Rhodobacteraceae are key players in microbiome assembly of the diatom Asterionellopsis glacialis.

The complex interactions between bacterioplankton and phytoplankton have prompted numerous studies that investigate phytoplankton microbiomes with the aim of characterizing beneficial or opportunistic taxa and elucidating core bacterial members. Oftentimes, this knowledge is garnered through 16S rRNA gene profiling of microbiomes from phytoplankton isolated across spatial and temporal scales, yet these studies do not offer insight into microbiome assembly and structuring. In this study, we aimed to identify taxa central to structuring and establishing the microbiome of the ubiquitous diatom Asterionellopsis glacialis. We introduced a diverse environmental bacterial community to A. glacialis in nutrient-rich or nutrient-poor media in a continuous dilution culture setup and profiled the bacterial community over 7 days. 16S rRNA amplicon sequencing showed that cyanobacteria (Coleofasciculaceae) and Rhodobacteraceae dominate the microbiome early on and maintain a persistent association throughout the experiment. Differential abundance, co-abundance networks, and differential association analyses revealed that specific members of the family Rhodobacteraceae, particularly Sulfitobacter amplicon sequence variants, become integral members in microbiome assembly. In the presence of the diatom, Sulfitobacter species and other Rhodobacteraceae developed positive associations with taxa that are typically in high abundance in marine ecosystems (Pelagibacter and Synechococcus), leading to restructuring of the microbiome compared to diatom-free controls. These positive associations developed predominantly under oligotrophic conditions, highlighting the importance of investigating phytoplankton microbiomes in as close to natural conditions as possible to avoid biases that develop under routine laboratory conditions. These findings offer further insight into phytoplankton-bacteria interactions and illustrate the importance of Rhodobacteraceae, not merely as phytoplankton symbionts but as key taxa involved in microbiome assembly. IMPORTANCE: Most, if not all, microeukaryotic organisms harbor an associated microbial community, termed the microbiome. The microscale interactions that occur between these partners have global-scale consequences, influencing marine primary productivity, carbon cycling, and harmful algal blooms to name but a few. Over the last decade, there has been a growing interest in the study of phytoplankton microbiomes, particularly within the context of bloom dynamics. However, long-standing questions remain regarding the process of phytoplankton microbiome assembly. The significance of our research is to tease apart the mechanism of microbiome assembly with a particular focus on identifying bacterial taxa, which may not merely be symbionts but architects of the phytoplankton microbiome. Our results strengthen the understanding of the ecological mechanisms that underpin phytoplankton-bacteria interactions in order to accurately predict marine ecosystem responses to environmental perturbations.

Fontisubflavum oceani gen. nov., sp. nov., isolated from the deep-sea cold seep water of South China Sea.

In this study, we report a Gram-stain-negative, rod-shaped, atrichous and aerobic bacterial strain named CSW1921T, which was isolated from the deep-sea water of a cold seep in South China Sea. Growth of strain CSW1921T occurred at 10.0-35.0 °C (optimum, 30 °C), pH 5.0-10.0 (optimum, pH 8.0-9.0) and with 0-9.0 % (w/v) NaCl (optimum, 1.0-2.0 %). Phylogenetic tree analysis based on 16S rRNA gene sequence or the genomic sequence indicated that strain CSW1921T belonged to the family Rhodobacteraceae and was closely related to Rhodophyticola porphyridii MA-7-27T (97.5 % sequence similarity). Genomic analysis indicated that strain CSW1921T contains a circular chromosome of 3 592 879 bp with G+C content of 60.5 mol%. The predominant respiratory quinone of CSW1921T was ubiquinone-10. The polar lipids of CSW1921T contained phosphatidylglycerol, three unidentified aminolipids, two unidentified phospholipids and two unidentified lipids. The major fatty acids of strain CSW1921T contained C16 : 0, C18 : 1 ω7c 11-methyl and summed feature 8 (C18 : 1 ω7c). The average nucleotide identity, DNA-DNA hybridization and average amino acid identity values between strain CSW1921T and members of its related species were 68.02-69.08 %, 12.7-12.9 % and 46.87-48.08 %, respectively, which were lower than the recommended threshold values for bacterial species or genus delineation. Phylogenetic, physiological, biochemical and morphological analyses suggested that strain CSW1921T represents a novel genus and a novel species of the family Rhodobacteraceae, and the name Fontisubflavum oceani gen. nov., sp. nov. is proposed with the type strain CSW1921T (=MCCC 1K08371T=KCTC 92834T).

