Environmental Engineering Reference
In-Depth Information
biotically favorable form of bound nitrogen. The anthropogenic supply of reduced
nitrogen to the biosphere in the form of ammonia, for example during environ-
mental fertilization, livestock farming, and industrial processes, is mandatory in
feeding an increasing world population. In this chapter, environmental ammonia
pollution is linked to the activity of microbial metalloenzymes involved in respira-
tory energy metabolism and bioenergetics. Ammonia-producing multiheme
cytochromes c are discussed as paradigm enzymes.
Keywords biogeochemical nitrogen cycle ￿ climate change ￿ cytochrome c nitrite
reductase ￿ multiheme cytochrome c family ￿ NrfA
Please cite as: Met. Ions Life Sci . 14 (2014) 211-236
1
Introduction
The biogeochemical nitrogen cycle has received considerable attention over the
past decades because of its global importance for life on Earth (see also Chapters 7
and 8 in this topic) [ 1 - 7 ]. Nitrogen is a basic element for life because it is a
component of essential biomolecules, such as amino acids, proteins, and nucleic
acids. In the biosphere, nitrogen exists in several oxidation states, ranging from +5
as in the nitrate anion (NO 3 )to
3 as in ammonia (NH 3 ; IUPAC name azane), and
the ammonium cation, NH 4 . Interconversions of the various nitrogen species
constitute the global biogeochemical nitrogen cycle, which is sustained by biolog-
ical processes with microorganisms playing a predominant role (Figure 1 )[ 8 ].
Most remarkably, microbes perform these many chemical reactions in every nook
and cranny from the near surface to the depths, including even the most extreme
environments [ 9 ].
In the context of this article, the most notable nitrogen compound conversions
are (i) nitrification (NH 3 !
NO 3 ), equation ( 1 ), (ii) denitrification (NO 3 !
N 2 ),
equation ( 2 ), whereby nitrate is successively transformed to nitrite (NO 2 ), nitrogen
monoxide (NO), dinitrogen monoxide (N 2 O), and dinitrogen (N 2 ), and (iii) nitrate
ammonification (NO 3 !
NH 3 ), equation ( 3 ), the latter using nitrite as intermediate
(Figure 1 ).
NO 3 þ
8e þ
9H þ
NH 3 þ
3H 2 O
!
ð
1
Þ
2NO 3 þ
10 e þ
12 H þ !
N 2 þ
6H 2 O
ð
2
Þ
NO 3 þ
8e þ
9H þ !
NH 3 þ
3H 2 O
ð
3
Þ
In addition, it was shown more recently that large scale conversion of fixed
inorganic nitrogen (i.e., NH 3 /NH 4
and NO 2 )toN 2 can occur through another
Search WWH ::




Custom Search