Browsing by Author "Michaelis, Walter"

Hexactinellid sponges are often considered to be the most ancient metazoans. Lipid biomarkers from 23 species were studied for information on their phylogenetic properties, particularly their disputed relation to the two other sponge classes (Demospongiae, Calcarea). The most prominent lipid compounds in the Hexactinellida comprise C-28 to C-32 polyenoic fatty acids. Their structures parallel the unique patterns found in demosponge membrane fatty acids ('demospongic acids') and strongly support a close phylogenetic association of the Demospongiae and the Hexactinellida. Both taxa also show unusual mid-chain methylated fatty acids (C-15-C-25) and irregular C-25- and C-40-isoprenoid hydrocarbons, tracers for specific eubacteria and Archaea, respectively. These biomarkers indicate a similar, highly conservative symbiont community, although some shift in the abundance of the associated microbiota was observed. The lack of these features in calcareous sponges further contradicts the still common view that Calcarea and Demospongiae are more closely related to each other than either is to the Hexactinellida.

A comprehensive approach using palaeontology, petrography, stable isotope geochemistry and biomarker analyses was applied to the study of seven small methane-seep carbonate deposits. These deposits are in the Oligocene part of the Lincoln Creek Formation, exposed along the Canyon and Satsop Rivers in western Washington. Each deposit preserves invertebrate fossils, many representing typical seep biota. Authigenic carbonates with delta(13)C values as low as -51parts per thousand PDB reveal that the carbon is predominately methane derived. Carbonates contain the irregular isoprenoid hydrocarbons 2,6,11,15-tetramethylhexadecane (crocetane) and 2,6,10,15,19-pentamethylicosane (PMI), lipid biomarkers diagnostic for archaea. These lipids are strongly depleted in C-13 (delta(13)C values as low as -120parts per thousand PDB), indicating that archaea were involved in the anaerobic oxidation of methane. Small filaments preserved in the carbonate may represent methanotrophic archaea. Archaeal methanogenesis induced the formation of a late diagenetic phase, brownish calcite, consisting of dumbbell-shaped crystal aggregates that exhibit delta(13)C values as high as +7parts per thousand PDB. Clotted microfabrics of primary origin point to microbial mediation of carbonate precipitation. Downward-directed carbonate aggregation in the seeps produced inverted stromatactoid cavities. Large filaments, interpreted as green algae based on their size, shape, arrangement and biomarkers, imply that deposition occurred, in places, in water no deeper than 210 m.

A Miocene methane-seep limestone from the Romagna Apennine (Pietralunga, Italy) was found to contain an extraordinarily well-preserved microbial mat consisting of filamentous fossils. Individual filaments of the lithified Pietralunga mat are 50 to 80 mum in diameter and resemble the sulfide-oxidizing bacterium Beggiatoa . Mats of sulfur bacteria are common around modern methane-seeps, but have not yet been reported from ancient seep limestones. This is thought to be related to the conditions prevailing in metabolically active mats of sulfur bacteria that do not favor carbonate formation. The preservation of the Pietralunga mat was most likely caused by a sudden change from oxidizing to anoxic conditions, leading to the rapid carbonate precipitation induced by anaerobic oxidation of methane. Lipid biomarkers specific for archaea and sulfate-reducing bacteria linked with the anaerobic oxidation of methane co-occur with compounds derived from methanotrophic bacteria and ciliates. These findings confirm a close proximity of oxic and anoxic conditions, as required for the growth of sulfide-oxidizing bacteria in the methane-based ecosystem. The lack of earlier reports on fossilized thiotrophic mats in seep limestones is most likely related to the rarity of environmental changes rapid enough to preserve the filaments rather than to a lower frequency of thiotrophic mats around methane-seeps in the geological past.