Defluviimonas sediminis sp. nov., isolated from mangrove sediment.

A Gram-stain-negative, facultatively aerobic, motile and ovoid- to rod-shaped bacterium, designated as FT324T, was isolated from a surface mangrove sediment sample from Shenzhen, PR China. The taxonomic position of strain FT324T was determined by a combination of phylogenetic, physiological, biochemical and chemotaxonomic analyses. Strain FT324T grew at 20-40 °C (optimum, 30-37 °C), pH 5.0-9.0 (optimum, pH 8.0) and in the presence of 0-3 % (w/v) NaCl (optimum, 1 %). Its full-length 16S rRNA gene sequence was the most similar to Frigidibacter oleivorans XJ4T (97.4 %), followed by Defluviimonas denitrificans DSM 18921T (96.62 %), Pseudothioclava arenosa CAU 1312T (96.54 %) and Defluviimonas nitratireducens DL5-4T (96.47 %). The major fatty acids (>10 %) of FT324T were C19 : 0 cyclo ω8c (51.9 %) and summed feature 8(29.6 %). The predominant respiratory quinone was Q-10. Its polar lipid profile contained phosphatidylethanolamine, phosphatidylmethylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, one unidentified aminolipid, one unidentified lipid and two unidentified phospholipids. Its estimated genome size was 4 294 115 bp and the genomic DNA G+C content was 69.6 mol%. Based on its distinct phenotypic, chemotaxonomic and phylogenetic characteristics, strain FT324T should represent a novel species of the genus Defluviimonas, for which the name Defluviimonas sediminis sp. nov. is proposed (=MCCC 1K07685T=KCTC 92477T).

Falsirhodobacter algicola sp. nov., a member of the Rhodobacteraceae isolated from the marine red algae Grateloupia sp.

A Gram-negative, pale yellow-pigmented, non-flagellated, motile, rod-shaped and aerobic bacterium, designated strain PG104T, was isolated from red algae Grateloupia sp. collected from the coastal area of Pohang, Republic of Korea. Growth of strain PG104T was observed at 15-35 °C (optimum, 30 °C), pH 6.0-10.0 (optimum, pH 7.5-8.0) and in the presence of 0-8.0 % (w/v) NaCl (optimum, 5.0 %). The predominant fatty acids included C17 : 0, C18 : 0, 11-methyl C18 : 1 ω7c and summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c) and the major respiratory quinone was Q-10. Polar lipids included phosphatidylethanolamine, phosphatidylcholine, phosphatidylglycerol, diphosphatidylglycerol, one unidentified lipid and one unidentified aminolipid. Phylogenetic analysis based on the 16S rRNA gene sequences indicated that strain PG104T formed a phylogenetic lineage with members of the genus Falsirhodobacter and exhibited 16S rRNA gene sequence similarities of 97.1 and 96.6 % to Falsirhodobacter deserti W402T and Falsirhodobacter halotolerans JA744T, respectively. The complete genome of strain PG104T consisted of a single circular chromosome of approximately 2.8 Mbp with five plasmids. Based on polyphasic taxonomic data, strain PG104T represents a novel species in the genus Falsirhodobacter, for which the name Falsirhodobacter algicola sp. nov. is proposed. The type strain of Falsirhodobacter algicola is PG104T (=KCTC 82230T=JCM 34380T).

Rhabdonatronobacter sediminivivens gen. nov., sp. nov. isolated from the sediment of Hutong Qagan Soda Lake.

