identity values of 74.0-81.3 % and in silico DNA-DNA hybridization values of 18.5-23.1 % with Aurantiacibacter type strains, while strain Z2T had values of 73.3-78.7 % and 14.5-33.3 % with Qipengyuania type strains. The genomic DNA G+C contents of strains H149T and Z2T were 64.3 and 61.8 %, respectively. Based on the genetic, genomic, phylogenetic, physiological and chemotaxonomic results, strains H149T (=KCTC 8397T=MCCC 1K08920T) and Z2T (=KCTC 8396T=MCCC 1K08946T) are concluded to represent two novel Erythrobacteraceae species for which the names Aurantiacibacter hainanensis sp. nov. and Qipengyuania zhejiangensis sp. nov. are proposed, respectively.

The Diversity and Metabolism of Culturable Nitrate-Reducing Bacteria from the Photic Zone of the Western North Pacific Ocean

To better understand bacterial communities and metabolism under nitrogen deficiency, 154 seawater samples were obtained from 5 to 200 m at 22 stations in the photic zone of the Western North Pacific Ocean. Total 634 nitrate-utilizing bacteria were isolated using selective media and culture-dependent methods, and 295 of them were positive for nitrate reduction. These nitrate-reducing bacteria belonged to 19 genera and 29 species and among them, Qipengyuania flava, Roseibium aggregatum, Erythrobacter aureus, Vibrio campbellii, and Stappia indica were identified from all tested seawater layers of the photic zone and at almost all stations. Twenty-nine nitrate-reducing strains representing different species were selected for further the study of nitrogen, sulfur, and carbon metabolism. All 29 nitrate-reducing isolates contained genes encoding dissimilatory nitrate reduction or assimilatory nitrate reduction. Six nitrate-reducing isolates can oxidize thiosulfate based on genomic analysis and activity testing, indicating that nitrate-reducing thiosulfate-oxidizing bacteria exist in the photic zone. Five nitrate-reducing isolates obtained near the chlorophyll a-maximum layer contained a dimethylsulfoniopropionate synthesis gene and three of them contained both dimethylsulfoniopropionate synthesis and cleavage genes. This suggests that nitrate-reducing isolates may participate in dimethylsulfoniopropionate synthesis and catabolism in photic seawater. The presence of multiple genes for chitin degradation and extracellular peptidases may indicate that almost all nitrate-reducing isolates (28/29) can use chitin and proteinaceous compounds as important sources of carbon and nitrogen. Collectively, these results reveal culturable nitrate-reducing bacterial diversity and have implications for understanding the role of such strains in the ecology and biogeochemical cycles of nitrogen, sulfur, and carbon in the oligotrophic marine photic zone.

Aurantiacibacter sediminis sp. nov., a marine bacterium isolated from a tidal flat

A yellow-coloured bacterium, designated as strain JGD-13T, was isolated from a tidal flat in the Republic of Korea. Cells were Gram-stain-negative, aerobic, non-flagellated and rod-shaped. Growth was observed at 4–42 °C (optimum, 30 °C), at pH 6.0–12.0 (pH 7.0–8.0) and at 1–7 % (w/v) NaCl concentration (3 %). The 16S rRNA gene sequence analysis indicated that strain JGD-13T was closely related to Aurantiacibacter gangjinensis K7-2T with a sequence similarity of 98.2 %, followed by Aurantiacibacter aquimixticola JSSK-14T (98.1 %), Aurantiacibacter atlanticus s21-N3T (97.6 %), Aurantiacibacter zhengii V18T (97.6 %) and Aurantiacibacter luteus KA37T (97.5 %). The average nucleotide identity and digital DNA–DNA hybridization values with related strains were 70.3–76.2 % and 18.5–20.3 %. The genomic DNA G+C content was 60.2 mol%. Phylogenetic analysis using the maximum-likelihood method showed that strain JGD-13T formed a clade with A. aquimixticola JSSK-14T and A. gangjinensis K7-2T. The major fatty acids were summed feature 8 (39.7 %) and C17 : 1  ω6c (14.4 %). The predominant respiratory quinone was ubiquinone-10. The polar lipids were phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine, one sphingoglycolipid and three unidentified lipids. On the basis of phylogenetic, phenotypic and chemotaxonomic characteristics, strain JGD-13T represents a novel species within the genus Aurantiacibacter , for which the name Aurantiacibacter sediminis JGD-13Tsp. nov. is proposed. The type strain is JGD-13T (=KCTC 72892T=KACC 21676T=JCM 33995T).