C-13-depleted E and Z n-tricos-10-enes are prominent biomarkers in an anaerobic microbial mat at Black Sea methane seeps. These n-alkenes co-occur with archaeal irregular C-25 isoprenoid hydrocarbons, namely 2,6,10,15,19-pentamethylicosanc (PMI) and -enes (PMI Delta). Low delta C-13-values (-73 and -77 parts per thousand) for n-tricosenes and PMI imply the anabolism of methane carbon by their source biota. The n-tricosenes apparently originate from microorganisms closely associated with, if not identical to isoprenoid-producing, methane-metabolizing Archaea. Methane-seep deposits of Tertiary to Jurassic ages showed the absence of n-tricosenes, but C-13-depleted n-tricosane (delta C-13 as low as -87 parts per thousand), a plausible diagenetic product, was observed in enhanced concentrations in 7 out of 9 samples studied. It is proposed that a preference of n-tricosane over the enveloping n-alkanes may provide a specific hydrocarbon fingerprint for the anaerobic cycling of methane in ancient settings. (C) 2001 Published by Elsevier Science Ltd.

Associated microorganisms have been described in numerous marine sponges. Their metabolic activity, however, has not yet been investigated in situ. We quantified for the first time microbial processes in a living sponge. Sulfate reduction rates of up to 1200 nmol cm(-3) d(-1) were measured in the cold-water bacteriosponge Geodia barretti. Oxygen profiles and chemical analysis of sponge tissue and canal water revealed steep oxygen gradients and a rapid turnover of oxygen and sulfide, dependent on the pumping activity of the sponge. Identification of the microbial community with fluorescently labelled oligonucleotide probes ( FISH) indicates the presence of sulfate-reducing bacteria belonging to the Desulfoarculus/Desulfomonile/Syntrophus-cluster in the choanosome of this sponge. Analysis of lipid biomarkers indicates biomass transfer from associated sulfate-reducing bacteria or other anaerobic microbes to sponge cells. These results show the presence of an anoxic micro-ecosystem in the sponge G. barretti, and imply mutualistic interactions between sponge cells and anaerobic microbes. Understanding the importance of anaerobic processes within the sponge/microbe system may help to answer unsolved questions in sponge ecology and biotechnology.

Calcium carbonate precipitation and microbialite formation at highly supersaturated mixing zones of thermal spring waters and alkaline lake water have been investigated at Pyramid Lake, Nevada. Without precipitation, pure mixing should lead to a nearly 100-fold supersaturation at 40°C. Physicochemical precipitation is modified or even inhibited by the properties of biofilms, dependent on the extent of biofilm development and the current precipitation rate. Mucus substances (extracellular polymeric substances, EPS, e.g., of cyanobacteria) serve as effective Ca2+-buffers, thus preventing seed crystal nucleation even in a highly supersaturated macroenvironment. Carbonate is then preferentially precipitated in mucus-free areas such as empty diatom tests or voids. After the buffer capacity of the EPS is surpassed, precipitation is observed at the margins of mucus areas. Hydrocarbon biomarkers extracted from (1) a calcifying Phormidium-biofilm, (2) the stromatolitic carbonate below, and (3) a fossil 'tufa' of the Pleistocene pinnacles, indicate that the cyanobacterial primary producers have been subject to significant temporal changes in their species distribution. Accordingly, the species composition of cyanobacterial biofilms does not appear to be relevant for the formation of microbial carbonates in Pyramid Lake. The results demonstrate the crucial influence of mucus substances on carbonate precipitation in highly supersaturated natural environments.

Gas seeps in the euxinic northwestern Black Sea provide an excellent opportunity to study anaerobic, methane-based ecosystems with minimum interference froin oxygen -dependent processes. An integrated approach using fluorescence- and electron microscopy, fluorescence in situ hybridization, lipid biomarkers, stable isotopes (delta(13)C), and petrography revealed insight into the anatomy of concretionary methane-derived carbonates currently forming within the sediment around seeps. Some of the carbonate concretions have been found to be surrounded by microbial mats. The mats harbour colonies of sulphate-reducing bacteria (DSS-group), and archaea (ANME-1), putative players in the anaerobic oxidation of methane. Isotopically-depleted lipid biomarkers indicate an uptake of methane carbon into the biomass of the mat biota, Microbial metabolism sustains the precipitation of concretionary carbonates, significantly depleted in C-13. The concretions consist of rectangularly orientated, rod- to dumbbell-shaped crystal aggregates made of fibrous high Mg-calcite. The sulphate-reducing bacteria exhibit intracellular storage inclusions, and magnetosomes with greigite (Fe3S4), indicating that iron cycling is involved in the metabolism of the microbial population. Transfer of Fe3+ into the cells is apparently mediated by abundant extracellular vesicles resembling known bacterial sideropbore vesicles (marinobactine) in size (20 to 100 nm) and structure. (c) 2005 Elsevier B.V. All rights reserved.