A novel Gram-stain-negative bacterium, designated as IM2376T, was isolated from the sediment of Hutong Qagan Lake in the Ordos, Inner Mongolia Autonomous Region of China. Phylogenetic analysis based on 16S rRNA gene sequence revealed that the strain IM2376T had the highest similarity with Roseinatronobacter thiooxidans DSM 13087T (96.2%) and Rhodobaca bogoriensis LBB1T (96.2%) of the family Rhodobacteraceae. Genomic relatedness analyses showed that strain IM2376T was clearly distinguished from other species in the family Rhodobacteraceae, with average nucleotide identities, average amino acid identities, and in silico DNA-DNA hybridization values not more than 74.1, 68.5, and 20.2%, respectively. The fatty acids were mainly composed of C18:1ω7c (64.9%), iso-C16:0 (16.3%), and C16: 1ω7c/C16:1ω6c (6.0%). The major polar lipids were diphosphatidylglycerol, phosphatidylglycerol, and phosphatidylcholine. The predominant ubiquinone was Q-10 (94.9%). The genomic DNA G + C content was 66 mol%. Based on all these results, strain IM2376T was considered a novel species of a new genus in the family Rhodobacteraceae, for which the name Rhabdonatronobacter sediminivivens gen. nov., sp. nov. is proposed. The type strain of Rhabdonatronobacter sediminivivens is IM2376T (= CGMCC 1.17852T = KCTC 92134T).

Thalassococcus arenae sp. nov. isolated from sea sand.

A Gram-negative, aerobic, rod-shaped bacterium, designated strain CAU 1522T, was isolated from a sea sand sample collected from the Republic of Korea. Optimal growth of strain CAU 1522T ensued at 30 °C, pH 7.5, and 1.0% (w/v) NaCl. Strain CAU 1522T was affiliated to the genus Thalassococcus with high similarity to T. lentus KCTC 32084T (97.5%), T. profundi MCCC 1K03253T (96.5%), and T. halodurans JCM 13833T (96.1%) according to phylogenetic analysis based on 16S rRNA gene sequences. The whole genome of strain CAU 1522T was 3.7 Mb in length and included 7 contigs and 3599 protein-coding genes, with a G + C content of 65.4 mol%. The predominant cellular fatty acids were C18:1 ω6c and/or C18:1 ω7c (summed feature 8), with Q-10 being the sole isoprenoid quinone. The polar lipids included phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, phosphoglycolipid, and an unidentified lipid. These phenotypic, chemotaxonomic, and phylogenetic data support that strain CAU 1522T is a novel Thalassococcus species, for which the name T. arenae sp. nov. is proposed. The type strain is CAU 1522T (= KCTC 72545T = MCCC 1K04064T).

Arenibacterium arenosum sp. nov., isolated from sea sand.

A Gram-negative, non-motile, short rod-shaped aerobic bacterial strain CAU 1593T was isolated from a coastal sand sample collected in the Republic of Korea. Cells of strain CAU 1593T grew optimally at 30 °C and pH 7.5 in 4% (w/v) NaCl. Phylogenetic analysis based on the 16S rRNA gene sequence revealed that strain CAU 1593T had the highest similarity to Arenibacterium halophilum (97.5%). The whole genome of strain CAU 1593T was 3,979,826 bp with 26 contigs, and the DNA G + C content was 64.3 mol%. The major fatty acid of strain CAU 1593 T was summed feature 8 (C18:1 ω7c/C18:1 ω6c). Q-10 was the only respiratory quinone. The polar lipids were composed of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, two phosphoglycolipids, an unidentified glycolipid, and an unidentified lipid. Based on the results of chemotaxonomic, phylogenetic, and phenotypic analyses, strain CAU 1593T represents a novel species in the genus Arenibacterium, which is named Arenibacterium arenosum sp. nov. The type strain is CAU 1593T (= KCTC 82402T = MCCC 1K05671T).

Algicella marina gen. nov., sp. nov., a novel marine bacterium isolated from a Pacific red alga.

A novel Gram-staining negative, strictly aerobic, rod-shaped, and non-motile bacterium, designated strain 9Alg 56T, was isolated from the red alga Tichocarpus crinitus. The phylogenetic analysis based on 16S rRNA gene sequences placed the novel strain within the family Rhodobacteraceae, the order Rhodobacterales, the class Alphaproteobacteria, the phylum Pseudomonadota. The nearest neighbors of the new strain were Pontivivens insulae KCTC 42458T, Oceanibium sediminis KCTC 62076T, Halovulum dunhuangense YYQ-30T and Monaibacterium marinum C7T with 16S rRNA gene sequence similarity of 94.7, 94.4%, 93.1 and 92.7%, respectively. The AAI/ANI/dDDH values between 9Alg 56T and the five species of the closest genera (Pontivivens, Oceanibium, Halovulum, Monaibacterium, and 'Oceanomicrobium') were 58.63-63.91%/ 75.91-77.37%/ 19.3-20.4%. The prevalent fatty acids of strain 9Alg 56T were C18:1 ω7c, C18:0 and C14:0 3-OH. The polar lipid profile consisted of phosphatidylethanolamine, phosphatidylglycerol, phosphatidic acid, phosphatidylcholine, and two unidentified lipids. The DNA G+C content of strain 9Alg 56T was 61.5 mol%. A combination of the genotypic and phenotypic data showed that the algal isolate represents a novel genus and species, for which the name Algicella marina gen. nov., sp. nov. is proposed. The type strain is 9Alg 56T (= KCTC 72005T = KMM 6775T).

