Reinterpretation of lycopane as a biomarker of archaea based on its occurrence in authigenic sulfur-bearing carbonates
Year: 2024
Type: article
Abstract: The tail-to-tail linked C 40 isoprenoid hydrocarbon lycopane is a biomarker found in a wide variety of environments and in some extremophilic archaea but is also a possibly degradation product of a carotenoid (bacterioruberin) as well as plants (various lycopenes) and green algae (lycopadiene). Although potential producers are known, the source of lycopane in water-column and sedimentary environments is commonly ambiguous. In this study, the occurrence of 13 C-depleted lycopane (δ 13 C = −114 to −106 ‰) in authigenic, sulfur-bearing carbonates from Monte Palco (Sicily) is used to re-evaluate the environmental significance of lycopane. In the Monte Palco authigenic carbonates, lycopane is accompanied by other, similarly 13 C-depleted apolar isoprenoids such as PMI, squalane, and sulfurized homologues, including a tail-to-tail linked C 35 isoprenoid , as well as typical lipids of anaerobic methanotrophic archaea (ANME) like glycerol dibiphytanyl glycerol tetraether (GDGT)-0, −2, archaeol, and sn 3-hydroxyarchaeol. The δ 13 C values of lycopane reveal linear correlations with values of PMI and squalane ( n = 7; r 2 = 0.71 and 0.82, respectively), probably reflecting a similar cellular function of the tail-to-tail linked isoprenoids in the archaeal source organisms. Lycopane is interpreted to represent a membrane intercalant, produced in response to extreme environmental conditions. The new observations resulting from the analysis of the Monte Palco authigenic carbonates – including the similarities in 13 C-depletion of PMI, squalane, and lycopane but also with other archaeal membrane lipids like archaeol, sn3 -hydroxyarchaeol, and GDGT-0 (measured as ether-cleaved biphytanes) – allowed us to re-interpret the potential source organism of lycopane in modern and ancient anoxic and euxinic basins (Cariaco Trench , Black Sea, late Cenomanian black shales of the Cape Verde Basin). These new data agree with unknown archaea as producers of lycopane as a response to environmental stress at chemoclines. The previous interpretation of lycopane as a biomarker of photoautotrophic bacteria in anoxic basins is challenged by our new findings. An alternative explanation for these occurrences is lycopane production by Marine Group II Euryarchaeota , archaea closely associated with primary producers. Lycopane production by archaea is probably more widespread than previously recognized. Future research should evaluate the potential of lycopane as a biomarker of archaeal adaptation to extreme environmental conditions.
Source: Chemical Geology
Institution: Universität Hamburg
Language: English
Subfield: Environmental Chemistry
Field: Environmental Science
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $3,420
Award: G2234152880
OpenAlex ID: W4402547462