Natronospira bacteriovora sp. nov., and Natronospira elongata sp. nov., extremely salt-tolerant predatory proteolytic bacteria from soda lakes and proposal to classify the genus Natronospira into Natronospiraceae fam. nov., and Natronospirales ord. nov., within the class Gammaproteobacteria.

The genus Natronospira is represented by a single species of extremely salt-tolerant aerobic alkaliphilic proteolytic bacterium, isolated from hypersaline soda lakes. When cells of Gram-positive cocci were used as a substrate instead of proteins at extremely haloalkaline conditions, two new members of this genus were enriched and isolated in pure culture from the same sites. Strains AB-CW1 and AB-CW4 are obligate aerobic heterotrophic proteolytic bacteria able to feed on both live and dead cells of staphylococci and a range of proteins and peptides. Similar to the type species, N. proteinivora, the isolates are extremely salt-tolerant obligate alkaliphiles. However, N. proteinivora was unable to use bacterial cells as a substrate. Electron microscopy showed direct contact between the prey and predator cells. Functional analysis of the AB-CW1 and AB-CW4 genomes identified two sets of genes coding for extracellular enzymes potentially involved in the predation and proteolysis, respectively. The first set includes several copies of lysozyme-like GH23 peptidoglycan-lyase and murein-specific M23 [Zn]-di-peptidase enabling the cell wall degradation. The second set features multiple copies of secreted serine and metallopeptidases apparently allowing for the strong proteolytic phenotype. Phylogenomic analysis placed the isolates into the genus Natronospira as two novel species members, and furthermore indicated that this genus forms a deep-branching lineage of a new family (Natronospiraceae) and order (Natronospirales) within the class Gammaproteobacteria. On the basis of distinct phenotypic and genomic properties, strain AB-CW1T (JCM 335396 = UQM 41579) is proposed to be classified as Natronospira elongata sp. nov., and AB-CW4T (JCM 335397 = UQM 41580) as Natronospira bacteriovora sp. nov.

Selective lipid recruitment by an archaeal DPANN symbiont from its host.

The symbiont Ca. Nanohaloarchaeum antarcticus is obligately dependent on its host Halorubrum lacusprofundi for lipids and other metabolites due to its lack of certain biosynthetic genes. However, it remains unclear which specific lipids or metabolites are acquired from its host, and how the host responds to infection. Here, we explored the lipidome dynamics of the Ca. Nha. antarcticus - Hrr. lacusprofundi symbiotic relationship during co-cultivation. By using a comprehensive untargeted lipidomic methodology, our study reveals that Ca. Nha. antarcticus selectively recruits 110 lipid species from its host, i.e., nearly two-thirds of the total number of host lipids. Lipid profiles of co-cultures displayed shifts in abundances of bacterioruberins and menaquinones and changes in degree of bilayer-forming glycerolipid unsaturation. This likely results in increased membrane fluidity and improved resistance to membrane disruptions, consistent with compensation for higher metabolic load and mechanical stress on host membranes when in contact with Ca. Nha. antarcticus cells. Notably, our findings differ from previous observations of other DPANN symbiont-host systems, where no differences in lipidome composition were reported. Altogether, our work emphasizes the strength of employing untargeted lipidomics approaches to provide details into the dynamics underlying a DPANN symbiont-host system.

Natronoglomus mannanivorans gen. nov., sp. nov., beta-1,4-mannan utilizing natronoarchaea from hypersaline soda lakes.