Pontibrevibacter nitratireducens gen. nov., sp. nov., a member of the family Rhodobacteraceae isolated from seawater of the Indian Ocean and intertidal zone.

Two Gram-stain-negative, facultatively anaerobic, non-motile, rod-shaped bacteria, strains h42T and ALG8, were isolated individually from the Indian Ocean and intertidal zone of Zhoushan, China. The results of 16S rRNA gene sequence analysis showed that the sequence similarity between strains h42T and ALG8 was 99.7 %, and the closest related strains were Monaibacterium marinum C7T (97.77 and 97.62 %) and Pontivivens insulae GYSW-23T (95.31 and 95.45 %). Phylogenetic analysis based on 16S rRNA gene sequences shows that these two novel strains belong to a distinct new lineage of the family Rhodobacteraceae in the order Rhodobacterales. The average nucleotide identity and in silico DNA-DNA hybridization values between the two novel strains and M. marinum C7T and P. insulae GYSW-23T were 72.73-78.15 % and 19.70-20.80 %, respectively. The DNA G+C content of strains h42T and ALG8 was 62.36 % and 62.17 mol %. The major fatty acids (>10 %) in strain h42T were C18 : 0, C19 : 0 cyclo ω8c and summed feature 8 (C18 : 1 ω6c and/or C18 : 1 ω7c), and in strain ALG8 were C19 : 0 cyclo ω8c and summed feature 8 (C18 : 1ω6c and/or C18 : 1 ω7c). The predominant isoprenoid ubiquinone of the two novel strains was Q-10; their major polar lipids were identified as diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, two unidentified glycolipids, an unidentified aminoglycolipid, an unidentified phospholipid and an unidentified lipid. Based on the results of the morphological, physiological, chemotaxonomic and phylogenetic analysis of these two strains, a novel species of a new genus in the family Rhodobacteraceae is proposed, named as Pontibrevibacter nitratireducens gen. nov., sp. nov. The type strain and non-type strain of P. nitratireducens are h42T (=KCTC 72875T=CGMCC 1.17849T=MCCC 1K04735T) and ALG8 (=KCTC 82194=MCCC 1K04733).

Sagittula salina sp. nov., isolated from marine waste.

A novel Gram-stain-negative, non-motile, halophilic bacterium designated strain M10.9XT was isolated from the inner sediment of an aluminium can collected from the Mediterranean Sea (València, Spain). Cells of strain M10.9XT were rod-shaped and occasionally formed aggregates. The strain was oxidase-negative and catalase-positive, and showed a slightly psychrophilic, neutrophilic and slightly halophilic metabolism. The phylogenetic analyses revealed that strain M10.9XT was closely related to Sagittula stellata E-37T and Sagittula marina F028-2T. The genomic G+C content of strain M10.9XT was 65.2 mol%. The average nucleotide identity and digital DNA-DNA hybridization values were 76.6 and 20.9 %, respectively, confirming its adscription to a new species within the genus Sagittula. The major cellular fatty acids were C18 : 1 ω7c/C18 : 1 ω6c and C16 : 0. The polar lipids consisted of phosphatidylglycerol, phosphatidylethanolamine, an unidentified aminolipid, an unidentified glycolipid, an unidentified phospholipid and an unidentified lipid. According to the resuts of a polyphasic study, strain M10.9XT represents a novel species of the genus Sagittula for which the name Sagittula salina sp. nov. (type strain M10.9XT=DSM 112301T=CECT 30307T) is proposed.

Limibaculum sediminis sp. nov., isolated from mangrove sediment.

