Chemoorganotrophic Bacteria From Lake Fryxell, Antarctica, Including Pseudomonas Strain LFY10, a Cold-Adapted, Halotolerant Bacterium Useful in Teaching Labs.

Jennifer M Baker,Anna M G Cunningham,Chelsea L Reeves,Emily R Huffman,Nicole A Vander Schaaf,Anna C Hang,Carli J Riester,W Matthew Sattley,Michael T Madigan

doi:10.3389/fmicb.2019.00156

Jennifer M Baker, Anna M G Cunningham + Show 7 more

Open Access

https://doi.org/10.3389/fmicb.2019.00156

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Abstract

Lake Fryxell, situated in the McMurdo Dry Valleys of Antarctica, is an intriguing aquatic ecosystem because of its perennial ice cover, highly stratified water column, and extreme physicochemical conditions, which collectively restrict lake biodiversity to solely microbial forms. To expand our current understanding of the cultivable biodiversity of Lake Fryxell, water samples were collected from depths of 10 and 17 m, and pure cultures of eight diverse strains of aerobic, chemoorganotrophic bacteria were obtained. Despite having high 16S rRNA gene sequence similarity to mesophilic bacteria inhabiting various temperate environments, all Lake Fryxell isolates were psychrotolerant, with growth occurring at 0°C and optimal growth from 18–24°C for all isolates. Phylogenetic analyses showed the isolates to be members of six taxonomic groups, including the genera Brevundimonas, Arthrobacter, Sphingobium, Leifsonia, and Pseudomonas, as well as the family Microbacteriaceae (one strain could not reliably be assigned to a specific genus based on our analysis). Pseudomonas strain LFY10 stood out as a useful tool for teaching laboratory activities because of its substantial cold adaptation (visible growth is evident in 1–2 days at 4°C), beta-hemolytic activity, and halotolerance to 8.5% (w/v) NaCl. These cold-adapted bacteria likely play a role in carbon mineralization and other nutrient cycling in Lake Fryxell, and their characterization broadens our understanding of microbial biodiversity in aquatic polar ecosystems.

Highlights

The McMurdo Dry Valleys of East Antarctica (Figure 1A) comprise a windswept polar desert that receives minimal annual precipitation (3–50 mm water equivalent per year; Fountain et al, 2009) and consists of nutrient-poor, rocky–sandy soils
Antarctic lakes exhibit a surprising degree of microbial diversity, we have relatively few isolates from these ecosystems compared to temperate aquatic environments and know little of their genetic or biochemical potential. We have employed both defined and complex culture media and specific incubation conditions to enrich for cold-adapted, chemoorganotrophic bacteria from different depths of the Lake Fryxell water column. These enrichments yielded pure cultures of eight diverse strains of bacteria, and here we describe the morphology, physiology, and phylogeny of these isolates with a focus on Pseudomonas strain LFY10, a potentially useful strain for teaching laboratories in microbiology
A total of eight strains of cold-active, aerobic, chemoorganotrophic bacteria were isolated from the Lake Fryxell water samples: five strains from a depth of 10 m and three strains from a depth of 17 m (Table 1)

Summary

Introduction

The McMurdo Dry Valleys of East Antarctica (Figure 1A) comprise a windswept polar desert that receives minimal annual precipitation (3–50 mm water equivalent per year; Fountain et al, 2009) and consists of nutrient-poor, rocky–sandy soils. Antarctic Bacteria From Lake Fryxell conditions, including constant freezing temperatures, nutrient limitation, and low incident light with long periods of almost total darkness during the austral winter. Lake Fryxell, located in Taylor Valley, has a water column of 18 m covered by 5–6 m of ice that prevents wind mixing and limits light penetration (Figure 1B). Lake Fryxell waters are fresh and supersaturated with trapped gasses, especially O2 from phytoplankton photosynthesis (Vincent, 1981; Priscu et al, 1987; Figure 1C). Deeper strata are brackish and anoxic and experience the upward diffusion of dissolved sulfide produced by sulfate-reducing bacteria (Karr et al, 2005; Sattley and Madigan, 2010; Figure 1C). Dissolved O2 and benthic sulfide coexist as opposing gradients to produce a biologically active chemocline from 9–10.5 m, wherein numbers of sulfur-oxidizing bacteria peak (Sattley and Madigan, 2006)

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