Energetic and Environmental Constraints on the Community Structure of Benthic Microbial Mats in Lake Fryxell, Antarctica

Abstract

Ecological communities are regulated by the flow of energy through environments. Energy flow is typically limited by access to photosynthetically active radiation (PAR) and oxygen concentration (O2). The microbial mats growing on the bottom of Lake Fryxell, Antarctica, have well-defined environmental gradients in PAR and (O2). We analyzed the metagenomes of layers from these microbial mats to test the extent to which access to oxygen and light controls community structure. We found variation in the diversity and relative abundances of Archaea, Bacteria and Eukaryotes across three (O2) and PAR conditions: high (O2) and maximum PAR, variable (O2) with lower maximum PAR, and low (O2) and maximum PAR. We found distinct communities structured by the optimization of energy use on a millimeter-scale across these conditions. In mat layers where (O2) was saturated, PAR structured the community. In contrast, (O2) positively correlated with diversity and affected the distribution of dominant populations across the three habitats, suggesting that meter-scale diversity is structured by energy availability. Microbial communities changed across covarying gradients of PAR and (O2). The comprehensive metagenomic analysis suggests that the benthic microbial communities in Lake Fryxell are structured by energy flow across both meter- and millimeter-scales.

Metabolic Capacity of the Antarctic Cyanobacterium Phormidium pseudopriestleyi That Sustains Oxygenic Photosynthesis in the Presence of Hydrogen Sulfide

“…Notably, hdrA2, hdrB2, and hdrC2 , are present, which code for heterodisulfide reductase, an enzyme typically found in methanogens. Previous work has found these genes at 9.8 m depth in Lake Fryxell, and consistent with the content of the MAG, the capacity for methanogenesis ( hdrD ) was absent [ 91 ]. The presence of hdrB may indicate capacity for flavin-based electron bifurcation [ 92 ].…”

Environmental controls and habitat connectivity of phototrophic microbial mats and bacterioplankton communities in an Antarctic freshwater system

“…Cyanobacteria. These observations agree with studies conducted in lakes Bonney Fryxell, Hoare and Miers (39,40) suggesting differences between the bacterial benthos and plankton are widespread in Antarctic dry valley lakes. The cyanobacterial composition of the mats in the system was dominated at genus level by Tychonema, Phormidium and Leptolyngbya, which also agrees with previous studies on microbial mats in Southern Victoria land (19,41).…”

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.…”