Beta-mannans are insoluble plant polysaccharides with beta-1,4-linked mannose as the backbone. We used three forms of this polysaccharide, namely, pure mannan, glucomannan, and galactomannan, to enrich haloarchaea, which have the ability to utilize mannans for growth. Four mannan-utilizing strains obtained in pure cultures were closely related to each other on the level of the same species. Furthermore, another strain selected from the same habitats with a soluble beta-1,4-glucan (xyloglucan) was also able to grow with mannan. The phylogenomic analysis placed the isolates into a separate lineage of the new genus level within the family Natrialbaceae of the class Halobacteria. The strains are moderate alkaliphiles, extremely halophilic, and aerobic saccharolytics. In addition to the three beta-mannan forms, they can also grow with cellulose, xylan, and xyloglucan. Functional genome analysis of two representative strains demonstrated the presence of several genes coding for extracellular endo-beta-1,4-mannanase from the GH5_7 and 5_8 subfamilies and the GH26 family of glycosyl hydrolases. Furthermore, a large spectrum of genes encoding other glycoside hydrolases that were potentially involved in the hydrolysis of cellulose and xylan were also identified in the genomes. A comparative genomics analysis also showed the presence of similar endo-beta-1,4-mannanase homologs in the cellulotrophic genera Natronobiforma and Halococcoides. Based on the unique physiological properties and the results of phylogenomic analysis, the novel mannan-utilizing halolarchaea are proposed to be classified into a new genus and species Natronoglomus mannanivorans gen. nov., sp. nov. with the type strain AArc-m2/3/4 (=JCM 34861=UQM 41565).

Developing a genetic approach to target cyanobacterial producers of heterocyte glycolipids in the environment.

Heterocytous cyanobacteria are important players in the carbon and nitrogen cycle. They can fix dinitrogen by using heterocytes, specialized cells containing the oxygen-sensitive nitrogenase enzyme surrounded by a thick polysaccharide and glycolipid layer which prevents oxygen diffusion and nitrogenase inactivation. Heterocyte glycolipids can be used to detect the presence of heterocytous cyanobacteria in present-day and past environments, providing insight into the functioning of the studied ecosystems. However, due to their good preservation throughout time, heterocyte glycolipids are not ideal to detect and study living communities, instead methods based on DNA are preferred. Currently cyanobacteria can be detected using untargeted genomic approaches such as metagenomics, or they can be specifically targeted by, for example, the use of primers that preferentially amplify their 16S rRNA gene or their nifH gene in the case of nitrogen fixing cyanobacteria. However, since not all cyanobacterial nitrogen fixers are heterocytous, there is currently no fast gene-based method to specifically detect and distinguish heterocytous cyanobacteria. Here, we developed a PCR-based method to specifically detect heterocytous cyanobacteria by designing primers targeting the gene (hglT) encoding the enzyme responsible for the last step in the biosynthesis of heterocyte glycolipid (i.e., a glycosyltransferase). We designed several primer sets using the publicly available sequences of 23 heterocytous cyanobacteria, after testing them on DNA extracts of 21 heterocyte-forming and 7 non-heterocyte forming freshwater cyanobacteria. The best primer set was chosen and successfully used to confirm the presence of heterocytous cyanobacteria in a marine environmental sample.

Dominance of mixed ether/ester, intact polar membrane lipids in five species of the order Rubrobacterales: Another group of bacteria not obeying the "lipid divide".

The composition of the core lipids and intact polar lipids (IPLs) of five Rubrobacter species was examined. Methylated (ω-4) fatty acids (FAs) characterized the core lipids of Rubrobacter radiotolerans, R. xylanophilus and R. bracarensis. In contrast, R. calidifluminis and R. naiadicus lacked ω-4 methyl FAs but instead contained abundant (i.e., 34-41 % of the core lipids) ω-cyclohexyl FAs not reported before in the order Rubrobacterales. Their genomes contained an almost complete operon encoding proteins enabling production of cyclohexane carboxylic acid CoA thioester, which acts as a building block for ω-cyclohexyl FAs in other bacteria. Hence, the most plausible explanation for the biosynthesis of these cyclic FAs in R. calidifluminis and R. naiadicus is a recent acquisition of this operon. All strains contained 1-O-alkyl glycerol ether lipids in abundance (up to 46 % of the core lipids), in line with the dominance (>90 %) of mixed ether/ester IPLs with a variety of polar headgroups. The IPL head group distribution of R. calidifluminis and R. naiadicus differed, e.g. they lacked a novel IPL tentatively assigned as phosphothreoninol. The genomes of all five Rubrobacter species contained a putative operon encoding the synthesis of the 1-O-alkyl glycerol phosphate, the presumed building block of mixed ether/ester IPLs, which shows some resemblance with an operon enabling ether lipid production in various other aerobic bacteria but requires more study. The uncommon dominance of mixed ether/ester IPLs in Rubrobacter species exemplifies our recent growing awareness that the lipid divide between archaea and bacteria/eukaryotes is not as clear cut as previously thought.

