Abstract
The permanently ice-covered lakes of the McMurdo Dry Valleys, Antarctica are distinctive ecosystems that consist strictly of microbial communities. In this study, water samples were collected from Lake Vanda, a stratified Dry Valley lake whose upper waters (from just below the ice cover to nearly 60 m) are highly oligotrophic, and used to establish enrichment cultures. Six strains of psychrotolerant, heterotrophic bacteria were isolated from lake water samples from a depth of 50 or 55 m. Phylogenetic analyses showed the Lake Vanda strains to be species of Nocardiaceae, Caulobacteraceae, Sphingomonadaceae, and Bradyrhizobiaceae. All Lake Vanda strains grew at temperatures near or below 0 °C, but optimal growth occurred from 18 to 24 °C. Some strains showed significant halotolerance, but no strains required NaCl for growth. The isolates described herein include cold-active species not previously reported from Dry Valley lakes, and their physiological and phylogenetic characterization broadens our understanding of these limnologically unique lakes.
Highlights
Lake Vanda is a stratified lake about 75 m deep located in Wright Valley of the McMurdo DryValleys, Antarctica, a region that experiences subzero average temperatures and extremely low (~10 mm) annual precipitation [1]
Our analyses reveal species not previously recognized from any Dry Valley lake and compare these cold-active strains to previously described Dry Valley lake species
The major phenotypic properties of the Lake Vanda strains are shown in Table 1, and photomicrographs of all strains are shown in Figures 2A and 3A
Summary
Lake Vanda is a stratified lake about 75 m deep located in Wright Valley of the McMurdo DryValleys, Antarctica, a region that experiences subzero average temperatures and extremely low (~10 mm) annual precipitation [1]. Microorganisms inhabiting the lake are isolated from their surroundings by a permanent ice cover of approximately 3.5 m, which limits the penetration of light and inhibits wind mixing of the water column. The waters of Lake Vanda range from fresh and cold (~4 °C) just below the ice cover to hypersaline and surprisingly warm (~24 °C) just above the sediments (Figure 1). At depths of 50–55 m, Lake Vanda waters are approximately 10–12 °C with a pH of 6.5–7 [3]. Levels of dissolved organic carbon (DOC) in Lake Vanda are quite low (
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