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Abstract Gas bubbles directly influence the macromorphology of benthic microbial mats resulting in preservable biosedimentary structures. This study characterizes the morphology and distribution of microbial mats growing in gas‐supersaturated, perennially ice‐covered lakes Fryxell, Joyce, and Hoare of the McMurdo Dry Valleys of Antarctica. Photosynthetic benthic mats within the gas‐supersaturated zone trap oxygen‐rich bubbles and become buoyant, tearing off the bottom as “liftoff mats.” These liftoff mats form a succession of morphologies starting with bubble‐induced deformation of flat mats into tent, ridge, and finger liftoff mat. With progressive deformation, mats tear, forming sheet liftoff, while multiple cycles of deformation and tearing transform sheet into strip liftoff. Some mats detach from the substrate and float to the underside of the ice. The depth range of the liftoff zone has varied over time at each lake. Downslope expansion of bubble formation brings previously bubble‐free, deep‐water pinnacle mats into the liftoff zone. When the liftoff zone shallows, liftoff mats at the deeper end deflate and can become scaffolding for additional mat growth. The superposition and relative orientation of liftoff and pinnacle mats can be used to track the maximum depth of the liftoff zone and changes in gas saturation state in these lakes through time. Our results demonstrate that gas bubbles, even when they are transitory, can exert a significant impact on the morphology of microbial mats at larger scales. This provides a way to identify similar structures and gas supersaturated environments in the biosedimentary record. 

ABSTRACT We recovered 57 bacterial metagenome-assembled genomes (MAGs) from benthic microbial mat pinnacles from Lake Vanda, Antarctica. These MAGs provide access to genomes from polar environments and can assist in culturing and utilizing these Antarctic bacteria. 

Cyanobacteria form diverse communities and are important primary producers in Antarctic freshwater environments, but their geographic distribution patterns in Antarctica and globally are still unresolved. There are however few genomes of cultured cyanobacteria from Antarctica available and therefore metagenome-assembled genomes (MAGs) from Antarctic cyanobacteria microbial mats provide an opportunity to explore distribution of uncultured taxa. These MAGs also allow comparison with metagenomes of cyanobacteria enriched communities from a range of habitats, geographic locations, and climates. However, most MAGs do not contain 16S rRNA gene sequences, making a 16S rRNA gene-based biogeography comparison difficult. An alternative technique is to use large-scale k-mer searching to find genomes of interest in public metagenomes. This paper presents the results of k-mer based searches for 5 Antarctic cyanobacteria MAGs from Lake Fryxell and Lake Vanda, assigned the namesPhormidium pseudopriestleyiFRX01,Microcoleussp. MP8IB2.171,Leptolyngbyasp. BulkMat.35,Pseudanabaenaceae cyanobacteriumMP8IB2.15, andLeptolyngbyaceae cyanobacteriumMP9P1.79 in 498,942 unassembled metagenomes from the National Center for Biotechnology Information (NCBI) Sequence Read Archive (SRA). TheMicrocoleussp. MP8IB2.171 MAG was found in a wide variety of environments, theP. pseudopriestleyiMAG was found in environments with challenging conditions, theLeptolyngbyaceae cyanobacteriumMP9P1.79 MAG was only found in Antarctica, and theLeptolyngbyasp. BulkMat.35 andPseudanabaenaceae cyanobacteriumMP8IB2.15 MAGs were found in Antarctic and other cold environments. The findings based on metagenome matches and global comparisons suggest that these Antarctic cyanobacteria have distinct distribution patterns ranging from locally restricted to global distribution across the cold biosphere and other climatic zones. 

Cyanobacteria in polar environments face environmental challenges, including cold temperatures and extreme light seasonality with small diurnal variation, which has implications for polar circadian clocks. However, polar cyanobacteria remain underrepresented in available genomic data, and there are limited opportunities to study their genetic adaptations to these challenges. This paper presents four new Antarctic cyanobacteria metagenome-assembled genomes (MAGs) from microbial mats in Lake Vanda in the McMurdo Dry Valleys in Antarctica. The four MAGs were classified asLeptolyngbyasp. BulkMat.35,Pseudanabaenaceae cyanobacteriumMP8IB2.15,Microcoleussp. MP8IB2.171, andLeptolyngbyaceae cyanobacteriumMP9P1.79. The MAGs contain 2.76 Mbp – 6.07 Mbp, and the bin completion ranges from 74.2–92.57%. Furthermore, the four cyanobacteria MAGs have average nucleotide identities (ANIs) under 90% with each other and under 77% with six existing polar cyanobacteria MAGs and genomes. This suggests that they are novel cyanobacteria and demonstrates that polar cyanobacteria genomes are underrepresented in reference databases and there is continued need for genome sequencing of polar cyanobacteria. Analyses of the four novel and six existing polar cyanobacteria MAGs and genomes demonstrate they have genes coding for various cold tolerance mechanisms and most standard circadian rhythm genes with theLeptolyngbyasp. BulkMat.35 andLeptolyngbyaceae cyanobacteriumMP9P1.79 containedkaiB3, a divergent homolog ofkaiB.