Disentangling the lipid divide: Identification of key enzymes for the biosynthesis of membrane-spanning and ether lipids in Bacteria.

Bacterial membranes are composed of fatty acids (FAs) ester-linked to glycerol-3-phosphate, while archaea have membranes made of isoprenoid chains ether-linked to glycerol-1-phosphate. Many archaeal species organize their membrane as a monolayer of membrane-spanning lipids (MSLs). Exceptions to this "lipid divide" are the production by some bacterial species of (ether-bound) MSLs, formed by tail-to-tail condensation of FAs resulting in the formation of (iso) diabolic acids (DAs), which are the likely precursors of paleoclimatological relevant branched glycerol dialkyl glycerol tetraether molecules. However, the enzymes responsible for their production are unknown. Here, we report the discovery of bacterial enzymes responsible for the condensation reaction of FAs and for ether bond formation and confirm that the building blocks of iso-DA are branched iso-FAs. Phylogenomic analyses of the key biosynthetic genes reveal a much wider diversity of potential MSL (ether)-producing bacteria than previously thought, with importantt implications for our understanding of the evolution of lipid membranes.

Natranaeroarchaeum sulfidigenes gen. nov., sp. nov., carbohydrate-utilizing sulfur-respiring haloarchaeon from hypersaline soda lakes, a member of a new family Natronoarchaeaceae fam. nov. in the order Halobacteriales.

A pure culture of alkaliphilic haloarchaeon strain AArc-ST capable of anaerobic growth by carbohydrate-dependent sulfur respiration was obtained from hypersaline lakes in southwestern Siberia. According to phylogenetic analysis, AArc-ST formed a new genus level branch most related to the genus Natronoarchaeum in the order Halobacteriales. The strain is facultatively anaerobic with strictly respiratory metabolism growing either by anaerobic respiration with elemental sulfur and thiosulfate as the electron acceptors or by aerobic respiration at microoxic conditions. Thiosulfate is reduced partially to sulfide and sulfite. It is a first sulfur-reducing alkaliphilic haloarchaeon utilizing sugars, starch and glycerol as substrates for anaerobic growth. It is extremely halophilic (optimum at 3.5 M total Na+) and obligately alkaliphilic (optimum at pH 9.5). The dominant polar lipids include PG and PGP-Me with the archaeol (C20-C20) or extended archaeol (C20-C25) cores. The dominant respiratory lipoquinone is MK-8:8. On the basis of unique physiological properties and results of phylogenetic analysis, the soda lake isolate is suggested to be classified into a novel genus and species Natranaeroarchaeum sulfidigenes gen. nov., sp. nov. (=JCM 34033T = UNIQEM U1000T). Furthermore, on the bases of phylogenomic reconstruction, a new family Natronoarchaeaceae fam. nov. is proposed within the order Halobacteriales incorporating Natranaeroarchaeum and three related genera: Natronoarchaeum, Salinarchaeum and Halostella.

Anatilimnocola floriformis sp. nov., a novel member of the family Pirellulaceae from a boreal lake, and emended description of the genus Anatilimnocola.

