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Appl. Environ. Microbiol., Aug 1995, 2852-2858, Vol 61, No. 8
JP Carter, YH Hsaio, S Spiro and DJ Richardson
Several laboratory strains of gram-negative bacteria are known to be able
to respire nitrate in the presence of oxygen, although the physiological
advantage gained from this process is not entirely clear. The contribution
that aerobic nitrate respiration makes to the environmental nitrogen cycle
has not been studied. As a first step in addressing this question, a
strategy which allows for the isolation of organisms capable of reducing
nitrate to nitrite following aerobic growth has been developed. Twenty-nine
such strains have been isolated from three soils and a freshwater sediment
and shown to comprise members of three genera (Pseudomonas, Aeromonas, and
Moraxella). All of these strains expressed a nitrate reductase with an
active site located in the periplasmic compartment. Twenty-two of the
strains showed significant rates of nitrate respiration in the presence of
oxygen when assayed with physiological electron donors. Also isolated was
one member of the gram-positive genus Arthrobacter, which was likewise able
to respire nitrate in the presence of oxygen but appeared to express a
different type of nitrate reductase. In the four environments studied,
culturable bacteria capable of aerobic nitrate respiration were isolated in
significant numbers (10(4) to 10(7) per g of soil or sediment) and in three
cases were as abundant as, or more abundant than, culturable bacteria
capable of denitrification. Thus, it seems likely that the corespiration of
nitrate and oxygen may indeed make a significant contribution to the flux
of nitrate to nitrite in the environment.
Copyright © 1995, American Society for Microbiology
Soil and sediment bacteria capable of aerobic nitrate respiration
School of Biological Sciences, University of East Anglia, Norwich, United Kingdom.
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