bacterial physiology

[dwd5813]

my question comes from a discussion regarding water changes when first establishing a new system. some say that it is a good idea to remove water during the cycle to prevent skyrocketing ammonia levels from doing harm to sensitive life present on live rock. others, myself included, argue that since the ammonia produced by this dieoff fuels the growth of bacteria it should be left to be used biologically. on the one hand, preserving the life on the rock is ideal, since that is the benefit of using live rock in the first place. on the other, if bacterial colonies are not allowed to reach a certain level, the result will be an insufficient biofilter.

my question is this: what is the uptake method used by bacteria in the assimilation of ammonia? my understanding is that there is no active feeding system present, and that nutrients simply diffuse through the cell wall. correct or incorrect? if the ammonia is removed from the water column, wont that also take away from the ability of the colony to grow?

 

[cutegecko3]

not true.the bacteria multiply at a constant rate increasing ammonia or reducing it isnt going to change that.doing water changes is beneficial to organisms on the rock your trying to keep alive.if you want it cycle faster add more bacteria.

 

[dwd5813]

maybe i added too much background information. i'm not looking to debate the fastest way to cycle a tank.

biologically speaking, how do bacteria assimilate ammonia?

 

[cutegecko3]

I read an article about that last winter and if i remember correctly it stated that they have a kind of mouth for ingesting it.

 

[dwd5813]

can you find a link to that article?

 

[tydtran]

I think incorrect.

I cannot identify the specific transporters involved, but it is a generally true statement that the entry of NH3 and NH4 into any cell (prokaryote and eukaryote) is tightly regulated. This means that there are protein channels specific for these compounds and that the channels are gated. The bacteria decide when to let these compounds in by opening the channels. They also have ATPases (think of them as energy using pumps) which, when needed, can move these compounds against their concentration gradients.

To resolve your question more specifically, we would have to know about the enzymes that convert the NH3/NH4 to less toxic derivatives. The critical question is at what concentration of NH3/NH4 does the enzymatic machinery become saturated. This is the concentration that you want for max NH3/NH4 metabolism by bacteria. Above this concentration, excess ammonia in the system is potentially toxic to the bacteria in question. I tried to look up the Michaelis/Menton constants for the NH2/NH4 metabolism for denitrifying bacteria but haven't found it yet. I'll get back with the numbers if I can find them.

 

[m2434]

Re: bacterial physiology

my question is this: what is the uptake method used by bacteria in the assimilation of ammonia? my understanding is that there is no active feeding system present, and that nutrients simply diffuse through the cell wall. correct or incorrect? if the ammonia is removed from the water column, wont that also take away from the ability of the colony to grow? [/B]

Observed high internal ammonia concentrations, may make passive transport unlikely, because external levels probably wouldn't be high enough in an aquarium (or your in trouble!). Schmidt et al. (2004), found evidence for inhibition of ammonium accumulation in the presence of UCPs, suggesting an active transport system. I don't know of any further classification of the system if any exists.


Schmidt I, Look C, Bock E, Jetten MS.
Ammonium and hydroxylamine uptake and accumulation in Nitrosomonas. Microbiology. 2004 May;150(Pt 5):1405-12.

 

[m2434]

Sorry should say "high internal ammonium".

Also, to clarify, I should add that at the high pH of an aquarium, the level of ammonia would be higher and my best guess would be to assume a similar mechanism....

 

[MCsaxmaster]

Agreed, active transport is most likely. At seawater pH most of the ammonia is still ammonium (NH4+) which cannot diffuse significantly across cell membranes. Most bacteria and algae have at least one if not several membrane-bound transporters.

cj

 

[Spracklcat]

Agree with active transport above, and doing water changes to keep you ammonia lower will not slow your cycle much if at all. The benefit to "manageable ammonia" during the cycle not killing your live rock is greater than any possible benefit to having higher ammonia.

Don't forget too--bacteria require more than ammonia to live, and if those other things are limited, all the ammonia in the world isn't going to make them grow faster.

 

[m2434]

<a href=showthread.php?s=&postid=10919546#post10919546 target=_blank>Originally posted</a> by MCsaxmaster
At seawater pH most of the ammonia is still ammonium (NH4+).

cj

right, good point, I think typical ratios reef type environments are something like ~90% ammonium!

 

[mesocosm]

Greetings All !

<a href=showthread.php?s=&postid=10903664#post10903664 target=_blank>Originally posted</a> by dwd5813
... there is no active feeding system present, and that nutrients simply diffuse through the cell wall. correct or incorrect? ...

Incorrect. Almost all solutes, such as sugars, amino acids, peptides, nucleosides, and ions are taken up by cells by active transport. Except for water and some lipid-soluble molecules, few compounds can enter the cell by simple or passive diffusion.

<a href=showthread.php?s=&postid=10904059#post10904059 target=_blank>Originally posted</a> by dwd5813
... biologically speaking, how do bacteria assimilate ammonia?

"Active transport" is the correct answer ... :thumbsup:

More specifically, ammonia uptake in bacteria is facilitated by a family of membrane proteins known as the ammonium transport family (commonly abbreviated as 'Amt'). The membrane protein ("ammonia channel") most commonly utilized by bacteria is refered to as 'AmtB'. It is typically regulated by a protein designated as 'GlnK'. It is the AmtB-GlnK complex that is usually responsible for the regulation of ammonia uptake by bacterial cells.

Here's a cool graphic of the AmtB-GlnK complex:
http://www.psi.ch/medien/medien_bilder/AmtB_GlnK_gross.jpg


The graphic was extracted from here:
Another piece of membrane protein puzzle solved; how cells regulate ammonium uptake can be better understood.
John Innes Center
January 2007
http://www.jic.ac.uk/corporate/media-and-public/current-releases/070124.htm

<a href=showthread.php?s=&postid=10903839#post10903839 target=_blank>Originally posted</a> by cutegecko3
... the bacteria multiply at a constant rate increasing ammonia or reducing it isnt going to change that. ...

No offense intended, but this is simply incorrect. The amount of available NH3/NH4 in the water column can definitely change both colony growth rates, and cellular uptake kinetics.

<a href=showthread.php?s=&postid=10903664#post10903664 target=_blank>Originally posted</a> by dwd5813
... if the ammonia is removed from the water column, wont that also take away from the ability of the colony to grow?

Absolutely !



HTH
:thumbsup: