Structure Revision of a Widespread Marine Sulfonolipid Class Based on Isolation and Total Synthesis.

The cosmopolitan marine Roseobacter clade is of global biogeochemical importance. Members of this clade produce sulfur-containing amino lipids (SALs) involved in biofilm formation and marine surface colonization processes. Despite their physiological relevance and abundance, SALs have only been explored through genomic mining approaches and lipidomic studies based on mass spectrometry, which left the relative and absolute structures of SALs unresolved, hindering progress in biochemical and functional investigations. Herein, we report the structural revision of a new group of SALs, which we named cysteinolides, using a combination of analytical techniques, isolation and degradation experiments and total synthetic efforts. Contrary to the previously proposed homotaurine-based structures, cysteinolides are composed of an N,O-acylated cysteinolic acid-containing head group carrying various different (α-hydroxy)carboxylic acids. We also performed the first validated targeted-network based analysis, which allowed us to map the distribution and structural diversity of cysteinolides across bacterial lineages. Beyond offering structural insight, our research provides SAL standards and validated analytical data. This information holds significance for forthcoming investigations into bacterial sulfonolipid metabolism and biogeochemical nutrient cycling within marine environments.

Muriiphilus fusiformis gen. nov., sp. nov., a novel non-marine bacterium belonging to the Roseobacter group, and reclassification of Maritimibacter lacisalsi (Zhong et al. 2015) as Muriicola lacisalsi gen. nov., comb. nov.

An aerobic, Gram-stain-negative, non-sporulating, flagellated and spindle-like bacterium, designated HY14T, was isolated from a pickle-processing factory wastewater sample. The isolate chemoheterotrophically grew at 4-42 °C (optimum, 35 °C) and pH 5.5-9.0 (optimum, pH 6.0-6.5). Salt was required for growth (0.5-12 % NaCl, w/v). A deep brown and water-soluble uncharacterized pigment was produced when grown in certain media. The predominant fatty acids (>5 %) included C16 : 0, C18 : 1 ω7c, 11-methyl C18 : 1 ω7c and C19 : 0 cyclo ω8c. The polar lipid profile consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylcholine, two unidentified aminolipids, two unidentified phospholipids, two unidentified glycolipids and five unknown lipids. The major isoprenoid quinone was ubiquinone-10. Pairwise alignment based on 16S rRNA gene sequences indicated that strain HY14T had the highest sequence similarity to genera Maritimibacter (95.61-96.05 %) and Boseongicola (95.82 %). Phylogenetic analysis based on core genome illustrated that strain HY14T formed a monophyletic lineage with members of the genus Maritimibacter in the clade of the Roseobacter group in the family Rhodobacteraeceae. The core-gene average amino acid identity used to define bacterial genera by a threshold of 60-80 % was calculated to be 68.56-76.5 % between HY14T and closely related taxa. Several genomic characteristics, such as carrying two RuBisCO-mediated pathways and different osmoprotectant transport pathways, exhibited the genotypic discrepancies of strain HY14T. Based on the polyphasic taxonomic characterization, strain HY14T is considered to represent a novel species of a novel genus belonging to the family Rhodobacteraeceae, for which the name Muriiphilus fusiformis gen. nov., sp. nov. is proposed. The type strain is HY14T (=CGMCC 1.15973T=KCTC 52499T). Maritimibacter lacisalsi (Zhong et al. 2015) is considered to diverge from Maritimibacter alkaliphilus at the genus level, and should be reassigned as a novel genus, for which the name Muriicola lacisalsi gen. nov., comb. nov. is proposed.

Photoreduction of carotenoids in the aerobic anoxygenic photoheterotrophs probed by real time Raman spectroscopy.

The Aerobic anoxygenic phototrophic bacteria (AAPB) Roseobacter denitrificans and Roseobacter litoralis are widespread in the bacterioplankton community with a particular role in the marine carbon cycle. Measurements of carotenoids isolated from dark-grown cells indicated the presence of spheroidenone (SO, N = 11) and of 3,4 dihydrospheroidenone (N = 10) in the carotenoids isolated from illuminated cells. Time-dependent Raman 514 nm excitation experiments of R. denitrificans and R. litoralis cells grown under illumination demonstrated that v1 (C=C) of SO exhibits a time-dependent substantial frequency upshift relative to its frequency in the dark-grown cells, in a manner resembling shorting the conjugation length (N). We suggest that the irreversible dark-SO to light- 3,4 dihydrospheroidenone transition observed in the intact carotenoids of R. denitrificans and R. litoralis cells is an operative photoreduction strategy of SO containing AAPB that affects the energy transfer mechanism.

Description of Palleronia rufa sp. nov., a biofilm-forming and AHL-producing Rhodobacteraceae, reclassification of Hwanghaeicola aestuarii as Palleronia aestuarii comb. nov., Maribius pontilimi as Palleronia pontilimi comb. nov., Maribius salinus as Palleronia salina comb. nov., Maribius pelagius as Palleronia pelagia comb. nov. and emended description of the genus Palleronia.

Strain MOLA 401T was isolated from marine waters in the southwest lagoon of New Caledonia and was shown previously to produce an unusual diversity of quorum sensing signaling molecules. This strain was Gram-negative, formed non-motile cocci and colonies were caramel. Optimum growth conditions were 30°C, pH 8 and 3% NaCl (w/v). Based on 16S rRNA gene sequence analysis, this strain was found to be closely related to Pseudomaribius aestuariivivens NBRC 113039T (96.9% of similarity), Maribius pontilimi DSM 104950T (96.4% of similarity) and Palleronia marisminoris LMG 22959T (96.3% of similarity), belonging to the Roseobacter group within the family Rhodobacteraceae. As its closest relatives, strain MOLA 401T is able to form a biofilm on polystyrene, supporting the view of Roseobacter group strains as prolific surface colonizers. An in-depth genomic study allowed us to affiliate strain MOLA 401T as a new species of genus Palleronia and to reaffiliate some of its closest relatives in this genus. Consequently, we describe strain MOLA 401T (DSM 106827T=CIP 111607T=BBCC 401T) for which we propose the name Palleronia rufa sp. nov. We also propose to emend the description of the genus Palleronia and to reclassify Maribius and Hwanghaeicola species as Palleronia species.

The marine bacterium Phaeobacter inhibens secures external ammonium by rapid buildup of intracellular nitrogen stocks.

Reduced nitrogen species are key nutrients for biological productivity in the oceans. Ammonium is often present in low and growth-limiting concentrations, albeit peaks occur during collapse of algal blooms or via input from deep sea upwelling and riverine inflow. Autotrophic phytoplankton exploit ammonium peaks by storing nitrogen intracellularly. In contrast, the strategy of heterotrophic bacterioplankton to acquire ammonium is less well understood. This study revealed the marine bacterium Phaeobacter inhibens DSM 17395, a Roseobacter group member, to have already depleted the external ammonium when only ∼⅓ of the ultimately attained biomass is formed. This was paralleled by a three-fold increase in cellular nitrogen levels and rapid buildup of various nitrogen-containing intracellular metabolites (and enzymes for their biosynthesis) and biopolymers (DNA, RNA and proteins). Moreover, nitrogen-rich cells secreted potential RTX proteins and the antibiotic tropodithietic acid, perhaps to competitively secure pulses of external ammonium and to protect themselves from predation. This complex response may ensure growing cells and their descendants exclusive provision with internal nitrogen stocks. This nutritional strategy appears prevalent also in other roseobacters from distant geographical provenances and could provide a new perspective on the distribution of reduced nitrogen in marine environments, i.e. temporary accumulation in bacterioplankton cells.

An Unprecedented Medium-Chain Diunsaturated N-acylhomoserine Lactone from Marine Roseobacter Group Bacteria.

N-acylhomoserine lactones (AHLs), bacterial signaling compounds involved in quorum-sensing, are a structurally diverse group of compounds. We describe here the identification, synthesis, occurrence and biological activity of a new AHL, N-((2E,5Z)-2,5-dodecadienoyl)homoserine lactone (11) and its isomer N-((3E,5Z)-3,5-dodecadienoyl)homoserine lactone (13), occurring in several Roseobacter group bacteria (Rhodobacteraceae). The analysis of 26 strains revealed the presence of 11 and 13 in six of them originating from the surface of the macroalgae Fucus spiralis or sediments from the North Sea. In addition, 18 other AHLs were detected in 12 strains. Compound identification was performed by GC/MS. Mass spectral analysis revealed a diunsaturated C12 homoserine lactone as structural element of the new AHL. Synthesis of three likely candidate compounds, 11, 13 and N-((2E,4E)-2,4-dodecadienoyl)homoserine lactone (5), revealed the former to be the natural AHLs. Bioactivity test with quorum-sensing reporter strains showed high activity of all three compounds. Therefore, the configuration and stereochemistry of the double bonds in the acyl chain seemed to be unimportant for the activity, although the chains have largely different shapes, solely the chain length determining activity. In combination with previous results with other Roseobacter group bacteria, we could show that there is wide variance between AHL composition within the strains. Furthermore, no association of certain AHLs with different habitats like macroalgal surfaces or sediment could be detected.

Distribution of eukaryotic serine racemases in the bacterial domain and characterization of a representative protein in Roseobacter litoralis Och 149.

Two distinct bacterial and eukaryotic serine racemases (SRs) have been identified based on phylogenetic and biochemical characteristics. Although some reports have suggested that marine heterotrophic bacteria have the potential to produce d-serine, the gene encoding bacterial SRs is not found in those bacterial genomes. In this study, using in-depth genomic analysis, we found that eukaryotic SR homologues were distributed widely in various bacterial genomes. Additionally, we selected a eukaryotic SR homologue from a marine heterotrophic bacterium, Roseobacter litoralis Och 149 (RiSR), and constructed an RiSR gene expression system in Escherichia coli for studying the properties of the enzyme. Among the tested amino acids, the recombinant RiSR exhibited both racemization and dehydration activities only towards serine, similar to many eukaryotic SRs. Mg2+ and MgATP enhanced both activities of RiSR, whereas EDTA abolished these enzymatic activities. The enzymatic properties and domain structure of RiSR were similar to those of eukaryotic SRs, particularly mammalian SRs. However, RiSR showed lower catalytic efficiency for L-serine dehydration (kcat/Km=0.094 min(-1) mM(-1)) than those of eukaryotic SRs reported to date (kcat/Km=0.6-21 min(-1) mM(-1)). In contrast, the catalytic efficiency for L-serine racemization of RiSR (kcat/Km=3.14 min(-1) mM(-1)) was 34-fold higher than that of l-serine dehydration. These data suggested that RiSR primarily catalysed serine racemization rather than dehydration.

Homoserine Lactones, Methyl Oligohydroxybutyrates, and Other Extracellular Metabolites of Macroalgae-Associated Bacteria of the Roseobacter Clade: Identification and Functions.

Twenty-four strains of marine Roseobacter clade bacteria were isolated from macroalgae and investigated for the production of quorum-sensing autoinducers, N-acylhomoserine lactones (AHLs). GC/MS analysis of the extracellular metabolites allowed us to evaluate the release of other small molecules as well. Nineteen strains produced AHLs, ranging from 3-OH-C10:0-HSL (homoserine lactone) to (2E,11Z)-C18:2-HSL, but no specific phylogenetic or ecological pattern of individual AHL occurrence was observed when cluster analysis was performed. Other identified compounds included indole, tropone, methyl esters of oligomers of 3-hydroxybutyric acid, and various amides, such as N-9-hexadecenoylalanine methyl ester (9-C16:1-NAME), a structural analogue of AHLs. Several compounds were tested for their antibacterial and antialgal activity on marine isolates likely to occur in the habitat of the macroalgae. Both AHLs and 9-C16:1-NAME showed high antialgal activity against Skeletonema costatum, whereas their antibacterial activity was low.

Ultrafast excited state processes in Roseobacter denitrificans antennae: comparison of isolated complexes and native membranes.

Roseobacter (Rsb.) denitrificans is a marine aerobic anoxygenic photosynthetic purple bacterium with an unusually high-800 nm absorption band. Ultrafast excited state processes have been intensively studied in the past in order to understand why the energy transfer efficiency between photosynthetic antennae approaches unity and recently it has been proved that the organization of the antennae proteins within the membranes plays an important role. Thanks to the development of genetic manipulation and to the capability of Rsb. denitrificans to grow anaerobically as well, it is possible to construct several mutants in order to compare the ultrafast dynamics between isolated complexes and complexes embedded in membrane environments. Time resolved fluorescence and transient absorption have been applied to isolate LH2, genetically modified membranes with LH2-only and wild type membranes with both LH2 and LH1 antennae of Rsb. denitrificans, in order to understand the effect of the membrane environment on the energy transfer efficiency. A global analysis is applied to calculate the lifetime of the excited states of LH2 and LH1, and although there is shortening of the relaxation lifetime of the LH2-only membranes with respect to the isolated LH2, we find an energy transfer efficiency from LH2 to LH1 of 95%, which still approaches unity.

The structure of RdDddP from Roseobacter denitrificans reveals that DMSP lyases in the DddP-family are metalloenzymes.

Marine microbes degrade dimethylsulfoniopropionate (DMSP), which is produced in large quantities by marine algae and plants, with DMSP lyases into acrylate and the gas dimethyl sulfide (DMS). Approximately 10% of the DMS vents from the sea into the atmosphere and this emission returns sulfur, which arrives in the sea through rivers and runoff, back to terrestrial systems via clouds and rain. Despite their key role in this sulfur cycle DMSP lyases are poorly understood at the molecular level. Here we report the first X-ray crystal structure of the putative DMSP lyase RdDddP from Roseobacter denitrificans, which belongs to the abundant DddP family. This structure, determined to 2.15 Å resolution, shows that RdDddP is a homodimeric metalloprotein with a binuclear center of two metal ions located 2.7 Å apart in the active site of the enzyme. Consistent with the crystallographic data, inductively coupled plasma mass spectrometry (ICP-MS) and total reflection X-ray fluorescence (TRXF) revealed the bound metal species to be primarily iron. A 3D structure guided analysis of environmental DddP lyase sequences elucidated the critical residues for metal binding are invariant, suggesting all proteins in the DddP family are metalloenzymes.

Photosynthetic characteristics of marine aerobic anoxygenic phototrophic bacteria Roseobacter and Erythrobacter strains.

A coastal Roseobacter strain of marine aerobic anoxygenic phototrophic bacteria (AAnPB) was isolated and phylogenetically determined. The strain OBYS 0001 was characterized by its physiological and biochemical properties with reference to the Erythrobacter longus type strain NBRC 14126. When grown in batch cultures, the growth curves of the both strains were similar. Cellular bacteriochlorophyll a concentrations of the strains reached the maxima in the stationary growth conditions. In vivo fluorescence excitation/optical density spectra between 470 and 600 nm for OBYS 0001 represented higher values than NBRC 14126. Variable fluorescence measurements revealed that the functional absorption cross section (σ) of the bacterial photosynthetic complexes for OBYS 0001 was significantly higher than that for NBRC 14126 under green excitation. These results suggest that Roseobacter can capture green light more efficiently than Erythrobacter for photosynthesis. The photochemical quantum efficiencies (F (v)/F (m)) of the bacterial photosynthetic complexes for OBYS 0001 were consistently lower than those for NBRC 14126. A relationship between the growth rate and F (v)/F (m) was significant for OBYS 0001, but that was not found for NBRC 14126. These results suggested that F (v)/F (m) for AAnPB could not be used as a proxy of the growth rate which is consistent with their mostly heterotrophic characters.

Molecular origins and consequences of High-800 LH2 in Roseobacter denitrificans.

Roseobacter denitrificans is a marine bacterium capable of using a wide variety of different metabolic schemes and in particular is an anoxygenic aerobic photosynthetic bacterium. In the work reported here we use a deletion mutant that we have constructed to investigate the structural origin of the unusual High-800 light-harvesting complex absorption in this bacterium. We suggest that the structure is essentially unaltered when compared to the usual nonameric complexes but that a change in the environment of the C(13:1) carbonyl group is responsible for the change in spectrum. We tentatively relate this change to the presence of a serine residue in the α-polypeptide. Surprisingly, the low spectral overlap between the peripheral and core light-harvesting systems appears not to compromise energy collection efficiency too severely. We suggest that this may be at the expense of maintaining a low antenna size.

Energy transfer in an LH4-like light harvesting complex from the aerobic purple photosynthetic bacterium Roseobacter denitrificans.

A peripheral light-harvesting complex from the aerobic purple bacterium Roseobacter (R.) denitrificans was purified and its photophysical properties characterized. The complex contains two types of pigments, bacteriochlorophyll (BChl) a and the carotenoid (Car) spheroidenone and possesses unique spectroscopic properties. It appears to lack the B850 bacteriochlorophyll a Q(y) band that is typical for similar light-harvesting complex 2 antennas. Circular dichroism and low temperature steady-state absorption spectroscopy revealed that the B850 band is present but is shifted significantly to shorter wavelengths and overlaps with the B800 band at room temperature. Such a spectral signature classifies this protein as a member of the light-harvesting complex 4 class of peripheral light-harvesting complexes, along with the previously known light-harvesting complex 4 from Rhodopseudomonas palustris. The influence of the spectral change on the light-harvesting ability was studied using steady-state absorption, fluorescence, circular dichroism, femtosecond and microsecond time-resolved absorption and time-resolved fluorescence spectroscopies. The results were compared to the properties of the similar (in pigment composition) light-harvesting complex 2 from aerobically grown Rhodobacter sphaeroides and are understood within the context of shared similarities and differences and the putative influence of the pigments on the protein structure and its properties.

Phage resistance of a marine bacterium, Roseobacter denitrificans OCh114, as revealed by comparative proteomics.

Roseobacter is a dominant lineage in the marine environment. This group of bacteria is diverse in terms of both their phylogenetic composition and their physiological potential. Roseobacter denitrificans OCh114 is one of the most studied bacteria of the Roseobacter lineage. Recently, a lytic phage (RDJLPhi1) that infects this bacterium was isolated and a mutant strain (M1) of OCh114 that is resistant to RDJLPhi1 was also obtained. Here, we investigate the mechanisms supporting phage resistance of M1. Our results excluded the possibilities of several phage resistance mechanisms, including abortive infection, lysogeny, and the clustered regularly interspaced short palindromic repeats (CRISPRs) related mechanism. Adsorption kinetics assays revealed that adsorption inhibition might be a potential cause for the phage resistance of M1. Comparative proteomic analysis of M1 and OCh114 revealed significant changes in the membrane protein compliment of these bacteria. Five membrane proteins with important biological functions were significantly down-regulated in the phage-resistant M1. Meanwhile, several outer membrane porins with different modifications and an OmpA family domain protein were markedly up-regulated. We hypothesize that the down-regulated membrane proteins in M1 may serve as the potential phage receptors, whose absence prevented the adsorption of phage RDJLPhi1 to host cells and subsequent infection.

Antibacterial activity of marine culturable bacteria collected from a global sampling of ocean surface waters and surface swabs of marine organisms.

