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Abstract: Recent studies have shown that glycerol dialkyl glycerol tetraether (GDGT) lipids, thought be unique for (hyper)thermophilic archaea, are also present in non-thermophilic archaea and environments. In this study, an unusual H-shaped isoprenoid GDGT, in which the two biphytanyl carbon skeletons are covalently bound by a carbon–carbon bond, was unambiguously identified in a number of sediments from marine and lacustrine environments. Its abundance varies from 0.2% to 6% of isoprenoid GDGTs. The H-shaped isoprenoid GDGT was originally identified in hyperthermophilic archaea and its presence in marine and lacustrine sediments suggests it is also synthesized by certain non-thermophilic relatives, possibly Euryarchaeota. [Copyright &y& Elsevier]

The branched vs. isoprenoid tetraethers (BIT) index, which is based on the relative abundance of non-isoprenoidal, so-called branched glycerol dialkyl glycerol tetraethers (brGDGTs) versus a structurally related isoprenoid GDGT “crenarchaeol”, has been used to trace soil organic carbon (OC) from the continent to the ocean. However, it has been found in some locations that the BIT index can be primarily influenced by crenarchaeol concentrations and brGDGT production in fresh water rather than by soil-derived brGDGT concentrations. This may hamper the application of this proxy as an indicator for the input of soil OC. In order to constrain the applicability of the BIT index along the southern Portuguese continental margin, we examined the source of brGDGTs and crenarchaeol, by investigating their concentration and distribution as well as variations in the BIT index in marine surface sediments from five transects (Douro, Mondego, Estremadura, Tagus, and Sado) and in marine suspended particulate matter (SPM) from the Douro and Tagus transects. Higher BIT values and brGDGT concentrations (normalized to OC content) were found close to the river mouths and coast than in deep offshore sites. This clearly indicated the continental input of brGDGTs and revealed that, at least in this setting, the BIT index was primarily influenced by the delivery of brGDGTs from the rivers. BrGDGT concentrations and distributions in sediments and SPM close to the rivers were similar to those of SPM in the Tagus River. This indicates that degradation processes in the estuaries had no significant effect on the riverine brGDGTs. Therefore, brGDGTs should be a good indicator for the recalcitrant OC fraction transported from the continent to the ocean. Our results also indicated that there are multiple sources of brGDGTs in the marine environment, i.e. the water column and the sediment, which complicates the use of the brGDGT distribution as an indicator for terrestrial vs. marine produced brGDGTs. [ABSTRACT FROM AUTHOR]

Isotopic analyses of Candidatus "Brocadia anammoxidans," a chemolithoautotrophic bacterium that anaerobically oxidizes ammonium (anammox), show that it strongly fractionates against 13C; i.e., lipids are depleted by up to 47‰ versus CO2. Similar results were obtained for the anammox bacterium Candidatus "Scalindua sorokinii," which thrives in the anoxic water column of the Black Sea, suggesting that different anammox bacteria use identical carbon fixation pathways, which may be either the Calvin cycle or the acetyl coenzyme A pathway. [ABSTRACT FROM AUTHOR]