A Gram-stain-negative, cream-coloured, aerobic, motile and ovoid- to rod-shaped bacterium, designated as FT325T, was isolated from mangrove sediment collected in Shenzhen, PR China. The taxonomic position of strain FT325T was established by phylogenetic, physiological, biochemical and chemotaxonomic analyses. Strain FT325T grew optimally at 37-40 °C and pH 6.0 in the presence of 0 % (w/v) NaCl. Results of 16S rRNA gene sequence analysis showed that strain FT325T was most similarly related to Limibaculum halophilum CAU 1123T (96.2 %), Phaeovulum vinaykumarii DSM 18714T (93.9%) and Amaricoccus solimangrovi HB 172011T (93.7 %). The major fatty acids (>10 %) were C18 : 1 ω7c (60.0 %) and 11-methyl C18 : 1 ω7c (16.7 %). The sole respiratory quinone was Q-10. The polar lipids were phosphatidylglycerol, one unidentified glycolipid, three unidentified aminolipids and three unidentified phospholipids. Its estimated genome size was 4 318 768 bp and the genomic DNA G+C content was 69.6 mol%. Based on its distinct phenotypic, chemotaxonomic and phylogenetic characteristics, strain FT325T represents a novel species of the genus Limibaculum, for which the name Limibaculum sediminis sp. nov. is proposed (=MCCC 1K07397T=KCTC 92313T).

Pseudophaeobacter flagellatus sp. nov., isolated from coastal water.

A Gram-stain-negative, aerobic, motile, rod-shaped novel bacterial strain, designated as MA21411-1T, was isolated from the Korean coast. The colonies were white-yellow-coloured, smooth, convex and entire, spherical and 1.0-1.8 mm in diameter. Phylogenetic analysis based on the 16S rRNA gene sequence showed that strain MA21411-1T is closely related to species of the genus Pseudophaeobacter. The 16S rRNA gene sequence similarities between strain MA21411-1T and Pseudophaeobacter arcticus DSM 23566T, Phaeobacter porticola DSM 103148T and Pseudophaeobacter leonis DSM 25627T were 98.31, 97.80 and 97.28 %, respectively. Strain MA21411-1T has a draft genome size of 4 294 042 bp, annotated with 4125 protein-coding genes, and 53 tRNA, three rRNA and one tmRNA genes. The genomic DNA G+C content was 59.2 mol%. Comparative genome analysis revealed that the average nucleotide identity, digital DNA-DNA hybridization and average amino acid identity values among strain MA21411-1T and other related species were below the cut-off levels of 95, 70 and 95.5 %, respectively. The growth temperature range for growth was 15-28 °C (optimum, 25 °C), pH range was 6.0-9.0 (optimum, pH 6.0), and salt tolerance range was 0.5-4 % (optimum 0.5 %). Ubiquinone-10 was the sole quinone present in MA21411-1T and all three closely related strains. The major cellular fatty acid (>10 %) of the strain was summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c). The polar lipid profile contained phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine and four unidentified polar lipids. Based on the phylogenetic tree, as well as phenotypic, chemotaxonomic and genomic features, strain MA21411-1T represents a novel species of the genus Pseudophaeobacter, for which the name Pseudophaeobacter flagellatus sp. nov. is proposed. The type strain is MA21411-1T (=KCTC 92095T=GDMCC 1.2988T).

Szabonella alba gen. nov., sp. nov., a motile alkaliphilic bacterium of the family Rhodobacteraceae isolated from a soda lake.

A Gram-stain-negative, oxidase- and catalase-positive, rod-shaped, creamy white coloured bacterial strain, DMG-N-6T, was isolated from a water sample of Lake Ferto/Neusiedler See (Hungary). Phylogenetic analysis based on 16S rRNA gene sequences revealed that the strain forms a distinct linage within the family Rhodobacteraceae. Its closest relatives are Tabrizicola alkalilacus DJCT (96.76% similarity) and Tabrizicola piscis K13M18T (96.76%), followed by Tabrizicola sediminis DRYC-M-16T (96.69 %), Rhodobacter sediminicola JA983T (96.62 %), Tabrizicola aquatica RCRI19T (96.47 %) and Cereibacter johrii JA192T (96.18 %). The novel bacterial strain favours an alkaline environment (pH 8.0-12.0) and grows optimally at 18-28°C in the presence of 2-4 % (w/v) NaCl. Cells of DMG-N-6T were motile by a single subpolar flagellum. Bacteriochlorophyll a was not detected. The predominant respiratory quinone was ubiquinone Q-10. The major cellular fatty acid was C18:1 ω7c. The polar lipid profile comprised phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylserine, phosphatidylcholine, an unidentified phospholipid and five unidentified lipids. The assembled draft genome of strain DMG-N-6T had 52 contigs with a total length of 4 219 778 bp and a G+C content of 64.3 mol%. Overall genome-related indices (ANI <77.8 %, AAI <69.0 %, dDDH <19.6 %) with respect to close relatives were all significantly below the corresponding threshold to demarcate bacterial genus and species. Strain DMG-N-6T (=DSM 108208T=NCAIM B.02645T) is strongly different from its closest relatives and is suggested as the type strain of a novel species of a new genus in the family Rhodobacteraceae, for which the name Szabonella alba gen. nov., sp. nov. is proposed.