The associated microbial community in the mesohyl of the Arctic deep-water sponge Tentorium semisuberites Schmidt, 1870 (Hadromerida, Demospongiae) is dominated by Archaea. This is the result of an integral approach applying analyses of microbial lipid biomarkers as well as microscopic investigations using differential fluorescence in situ hybridisation with universal probes and counterstaining with 4 ',6 '-diamidino-2-phenylindole (DAPI) on sponge sections based on samples collected in the Greenland Sea in 2001, 2002 and 2005. The distribution of isoprenoidal C-40 hydrocarbons of the biphytane series suggests that affiliates of both major archaeal kingdoms, the Crenarchaeota and the Euryarchaeota, are present in the choanosome of T. semisuberites. Positive signals using the oligonucleotide probe ARCH915 indicate high numbers of Archaea in the mesohyl of this sponge. Based on optical estimations 70-90% of all microbial DAPI signals accounted for archaeal cells. Archaea in these high proportions have never been described in an Arctic deep-sea hadromerid sponge, nor in any other demosponge species. Similar observations in specimens collected over a time scale of 4 years suggest permanent sponge-Archaea associations.

Bacteriohopanepolyols (BHPs) are lipid constituents of many bacterial groups. Geohopanoids, the diagenetic products, are therefore ubiquitous in organic matter of the geosphere. To examine the potential of BHPs Lis environmental markers in marine sediments, we investigated a Holocene sediment core from the Black Sea. The concentrations of BHPs mirror the environmental shift front a well-mixed lake to a stratified marine environment by a strong and gradual increase from low values (similar to 30 mu g g (1) TOC) in the oldest sediments to similar to 170 mu g g (1) TOC in sediments representing the onset of a permanently anoxic water body at about 7500 years before present (BP). This increase in BHP concentrations was most likely caused by a strong increase in bacterioplanktonic paleoproductivity brought about by several ingressions of Mediterranean Sea waters at the end of the lacustrine stage (similar to 9500 years BP). delta(15)N values coevally decreasing with increasing BHP concentrations may indicate a shift from a phosphorus- to a nitrogen-limited setting supporting growth of N(2)-fixing, BHP-producing bacteria. In sediments of the last similar to 3000 years BHP concentrations have remained relatively stable at about 50 mu g g(-1) TOC. The distributions of major BHPs did not change significantly during the shift from lacustrine for oligohaline) to marine conditions. Tetrafunctionalized BHPs prevailed throughout the entire sediment core. with the common bacteriohopanetetrol and 35-aminobacteriohopanetriol and the rare 35-aminobacteriohopenetriol, so far only known from a purple non-sulfur alpha-proteobacterium. being the main components. Other BHPs specific to cyanobacteria and pelagic methanotrophic bacteria were also round but only in much smaller amounts. Our results demonstrate that BHPs from microorganisms living in deeper biogeochemical zones of marine Water Columns are underrepresented or even absent in the sediment compared to the BHPs of bacteria present in the euphotic zone. Obviously, the assemblage of molecular fossils in the sediments does not represent an integrated image of the entire community living in the water column. Remnants of organisms living in zones where effective transport mechanisms - such as the fecal pellet express exist are accumulated while those of others are underrepresented. Our work shows a high stability of BHPs over geological time scales. Largely uniform distributions and only minor changes in Structures like an increasing prevalence of saturated over unsaturated BHPs with time were observed. Consequently, sedimentary BHP distributions are less Suitable its markers for in Situ living bacteria but are useful for paleoreconstructions of bacterioplanktonic communities and productivity changes. (C) 2008 Elsevier Ltd. All rights reserved.

