Microbial Mat Communities along an Oxygen Gradient in a Perennially Ice-Covered Antarctic Lake

Abstract

Lake Fryxell is a perennially ice-covered lake in the McMurdo Dry Valleys, Antarctica, with a sharp oxycline in a water column that is density stabilized by a gradient in salt concentration. Dissolved oxygen falls from 20 mg liter ؊1 to undetectable over one vertical meter from 8.9-to 9.9-m depth. We provide the first description of the benthic mat community that falls within this oxygen gradient on the sloping floor of the lake, using a combination of micro-and macroscopic morphological descriptions, pigment analysis, and 16S rRNA gene bacterial community analysis. Our work focused on three macroscopic mat morphologies that were associated with different parts of the oxygen gradient: (i) "cuspate pinnacles" in the upper hyperoxic zone, which displayed complex topography and were dominated by phycoerythrin-rich cyanobacteria attributable to the genus Leptolyngbya and a diverse but sparse assemblage of pennate diatoms; (ii) a less topographically complex "ridge-pit" mat located immediately above the oxic-anoxic transition containing Leptolyngbya and an increasing abundance of diatoms; and (iii) flat prostrate mats in the upper anoxic zone, dominated by a green cyanobacterium phylogenetically identified as Phormidium pseudopriestleyi and a single diatom, Diadesmis contenta. Zonation of bacteria was by lake depth and by depth into individual mats. Deeper mats had higher abundances of bacteriochlorophylls and anoxygenic phototrophs, including Chlorobi and Chloroflexi. This suggests that microbial communities form assemblages specific to niche-like locations. Mat morphologies, underpinned by cyanobacterial and diatom composition, are the result of local habitat conditions likely defined by irradiance and oxygen and sulfide concentrations.

Hidden biofilms in a far northern lake and implications for the changing Arctic

“…Leptolyngbya is a filamentous, globally distributed genus found in tropical, 18 temperate, 19 and polar microbial mats. 4 At a finer taxonomic scale, many of the abundant OTUs were found to be closely related to Antarctic cyanobacteria (Supplementary Fig. S4), consistent with the global distribution of cold-dwelling ecotypes of cyanobacteria.…”

“…Similar to Antarctic lake communities, 4 potentially nitrogen-fixing cyanobacteria of the order Nostocales were rare in the deep biofilms (<0.01 % of bacterial reads) but abundant in the moat communities (6.2 %; Supplementary Fig. S3), that might indicate N-limitation or greater relative phosphorus availability in the moat area.…”

Bacterial Diversity of a Microbial Mat from Hot Spring at Wartawan Beach, Lampung and Its Potential as a Source of Hydrogenases

“…In addition, Pseudanabaena sp., Leptolyngbya sp. were found inhabited in cold temperature (Jungblut et al, 2016), whereas Halomicronema sp. in hypersaline mat (Fourçans et al, 2006).…”

“…Cyanobacteria 16S rRNA gene diversity showed that the microbial mat contained Pseudanabaena sp., Leptolyngbya sp., Halomicronema sp., Stanieria cyanosphaera, Neolyngbya maris-brasilis. These species were known as members of mat bacterial communities (Fourçans et al, 2006;Jungblut et al, 2016) except Stanieria cyanosphaera, Neolyngbya maris-brasilis which from marine benthics (Caires et al, 2018;Silva & Pienaar, 2000). In addition, Pseudanabaena sp., Leptolyngbya sp.…”

Unusual microbial mat‐related structural diversity 2.1 billion years ago and implications for the Francevillian biota

“…ally ice-covered Antarctic lake have shown the specific assemblage of a photosynthetic microbial ecosystem(Jungblut et al, 2016;Sumner, Hawes, Mackey, Jungblut, & Doran, 2015), with cyanobac-teria forming tuft-related structures exclusively found in the oxic zone where irradiance is at its highest, whereas flat bacterial mats of anoxygenic photoautotrophs are restricted to the deeper euxinic zone experiencing lower irradiance. Thus, "elephant-skin" and tufted structures may possibly have a link with oxygenic photoautotrophic micro-organisms.…”