Lacelle et al. 2012), resulting in unique cryogenic processes. Parts of the valley have
no active layer whatsoever. Here sublimation processes dominate. Isotopic measurements indicate that the water-ice content of the ice-cemented permafrost is
condensation-diffusion in origin, from the past 100 Ka years to present, as opposed
to liquid water deposited prior to freezing (Lacelle et al. 2013). As a result of the
harsh conditions, life in University Valley is purely microbial; there are no plants or
animals in the valley, and birds cannot be seen flying overhead. The presence of
microbial life can be detected using standard microbiological techniques, and the
soils are extremely low in biomass. Direct microscopy indicates the soils contain
1000’s of cells per gram of soil (Goordial et al. 2016), orders of magnitude lower
than lower-elevation Dry Valleys, or permafrost of similar latitude in the Arctic
(Goordial et al. 2013; Goordial and Whyte 2014). The presence of microorganisms
in the soils is also detected via molecular techniques (DNA based), confirming the
presence of diverse bacterial and fungal organisms. Like many other lower-elevation
Dry Valleys, Archaea do not seem to be abundant or diverse in this system.
A number of studies have established the ubiquitous presence of microbial life in
Dry Valley permafrost soils via microscopy or DNA sequencing (Bakermans et al.
2014; Lee et al. 2012; Monteiro et al. 2020). However, such cell counts and DNA
molecular approaches cannot distinguish between active microbial life, dormant life,
or the DNA of life that has been preserved in the arid and sub-zero conditions,
similar to a freezer where molecular extracts and glycerol stocks of microbial
cultures are commonly kept for long-term storage. Though microorganisms are
unambiguously present in the University Valley soils, unlike all other permafrost
examined to date from other locations on Earth, metabolically active microbial life
cannot be detected via in situ gas flux measurements, nor in the laboratory at in situ
relevant sub-zero temperatures (Goordial et al. 2016). Past efforts to detect life in
these soils include highly sensitive radiolabelled substrate mineralization assays
(radiorespiration assays) carried out over 2 years, similar to the detection assays
employed on Mars in the Viking lander mission to detect alien life (Horowitz et al.
1976). The absence of observable activity is not altered by the addition of nitrogen
and phosphorus sources to soils; thus, nutrient limitation is not a likely factor. The
addition of a known psychrophile to University Valley soil microcosms does result
in measurable respiration, and thus soil toxicity can be ruled out. In the past, efforts
to extract RNA which would indicate active microbiota have not been successful.
Similar cold temperatures are present in many other cryoenvironments, and it is not
likely that temperature itself is prohibitive to life in University Valley, so much as the
corresponding unavailability of liquid water. Due to the location of University
Valley, inland and high elevation, the influence of salts from the ocean is negligible,
and solute concentrations in the soil are too low to facilitate the formation of veins of
briny water in the ice. Combining soil temperature data over 3 years with soil
geochemistry indicates that the conditions which would permit liquid water to be
present, even as a thin film of water, are not met in University Valley for more than
74 cumulative hours per year (Lacelle et al. 2013; Goordial et al. 2016).
Microbial activity measurements are rare in dry permafrost-affected sites on Earth
(Horowitz et al. 1972; Goordial et al. 2016; Gilichinsky et al. 2007; Bakermans et al.
6 When the Vital Signs of Microbial Life Go Cold, Does That Mean the Pulse Is. . .
119
no active layer whatsoever. Here sublimation processes dominate. Isotopic measurements indicate that the water-ice content of the ice-cemented permafrost is
condensation-diffusion in origin, from the past 100 Ka years to present, as opposed
to liquid water deposited prior to freezing (Lacelle et al. 2013). As a result of the
harsh conditions, life in University Valley is purely microbial; there are no plants or
animals in the valley, and birds cannot be seen flying overhead. The presence of
microbial life can be detected using standard microbiological techniques, and the
soils are extremely low in biomass. Direct microscopy indicates the soils contain
1000’s of cells per gram of soil (Goordial et al. 2016), orders of magnitude lower
than lower-elevation Dry Valleys, or permafrost of similar latitude in the Arctic
(Goordial et al. 2013; Goordial and Whyte 2014). The presence of microorganisms
in the soils is also detected via molecular techniques (DNA based), confirming the
presence of diverse bacterial and fungal organisms. Like many other lower-elevation
Dry Valleys, Archaea do not seem to be abundant or diverse in this system.
A number of studies have established the ubiquitous presence of microbial life in
Dry Valley permafrost soils via microscopy or DNA sequencing (Bakermans et al.
2014; Lee et al. 2012; Monteiro et al. 2020). However, such cell counts and DNA
molecular approaches cannot distinguish between active microbial life, dormant life,
or the DNA of life that has been preserved in the arid and sub-zero conditions,
similar to a freezer where molecular extracts and glycerol stocks of microbial
cultures are commonly kept for long-term storage. Though microorganisms are
unambiguously present in the University Valley soils, unlike all other permafrost
examined to date from other locations on Earth, metabolically active microbial life
cannot be detected via in situ gas flux measurements, nor in the laboratory at in situ
relevant sub-zero temperatures (Goordial et al. 2016). Past efforts to detect life in
these soils include highly sensitive radiolabelled substrate mineralization assays
(radiorespiration assays) carried out over 2 years, similar to the detection assays
employed on Mars in the Viking lander mission to detect alien life (Horowitz et al.
1976). The absence of observable activity is not altered by the addition of nitrogen
and phosphorus sources to soils; thus, nutrient limitation is not a likely factor. The
addition of a known psychrophile to University Valley soil microcosms does result
in measurable respiration, and thus soil toxicity can be ruled out. In the past, efforts
to extract RNA which would indicate active microbiota have not been successful.
Similar cold temperatures are present in many other cryoenvironments, and it is not
likely that temperature itself is prohibitive to life in University Valley, so much as the
corresponding unavailability of liquid water. Due to the location of University
Valley, inland and high elevation, the influence of salts from the ocean is negligible,
and solute concentrations in the soil are too low to facilitate the formation of veins of
briny water in the ice. Combining soil temperature data over 3 years with soil
geochemistry indicates that the conditions which would permit liquid water to be
present, even as a thin film of water, are not met in University Valley for more than
74 cumulative hours per year (Lacelle et al. 2013; Goordial et al. 2016).
Microbial activity measurements are rare in dry permafrost-affected sites on Earth
(Horowitz et al. 1972; Goordial et al. 2016; Gilichinsky et al. 2007; Bakermans et al.
6 When the Vital Signs of Microbial Life Go Cold, Does That Mean the Pulse Is. . .
119