Sterol preservation in hypersaline microbial mats
<p>Microbial mats are self-sustaining benthic ecosystems composed of highly diverse microbial communities. It has been proposed that microbial mats were widespread in Proterozoic marine environments, prior to the emergence of bioturbating organisms at the Precambrian–Cambrian transition. One c...
Main Authors: | , , , , |
---|---|
Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2020-02-01
|
Series: | Biogeosciences |
Online Access: | https://www.biogeosciences.net/17/649/2020/bg-17-649-2020.pdf |
id |
doaj-21e14f13e621449f843210a1364c9e3d |
---|---|
record_format |
Article |
spelling |
doaj-21e14f13e621449f843210a1364c9e3d2020-11-25T02:18:34ZengCopernicus PublicationsBiogeosciences1726-41701726-41892020-02-011764966610.5194/bg-17-649-2020Sterol preservation in hypersaline microbial matsY. Shen0V. Thiel1P. Suarez-Gonzalez2S. W. Rampen3J. Reitner4J. Reitner5Department of Geobiology, Geoscience Centre, Georg-August-Universität Göttingen, Göttingen, GermanyDepartment of Geobiology, Geoscience Centre, Georg-August-Universität Göttingen, Göttingen, GermanyÁrea de Geología, Universidad Rey Juan Carlos, Madrid, SpainDepartment of Geobiology, Geoscience Centre, Georg-August-Universität Göttingen, Göttingen, GermanyDepartment of Geobiology, Geoscience Centre, Georg-August-Universität Göttingen, Göttingen, Germany“Origin of Life” working group, Göttingen Academy of Sciences and Humanities, Göttingen, Germany<p>Microbial mats are self-sustaining benthic ecosystems composed of highly diverse microbial communities. It has been proposed that microbial mats were widespread in Proterozoic marine environments, prior to the emergence of bioturbating organisms at the Precambrian–Cambrian transition. One characteristic feature of Precambrian biomarker records is that steranes are typically absent or occur in very low concentrations. This has been explained by low eukaryotic source inputs, or degradation of primary produced sterols in benthic microbial mats (“mat-seal effect”). To better understand the preservational pathways of sterols in microbial mats, we analyzed freely extractable and carbonate-bound lipid fractions as well as decalcified extraction residues in different layers of a recent calcifying mat (<span class="inline-formula">∼1500</span> years) from the hypersaline Lake 2 on the island of Kiritimati, central Pacific. A variety of C<span class="inline-formula"><sub>27</sub></span>–C<span class="inline-formula"><sub>29</sub></span> sterols and distinctive C<span class="inline-formula"><sub>31</sub></span> 4<span class="inline-formula"><i>α</i></span>-methylsterols (4<span class="inline-formula"><i>α</i></span>-methylgorgosterol and 4<span class="inline-formula"><i>α</i></span>-methylgorgostanol, biomarkers for dinoflagellates) were detected in freely extractable and carbonate-bound lipid pools. These sterols most likely originated from organisms living in the water column and the upper mat layers. This autochthonous biomass experienced progressive microbial transformation and degradation in the microbial mat, as reflected by a significant drop in total sterol concentrations, up to 98 %, in the deeper layers, and a concomitant decrease in total organic carbon. Carbonate-bound sterols were generally low in abundance compared to the freely extractable portion, suggesting that incorporation into the mineral matrix does not play a major role in the preservation of eukaryotic sterols in this mat. Likewise, pyrolysis of extraction residues suggested that sequestration of steroid carbon skeletons into insoluble organic matter was low compared to hopanoids. Taken together, our findings argue for a major mat-seal effect affecting the distribution and preservation of steroids in the mat studied. This result markedly differs from recent findings made for another microbial mat growing in the nearby hypersaline Lake 22 on the same island, where sterols showed no systematic decrease with depth. The observed discrepancies in the taphonomic pathways of sterols in microbial mats from Kiritimati may be linked to multiple biotic and abiotic factors including salinity and periods of subaerial exposure, implying that caution has to be exercised in the interpretation of sterol distributions in modern and ancient microbial mat settings.</p>https://www.biogeosciences.net/17/649/2020/bg-17-649-2020.pdf |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