The purpose of the present study was to isolate marine culturable bacteria with antibacterial activity and hence a potential biotechnological use. Seawater samples (244) and 309 swab samples from biotic or abiotic surfaces were collected on a global Danish marine research expedition (Galathea 3). Total cell counts at the seawater surface were 5 x 10(5) to 10(6) cells/ml, of which 0.1-0.2% were culturable on dilute marine agar (20 degrees C). Three percent of the colonies cultured from seawater inhibited Vibrio anguillarum, whereas a significantly higher proportion (13%) of colonies from inert or biotic surfaces was inhibitory. It was not possible to relate a specific kind of eukaryotic surface or a specific geographic location to a general high occurrence of antagonistic bacteria. Five hundred and nineteen strains representing all samples and geographic locations were identified on the basis of partial 16S rRNA gene sequence homology and belonged to three major groups: Vibrionaceae (309 strains), Pseudoalteromonas spp. (128 strains), and the Roseobacter clade (29 strains). Of the latter, 25 strains were identified as Ruegeria mobilis or pelagia. When re-testing against V. anguillarum, only 409 (79%) retained some level of inhibitory activity. Many strains, especially Pseudoalteromonas spp. and Ruegeria spp., also inhibited Staphylococcus aureus. The most pronounced antibacterial strains were pigmented Pseudoalteromonas strains and Ruegeria spp. The inhibitory, pigmented Pseudoalteromonas were predominantly isolated in warmer waters from swabs of live or inert surfaces. Ruegeria strains were isolated from all ocean areas except for Arctic and Antarctic waters and inhibitory activity caused by production of tropodithietic acid.

Characterization of the photosynthetic apparatus and proteome of Roseobacter denitrificans.

The phototrophic capacity of aerobic anoxygenic phototrophic bacteria endows them with a selective advantage over other heterotrophic bacteria in the oligotrophic ocean. Here, we reported the phototrophic features and proteome of an aerobic phototrophic bacterium Roseobacter denitrificans under starvation stress. The fluorescence induction and relaxation measurements suggested that the photosynthetic capacity in R. denitrificans was preserved but was lower than in the photoautotrophic bacterium Rhodobacter sphaeroides. The existence of light-harvesting complexes (LH1 and LH2) and the reaction center (RC) in the native membrane were demonstrated through atomic force microscopy image analysis as direct evidence of their phototrophy. The homology-based LH1-RC complex structure was proposed in which RC was the Rb. sphaeroides homolog structure surrounded by the LH1. Moreover, the protein expression profiles of cells in the stationary phase under heterotrophic and mixotrophic conditions show that light enhanced or activated some proteins such as carbon monoxide dehydrogenase and NifU to cope with the low levels of amino acids and carbon sources under starvation conditions.

Identification and biosynthesis of tropone derivatives and sulfur volatiles produced by bacteria of the marine Roseobacter clade.

Bacteria of the Roseobacter clade are abundant marine bacteria and are important contributors to the global sulfur cycle. The volatiles produced by two of its members, Phaeobacter gallaeciensis and Oceanibulbus indolifex, were analyzed to investigate whether the released compounds are derived from sulfur metabolism, and which biosynthetic pathways are involved in their formation. Both bacteria emitted different sulfides and thioesters, including new natural compounds such as S-methyl phenylethanethioate (16) and butyl methanesulfonate (21). The S-methyl alkanoates were identified by comparison with standards that were synthesized from the respective methyl alkanoates by a new method using an easily prepared aluminium/sulfur reagent. Phaeobacter gallaeciensis is also able to produce tropone (37) in large amounts. Its biosynthesis was investigated by various feeding experiments, showing that 37 is formed via a deviation of the phenylacetate catabolism. The unstable tropone hydrate 42 was identified as an intermediate of the tropone biosynthesis that was also released together with tropolone (38).

High-resolution architecture of the outer membrane of the Gram-negative bacteria Roseobacter denitrificans.

The outer membrane of Gram-negative bacteria protects the cell against bactericidal substances. Passage of nutrients and waste is assured by outer membrane porins, beta-barrel transmembrane channels. While atomic structures of several porins have been solved, so far little is known on the supramolecular structure of the outer membrane. Here we present the first high-resolution view of a bacterial outer membrane gently purified maintaining remnants of peptidoglycan on the perisplasmic surface. Atomic force microscope images of outer membrane fragments of the size of approximately 50% of the bacterial envelope revealed that outer membrane porins are by far more densely packed than previously assumed. Indeed the outer membrane is a molecular sieve rather than a membrane. Porins cover approximately 70% of the membrane surface and form locally regular lattices. The potential role of exposed aromatic residues in the formation of the supramolecular assembly is discussed. Finally, we present first structural data of the outer membrane porin from the marine Gram-negative bacteria Roseobacter denitrificans, and we perform a sequence alignment with porins of known structure.

