H. Uemoto et al., Effect of oxygen concentration on nitrogen removal by Nitrosomonas europaea and Paracoccus denitrificans immobilized within tubular polymeric gel, J BIOSCI BI, 90(6), 2000, pp. 654-660
Tubular gel reactors containing Nitrosomonas europaea and Paracoccus denitr
ificans, which remove nitrogen from solutions through a process of nitrific
ation and denitrification, require oxygen for ammonia oxidation, the first
and rate-limiting step in the process. To accelerate ammonia oxidation, hig
h concentrations of oxygen were applied to the reactors instead of air. Alt
hough a 50% O-2 : N-2 gas mixture and pure oxygen were both toxic to free N
. europaea cells, they actually accelerated ammonia oxidation by N, europae
a immobilized within the tubular gel. Indeed, the rate of ammonia oxidation
by a tube exposed to pure oxygen was twice that of one exposed to 20% O-2
When the distribution of N. europaea cells within the tubes was investigate
d using a fluorescently-labeled antibody, colonies were found on the extern
al surface of the tube exposed to 20% O-2, but were located at a depth of 1
20-300 mum from the external surface in the case of the tube exposed to pur
e oxygen. The region between the external surface of the gel and the coloni
es apparently acted as a barrier, reducing the diffusion of oxygen and thus
protecting the cells from oxygen cytotoxicity.