Planctomycetes of the family Pirellulaceae are commonly addressed as budding aquatic bacteria with a complex lifestyle. Although this family is well represented by cultured and taxonomically characterized isolates, nearly all of them were obtained from brackish or marine habitats. The examples of described freshwater Pirellulaceae planctomycetes are limited to two species only, Pirellula staley and 'Anatilimnocola aggregata'. In this study, we characterized a novel freshwater planctomycete of the genus 'Anatilimnocola', strain PX40T, which was isolated from a boreal eutrophic lake. Strain PX40T was represented by budding, unpigmented, ellipsoidal to pear-shaped cells, which often occurred in characteristic flower-like rosettes. Cells were covered by bundles of fimbriae; crateriform-like structures were localized on a reproductive cell pole only. These planctomycetes were obligately aerobic, heterotrophic bacteria that utilized various sugars and some polysaccharides, and were highly sensitive to NaCl. Growth occurred in the pH range 5.0-7.5 (with an optimum at pH 6.5-7.0), and at temperatures between 15 and 30 °C (with an optimum at 22-25 °C). The major fatty acids of strain PX40T were C18:1ω9c, C16:0, and 16:1ω7c; cells also contained a wide variety of hydroxy- and dihydroxy-fatty acids and a C31:9 alkene. The major intact polar lipids were diacylglyceryl-(N,N,N)-trimethylhomoserines. The 16S rRNA gene sequence of strain PX40T displayed 96.6% similarity to that of 'Anatilimnocola aggregata' ETA_A8T. The genome of strain PX40T was 8.93 Mb in size and contained one copy of rRNA operon, 76 tRNA genes and 7092 potential protein-coding genes. The DNA G+C content was 57.8%. The ANI value between strain PX40T and 'Anatilimnocola aggregata' ETA_A8T was 78.3%, suggesting that these planctomycetes represent distinct species. We, therefore, propose a novel species of the genus 'Anatilimnocola', 'A. floriformis' sp. nov., with strain PX40T (= KCTC 92369T = VKM B-3621T = UQM 41463T) as the type strain.

Acetate Degradation at Low pH by the Moderately Acidophilic Sulfate Reducer Acididesulfobacillus acetoxydans gen. nov. sp. nov.

In acid drainage environments, biosulfidogenesis by sulfate-reducing bacteria (SRB) attenuates the extreme conditions by enabling the precipitation of metals as their sulfides, and the neutralization of acidity through proton consumption. So far, only a handful of moderately acidophilic SRB species have been described, most of which are merely acidotolerant. Here, a novel species within a novel genus of moderately acidophilic SRB is described, Acididesulfobacillus acetoxydans gen. nov. sp. nov. strain INE, able to grow at pH 3.8. Bioreactor studies with strain INE at optimum (5.0) and low (3.9) pH for growth showed that strain INE alkalinized its environment, and that this was more pronounced at lower pH. These studies also showed the capacity of strain INE to completely oxidize organic acids to CO2, which is uncommon among acidophilic SRB. Since organic acids are mainly in their protonated form at low pH, which increases their toxicity, their complete oxidation may be an acid stress resistance mechanism. Comparative proteogenomic and membrane lipid analysis further indicated that the presence of saturated ether-bound lipids in the membrane, and their relative increase at lower pH, was a protection mechanism against acid stress. Interestingly, other canonical acid stress resistance mechanisms, such as a Donnan potential and increased active charge transport, did not appear to be active.

Corrigendum: Hydrolytic Capabilities as a Key to Environmental Success: Chitinolytic and Cellulolytic Acidobacteria From Acidic Sub-arctic Soils and Boreal Peatlands.

[This corrects the article DOI: 10.3389/fmicb.2018.02775.].

Changes in the membrane lipid composition of a Sulfurimonas species depend on the electron acceptor used for sulfur oxidation.

Sulfurimonas species are among the most abundant sulfur-oxidizing bacteria in the marine environment. They are capable of using different electron acceptors, this metabolic flexibility is favorable for their niche adaptation in redoxclines. When oxygen is depleted, most Sulfurimonas spp. (e.g., Sulfurimonas gotlandica) use nitrate ([Formula: see text]) as an electron acceptor to oxidize sulfur, including sulfide (HS-), S0 and thiosulfate, for energy production. Candidatus Sulfurimonas marisnigri SoZ1 and Candidatus Sulfurimonas baltica GD2, recently isolated from the redoxclines of the Black Sea and Baltic Sea respectively, have been shown to use manganese dioxide (MnO2) rather than [Formula: see text] for sulfur oxidation. The use of different electron acceptors is also dependent on differences in the electron transport chains embedded in the cellular membrane, therefore changes in the membrane, including its lipid composition, are expected but are so far unexplored. Here, we used untargeted lipidomic analysis to reveal changes in the composition of the lipidomes of three representative Sulfurimonas species grown using either [Formula: see text] and MnO2. We found that all Sulfurimonas spp. produce a series of novel phosphatidyldiazoalkyl-diacylglycerol lipids. Ca. Sulfurimonas baltica GD2 adapts its membrane lipid composition depending on the electron acceptors it utilizes for growth and survival. When carrying out MnO2-dependent sulfur oxidation, the novel phosphatidyldiazoalkyl-diacylglycerol headgroup comprises shorter alkyl moieties than when sulfur oxidation is [Formula: see text]-dependent. This is the first report of membrane lipid adaptation when an organism is grown with different electron acceptors. We suggest novel diazoalkyl lipids have the potential to be used as a biomarker for different conditions in redox-stratified systems.

