6.4 Conclusion
Microorganisms, in various physiological states, play important, foundational roles
for the existence and persistence of life in cryoenvironments. Active microbiota play
the most obvious role in ecosystem function through the actions of their metabolism—converting and consuming carbon and electron donors and producing waste
products, all of which feedback into the environment. Replicating microorganisms
exert a similar effect—increasing the number of microorganisms and copy numbers
of key genes to carrying out a given function. Even dormant and dead cells play a
foundational role (Blazewicz et al. 2013). Dormant cells act as reservoirs for future
microbial community structure and function when environmental conditions may
change, and dead microorganisms can become cannibalized—becoming fuel for
other microorganisms to persist, in some environments for tens of thousands of years
(Bradley et al. 2019). Though cryoenvironments are primarily discussed here, these
physiological states and principles for ecosystem function apply in virtually every
environment.
University Valley permafrost shows an example of microbial activity that cannot
be measured using even highly sensitive methodologies—however, at one time the
soils of the valley were considered to be completely sterile, as no microorganisms
could be cultivated from them (Horowitz et al. 1972). Since then, the advent of
molecular techniques has resulted in an appreciation for how much diversity and
biomass these soils contain, as well as yielded insight into novel metabolic processes. More recently, studies examining the microbes in other cold soils have
demonstrated the ability to derive energy from trace, atmospheric amounts of carbon
monoxide and hydrogen to provide energy for the survival of microbial cells. These
exciting observations may prove to be a widespread capability, possibly occurring at
sub-zero temperatures in nutrient-poor settings (Ji et al. 2017; Greening et al. 2019;
Greening et al. 2016; Lynch et al. 2012; Lynch et al. 2014).
Like the ancient foundation stone that inspired this essay, sandstone rocks in this
University Valley are where life springs forth from and are the source of many of the
microorganisms that fall to the valley floor as the walls erode. Though not obviously
metabolically active, these populations will become the seeds for future microbial
communities, when the permafrost thaws on geologic timescales or potentially as a
result of wetting and thaw due to human-made climate change. There is also the
tantalizing possibility that these microorganisms may in fact be active, even at small
levels only sufficient for maintenance and survival, just not on scales that can be
detected easily by our current methods.
The impression I hope the reader can walk away with is that we are continually
learning more about the capabilities and extent of microbial life on Earth. It is
entirely possible (likely!) that our methods of detection of activity will become
more sensitive in the future, enabling detection of metabolic activity even when
“slow”. Continued cultivation efforts will surely yield novel psychrophiles in culture, as well as increased knowledge of their mechanisms for survival and activity.
What we learn about cryophilic life will inform how we think about the limits of life
6 When the Vital Signs of Microbial Life Go Cold, Does That Mean the Pulse Is. . .
125
Microorganisms, in various physiological states, play important, foundational roles
for the existence and persistence of life in cryoenvironments. Active microbiota play
the most obvious role in ecosystem function through the actions of their metabolism—converting and consuming carbon and electron donors and producing waste
products, all of which feedback into the environment. Replicating microorganisms
exert a similar effect—increasing the number of microorganisms and copy numbers
of key genes to carrying out a given function. Even dormant and dead cells play a
foundational role (Blazewicz et al. 2013). Dormant cells act as reservoirs for future
microbial community structure and function when environmental conditions may
change, and dead microorganisms can become cannibalized—becoming fuel for
other microorganisms to persist, in some environments for tens of thousands of years
(Bradley et al. 2019). Though cryoenvironments are primarily discussed here, these
physiological states and principles for ecosystem function apply in virtually every
environment.
University Valley permafrost shows an example of microbial activity that cannot
be measured using even highly sensitive methodologies—however, at one time the
soils of the valley were considered to be completely sterile, as no microorganisms
could be cultivated from them (Horowitz et al. 1972). Since then, the advent of
molecular techniques has resulted in an appreciation for how much diversity and
biomass these soils contain, as well as yielded insight into novel metabolic processes. More recently, studies examining the microbes in other cold soils have
demonstrated the ability to derive energy from trace, atmospheric amounts of carbon
monoxide and hydrogen to provide energy for the survival of microbial cells. These
exciting observations may prove to be a widespread capability, possibly occurring at
sub-zero temperatures in nutrient-poor settings (Ji et al. 2017; Greening et al. 2019;
Greening et al. 2016; Lynch et al. 2012; Lynch et al. 2014).
Like the ancient foundation stone that inspired this essay, sandstone rocks in this
University Valley are where life springs forth from and are the source of many of the
microorganisms that fall to the valley floor as the walls erode. Though not obviously
metabolically active, these populations will become the seeds for future microbial
communities, when the permafrost thaws on geologic timescales or potentially as a
result of wetting and thaw due to human-made climate change. There is also the
tantalizing possibility that these microorganisms may in fact be active, even at small
levels only sufficient for maintenance and survival, just not on scales that can be
detected easily by our current methods.
The impression I hope the reader can walk away with is that we are continually
learning more about the capabilities and extent of microbial life on Earth. It is
entirely possible (likely!) that our methods of detection of activity will become
more sensitive in the future, enabling detection of metabolic activity even when
“slow”. Continued cultivation efforts will surely yield novel psychrophiles in culture, as well as increased knowledge of their mechanisms for survival and activity.
What we learn about cryophilic life will inform how we think about the limits of life
6 When the Vital Signs of Microbial Life Go Cold, Does That Mean the Pulse Is. . .
125