"Stoutman" .@. wrote in
m:

Here's another quote for you... I managed to dig it out of an article
published in the Plant and Soil journal in 1972.

"Summary: ...ammonium concentrations in excess of 200 ppm N
reinforced population imbalances conductive to accumulation of
nitrite over
time in mixed cultures of Nitrosomonas europaea and Nitrobacter
agilis. Nitrate production proceeded at a low, linear rate
characteristic for a nonproliferating population, indicating a
bacteriostatic effect of ammonium
or free ammonia on growth of Nitrobacter rather than an inhibitory
effect on nitrite oxidation."

Just because nitrate production proceeded at a linear rate with
accumulation of nitrite over time does not imply that NH3 production
hinders the ability of nitrobacter to metabolize nitrite.

No it doesn't. What the study found is that the high levels of NH3 do not
hinder the ability of Nitrobacter to oxidize NO2-, but rather it has a
bacteriostatic effect, meaning it inhibits the growth of Nitrobacter in
that environment. The rate of conversation of NH3 into NO2- increased in
the experiment indicating a proliferation of Nitrosomonas in that
environment, however the conversion of NO2- into NO3- proceeded at a linear
rate indicating a nonproliferation of Nitrobacter in that same environment.

They study ran another experiment in which they infused a medium with both
bacterial strains and then enriched each with a graded dose of NH3 and NO2-
in order to populate the medium, after which they increased the
concentration of available NH3 as they did in the previous experiment.
What they found is that the NH3 was converted into NO3- with no measurable
levels of NO2- detected, confirming what was indicated in the previous
study. Established Nitrobacter is able to oxidize its food source
perfectly well in concentrated NH3 environment.


How do they know that the bacteriostatic effect they are describing is
a result of high NH3 concentration? Is this discussed in the
publication or are they making assumptions?

Does the nitrate production proceed at an increased rate as the NH3
concentration drops? This would support their claim.

It was a controlled experiment that took place under laboratory conditions.
The variable in the experiment was the amount of NH3 given to the cultures.
The rate of proliferation of Nitrobacter was found to be directly effected
by the concentration of NH3. So yes, the rate of conversion of NO2- into
NO3- increased in relation to low NH3 concentrations.

You may be able to find the article yourself at a local university library.

Title: Bacteriostatic effect of ammonium on Nitrobacter agilis in mixed
culture with Nitrosomonas europaea
Journal: Plant and Soil
Publisher: Springer Netherlands
Subject: Biomedical and Life Sciences and Earth and Environmental Science
Issue: Volume 36, Numbers 1-3 / February, 1972
Pages 521-527


I am not being glib, but I will admit I come off harsh at times. My
apologies.

Understood, perhaps I judged too quickly. I apologize as well.