Changes in the Distribution of Membrane Lipids during Growth of Thermotoga maritima at Different Temperatures: Indications for the Potential Mechanism of Biosynthesis of Ether-Bound Diabolic Acid (Membrane-Spanning) Lipids.

Membrane-spanning lipids are present in a wide variety of archaea, but they are rarely in bacteria. Nevertheless, the (hyper)thermophilic members of the order Thermotogales harbor tetraester, tetraether, and mixed ether/ester membrane-spanning lipids mostly composed of core lipids derived from diabolic acids, C30, C32, and C34 dicarboxylic acids with two adjacent mid-chain methyl substituents. Lipid analysis of Thermotoga maritima across growth phases revealed a decrease of the relative abundance of fatty acids together with an increase of diabolic acids with independence of growth temperature. We also identified isomers of C30 and C32 diabolic acids, i.e., dicarboxylic acids with only one methyl group at C-15. Their distribution suggests they are products of the condensation reaction but are preferably produced when the length of the acyl chains is not optimal. Compared with growth at the optimal temperature of 80°C, an increase of glycerol ether-derived lipids was observed at 55°C. Our analysis only detected diabolic acid-containing intact polar lipids with phosphoglycerol (PG) head groups. Considering these findings, we hypothesize a biosynthetic pathway for the synthesis of membrane-spanning lipids based on PG polar lipid formation, suggesting that the protein catalyzing this process is a membrane protein. We also identified, by genomic and protein domain analyses, a gene coding for a putative plasmalogen synthase homologue in T. maritima that is also present in other bacteria producing sn-1-alkyl ether lipids but not plasmalogens, suggesting it is involved in the conversion of the ester-to-ether bond in the diabolic acids bound in membrane-spanning lipids. IMPORTANCE Membrane-spanning lipids are unique compounds found in most archaeal membranes, but they are also present in specific bacterial groups like the Thermotogales. The synthesis and physiological role of membrane-spanning lipids in bacteria represent an evolutionary and biochemical open question that points to the differentiation of the membrane lipid composition. Understanding the formation of membrane-spanning lipids is crucial to solving this question and identifying the enzymatic and biochemical mechanism performing this procedure. In the present work, we found changes at the core lipid level, and we propose that the growth phase drives the biosynthesis of these lipids rather than temperature. Our results identified physiological conditions influencing the membrane-spanning lipid biosynthetic process, which can further clarify the pathway leading to the biosynthesis of these compounds.

Microbial membrane lipid adaptations to high hydrostatic pressure in the marine environment.

The deep-sea is characterized by extreme conditions, such as high hydrostatic pressure (HHP) and near-freezing temperature. Piezophiles, microorganisms adapted to high pressure, have developed key strategies to maintain the integrity of their lipid membrane at these conditions. The abundance of specific membrane lipids, such as those containing unsaturated and branched-chain fatty acids, rises with increasing HHP. Nevertheless, this strategy is not universal among piezophiles, highlighting the need to further understand the effects of HHP on microbial lipid membranes. Challenges in the study of lipid membrane adaptations by piezophiles also involve methodological developments, cross-adaptation studies, and insight into slow-growing piezophiles. Moreover, the effects of HHP on piezophiles are often difficult to disentangle from effects caused by low temperature that are often characteristic of the deep sea. Here, we review the knowledge of membrane lipid adaptation strategies of piezophiles, and put it into the perspective of marine systems, highlighting the future challenges of research studying the effects of HHP on the microbial lipid composition.

