could be observed down to À15
C (Goordial et al. 2016). This experiment utilized
the exact same radiorespiration carbon mineralization methodology that could not
detect activity at sub-zero temperatures in the University Valley soils that contained
three orders of magnitude less biomass. These experiments draw a crude line,
between À5
C and À 15
C where cellular replication stops, but non-growth
activity persists. What the mechanisms allowing these physiological shifts are, and
how levels of activity may change on geological timescales remains an intriguing
outstanding question.
6.2.3 The Rocks of Life in University Valley: Cryptoendoliths
Though active life in the dry and underlying ice-cemented permafrost may be
difficult to detect, the valley itself is not void of thriving microbial communities, if
one knows where to look. The valley walls are composed of porous Beacon
sandstone, trapping and holding what little moisture is available within pore spaces
inside the rock. In the summer, the sun warms the rocks above ambient air temperatures. In comparison to the 74 h per year where moist conditions can be present in
University Valley soils, boulders in a valley with similar environmental conditions
(1650 m.a.s.l) are found to have moisture for over 700 h per year (Friedmann et al.
1993). As a result, hidden mere millimetres beneath the rock surface, in these
warmer and wetter conditions, is a dense and colourful microbial community that
cannot be seen without breaking open the rock (Fig. 6.2).
Cryptoendolithic (“hidden within rock”) microbial communities are trophically
simple communities, commonly visible as coloured bands beneath the surface of
sandstone, gypsum and other siliceous rocks (Makhalanyane et al. 2014). They are
composed of lichenized or free-living fungi (black or dark green band), photoautotrophic algae or cyanobacteria (green band) and heterotrophic bacteria (Friedmann
et al. 1988; Friedmann et al. 1993; Selbmann et al. 2005; Coleine et al. 2018; Cary
et al. 2010). Colonized Beacon sandstone, such as what composes the walls of
University Valley, is widely colonized by cryptoendoliths. The translucent rock
substrate allows light to penetrate into the pore spaces, providing energy for the
photoautotrophs, which in turn fix carbon for the heterotrophic communities. In
University Valley, a black band is found at the surface of the rock (Fig. 6.2b)
composed of black yeast fungi with high contents of melanin and lichenized algae
(Goordial et al. 2017). The high melanin content of the fungi protects the photoautotrophic algae and heterotrophic organisms deeper within the rock from harmful
UV radiation found in high amounts in the Antarctic at high elevation. The narrow
bands of colour correspond to a narrow zone of habitability where light conditions
are “just right”, and moisture and sun can permit increased metabolic activity.
Though the rocks are warmed in the summer, sub-zero temperatures still persist in
the rocks throughout the year. In stark contrast to the permafrost soils, metabolic
activity at sub-zero temperatures, by both heterotrophic and photoautotrophic communities, is easily identified. Using the same radiorespiration assays as on the soils,
122
J. M. Goordial
C (Goordial et al. 2016). This experiment utilized
the exact same radiorespiration carbon mineralization methodology that could not
detect activity at sub-zero temperatures in the University Valley soils that contained
three orders of magnitude less biomass. These experiments draw a crude line,
between À5
C and À 15
C where cellular replication stops, but non-growth
activity persists. What the mechanisms allowing these physiological shifts are, and
how levels of activity may change on geological timescales remains an intriguing
outstanding question.
6.2.3 The Rocks of Life in University Valley: Cryptoendoliths
Though active life in the dry and underlying ice-cemented permafrost may be
difficult to detect, the valley itself is not void of thriving microbial communities, if
one knows where to look. The valley walls are composed of porous Beacon
sandstone, trapping and holding what little moisture is available within pore spaces
inside the rock. In the summer, the sun warms the rocks above ambient air temperatures. In comparison to the 74 h per year where moist conditions can be present in
University Valley soils, boulders in a valley with similar environmental conditions
(1650 m.a.s.l) are found to have moisture for over 700 h per year (Friedmann et al.
1993). As a result, hidden mere millimetres beneath the rock surface, in these
warmer and wetter conditions, is a dense and colourful microbial community that
cannot be seen without breaking open the rock (Fig. 6.2).
Cryptoendolithic (“hidden within rock”) microbial communities are trophically
simple communities, commonly visible as coloured bands beneath the surface of
sandstone, gypsum and other siliceous rocks (Makhalanyane et al. 2014). They are
composed of lichenized or free-living fungi (black or dark green band), photoautotrophic algae or cyanobacteria (green band) and heterotrophic bacteria (Friedmann
et al. 1988; Friedmann et al. 1993; Selbmann et al. 2005; Coleine et al. 2018; Cary
et al. 2010). Colonized Beacon sandstone, such as what composes the walls of
University Valley, is widely colonized by cryptoendoliths. The translucent rock
substrate allows light to penetrate into the pore spaces, providing energy for the
photoautotrophs, which in turn fix carbon for the heterotrophic communities. In
University Valley, a black band is found at the surface of the rock (Fig. 6.2b)
composed of black yeast fungi with high contents of melanin and lichenized algae
(Goordial et al. 2017). The high melanin content of the fungi protects the photoautotrophic algae and heterotrophic organisms deeper within the rock from harmful
UV radiation found in high amounts in the Antarctic at high elevation. The narrow
bands of colour correspond to a narrow zone of habitability where light conditions
are “just right”, and moisture and sun can permit increased metabolic activity.
Though the rocks are warmed in the summer, sub-zero temperatures still persist in
the rocks throughout the year. In stark contrast to the permafrost soils, metabolic
activity at sub-zero temperatures, by both heterotrophic and photoautotrophic communities, is easily identified. Using the same radiorespiration assays as on the soils,
122
J. M. Goordial