What do nitrifying bacteria really want?

[wetmanNY]

Every week or so, somebody posts here how their nitrogen cycle is stuck on "spin-dry" or something-- and I mumble something about nitrifiers being tender yada yada yada...

So here's grist for our mill:

G.A. Vazquez-Rodriguez and J.-L. Rols worked up a "Study of the nitrification process with activated sludge: inhibiting effect of ammonia on nitrifying bacteria" in Rev. Sci. Eau vol. 10 (3) : 359-375. ((1997) There's an English abstract (http://www.rse.uquebec.ca/ang/vol10/v10n3a4.htm) .

The authors of the paper measured the respiration of nitrifying bacterial communities to assess the inhibition that ammonia exerted. The influences of pH, temperature, and the free ammonia concentration (NH3-N) were studied. The maximum activity of the nitrifying bacteria was found at pH 7.8 and at 29oC (ca84oF), with the 90% range of maximum activity lying between pH values of 7.5 and 8.1. For a concentration of 11.4 mg NH3-N, (pretty stiff) a nitrification inhibition degree of 60% was reached.

It's always handy to have some figures...

[mogurnda]

I guess they always have something to talk about at parties.

[RTR]

A concentration of 11+ mg NH3-N (per l I assume?) is massive - ~50ppm ammonia.

[beviking]

But what was the Color of the media they were propogating the bacteria on???

It's all about the color man...the pink and blue hues, flowing together...oh, got off topic there. Sorry!

90% btween 7.5 and 8.1 huh. Are the effects of ammonia on bacteria the same as fish? You know, the whole logrithmic (sp?) scale and ammonia being more toxic at lower ph? Ooh, almost had a cognitive thought:D

[anonapersona]

So, people who are doing fishless cycling need to be careful if their pH is low? Even below 7.0? Is there some limit on the ammonia one ought to use when starting with low pH water?

I've always thought that the common method (?) of adding ammonia to keep the level at 5.0ppm daily seemed too much. More natural would be to determine ewhat ammount it took to get that high and then keep that daily addition lat that level (keeping the faux bioload constant)

anona, who cycled with a delicate fancy goldfish who now has curled gills

[JSchmidt]

Did the article mention other concentrations of ammonia and their effect on nitrification? It would be interesting to know if the relationship is linear or non-linear...

Kinda sounds like 5 ppm isn't too high for fishless cycling.

Interesting bit of info, Wetman!

Jim

[wetmanNY]

Yes they did. (Hit those html links, Schmidt!) In fact, they measured oxygen consumption ("respirometric measurements") at ammonia concentrations ranging from 0.1 to 70 mg NH3-N/l. That would include levels more like the ones we use in fishless cycling, RTR. Though the abstract doesn't give values for inhibition of nitrifying bacteria at other levels of NH3-N, the authors drew back from any sweeping conclusion: "Inhibitory effects of ammonia on nitrifying bacteria activity seem to be complex and strongly dependent on other environmental factors which modify the dynamics of biomass growth."


...hmm, maybe we coulda tol' them that!

Still, this kind of stuff relates pretty directly to our fishtank struggles, eh!

[JSchmidt]

Thanks, Wetman. I hadn't noticed you had linked to the abstract -- I should have expected it, given your thoroughness. I might try to hunt down a translation of the full article or a citation of the article in English. It's been in print long enough that someone must have cited it.

Thanks again,
Jim

[wetmanNY]

If you do find it, and some of it sheds light on fishless cycles, you'll pass it on I know.

[TomFromStLouis]

and I guess in this case it is me. So I will ask the stupid question: what does this mean to me the fish keeper?

As I read it, fishless cycling happens quickest at a pH of 7.8 with a temp of 29*C. That much I think I understand. The inhibition thing confuses me though. Are they suggesting that at higher levels of ammonia (X? ppm) there is effectively TOO MUCH food for our ammonia eaters and the population's growth is inhibited x%? If so, what is the correct dosing level for quickest fishless cycle? Is there any other Tom-level conclusions I should draw here?

[wetmanNY]

Are they suggesting that at higher levels of ammonia (X? ppm) there is effectively TOO MUCH food for our ammonia eaters and the population's growth is inhibited x%?

Yes. We noticed that ourselves when people tried to "speed up" fishless cycling and gave a dose >5ppm.

If so, what is the correct dosing level for quickest fishless cycle?

