I just read another study that directly contradicted your study about Nitrosomonas being affected by high nitrites. So, that's confusing. However my study is from 1998 and yours was 2002. They seem to directly contradict each other =|
Source:
Loss of Ammonia Monooxygenase Activity in Nitrosomonas europaea upon Exposure to Nitrite
“
Nitrosomonas europaea, an obligate ammonia-oxidizing bacterium, lost an increasing amount of ammonia oxidation activity upon exposure to increasing concentrations of nitrite, the primary product of ammonia-oxidizing metabolism.”
“The loss of AMO activity via nitrite occurred under both aerobic and anaerobic conditions, and more activity was lost under alkaline than under acidic conditions except in the presence of large concentrations (20 mM) of nitrite. These results indicate that nitrite toxicity in
N. europaea is mediated by a unique mechanism that is specific for AMO.”
High pH = more loss of activity
“ammonia oxidation is an acidogenic reaction. As the pH of the incubation medium decreases during ammonia oxidation, the NH3-NH4+ equilibrium is shifted away from NH3, the true substrate of AMO (
23). Ammonia oxidation ceases at about pH 6, partially because of the reduced concentration of NH3”
Just another place they talk about how the cycle reduces pH
“At the point of maximal cell growth in phosphate-buffered medium with an initial ammonium concentration of 50 mM, the concentration of nitrite is typically around 20 to 25 mM, and the rest of the ammonium remains unoxidized.
In a previous study, we showed that this remaining NH3-NH4+ pool, or other substrates of AMO, had a specific protective effect on the AMO activity of N. europaea cells (
22). In incubations where the ammonium was completely consumed, the cells lost up to 80% of their ammonia-oxidizing activity over a 24-h period (
22). In the present paper, we show that this specific loss of AMO activity in cells of
N. europaea is due to the toxicity of accumulated nitrite in the incubation medium.”
Underlined part = presence of ammonia protects the AMO from the high nitrites? Did I read that correctly?
“only a few reports describing the toxicity of nitrite in ammonia-oxidizing bacteria have been published, and the mechanism of toxicity remains unclear. In one study, nitrite toxicity in
Nitrosomonas sp. occurred only at very high concentrations (greater than 30 mM) of nitrite, and this effect, as measured by the ability of the cells to consume O2, was greater during the lag phase than during the log phase of growth at several different pH values tested (
16). Nitrite was also toxic for cells in the log phase of growth, but only at acidic pH values, and the loss of activity was reversible upon washing of the cells”
“Because batch cultures of
N. europaea accumulate large concentrations of nitrite, greater than 20 mM, and reach a pH of about 6, it is surprising that the cells are not more susceptible to nitrite toxicity”
“The present study shows that nitrite can cause a specific loss of ammonia-oxidizing activity in
N. europaea cells at lower concentrations than those previously considered (5 to 20 mM). The loss of activity is specific to AMO and occurs under both acidic and alkaline conditions.
In the presence of substrates of AMO, the loss of activity was not observed. Furthermore, the loss of activity was not reversible by washing the cells. Lastly, nitrite appears to specifically target the AMO enzyme in a manner different from that of characterized inactivators of AMO.”
Substrates = food in these science-y papers
So if there was still ammonia, everything was fine.
“The trend of ammonia oxidation activity loss was correlated with the relative proportions of nitrite produced and ammonium remaining in the incubation medium after 24 h (Fig.
(Fig.1B).1B). The accumulation of nitrite in the medium was proportional to the initial concentration of ammonium up to 20 mM. In incubations containing 25 to 50 mM ammonium, nitrite accumulation ceased after reaching about 21 mM. At this point, the limiting pH for ammonia oxidation, 5.7 to 6.0, was reached. The
greatest losses of ammonia oxidation activity were observed with the largest concentrations of nitrite, from 15 to 21 mM, and the smallest concentrations of ammonium, from 0 to 5 mM, remaining in the medium after the 24-h incubation.”
So when the ammonia got really low and the nitrites got really high, that's when it got bad.
What does this mean for our process?
“After the incubations with nitrite, cells were sedimented, washed, and resuspended in sodium phosphate buffer for 48 h to determine if the effect of nitrite was reversible. No activity was recovered during these incubations, suggesting an irreversible inactivation of the ammonia oxidation activity by nitrite”
If the ammonia bacteria get stunted, they don't recover.
“although the interactions between ammonia- and nitrite-oxidizing bacteria are dependent upon several factors including substrate availability, O2, and pH (
14), the toxic effect of nitrite on ammonia oxidizers could be ameliorated by the close physical association between the two bacterial groups as observed in soils and bioreactors (
15,
18). The close physical positioning of ammonia and nitrite oxidizers in the natural environment is useful for both energetic reasons and the prevention of substrate accumulation that could be toxic or could lead to the formation of toxic by-products, especially in environments where nitrite cannot simply diffuse away (
8). Therefore, this study suggests that the challenge for ammonia-oxidizing bacteria in natural systems is not only survival with an inconstant energy source but also avoidance of toxic product formation once the ammonia has been converted to nitrite”
Basically just says: The natural biological cycle protects the cells from dying to nitrite, in natural environents.
Fingers crossed!