Thalassococcus halodurans gen. nov., sp. nov., a novel halotolerant member of the Roseobacter clade isolated from the marine sponge Halichondria panicea at Friday Harbor, USA.

A Gram-negative, non-pigmented, ovoid-shaped, strictly aerobic, catalase- and oxidase-positive and highly halotolerant bacterial strain that was devoid of swimming and gliding motility, designated UST050418-052(T), was isolated from the surface of the marine sponge Halichondria panicea at Friday Harbor, WA, USA. Strain UST050418-052(T) required NaCl for growth and could tolerate salt concentrations of up to 18 %. The primary respiratory quinone was ubiquinone-10 and the DNA G+C content was 57.8 mol%. The predominant fatty acids were the saturated fatty acids 16 : 0 and 18 : 0 and the monounsaturated fatty acids 18 : 1 omega 7c and 18 : 1 omega 9c, altogether representing 82.9 % of the total. Phylogenetic analysis based on the 16S rRNA gene sequence placed UST050418-052(T) in a distinct lineage within the Roseobacter clade in the family Rhodobacteraceae, with 95.0-95.8 % sequence similarity to members of the nearest genus Thalassobius. The DNA-DNA relatedness between UST050418-052(T) and Thalassobius gelatinovorus IAM 12617(T) was 9 %. Strain UST050418-052(T) could be differentiated from closely related members of the Roseobacter clade by a number of chemotaxonomic and phenotypic characteristics such as its distinct fatty acid profile, ability to reduce nitrate to nitrite and inability to utilize citrate, succinate, L-arginine and pyruvate. Based on the phylogenetic, chemotaxonomic and phenotypic evidence presented in this study, we suggest that strain UST050418-052(T) represents a novel genus in the family Rhodobacteraceae. The name Thalassococcus halodurans gen. nov., sp. nov., is thus proposed. The type strain of Thalassococcus halodurans is UST050418-052(T) (=JCM 13833(T) =NRRL B-41465(T)).

Wenxinia marina gen. nov., sp. nov., a novel member of the Roseobacter clade isolated from oilfield sediments of the South China Sea.

An aerobic and heterotrophic, Gram-negative bacterial isolate, strain HY34(T), was isolated from sediment of an oilfield in the South China Sea, China. The taxonomy of strain HY34(T) was studied by phenotypic and phylogenetic methods. Strain HY34(T) formed faint-pink colonies on marine agar 2216. Cells of strain HY34(T) were non-motile, ovoid or short rods. Strain HY34(T) was positive for catalase and oxidase, and nitrate was reduced to nitrite. The nearly complete 16S rRNA gene sequence of strain HY34(T) was obtained and sequence analysis showed that it, together with the genus Rubellimicrobium, formed a distinct clade close to some members of the Roseobacter clade in the family Rhodobacteraceae, and it showed highest sequence similarities to Oceanicola granulosus HTCC2516(T) (93.8 %), Silicibacter lacuscaerulensis ITI-1157(T) (93.3 %), Dinoroseobacter shibae DFL 12(T) (93.3 %) and Rubellimicrobium thermophilum C-lvk-R2A-2(T) (92.2 %). Bacteriochlorophyll a was not detected. The ubiquinone system was Q-10. The major polar lipids were phosphatidylglycerol, phosphatidylcholine and an unidentified glycolipid. The major fatty acids (>10 %) were C(18 : 1) omega 7c and C(16 : 0). The DNA G+C content of this strain was 69.4 mol%. A polyphasic analysis supported the conclusion that this strain represents a novel genus and species, which we designated Wenxinia marina gen. nov., sp. nov. The type strain of Wenxinia marina is HY34(T) (=CGMCC 1.6105(T) =JCM 14017(T)).