title: Brine assemblages of ultrasmall microbial cells within the ice cover of Lake Vida, Antarctica.
abstract: The anoxic and freezing brine that permeates Lake Vida's perennial ice below 16 m contains an abundance of very small (≤0.2-μm) particles mixed with a less abundant population of microbial cells ranging from >0.2 to 1.5 μm in length. Fluorescent DNA staining, electron microscopy (EM) observations, elemental analysis, and extraction of high-molecular-weight genomic DNA indicated that a significant portion of these ultrasmall particles are cells. A continuous electron-dense layer surrounding a less electron-dense region was observed by EM, indicating the presence of a biological membrane surrounding a cytoplasm. The ultrasmall cells are 0.192 ± 0.065 μm, with morphology characteristic of coccoid and diplococcic bacterial cells, often surrounded by iron-rich capsular structures. EM observations also detected the presence of smaller unidentified nanoparticles of 0.020 to 0.140 μm among the brine cells. A 16S rRNA gene clone library from the brine 0.1- to 0.2-μm-size fraction revealed a relatively low-diversity assemblage of Bacteria sequences distinct from the previously reported >0.2-μm-cell-size Lake Vida brine assemblage. The brine 0.1- to 0.2-μm-size fraction was dominated by the Proteobacteria-affiliated genera Herbaspirillum, Pseudoalteromonas, and Marinobacter. Cultivation efforts of the 0.1- to 0.2-μm-size fraction led to the isolation of Actinobacteria-affiliated genera Microbacterium and Kocuria. Based on phylogenetic relatedness and microscopic observations, we hypothesize that the ultrasmall cells in Lake Vida brine are ultramicrocells that are likely in a reduced size state as a result of environmental stress or life cycle-related conditions.
authors.forename: Emanuele
authors.initials: E
authors.lastname: Kuhn
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Ichimura
authors.forename: Vivian
authors.initials: V
authors.lastname: Peng
authors.forename: Christian H
authors.initials: CH
authors.lastname: Fritsen
authors.forename: Gareth
authors.initials: G
authors.lastname: Trubl
authors.forename: Peter T
authors.initials: PT
authors.lastname: Doran
authors.forename: Alison E
authors.initials: AE
authors.lastname: Murray
mesh_terms: D000864:Antarctic Regions; D001419:Bacteria / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D004269:DNA, Bacterial / Q000235:genetics; D046448:Ice Cover / Q000382:microbiology*; D060106:Lakes / Q000382:microbiology*; D008969:Molecular Sequence Data; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012492:Salts / Q000737:chemistry / Q000378:metabolism*
chemical_list: D004269:DNA, Bacterial; D012336:RNA, Ribosomal, 16S; D012492:Salts; C017082:brine
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