compounds, contribute to the foundation of the magic called “Life” on planet Earth,
if not in the entire universe.
Nitrogen is an essential element in two of the four macromolecules constituting
both the blueprint (nucleic acids) and the toolkit (Proteins) that dynamically executes
(the blueprint instructions into a) functioning metabolism, thereby critically contributing to the hallmarks of life as we know it (evolution, emancipation, and
communication of cells). However, it is actually the incredible versatility of redox
reactivity of simple nitrogen molecules that steered life to its present diversity.
Ironically, this incredible versatility in redox reactivity of nitrogen molecules represents also the greatest danger to a continued existence of metazoan life on the planet.
The cause for unleashing this destructive potential is not the aforementioned central
place of nitrogen in life’s processes, but rather the ill-natured, albeit often
unintended, far-reaching activities of human ingenuity and industriousness. The
platform for this disastrous outcome is the connectedness of nitrogen compounds
at different oxidation states through spontaneous and facilitated electron transfer
reactions, individually and organized in pathways, which constitute the global
nitrogen cycle (Fig. 9.1a). This biogeochemical cycle together with others cycling
carbon, sulfur, iron, and other redox-active elemental compounds as well as plate
tectonics keep the planet eligible for life. Interestingly, life itself is the active driver
of these biogeochemical cycles: microorganisms. While this might read like a
circulus vitiosus, it does so only in the absence of clues about how microorganisms
came to be (origin of life). Once the single-celled archaea and bacteria came into
being on an initially bare giant rock that eventually became our blue planet, they
diversified, driven by horizontal gene transfers and viral transductions and quickly
emerged as the drivers of biogeochemical nutrient cycles.
The “secret” to the evolved capability of single cell microbes to push all the
biogeochemical cycles is the organization of their metabolisms in functional modules (Fig. 9.1), correlating with a modular organization of its encoding genetic
information. Modular organization of genes and polygenic transcriptional units in
the genomes of archaea and bacteria provides two advantages: (1) modular sections
and even entire modules can be exchanged between microbes even across large
taxonomic distances by lateral transfer, and (2) the co-location of genes and polygenic transcriptional units provides for a variety of regulatory opportunities suited
for coordinating cellular emancipation and communication activities. The modular
structural and functional organization of metabolism enabled the evolution of
acclimation and adaptation of microbes at the levels of cells, populations, and
communities. This was particularly useful during and after the shift from an anoxic
Earth to increasingly oxic hydro- and atmospheres. Existing modules supporting
electron flow using terminal acceptors other than oxygen could simply be modified
by extension or substitution with those suited to reduce oxygen, which was accomplished, in part, by the emergence of a diverse complement of quinone-reactive
protein (QRP) complexes that used copper as redox-active transition metal: the heme
copper oxidases. This emerging diverse array of high-throughput, oxygen-reducing,
terminal oxidases was the basis for an expansion of catabolic pathways with modular
units capable of high-throughput oxidation of reduced substrates.
9 Mutagens, Radicals, Rocket Fuel, and Laughing Gas: Stringing Metabolic Modules. . .
153
if not in the entire universe.
Nitrogen is an essential element in two of the four macromolecules constituting
both the blueprint (nucleic acids) and the toolkit (Proteins) that dynamically executes
(the blueprint instructions into a) functioning metabolism, thereby critically contributing to the hallmarks of life as we know it (evolution, emancipation, and
communication of cells). However, it is actually the incredible versatility of redox
reactivity of simple nitrogen molecules that steered life to its present diversity.
Ironically, this incredible versatility in redox reactivity of nitrogen molecules represents also the greatest danger to a continued existence of metazoan life on the planet.
The cause for unleashing this destructive potential is not the aforementioned central
place of nitrogen in life’s processes, but rather the ill-natured, albeit often
unintended, far-reaching activities of human ingenuity and industriousness. The
platform for this disastrous outcome is the connectedness of nitrogen compounds
at different oxidation states through spontaneous and facilitated electron transfer
reactions, individually and organized in pathways, which constitute the global
nitrogen cycle (Fig. 9.1a). This biogeochemical cycle together with others cycling
carbon, sulfur, iron, and other redox-active elemental compounds as well as plate
tectonics keep the planet eligible for life. Interestingly, life itself is the active driver
of these biogeochemical cycles: microorganisms. While this might read like a
circulus vitiosus, it does so only in the absence of clues about how microorganisms
came to be (origin of life). Once the single-celled archaea and bacteria came into
being on an initially bare giant rock that eventually became our blue planet, they
diversified, driven by horizontal gene transfers and viral transductions and quickly
emerged as the drivers of biogeochemical nutrient cycles.
The “secret” to the evolved capability of single cell microbes to push all the
biogeochemical cycles is the organization of their metabolisms in functional modules (Fig. 9.1), correlating with a modular organization of its encoding genetic
information. Modular organization of genes and polygenic transcriptional units in
the genomes of archaea and bacteria provides two advantages: (1) modular sections
and even entire modules can be exchanged between microbes even across large
taxonomic distances by lateral transfer, and (2) the co-location of genes and polygenic transcriptional units provides for a variety of regulatory opportunities suited
for coordinating cellular emancipation and communication activities. The modular
structural and functional organization of metabolism enabled the evolution of
acclimation and adaptation of microbes at the levels of cells, populations, and
communities. This was particularly useful during and after the shift from an anoxic
Earth to increasingly oxic hydro- and atmospheres. Existing modules supporting
electron flow using terminal acceptors other than oxygen could simply be modified
by extension or substitution with those suited to reduce oxygen, which was accomplished, in part, by the emergence of a diverse complement of quinone-reactive
protein (QRP) complexes that used copper as redox-active transition metal: the heme
copper oxidases. This emerging diverse array of high-throughput, oxygen-reducing,
terminal oxidases was the basis for an expansion of catabolic pathways with modular
units capable of high-throughput oxidation of reduced substrates.
9 Mutagens, Radicals, Rocket Fuel, and Laughing Gas: Stringing Metabolic Modules. . .
153