Journal
APPLIED AND ENVIRONMENTAL MICROBIOLOGY
Volume 80, Issue 12, Pages 3687-3698Publisher
AMER SOC MICROBIOLOGY
DOI: 10.1128/AEM.00276-14
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Funding
- NSF [ANT-0739681, ANT-0739698, 0821619, 0949176]
- Fulbright/CAPES-BRAZIL [2163-08-8]
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The anoxic and freezing brine that permeates Lake Vida's perennial ice below 16 m contains an abundance of very small (<= 0.2-m) particles mixed with a less abundant population of microbial cells ranging from >0.2 to 1.5 mu m 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 mu m, 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 mu m among the brine cells. A 16S rRNA gene clone library from the brine 0.1- to 0.2-mu m-size fraction revealed a relatively low-diversity assemblage of Bacteria sequences distinct from the previously reported >0.2-mu m-cell-size Lake Vida brine assemblage. The brine 0.1- to 0.2-mu m-size fraction was dominated by the Proteobacteria-affiliated genera Herbaspirillum, Pseudo-alteromonas, and Marinobacter. Cultivation efforts of the 0.1- to 0.2-mu m-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.
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