Environmental controls on bacteriohopanepolyol profiles of benthic microbial mats from Lake Fryxell, Antarctica

Abstract

Bacteriohopanepolyols (BHPs) are pentacyclic triterpenoid lipids that contribute to the structural integrity and physiology of some bacteria. Because some BHPs originate from specific classes of bacteria, BHPs have potential as taxonomically and environmentally diagnostic biomarkers. For example, a stereoisomer of bacteriohopanetetrol (informally BHT II) has been associated with anaerobic ammonium oxidation (anammox) bacteria and suboxic to anoxic marine environments where anammox is active. As a result, the detection of BHT II in the sedimentary record and fluctuations in the relative abundance of BHT II may inform reconstructions of nitrogen cycling and ocean redox changes through the geological record. However, there are uncertainties concerning the sources of BHT II and whether or not BHT II is produced in abundance in non‐marine environments, both of which are pertinent to interpretations of BHT II signatures in sediments. To address these questions, we investigate the BHP composition of benthic microbial mats from Lake Fryxell, Antarctica. Lake Fryxell is a perennially ice‐covered lake with a sharp oxycline in a density‐stabilized water column. We describe the diversity and abundance of BHPs in benthic microbial mats across a transect from oxic to anoxic conditions. Generally, BHP abundances and diversity vary with the morphologies of microbial mats, which were previously shown to reflect local environmental conditions, such as irradiance and oxygen and sulfide concentrations. BHT II was identified in mats that exist within oxic to anoxic portions of the lake. However, anammox bacteria have yet to be identified in Lake Fryxell. We examine our results in the context of BHPs as biomarkers in modern and ancient environments.

A unique bacteriohopanetetrol stereoisomer of marine anammox

“…Previous HPLC studies of acetylated late-eluting BHT isomers assumed all the isomers were the same and any late-eluting BHT isomer was designated as ''BHT II" (e.g. Sáenz et al, 2011;Matys et al, 2017Matys et al, , 2019Kusch et al, 2018). As 'Ca.…”

“…However, the stereochemistry of a late-eluting BHT isomer in oxic and anoxic lacustrine systems was likewise identified and considered to be BHT II (e.g. Matys et al, 2019;Talbot et al, 2003). A late-eluting BHT isomer has also been found in oxic or seasonally anoxic marine settings (Kusch et al, 2018(Kusch et al, , 2019Matys et al, 2019).…”

“…Matys et al, 2019;Talbot et al, 2003). A late-eluting BHT isomer has also been found in oxic or seasonally anoxic marine settings (Kusch et al, 2018(Kusch et al, , 2019Matys et al, 2019). In some of these cases, identification of the stereochemistry of the BHT isomer may reveal that it was not BHT-x, and thus not produced by 'Ca.…”

DNA/RNA Preservation in Glacial Snow and Ice Samples

“…The potential loss of DNA and RNA during RNAlater -preserved sample washing is problematic for low-biomass glacial samples. In contrast to the use of RNAlater, many previous cryosphere studies addressing microbial community compositions froze filtered DNA samples at −20°C in the field ( Larose et al, 2013 ; Christner et al, 2014 ; Maccario et al, 2014 ; Purcell et al, 2014 ; Lutz et al, 2015b , 2016 , 2017 , 2019a , b ; Bergk Pinto et al, 2019 ; Malard et al, 2019 ; Els et al, 2020 ; Ramoneda et al, 2020 ; Winkel et al, 2022 ), while few studies used Zymo -preservation ( Trivedi et al, 2018 , 2020 ; Matys et al, 2019 ; Dillon et al, 2020 ; Lumian et al, 2021 ), and even fewer used RNAlater plus freezing ( Maccario et al, 2019 ). When no flash freezing and preservation of samples in a cryo-shipper exists, our results indicate that Zymo -preservation is a reasonable alternate option, although additional testing should be done to further help narrow the extraction boundary conditions for very low biomass samples as is often the case with snow and ice samples.…”

Revisiting the precursors of the most abundant natural products on Earth: A look back at 30+ years of bacteriohopanepolyol (BHP) research and ahead to new frontiers

“…The relative abundance of BHT isomer is substantially elevated in these samples and BHT isomer abundances in SPM sharply trace the ecological niche of anammox bacteria in the water column (e.g., Kusch et al, 2022). This may, however, may not be the case in lakes (e.g., Matys et al, 2019a). Care now needs to be taken not to confuse the two BHT isomers, i.e., reports of BHT-…”