title: 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.
authors.affiliation: Life Sciences Department, The Natural History Museum, London, United Kingdom a.jungblut@nhm.ac.uk.
authors.forename: Anne D
authors.initials: AD
authors.lastname: Jungblut
authors.affiliation: University of Canterbury, Christchurch, New Zealand.
authors.forename: Ian
authors.initials: I
authors.lastname: Hawes
authors.affiliation: Department of Earth and Planetary Sciences, University of California, Davis, Davis, California, USA.
authors.forename: Tyler J
authors.initials: TJ
authors.lastname: Mackey
authors.affiliation: Microbiology Graduate Group, University of California, Davis, Davis, California, USA.
authors.forename: Megan
authors.initials: M
authors.lastname: Krusor
authors.affiliation: Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana, USA.
authors.forename: Peter T
authors.initials: PT
authors.lastname: Doran
authors.affiliation: Department of Earth and Planetary Sciences, University of California, Davis, Davis, California, USA.
authors.forename: Dawn Y
authors.initials: DY
authors.lastname: Sumner
authors.affiliation: Microbiology Graduate Group, University of California, Davis, Davis, California, USA Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana, USA.
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Eisen
authors.affiliation: University of Canterbury, Christchurch, New Zealand.
authors.forename: Colin
authors.initials: C
authors.lastname: Hillman
authors.affiliation: University of Canterbury, Christchurch, New Zealand.
authors.forename: Alexander K
authors.initials: AK
authors.lastname: Goroncy
mesh_terms: D000864:Antarctic Regions; D001419:Bacteria / Q000145:classification / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D044822:Biodiversity; D046448:Ice Cover / Q000737:chemistry / Q000382:microbiology*; D060106:Lakes / Q000032:analysis / Q000382:microbiology*; D008969:Molecular Sequence Data; D010100:Oxygen / Q000032:analysis*; D010802:Phylogeny
chemical_list: D010100:Oxygen