We've been noticing that `5ppm is the max. But perhaps the "max" is not the fastest and most effective here... Personally, I feel that, as long as there's a detectable amount of any food, the bacteria that use that resource are still multiplying as fast as ever they can. A general fact of bacterial life. Once they're using up all of maybe 2ppm ammonia, you can sneak them a little more.

How much is too much? We don't really have the "Xppm"-- and they don't really, either, I guess.

Is there any other Tom-level conclusions I should draw here?

Perhaps there's less than meets the eye, eh.

[OrionGirl]

Actually, it means that the high ammonia concentrations inhibit the bacteria that break down the second stage--nitrites--rather than impacting the ammonia consuming bacteria. If I read that correctly.

Part of what I am curious about--is the inhibition of the bacteria's ability to process nitrites, or the ability of it to reproduce? I don't know how closely tied those two features are in bacteria, and my instinct is that anything that slows it's consumption slows reproduction similarly, though somewhat delayed? And, is it the ammonia, or is it the presumably decreased oxygen supply (thinking that an increased concentration of ammonia reduces the amount of oxygen dissolved in the water)...Which then factors in with pH, right?

[RTR]

DO and pH should be independent per se , but could in theory result in less than optimum DO due to biomass utilization (especially at 29C). But in the real world of tanks, O2 shortage should not happen. Note: I said should not , I did not say "does not"

In fact, it does not matter which bacertial type is suppressed, or whether the inhibtion is metabolic or reproductive - the end result is the same, interruped cycling. The two functions are awfully closely related in most bacteria anyway.

Remember, for these bacteria, nitrate is not primary food for mass-building, but primarily food as energy source - effectively what carbohydrates are to us - oxidizing either ammonia or nitrite yeild the energy with which the bug operates it metabolism. But for cycle purposes, we are more interested in building colony numbers (these bacteria are slow to multiply) which can then metabolize the quantities of metabolites which we need oxidized.

Edit: dissolved gases, including ammonia and O2, should be independent. One does not surplant the other.

[OrionGirl]

Okay--that makes sense. So (and I show my lack of chemistry here), the oxygen levels remain constant as ammonia increases, but does the ammonia also inhibit the ammonia consuming bacteria (literally starving in the land o' plenty), or just the nitrite consumers? Would it make sense to try building the population of nitrite consumers before the ammonia eaters?

I understand that the amount of oxygen remains constant for a given sample, but if there is more ammonia, could it be that the additional ammonia spreads the oxygen thinner? The bacteria would encounter 4 ammonias for each oxygen (for example!), and can't process the first ammonia until it encounters the oxygen molecule. Wouldn't this slow it down? Since it sounds like these samples were not agitated, the bacteria have to wait around until the natural slow movement of the solution brings the oxygen around. In a tank, though, this should not be the case, since filters move the water--with both ammonia and oxygen across the media. Does that make sense?

[TomFromStLouis]

OG,

My guess would be that ammonia density would not alter the bacterium's odds of running across an O2 molecule since the premise is that the O2 saturation is the same in each case. I base this on a middling knowledge of statistics and probablities, not on any specific knowledge of chemistry.

How'd I do Teach?

[OrionGirl]

If the sample size remains consistant, yes, but if you take a sample that already has a specific DO concentration and add ammonia to it, wouldn't that change the ratio?

[TomFromStLouis]

well yeah but we are talking about fairly low densities of ammonia (ppm) so effectively the change is nil.

If the O2 density was 100/1,000,000 and you add 5 ppm ammonia now the density of O2 would be 100/1,000,005. Not much difference there, so Mr. Bacterium would have essentially the same odds of running across O2 in either soup.

[OrionGirl]

Got it. I don't think in terms of numbers well--I prefer organizing my data to sit politely in rows and columns. Thanks!

[TomFromStLouis]

Originally posted by TomFromStLouis
Is there any other Tom-level conclusions I should draw here?

By the way, just so y'all don't think I don't know proper english, I realize the above should read "Ain't there any other..."

[RTR]

Also, any nutrient can beome toxic at some level - I mean, it would be possible to drown in chololate syrup. Ammonia is remarkably soluble, so there have to be levels at which it is toxic to the ammonia users. We have the rather high figure from the research for optimum, you have to imagine that toxicity would be well past that.

I find it impresive that the optimum temp is at 29C. That is a level we can reach in our tanks without extra heating.

[TomFromStLouis]

Originally posted by RTR
Also, any nutrient can beome toxic at some level - I mean, it would be possible to drown in chololate syrup.

"There are no toxins, only toxic doses." - someone smart