Y. Shen V. Thiel P. Suarez-Gonzalez S. W. Rampen J. Reitner J. Reitner |
spellingShingle |
Y. Shen V. Thiel P. Suarez-Gonzalez S. W. Rampen J. Reitner J. Reitner Sterol preservation in hypersaline microbial mats Biogeosciences |
author_facet |
Y. Shen V. Thiel P. Suarez-Gonzalez S. W. Rampen J. Reitner J. Reitner |
author_sort |
Y. Shen |
title |
Sterol preservation in hypersaline microbial mats |
title_short |
Sterol preservation in hypersaline microbial mats |
title_full |
Sterol preservation in hypersaline microbial mats |
title_fullStr |
Sterol preservation in hypersaline microbial mats |
title_full_unstemmed |
Sterol preservation in hypersaline microbial mats |
title_sort |
sterol preservation in hypersaline microbial mats |
publisher |
Copernicus Publications |
series |
Biogeosciences |
issn |
1726-4170 1726-4189 |
publishDate |
2020-02-01 |
description |
<p>Microbial mats are self-sustaining benthic ecosystems
composed of highly diverse microbial communities. It has been proposed that
microbial mats were widespread in Proterozoic marine environments, prior to
the emergence of bioturbating organisms at the Precambrian–Cambrian
transition. One characteristic feature of Precambrian biomarker records is
that steranes are typically absent or occur in very low concentrations. This
has been explained by low eukaryotic source inputs, or degradation of
primary produced sterols in benthic microbial mats (“mat-seal effect”). To
better understand the preservational pathways of sterols in microbial mats,
we analyzed freely extractable and carbonate-bound lipid fractions as well
as decalcified extraction residues in different layers of a recent
calcifying mat (<span class="inline-formula">∼1500</span> years) from the hypersaline Lake 2 on
the island of Kiritimati, central Pacific. A variety of C<span class="inline-formula"><sub>27</sub></span>–C<span class="inline-formula"><sub>29</sub></span>
sterols and distinctive C<span class="inline-formula"><sub>31</sub></span> 4<span class="inline-formula"><i>α</i></span>-methylsterols (4<span class="inline-formula"><i>α</i></span>-methylgorgosterol and 4<span class="inline-formula"><i>α</i></span>-methylgorgostanol, biomarkers for
dinoflagellates) were detected in freely extractable and carbonate-bound
lipid pools. These sterols most likely originated from organisms living in
the water column and the upper mat layers. This autochthonous biomass
experienced progressive microbial transformation and degradation in the
microbial mat, as reflected by a significant drop in total sterol
concentrations, up to 98 %, in the deeper layers, and a concomitant
decrease in total organic carbon. Carbonate-bound sterols were generally low
in abundance compared to the freely extractable portion, suggesting that
incorporation into the mineral matrix does not play a major role in the
preservation of eukaryotic sterols in this mat. Likewise, pyrolysis of
extraction residues suggested that sequestration of steroid carbon skeletons
into insoluble organic matter was low compared to hopanoids. Taken together,
our findings argue for a major mat-seal effect affecting the distribution
and preservation of steroids in the mat studied. This result markedly
differs from recent findings made for another microbial mat growing in the
nearby hypersaline Lake 22 on the same island, where sterols showed no
systematic decrease with depth. The observed discrepancies in the taphonomic
pathways of sterols in microbial mats from Kiritimati may be linked to
multiple biotic and abiotic factors including salinity and periods of
subaerial exposure, implying that caution has to be exercised in the
interpretation of sterol distributions in modern and ancient microbial mat
settings.</p> |
url |
https://www.biogeosciences.net/17/649/2020/bg-17-649-2020.pdf |
work_keys_str_mv |
AT yshen sterolpreservationinhypersalinemicrobialmats AT vthiel sterolpreservationinhypersalinemicrobialmats AT psuarezgonzalez sterolpreservationinhypersalinemicrobialmats AT swrampen sterolpreservationinhypersalinemicrobialmats AT jreitner sterolpreservationinhypersalinemicrobialmats AT jreitner sterolpreservationinhypersalinemicrobialmats |
_version_ |
1724881235686195200 |