Sedimentimonas flavescens gen. nov., sp. nov., isolated from sediment of Clam Island, Liaoning Province.

A novel Gram-stain negative, aerobic and ovoid to short rod shaped bacterium with a single polar flagellum, named strain B57T, was isolated from sediment of Clam Island, Liaoning Province, China. The optimal growth of this strain was found to occur at 37 °C, pH 6-6.5, and in the presence of 2% (w/v) NaCl. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain B57T forms a distinct lineage within the family Rhodobacteraceae, sharing high 16S rRNA gene sequence similarity with Sinirhodobacter populi sk2b1T (97.4%). The average amino acid identity of B57T and the closely related species were lower than the threshold level for genus delineation. The dominant respiratory quinone of strain B57T was identified as Q-10. The major fatty acids were found to be Summed Feature 8 (C18:1ω7c and/or C18:1ω6c), Summed Feature 3 (C16:1ω7c and/or C16:1ω6c) and C16: 0. The polar lipids were identified as phosphatidylcholine, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylmonomethylethanolamine, diphosphatidylglycerol, two unidentified phospholipids, one unidentified glycolipid, and one unidentified lipid. The DNA G + C content of strain B57T was determined to be 64.1 mol%. Based on the biochemical, phylogenetic and chemotaxonomic analysis, strain B57T is concluded to represent a novel species of a novel genus, for which the name Sedimentimonas flavescens gen. nov., sp. nov.is proposed. The type strain is B57T (= CGMCC1.19488T = KCTC 92053T).

Neotabrizicola shimadae gen. nov., sp. nov., an aerobic anoxygenic phototrophic bacterium harbouring photosynthetic genes in the family Rhodobacteraceae, isolated from a terrestrial hot spring.

A bacteriochlorophyll-containing bacterium, designated as strain N10T, was isolated from a terrestrial hot spring in Nagano Prefecture, Japan. Gram-stain-negative, oxidase- and catalase-positive and ovoid to rod-shaped cells showed the features of aerobic anoxygenic phototrophic bacteria, i.e., strain N10T synthesised bacteriochlorophylls under aerobic conditions and could not grow anaerobically even under illumination. Genome analysis found genes for bacteriochlorophyll and carotenoid biosynthesis, light-harvesting complexes and type-2 photosynthetic reaction centre in the chromosome. Phylogenetic analyses based on the 16S rRNA gene sequence and 92 core proteins revealed that strain N10T was located in a distinct lineage near the type species of the genera Tabrizicola and Xinfangfangia and some species in the genus Rhodobacter (e.g., Rhodobacter blasticus). Strain N10T shared < 97.1% 16S rRNA gene sequence identity with those species in the family Rhodobacteraceae. The digital DNA-DNA hybridisation, average nucleotide identity and average amino acid identity values with the relatives, Tabrizicola aquatica RCRI19T (an aerobic anoxygenic phototrophic bacterium), Xinfangfangia soli ZQBWT and R. blasticus ATCC 33485T were 19.9-20.7%, 78.2-79.1% and 69.1-70.1%, respectively. Based on the phenotypic features, major fatty acid and polar lipid compositions, genome sequence and phylogenetic position, a novel genus and species are proposed for strain N10T, to be named Neotabrizicola shimadae (= JCM 34381T = DSM 112087T). Strain N10T which is phylogenetically located among aerobic anoxygenic phototrophic bacteria (Tabrizicola), bacteriochlorophyll-deficient bacteria (Xinfangfangia) and anaerobic anoxygenic phototrophic bacteria (Rhodobacter) has great potential to promote studies on the evolution of photosynthesis in Rhodobacteraceae.