We propose that organic compounds found in a Miocene limestone from Marmorito (Northem Italy) are source markers for organic matter present in aneient methane vent systems (cold seeps). The limestone contains high concentrations of the tail-to-taillinked, acyclic C20 isoprenoid 2,6,11,15-tetramethylhexadecane (crocetane), a C25 homolog 2,6,10,15,19-pentamethylicosane (PME), and a distinctive glycerol ether lipid containing 3,7,1l,15-tetramethylhexadecyl (phytanyl-) moieties. The chemical structures of these biomarkers indicate a common origin from archaea. Their extreme1y l3C-depleted isotope compositions (813C "'" -108 to -115.6%0 PDB) suggest that the respective archaea have directly or indirectly introduced isotopically depleted, methane-derived carbon into their biomass. We postulate that a second major cluster of biomarkers showing heavier isotope values (8l3C "'" -88%0) is derived from sulfate-redueing bacteria (SRB). The observed biomarkers sustain the idea that methanogenic bacteria, in a syntrophic community with SRB, are responsible for the anaerobic oxidation of methane in marine sediments. Marmorito may thus represent a conceivable aneient scenario for methane consumption performed by a defined, two-membered bacterial consortium: (1) archaea that perform reversed methanogenesis by oxidizing methane and produeing CO2 and H2; and (2) SRB that consume the resulting H2. Furthermore, the respective organic molecules are, unlike other compounds, tightly bound to the crystalline carbonate phase. The Marmorito carbonates can thus be regarded as "cold seep microbialites" rather than mere "authigenic" carbonates.

Hopanoids are important lipid components of many bacterial groups and are therefore ubiquitous in soils, sediments, and rocks. Until recently, it was believed that the synthesis of hopanoids is restricted to at least microaerophilic bacteria and consequently geological findings of hopanoids were used as an indication for oxygenated settings. Recent studies, however, demonstrated the biosynthesis of hopanoids under strictly anoxic conditions by a few bacterial groups, although their relevance is still unclear. We therefore extended our previous work studying hopanoid production among members of the genus Desulfovibrio, a group of sulphate-reducing bacteria (SRB) widely distributed in marine sediments, water-logged soils, and oil reservoirs. We found three species (Desulfovibrio halophilus, Desulfovibrio vulgaris Hildenborough, and Desulfovibrio africanus) to be devoid of hopanoids. In contrast, Desulfovibrio bastinii contains high amounts of nonextended hopanoids and bacteriohopanepolyols, with diploptene, 17 beta(H),21 beta(H)-bacteriohopane-32,33,34,35-tetrol, and 17 beta(H),21 beta(H)-35-aminobacteriohopane-32,33,34-triol being the major compounds. Because the moderately halophilic D. bastinii was isolated from a deep subsurface oil formation water, a contribution of hopanoids by SRB to the intrinsic oil hopanoid inventory is feasible, which would influence hopanoidal compositions often used for organic-geochemical characterization purposes. Nevertheless, our data indicate that hopanoid production might be common, but not obligate in the genus Desulfovibrio.

The anaerobic oxidation of methane (AOM) is one of the major sinks of this substantial greenhouse gas in marine environments. Recent investigations have shown that diverse communities of anaerobic archaea and sulfate-reducing bacteria are involved in AOM. Most of the relevant archaea are assigned to two distinct phylogenetic clusters, ANME-11 and ANME-2. A suite of specific C-13-depleted lipids demonstrating the presence of consortia mediating AOM in fossil and recent environments has been established. Here we report on substantial differences in the lipid composition of microbial consortia sampled from distinct compartments of AOM-driven carbonate reefs growing in the northwestern Black Sea. Communities in which the dominant archaea are from the ANME-1 cluster yield internally cyclized tetraether lipids typical of thermophiles. Those in which ANME-2 archaea are dominant yield sn-2-hydroxyarchaeol accompanied by crocetane and crocetenes. The bacterial lipids from these communities are also distinct even though the sulfate-reducing bacteria all belong to the Desulfosarcina/Desulfococcus group. Nonisoprenoidal glycerol diethers are predominantly associated with ANME-1-dominated communities. Communities with ANME-2 yield mainly conventional, ester-linked diglycerides. ANME-1 archaea and associated sulfate-reducing bacteria seem to be enabled to use low concentrations of methane and to grow within a broad range of temperatures. Our results offer a tool for the study of recent and especially of fossil methane environments.