Comparative Genomics Reveals Genetic Diversity and Metabolic Potentials of the Genus Qipengyuania and Suggests Fifteen Novel Species

Members of the genus Qipengyuania are heterotrophic bacteria frequently isolated from marine environments with great application potential in areas such as carotenoid production. However, the genomic diversity, metabolic function, and adaption of this genus remain largely unclear. Here, 16 isolates related to the genus Qipengyuania were recovered from coastal samples and their genomes were sequenced. The phylogenetic inference of these isolates and reference type strains of this genus indicated that the 16S rRNA gene was insufficient to distinguish them at the species level; instead, the phylogenomic reconstruction could provide the reliable phylogenetic relationships and confirm 15 new well-supported branches, representing 15 putative novel genospecies corroborated by the digital DNA-DNA hybridization and average nucleotide identity analyses. Comparative genomics revealed that the genus Qipengyuania had an open pangenome and possessed multiple conserved genes and pathways related to metabolic functions and environmental adaptation, despite the presence of divergent genomic features and specific metabolic potential. Genetic analysis and pigment detection showed that the members of this genus were identified as carotenoid producers, while some proved to be potentially aerobic anoxygenic photoheterotrophs. Collectively, the first insight into the genetic diversity and metabolic potentials of the genus Qipengyuania will contribute to better understanding of the speciation and adaptive evolution in natural environments.

IMPORTANCE The deciphering of the phylogenetic diversity and metabolic features of the abundant bacterial taxa is critical for exploring their ecological importance and application potential. Qipengyuania is a genus of frequently isolated heterotrophic microorganisms with great industrial application potential. Numerous strains related to the genus Qipengyuania have been isolated from diverse environments, but their genomic diversity and metabolic functions remain unclear. Our study revealed a high degree of genetic diversity, metabolic versatility, and environmental adaptation of the genus Qipengyuania using comparative genomics. Fifteen novel species of this genus have been established using a polyphasic taxonomic approach, expanding the number of described species to almost double. This study provided an overall view of the genus Qipengyuania at the genomic level and will enable us to better uncover its ecological roles and evolutionary history.

Qipengyuania soli sp. nov., Isolated from Mangrove Soil

A novel Gram-stain-negative, non-motile, and rod-shaped bacterial strain, designated as 6D36^T, was isolated from mangrove soil and characterized by using a polyphasic taxonomic approach. Strain 6D36^T was found to grow at 10-37 °C (optimum, 28 °C), at pH 6.0-9.0 (optimum, 7.0) and in 0-8% (w/v) NaCl (optimum, 3%). The predominant cellular fatty acids of strain 6D36^T were summed feature 8 (C_19:1 ω7c and/or C_18:1 ω6c) and C_17:1 ω6c; the major polar lipids were diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, and sphingoglycolipid; the sole respiratory quinone was Q-10. The phylogenetic analysis based on 16S rRNA gene sequences showed that strain 6D36^T fell into the genus Qipengyuania and was closely related to "Erythrobacter mangrovi" MCCC 1K03690^T (98.5%), Qipengyuania citrea CGMCC 1.8703^T (97.6%), and Qipengyuania pelagi JCM 17468^T (97.4%). The phylogenomic analysis indicated that strain 6D36^T formed an independent branch distinct from reference-type strains of species within this genus. The digital DNA-DNA hybridization and average nucleotide identity values between strain 6D36^T and the three type strains above were, respectively, 20.2-21.3% and 79.5-81.5%, of which were far below their respective threshold for species definition, implying that the strain represents a novel genospecies. The genomic DNA G + C content was 63.3%. Based on phenotypic and genotypic characteristics, strain 6D36^T is concluded to represent a novel species of the genus Qipengyuania, for which the name Qipengyuania soli sp. nov., is proposed. The type strain of the species is 6D36^T (= GDMCC 1.1977^T = KCTC 82333^T).

Carotenoids produced by the deep-sea bacterium Erythrobacter citreus LAMA 915: detection and proposal of their biosynthetic pathway

Technologies based on synthetic biology to produce bacterial natural carotenoids depend on information regarding their biosynthesis. Although the biosynthetic pathway of common carotenoids is known, there are carotenoids whose pathways are not completely described. This work aimed to mine the genome of the deep-sea bacterium Erythrobacter citreus LAMA 915, an uncommon bacterium that forms yellow colonies under cultivation. This work further explores the potential application of the carotenoids found and low-cost substrates for bacterial growth. A combined approach of genome mining and untargeted metabolomics analysis was applied. The carotenoid erythroxanthin sulfate was detected in E. citreus LAMA 915 cell extract. A proposal for carotenoid biosynthesis by this bacterium is provided, involving the genes crtBIYZWG. These are responsible for the biosynthesis of carotenoids from the zeaxanthin pathway and their 2,2'-hydroxylated derivatives. E. citreus LAMA 915 extracts showed antioxidant and sun protection effects. Based on the high content of proteases and lipases, it was possible to rationally select substrates for bacterial growth, with residual oil from fish processing the best low-cost substrate selected. This work advances in the understanding of carotenoid biosynthesis and provides a genetic basis that can be further explored as a biotechnological route for carotenoid production.