Alexandriicola marinus gen. nov., sp. nov., a new member of the family Rhodobacteraceae isolated from marine phycosphere.

Two yellow-pigmented bacterial strains, LZ-14 T and ABI-LZ29, were isolated from the cultivable phycosphere microbiota of the highly toxic marine dinoflagellate Alexandrium catenella LZT09 and demonstrated obvious microalgae growth-promoting potentials toward the algal host. To elucidate the taxonomic status of the two bioactive bacterial strains, they were subjected to a polyphasic taxonomic characterization. Both strains were found to be Gram-negative, aerobic, rod-shaped and motile; to contain Q-10 as the predominant ubiquinone; summed feature 8, C16:0, C18:1 ω7c 11-methyl and summed feature 3 as the major fatty acids; and diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol and two unidentified phospholipids as the predominant polar lipids. Based on the phylogenetic analysis, phylogenomic inferences and phenotypic characteristics, the strains could be clearly distinguished from phylogenetically closely related species and formed a distinct monophyletic lineage in the family Rhodobacteraceae. The size of the draft genome of strain LZ-14 T is 4.615 Mb, with a DNA G + C content of 63.3 mol%. It contains ten predicted secondary metabolite biosynthetic gene clusters and core genes for bacterial exopolysaccharide biosynthesis. Therefore, strain LZ-14 T (= CCTCC AB 2017230 T = KCTC 62342 T) represents a novel species of a new genus, for which the name Alexandriicola marinus gen. nov., sp. nov., is proposed.

Sulfitobacter algicola sp. nov., isolated from green algae.

A novel Gram-stain-negative, aerobic, non-flagellated, non-motile, oval-rod-shaped and light pink to light tawny-pigmented bacterial strain (designated 1151T) were isolated from marine green algae obtained from the coastal seawater of Weihai, China. Strain 1151T was found to grow at 15-37 °C (optimum, 33 °C), pH 7.0-9.5 (optimum, 7.5-8.5) and in the presence of 1-6% (w/v) NaCl (optimum, 3%). Cells were oxidase-positive and catalase-positive. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain 1151T was a member of the genus Sulfitobacter and exhibited the hightest sequence similarity to Sulfitobacter indolifex DSM 14862T (96.6%), followed by the sequence similarity to Sulfitobacter aestuarii hydD52T (96.5%) and Sulfitobacter profundi SAORIC-263T (96.5%). The average nucleotide identity and digital DDH values between strain 1151T and Sulfitobacter indolifex DSM 14862T were 69.9% and 20.9%, respectively. The average amino acid identity between strain 1151T and Sulfitobacter pontiacus DSM 10014T (type strain of the type species) was 62.3%. Q-10 was detected as the sole respiratory quinone. The dominant cellular fatty acids were sum feature 8 (C18: 1ω7c; 44.1%), C20: 1ω7c (29.7%) and C18: 0 (11.7%). The DNA G + C content of strain 1151T was 51.8 mol%. The polar lipids included phosphatidylglycerol (PG), phosphatidylethanolamine (PE), phosphatidylcholine (PC), and three unidentified lipids (L1, L2 and L3). Based on the phylogenetic and phenotypic characteristics, strain 1151T is considered to represent a novel species of the genus Sulfitobacter, for which the name Sulfitobacter algicola sp. nov. is proposed. The type strain is 1151T (= KCTC 72513T = MCCC 1H00384T).

Pontivivens ytuae sp. nov., isolated from deep sea sediment of the Mariana Trench.

