beyond the typical lifespan of an individual cloud. Cloud propagation is known to
occur along storm fronts or under conditions where a cumulus cloud could potentially induce updrafts (Fovell and Kim 2003). Satellite imagery has tracked a
propagating cloud cluster crossing between ~85
o W and 165
E within a 5–10
o N
band between 22 July and 4 August 1967 (13 days) (Chang 1970). Airmasses that
reside within propagating clouds at lower altitudes can provide conditions that favor
the establishment of a microbial ecosystem in the troposphere, provided there are
aerosolized microorganisms capable of metabolic activity in these types of environments (Schuerger et al. 2013; Amato et al. 2017; Aalismail et al. 2019). Once
resident in the atmosphere, long-range dispersion of these microorganisms may
occur at planetary scales. Recent work conducted atop Puy de Dôme in France
(peak altitude ~1.5 km) found many cloud-associated microorganisms were metabolically active when spiked with nutrient sources (Vaitilingom et al. 2012;
Vaitilingom et al. 2013). More recent experiments conducted at this location
where the microorganisms were immediately fixed upon sample collection and
evaluated using DNA and RNA extracts demonstrated in situ metabolic activity
and a diverse community consisting of over 28,000 bacterial species (Amato et al.
2017). A study conducted at Mt. Bachelor Observatory (Bend, OR, peak altitude
~2.7 km) using a comparative RNA/DNA technique noted “Our observations
suggest that metabolically active bacteria exist in the atmosphere and that these
communities may be involved in the cycling of organic compounds in the atmosphere” (Klein et al. 2016). A number of different authors have presented the
hypothesis of the existence of life in the atmosphere and clouds of other planetary
bodies (Joseph 2019; Limaye et al. 2018).
Another location other than clouds where microbial atmospheric ecosystems may
occur is aquatic or terrestrial gas seeps. The lifespan of these types of environments
may exist on the order of hours to days depending on the stability of the gas plume,
and this may be affected by emission rate, wind speeds (low and high energy),
topography, and atmospheric phenomena such as inversions. Methane emissions or
seeps occur naturally and from anthropogenic sources. Natural sources include
wetlands, wildlife, volcanoes, and hydrocarbon deposits. Anthropogenic sources
(~60% of the global emissions) include landfills, agriculture (rice paddies), livestock, and hydrocarbon extraction operations and their use (Saunois et al. 2016). The
estimated global methane flux has been reported at ~500 Tg yr.
À1 (~500 million
metric tons), with landfills, rice paddies, wetlands, and soil contributing 40, 60,
110, and 140 Tg yr.
À1 , respectively (Boeckx and Van Cleemput 1996). Estimates of
methane emissions from livestock have ranged from 60 to 120 Tg yr.
À1 (Johnson
and Ward 1996). Methane-oxidizing microorganisms at seeps that occur on the
seafloor are known to function as the foundation of the foodweb in those islandlike ecosystems and show genetic similarities at a global scale (Ruff et al. 2015).
Near terrestrial seeps, children have been shown to harbor elevated concentrations of
the methanogen Methanobrevibacter smithii (common human gut flora) in their
intestines (de Araujo Filho et al. 2014). Within the atmosphere of swine confinement
buildings, methanogenic sequences dominated archaeal sequences in aerosol samples (Nehme et al. 2009). In regard to the presence of methanotrophic bacteria in
5 The Concept of Evanescent Microbial Ecosystems in Earth’s Atmosphere
109
occur along storm fronts or under conditions where a cumulus cloud could potentially induce updrafts (Fovell and Kim 2003). Satellite imagery has tracked a
propagating cloud cluster crossing between ~85
o W and 165
E within a 5–10
o N
band between 22 July and 4 August 1967 (13 days) (Chang 1970). Airmasses that
reside within propagating clouds at lower altitudes can provide conditions that favor
the establishment of a microbial ecosystem in the troposphere, provided there are
aerosolized microorganisms capable of metabolic activity in these types of environments (Schuerger et al. 2013; Amato et al. 2017; Aalismail et al. 2019). Once
resident in the atmosphere, long-range dispersion of these microorganisms may
occur at planetary scales. Recent work conducted atop Puy de Dôme in France
(peak altitude ~1.5 km) found many cloud-associated microorganisms were metabolically active when spiked with nutrient sources (Vaitilingom et al. 2012;
Vaitilingom et al. 2013). More recent experiments conducted at this location
where the microorganisms were immediately fixed upon sample collection and
evaluated using DNA and RNA extracts demonstrated in situ metabolic activity
and a diverse community consisting of over 28,000 bacterial species (Amato et al.
2017). A study conducted at Mt. Bachelor Observatory (Bend, OR, peak altitude
~2.7 km) using a comparative RNA/DNA technique noted “Our observations
suggest that metabolically active bacteria exist in the atmosphere and that these
communities may be involved in the cycling of organic compounds in the atmosphere” (Klein et al. 2016). A number of different authors have presented the
hypothesis of the existence of life in the atmosphere and clouds of other planetary
bodies (Joseph 2019; Limaye et al. 2018).
Another location other than clouds where microbial atmospheric ecosystems may
occur is aquatic or terrestrial gas seeps. The lifespan of these types of environments
may exist on the order of hours to days depending on the stability of the gas plume,
and this may be affected by emission rate, wind speeds (low and high energy),
topography, and atmospheric phenomena such as inversions. Methane emissions or
seeps occur naturally and from anthropogenic sources. Natural sources include
wetlands, wildlife, volcanoes, and hydrocarbon deposits. Anthropogenic sources
(~60% of the global emissions) include landfills, agriculture (rice paddies), livestock, and hydrocarbon extraction operations and their use (Saunois et al. 2016). The
estimated global methane flux has been reported at ~500 Tg yr.
À1 (~500 million
metric tons), with landfills, rice paddies, wetlands, and soil contributing 40, 60,
110, and 140 Tg yr.
À1 , respectively (Boeckx and Van Cleemput 1996). Estimates of
methane emissions from livestock have ranged from 60 to 120 Tg yr.
À1 (Johnson
and Ward 1996). Methane-oxidizing microorganisms at seeps that occur on the
seafloor are known to function as the foundation of the foodweb in those islandlike ecosystems and show genetic similarities at a global scale (Ruff et al. 2015).
Near terrestrial seeps, children have been shown to harbor elevated concentrations of
the methanogen Methanobrevibacter smithii (common human gut flora) in their
intestines (de Araujo Filho et al. 2014). Within the atmosphere of swine confinement
buildings, methanogenic sequences dominated archaeal sequences in aerosol samples (Nehme et al. 2009). In regard to the presence of methanotrophic bacteria in
5 The Concept of Evanescent Microbial Ecosystems in Earth’s Atmosphere
109