2014), and thus the observations in University Valley remain to be tested against
other sites to determine if these results are unique or whether such conditions
represent a true cold-arid limit to active life. Crucially, though a “pulse” or evidence
of in situ activity cannot be directly measured in University Valley soils, there is
substantial evidence that microbial life persists nonetheless.
6.2.1 Dormancy: The Foundation for Future Microbial
Structure and Function
Though no activity can be measured at sub-zero temperatures in University Valley
soils, using the same radiolabelled substrate mineralization assay, microbial respiration can be detected when the incubation temperatures are raised to 5
C, temperatures which would not have been experienced in this region for at least
150,000 years (Goordial et al. 2016; Lacelle et al. 2013). Classic cultivation techniques on solid agar media have yielded no isolated microorganisms; however, after
soils were held at 5
C for 1 month before cultivation attempts, four bacterial and two
fungal isolates were obtained from University Valley soils. Two of the isolates, a
bacterial Rhodococcus sp. and a yeast Rhodotorula sp., are capable of sub-zero
growth relevant to the conditions they were isolated from (Goordial et al. 2016;
Goordial et al. 2015; Goordial et al. 2016). This confirms that viable microbiota
persist in University Valley, evident when clement conditions are present.
Metagenomic analysis suggests that much of the DNA in University Valley soils
are from dead or merely surviving dormant cells (Goordial et al. 2017). The overall
functional potential of the soils shares the most similarity with permafrost soils in the
Arctic, not the nearby, lower-elevation Dry Valley surface soils. These functional
similarities are driven primarily by a relative enrichment in genes associated with
dormancy and sporulation and spore DNA protection. Dormancy is a reversible state
of reduced metabolic activity, typically in response to adverse environmental conditions. Dormant microbial cells can act as seedbanks, prolonging the persistence of
genotypic functions and specific populations of cells, and thus have important
consequences for community- and ecosystem-level processes once conditions
become clement again (Jones and Lennon 2010; Lennon and Jones 2011).
While dormancy is clearly an advantageous strategy for longevity and seeding
future microbial populations, it cannot go on indefinitely and has several disadvantages. Dormant microorganisms are less able to quickly respond to signals of
favourable conditions and changing environments, especially if the favourable
conditions are only short lived. The transition out of a dormant state requires energy,
and for the appropriate cellular machinery to respond to the new conditions (Lennon
and Jones 2011). While in a dormant state, cells are also subject to agents of genomic
decay, for example, background radiation which can cause mutations to accumulate,
inhibiting a cell’s ability to replicate and carry out cellular functions (effectively, the
death of a cell). There is evidence that on “short timescales”, dormancy may be an
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J. M. Goordial
other sites to determine if these results are unique or whether such conditions
represent a true cold-arid limit to active life. Crucially, though a “pulse” or evidence
of in situ activity cannot be directly measured in University Valley soils, there is
substantial evidence that microbial life persists nonetheless.
6.2.1 Dormancy: The Foundation for Future Microbial
Structure and Function
Though no activity can be measured at sub-zero temperatures in University Valley
soils, using the same radiolabelled substrate mineralization assay, microbial respiration can be detected when the incubation temperatures are raised to 5
C, temperatures which would not have been experienced in this region for at least
150,000 years (Goordial et al. 2016; Lacelle et al. 2013). Classic cultivation techniques on solid agar media have yielded no isolated microorganisms; however, after
soils were held at 5
C for 1 month before cultivation attempts, four bacterial and two
fungal isolates were obtained from University Valley soils. Two of the isolates, a
bacterial Rhodococcus sp. and a yeast Rhodotorula sp., are capable of sub-zero
growth relevant to the conditions they were isolated from (Goordial et al. 2016;
Goordial et al. 2015; Goordial et al. 2016). This confirms that viable microbiota
persist in University Valley, evident when clement conditions are present.
Metagenomic analysis suggests that much of the DNA in University Valley soils
are from dead or merely surviving dormant cells (Goordial et al. 2017). The overall
functional potential of the soils shares the most similarity with permafrost soils in the
Arctic, not the nearby, lower-elevation Dry Valley surface soils. These functional
similarities are driven primarily by a relative enrichment in genes associated with
dormancy and sporulation and spore DNA protection. Dormancy is a reversible state
of reduced metabolic activity, typically in response to adverse environmental conditions. Dormant microbial cells can act as seedbanks, prolonging the persistence of
genotypic functions and specific populations of cells, and thus have important
consequences for community- and ecosystem-level processes once conditions
become clement again (Jones and Lennon 2010; Lennon and Jones 2011).
While dormancy is clearly an advantageous strategy for longevity and seeding
future microbial populations, it cannot go on indefinitely and has several disadvantages. Dormant microorganisms are less able to quickly respond to signals of
favourable conditions and changing environments, especially if the favourable
conditions are only short lived. The transition out of a dormant state requires energy,
and for the appropriate cellular machinery to respond to the new conditions (Lennon
and Jones 2011). While in a dormant state, cells are also subject to agents of genomic
decay, for example, background radiation which can cause mutations to accumulate,
inhibiting a cell’s ability to replicate and carry out cellular functions (effectively, the
death of a cell). There is evidence that on “short timescales”, dormancy may be an
120
J. M. Goordial