A Gram-stain-negative, light pink-coloured, rod-shaped, flagellated and facultative anaerobic bacterial strain, designated MT2928T, was isolated from deep-sea sediment collected from the Mariana Trench. Growth of strain MT2928T occurred optimally at 28 °C, pH 8.0-9.0 and in the presence of 1.0-2.0 % (w/v) NaCl. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain MT2928T belongs to the genus Pontivivens and has the highest sequence similarity to Pontivivens insulae GYSW-23T (96.6 %). Genomic analysis indicated that strain MT2928T contains a circular chromosome of 4 199 362 bp with G+C content of 67.2 mol%. The strain did not produce bacteriochlorophyll a, but produced carotenoid. The predominant respiratory quinone of MT2928T was ubiquinone-10. The polar lipids of MT2928T contained diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, two unidentified lipids and two unidentified phospholipids. The major fatty acids of strain MT2928T contained summed feature 8 (C18 : 1 ω7c or/and C18 : 1 ω6c), C18 : 0 and summed feature 2 (iso-C16 : 1 I and/or C14 : 0 3-OH). On the basis of phylogenetic, physiological, biochemical and other phenotypic properties, strain MT2928T represents a novel species of the genus Pontivivens, and the name Pontivivens ytuae sp. nov. is proposed with the type species MT2928T (=MCCC 1K05575T=JCM 34320T).

Pseudopuniceibacterium antarcticum sp. nov., isolated from an Antarctic marine sponge.

A Gram-negative, aerobic, rod-shaped, non-motile bacterium, designated strain HQ09T, was isolated from a marine sponge off the coast of Fields Peninsula, West Antarctica. Strain HQ09T grew at 4-35 °C (optimum, 25 °C), pH 5-9 (optimum, pH 7.0), and with 1-10% NaCl (optimum, 2 %). Phylogenetic analysis based on the 16S rRNA gene sequences showed that strain HQ09T was affiliated with the genus Pseudopuniceibacterium in the family Rhodobacteraceae, sharing 99.64 % identity with the type strain of Pseudopuniceibacterium sediminis, the only known species in the genus. However, the low digital DNA-DNA hybridization (dDDH) (27.2 %) and average nucleotide identity (ANI) (83.63 %) values between strain HQ09T and the type strain of Pseudopuniceibacterium sediminis indicated that they did not belong to the same species. Strain HQ09T could also be differentiated from Pseudopuniceibacterium sediminis by many phenotypic characteristics. The major fatty acids (>5 %) of strain HQ09T were summed feature 8 (C18 : 1 ω7c/C18 : 1 ω6c), 11-methyl C18 : 1 ω7c, C16 : 0 and C19 : 0 cyclo ω8c. The polar lipids included phosphatidylglycerol, phosphatidylcholine, two unidentified aminolipids and one unidentified phospholipid. The predominant respiratory quinone was ubiquinone 10 (Q-10). The genomic DNA G+C content was 62.63 mol%. Four secondary metabolite biosynthetic gene clusters were detected in the genome, potentially producing ectoine and three types of unknown compounds. On the basis of the polyphasic evidences obtained in this study, strain HQ09T represents a novel species of the genus Pseudopuniceibacterium, for which the name Pseudopuniceibacterium antarcticum sp. nov. is proposed, with the type strain being HQ09T (=KCTC 52229T=CGMCC 1.15538T).

Roseibium limicola sp. nov., isolated from tidal mudflat.

A novel bacterium, designated strain CAU 1637T, was isolated from a tidal mudflat. Cells of strain CAU 1637T were Gram-stain-negative, aerobic, motile with single flagellum and rod-shaped. The optimum conditions for growth were observed at 30 °C, pH 6.0 and in the presence of 2 % (w/v) NaCl. The respiratory quinone was ubiquinone-10. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain CAU 1637T was closely related to the genus Roseibium, with the highest similarity to Roseibium aestuarii NRBC 112946T (97.4 %), followed by Roseibium hamelinense NRBC 16783T (96.8 %), Roseibium aquae JCM 19310T (96.4 %), Roseibium sediminis KCTC 52373T (95.8 %) and Roseibium denhamense JCM 10543T (95.3 %). The predominant cellular fatty acids were C18 : 1 ω7c 11-methyl and summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c). The major polar lipids consisted of diphosphatidylglycerol and phosphatidylglycerol. The average nucleotide identity values between the novel isolate and related strains ranged from 71.0 to 76.4 %, and the DNA-DNA hybridization values ranged from 19.3 to 20.3 %. The G+C content was 58.4 mol% and the whole-genome size was 4.6 Mb, which included 17 contigs and 3931 protein-coding genes. Based on the taxonomic data, strain CAU 1637T represents a novel species of the genus Roseibium, for which the name Roseibium limicola sp. nov. is proposed. The type strain is CAU 1637T (=KCTC 82429T=MCCC 1K06080T).