Reconstructing the diet, trophic level and migration pattern of mysticete whales based on baleen isotopic composition.

Baleen from mysticete whales is a well-preserved proteinaceous material that can be used to identify migrations and feeding habits for species whose migration pathways are unknown. Analysis of δ13C and δ15N values from bulk baleen have been used to infer migration patterns for individuals. However, this approach has fallen short of identifying migrations between regions as it is difficult to determine variations in isotopic shifts without temporal sampling of prey items. Here, we apply analysis of δ15N values of amino acids to five baleen plates belonging to three species, revealing novel insights on trophic position, metabolic state and migration between regions. Humpback and minke whales had higher reconstructed trophic levels than fin whales (3.7-3.8 versus 3-3.2, respectively) as expected due to different feeding specialization. Isotopic niche areas between baleen minima and maxima were well separated, indicating regional resource use for individuals during migration that aligned with isotopic gradients in Atlantic Ocean particulate organic matter. Phenylanine δ15N values confirmed regional separation between the niche areas for two fin whales as migrations occurred and elevated glycine and threonine δ15N values suggested physiological changes due to fasting. Simultaneous resolution of trophic level and physiological changes allow for identification of regional migrations in mysticetes.

The physiology and metabolic properties of a novel, low-abundance Psychrilyobacter species isolated from the anoxic Black Sea shed light on its ecological role.

Members of the Psychrilyobacter spp. of the phylum Fusobacteria have been recently suggested to be amongst the most significant primary degraders of the detrital organic matter in sulfidic marine habitats, despite representing only a small proportion (<0.1%) of the microbial community. In this study, we have isolated a previously uncultured Psychrilyobacter species (strains SD5T and BL5; Psychrilyobacter piezotolerans sp. nov.) from the sulfidic waters (i.e., 2000 m depth) of the Black Sea and investigated its physiology and genomic capability in order to better understand potential ecological adaptation strategies. P. piezotolerans utilized a broad range of organic substituents (carbohydrates and proteins) and, remarkably, grew at sulfide concentrations up to 32 mM. These flexible physiological properties were supported by the presence of the respective metabolic pathways in the genomes of both strains. Growth at varying hydrostatic pressure (0.1-50 MPa) was sustained by modifying its membrane lipid composition. Thus, we have isolated a novel member of the 'rare biosphere', which endures the extreme conditions and may play a significant role in the degradation of detrital organic matter sinking into the sulfidic waters of the Black Sea.

Halapricum desulfuricans sp. nov., carbohydrate-utilizing, sulfur-respiring haloarchaea from hypersaline lakes.

Nine pure cultures of neutrophilic haloaloarchaea capable of anaerobic growth by carbohydrate-dependent sulfur respiration were isolated from hypersaline lakes in southwestern Siberia and southern Russia. According to phylogenomic analysis the isolates were closely related to each other and formed a new species within the genus Halapricum (family Haloarculaceae). They have three types of catabolism: fermentative, resulting in H2 formation; anaerobic respiration using sulfur compounds as e-acceptors and aerobic respiration. Apart from elemental sulfur, all isolates can also use three different sulfoxides as acceptors and the type strain also grows with thiosulfate, reducing it partially to sulfide and sulfite. All strains utilized sugars and glycerol as the e-donors and C source for anaerobic growth and some can also grow with alpha-glucans, such as starch and dextrins. The major respiratory menaquinones are MK-8:8 and MK-8:7, but 5-19% consists of "thermoplasmata" quinones (MMK-8:8 and MMK-8:7), whose occurrence in haloarchaea is unprecedented. On the basis of their unique physiological properties and results of phylogenomic analysis, the isolates are suggested to be classified into a novel species Halapricum desulfuricans sp. nov. (type strain HSR12-2T = JCM 34032T = UNIQEM U1001T).

Lipidomics of Environmental Microbial Communities. I: Visualization of Component Distributions Using Untargeted Analysis of High-Resolution Mass Spectrometry Data.