Anaerobic methanotrophic archaea (ANME) are ubiquitous in marine sediments where sulfate dependent anaerobic oxidation of methane (AOM) occurs. Despite considerable progress in the understanding of AOM, physiological details are still widely unresolved. We investigated two distinct microbial mat samples from the Black Sea that were dominated by either ANME-1 or ANME-2. The C-13 lipid stable isotope probing (SIP) method using labelled substances, namely methane, bicarbonate, acetate, and methanol, was applied, and the substrate-dependent methanogenic capabilities were tested. Our data provide strong evidence for a versatile physiology of both, ANME-1 and ANME-2. Considerable methane production rates (MPRs) from CO2-reduction were observed, particularly from ANME-2 dominated samples and in the presence of methane, which supports the hypothesis of a co-occurrence of methanotrophy and methanogenesis in the AOM systems (AOM/MPR up to 2:1). The experiments also revealed strong methylotrophic capabilities through C-13-assimilation from labelled methanol, which was independent of the presence of methane. Additionally, high MPRs from methanol were detected in both of the mat samples. As demonstrated by the C-13-uptake into lipids, ANME-1 was found to thrive also under methane free conditions. Finally, C-35-isoprenoid hydrocarbons were identified as new lipid biomarkers for ANME-1, most likely functioning as a hydrogen sink during methanogenesis.

Massive microbial mats covering up to 4-meter-high carbonate buildups prosper at methane seeps in anoxic waters of the northwestern Black Sea shelf. Strong (13)C depletions indicate an incorporation of methane carbon into carbonates, bulk biomass, and specific lipids. The mats mainly consist of densely aggregated archaea ( phylogenetic ANME-1 cluster) and sulfate-reducing bacteria (Desulfosarcina/Desulfococcus group). If incubated in vitro, these mats perform anaerobic oxidation of methane coupled to sulfate reduction. Obviously, anaerobic microbial consortia can generate both carbonate precipitation and substantial biomass accumulation, which has implications for our understanding of carbon cycling during earlier periods of Earth's history.

The lipid assemblages of the "living fossil" stromatoporoid Astrosclera willeyana (Great Barrier Reet) and the demosponge Agelas aroides (Mediterranean Sea) were investigated. Large amounts of branched carboxylic acids are present in the sponges studied. These compounds include terminally branched carboxylic acids (isa -/anteisa-) and abundant mid-chain branched carboxylic acids (MBCA) wh ich are characterized by an intriguing variety of structural isomers present in the C 15- C25 range. The most prominent MBCA are comprised of isomeric methylhexadecanoic acids and methyloctadecanoic acids. A second cluster of MBCA includes methyldocosanoic acids and methyltetracosanoic acids, but other homologues are also present. Methyl branching points were generally observed between the w5- and w9-positions. These complex isomeric mixtures apparently derive from symbiotic bacteria living exclusively in demosponges. Comparison with hydrocarbon compositions of ancient carbonates reveals evidence that the MBCA found are potential lipid precursors of mid-chain branched monomethylalkanes often observed in fossil sediments and oils. As a working hypo thesis, we suggest that their bacterial source organisms have been widespread in the geological past, and are found " inherited" in the protective environment of distinctive sponge hosts in recent marine ecosystems. Furthermore, both sponges contain abundant linear, longchain C24- C26 dienoic "demospongic" acids. The demospongic acid distribution and the presence of phytanic acid in A. willeyana match the patterns found in A. aroides and other members of the Agelasida. These findings confirm the systematic position of A. willeyana within this demosponge taxon.