Bacteriohopanepolyols across environmental gradients in Lake Vanda, Antarctica

Abstract

Bacteriohopanepolyols (BHPs) are bacterial membrane lipids that may be used as biological or environmental biomarkers. Previous studies have described the diversity, distribution, and abundance of BHPs in a variety of modern environments. However, the regulation of BHP production in polar settings is not well understood. Benthic microbial mats from ice‐covered lakes of the McMurdo Dry Valleys, Antarctica provide an opportunity to investigate the sources, physiological roles, and preservation of BHPs in high‐latitude environments. Lake Vanda is one of the most stable lakes on Earth, with microbial communities occupying specific niches along environmental gradients. We describe the influence of mat morphology and local environmental conditions on the diversity and distribution of BHPs and their biological sources in benthic microbial mats from Lake Vanda. The abundance and diversity of C‐2 methylated hopanoids (2‐MeBHP) are of particular interest, given that their stable degradation products, 2‐methylhopanes, are among the oldest and most prevalent taxonomically informative biomarkers preserved in sedimentary rocks. Furthermore, the interpretation of sedimentary 2‐methylhopanes is of great interest to the geobiology community. We identify cyanobacteria as the sole source of 2‐MeBHP in benthic microbial mats from Lake Vanda and assess the hypothesis that 2‐MeBHP are regulated in response to a particular environmental variable, namely solar irradiance.

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

“…While BHPs have traditionally been considered most abundant in aerobic bacteria, the results of this study support the current hypothesis that hopanoid producers may be more diverse and abundant in low‐oxygen environments than previously thought, and possibly even more abundant than in environments that are well‐oxygenated. In fact, this may account for the high diversity of BHPs in benthic microbial mats from suboxic to anoxic portions of Lake Fryxell, as compared to nearby Lake Vanda (Matys et al., ) where benthic microbial mats remain in contact with well‐oxygenated water throughout the year. As a result, it is of considerable interest to further investigate the abundance, diversity, distribution, possible biological sources, and physiological functions of hopanoids in suboxic/anoxic environments.…”

“…However, unlike nearby Lake Vanda (Matys et al., ), organic matter preserved in benthic microbial mats may not only be produced in situ (by modern and ancient communities), but are also likely to contain some contribution of organic matter from the overlying water column. The Lake Fryxell water column is productive with bacterial concentrations ranging from 1.0–3.8 × 10 8 /L in the oxic portion of the water column (<9.5 m depth) and increase to 20 × 10 8 /L in anoxic bottom waters (>9.5 m depth; Laybourn‐Parry et al., ).…”

“…Cyanobacteria were identified as the only source of 2‐MeBHPs in Lake Vanda, based on the phylogeny of translated nucleotide sequences SHC and HpnP (Matys et al., ). 2‐MeBHPs and HpnP translated nucleotide sequences are also present in Lake Fryxell (Table S3).…”

“…In order to create a comparable dataset with Sutherland andHawes (2009), Mackey, Sumner, andJungblut (2017), and Matys et al (2019) the same LOI method was employed. After lipid extraction, all samples were dried and weighed in small ceramic crucibles.…”

“…Few studies have described BHPs in high latitude regions and in particular, Antarctica, despite the high diversity of BHPs identified relative to low‐latitude settings, including tetra‐ and penta‐functionalized, methylated, non‐methylated, and unsaturated BHPs identified there (Talbot et al., ; Cooke et al., ; Matys et al., ). Here, we describe BHP diversity and abundance in benthic microbial mats from Lake Fryxell, Antarctica.…”