Lipids, as one of the main building blocks of cells, can provide valuable information on microorganisms in the environment. Traditionally, gas or liquid chromatography coupled to mass spectrometry (MS) has been used to analyze environmental lipids. The resulting spectra were then processed through individual peak identification and comparison with previously published mass spectra. Here, we present an untargeted analysis of MS1 spectral data generated by ultra-high-pressure liquid chromatography coupled with high-resolution mass spectrometry of environmental microbial communities. Rather than attempting to relate each mass spectrum to a specific compound, we have treated each mass spectrum as a component, which can be clustered together with other components based on similarity in their abundance depth profiles through the water column. We present this untargeted data visualization method on lipids of suspended particles from the water column of the Black Sea, which included >14,000 components. These components form clusters that correspond with distinct microbial communities driven by the highly stratified water column. The clusters include both known and unknown compounds, predominantly lipids, demonstrating the value of this rapid approach to visualize component distributions and identify novel lipid biomarkers.

Lipidomics of Environmental Microbial Communities. II: Characterization Using Molecular Networking and Information Theory.

Structurally diverse, specialized lipids are crucial components of microbial membranes and other organelles and play essential roles in ecological functioning. The detection of such lipids in the environment can reveal not only the occurrence of specific microbes but also the physicochemical conditions to which they are adapted to. Traditionally, liquid chromatography coupled with mass spectrometry allowed for the detection of lipids based on chromatographic separation and individual peak identification, resulting in a limited data acquisition and targeting of certain lipid groups. Here, we explored a comprehensive profiling of microbial lipids throughout the water column of a marine euxinic basin (Black Sea) using ultra high-pressure liquid chromatography coupled with high-resolution tandem mass spectrometry (UHPLC-HRMS/MS). An information theory framework combined with molecular networking based on the similarity of the mass spectra of lipids enabled us to capture lipidomic diversity and specificity in the environment, identify novel lipids, differentiate microbial sources within a lipid group, and discover potential biomarkers for biogeochemical processes. The workflow presented here allows microbial ecologists and biogeochemists to process quickly and efficiently vast amounts of lipidome data to understand microbial lipids characteristics in ecosystems.

Total Synthesis of the Alleged Structure of Crenarchaeol Enables Structure Revision*.

Crenarchaeol is a glycerol dialkyl glycerol tetraether lipid produced exclusively in Archaea of the phylum Thaumarchaeota. This membrane-spanning lipid is undoubtedly the structurally most sophisticated of all known archaeal lipids and an iconic molecule in organic geochemistry. The 66-membered macrocycle possesses a unique chemical structure featuring 22 mostly remote stereocenters, and a cyclohexane ring connected by a single bond to a cyclopentane ring. Herein we report the first total synthesis of the proposed structure of crenarchaeol. Comparison with natural crenarchaeol allowed us to propose a revised structure of crenarchaeol, wherein one of the 22 stereocenters is inverted.

Organic Matter Type Defines the Composition of Active Microbial Communities Originating From Anoxic Baltic Sea Sediments.

Carbon cycling in anoxic marine sediments is dependent on uncultured microbial communities. Niches of heterotrophic microorganisms are defined by organic matter (OM) type and the different phases in OM degradation. We investigated how OM type defines microbial communities originating from organic-rich, anoxic sediments from the Baltic Sea. We compared changes in the sediment microbial community, after incubation with different stable isotope labeled OM types [i.e., particulate algal organic matter (PAOM), protein, and acetate], by using DNA stable isotope probing (DNA-SIP). Incorporation of 13C and/or 15N label was predominantly detected in members of the phyla Planctomycetes and Chloroflexi, which also formed the majority (>50%) of the original sediment community. While these phylum-level lineages incorporated label from all OM types, phylogenetic analyses revealed a niche separation at the order level. Members of the MSBL9 (Planctomycetes), the Anaerolineales (Chloroflexi), and the class Bathyarchaeota, were identified as initial degraders of carbohydrate-rich OM, while other uncultured orders, like the CCM11a and Phycisphaerales (Planctomycetes), Dehalococcoidia, and JG30-KF-CM66 (Chloroflexi), incorporated label also from protein and acetate. Our study highlights the importance of initial fermentation of complex carbon pools in shaping anoxic sediment microbial communities and reveals niche specialization at the order level for the most important initial degraders in anoxic sediments.