Bacteria, localized low pH, and Phosphate

[Floyd R Turbo]

Ok chemistry and biology nerds. Time to put you to the test. This might be an easy test but anyways...

Situation: you have algae growing on your rocks that you can't get to stop.

Potential source of algae: Rock is "soaked with phosphates", that is, rock has adsorbed phosphate or has gathered precipitated phosphate in the form of Calcium Phosphate.

http://reefkeeping.com/issues/2006-09/rhf/index.php

Just an excerpt as to what I am referring:

" A second mechanism for potential phosphate reduction when using high pH additives is the binding of phosphate to calcium carbonate surfaces. The absorption of phosphate from seawater onto aragonite is pH dependent, with the binding maximized at around pH 8.4 and with less binding occurring at lower and higher pH values. "

"many aquarists find that calcium and alkalinity levels are stable over long time periods with just that scenario. One way this can be true is if the excess calcium and alkalinity, which such additions typically add to the aquarium, are subsequently removed by precipitation of calcium carbonate (such as on heaters, pumps, sand, live rock, etc.). It is this ongoing precipitation of calcium carbonate, then, that may reduce the phosphate levels; phosphate binds to these growing surfaces and becomes part of the solid precipitate. "

"Simply keeping the pH high in a reef aquarium (8.4) may help prevent phosphate that binds to rock and sand from re-entering the water column. Allowing the pH to drop into the 7s, especially if it drops low enough to dissolve some of the aragonite, may serve to deliver phosphate to the water column. "

An excerpt from another related thread on another site:

Dissolution also is a function of solution kinetics, ie., Salinity, pH, temp, Alk, Ca++, etc. It is impossible to know where this is going to take place, only that low pH is a major dissolution factor and there is no real data at what pH that is but we can assume it will be in acid conditions. Calcium phosphate is much harder to dissolve that Calcium carbonate like Calcite or Aragonite. So, at least in pH water below 7.


Possible explanation (from someone on another site also):

"bacteria coat the phosphate bound live rock surface, slime it over and isolate it's chemistry, lower the pH to release the phosphate, then cackle evilly as they release it through their slime layer to destroy the system. Also, they could be in league with the hair algae roots, and are both working together"

Aside from the evil cackling, which is currently quite difficult to prove or disprove, this explanation seems like it might have a semblance of feasibility. But, I know nothing of this type of mechanism.

The other explanation that I have heard, and I now tend to disagree with, was that once phosphate levels in the water column were reduced, the phosphate that was bound in the rock/gravel was just "released" like it was just pleasantly traveling to an area of lower concentration or moving to the 'burbs. (Never mind that dissolving chemically bound phosphate requires a pH that would kill everything in the tank, that was just a technicality). Unless that indeed is possible, then I'll start believing that again.

But right now I'm a bit perplexed and would like to understand this mechanism a little better, and would like to also know if the bacteria-slime-pH-evil-cackle theory is a good one.

Enlighten!

[Nano sapiens]

This is a complex topic. It gets even more complex when contemplating the various chemical and biological mechanisms at work converting one phosphate species into another within a system. The short story is that no one that I know of has the complete story, but I think we know enough to get the general idea.

As we know, phosphate typically binds readily with calcareous surfaces. It can certainly be liberated from said surfaces by biological processes (typically benthic algae and/or bacteria). Lowered pH, which can occur in certain areas in the substrate and liverock from biological activity, can allow liberation of phosphate by bacterial action. If we follow the phosphate it could have a number of fates from being used by other organisms, being absorbed into the detritus, being precipitated in localized areas of high pH (Kalkwasser dosing site comes to mind), entering the water column, etc.

While not reef specific, this treatise on Phosphate in the enviroment (land and aquatic) is enlightening:

http://www.water.ncsu.edu/watershedss/info/phos.html

[bertoni]

If my memory is working, bacteria are known to reduce the pH and dissolve aragonite, although the quantity is small. Phosphate would be liberated in the process, if the rock has any. I'll look for an online reference.

[tmz]

Bacteria consume inorganic phosphate . They don't store it up under their mats. They incorporate it in their cells . If it's there along with the other nutrients they need they'll assimilate it and keep growing until one or more limiting nutrients slows them down. Then another bacteria species will take over that is less limited and so on until the bacterial cascade uses all the energy available to it.They don't isolate the chemistry any more than they cackle;they create chemical interactions that effect the tank as a whole.

How strongly Pi(inorganic phosphate) binds depends on the PO4 species and where it's bound .
Very little of what we call and measure as PO4 is actually PO4 ;most has a lesser negative charge(HPO4 ,H2PO4 for example),.
Some Pi is incorporated into a growing calcium carbonate crystal and stays there unless and until the aragonite dissolves as is the case in a calcium reactor which relies on localized acidic conditions for example.
Some Pi just sticks to the aragonite surface and is not encased in a growing crystal . In the later case it is accessible to equilibration with the water.
If you take a piece of live rock previously exposed to high PO4.it will leach back PO4 to the water column. If you keep it in water in a curing bin and maintain near 0 PO4 in the water it will stop leaching after one to three weeks.

In the tank, localized increases in acidity may occur and cause some dissolution of calcium carbonate crystals ,some bacterial activity contributes CO2 which may create acidic conditions sufficient to dissolve some of the aragonite. This is likely a a limited activity ,since as soon as a bit of calcium carbonate dissolves it boosts the local pH. Some of those calcium carbonate crystals do hold Pi,though So it's possible small amounts are added from localized low pH areas this way in a tank within normal reef tank pH but it should not be very much in a reasonably well maintained aquarium without excessive anoxic regions which may occur in areas clogged with refractory orgnaics ( resitive to bacteial breakdown) like fulic and humnic substances for example.

The biggest contributor of phosphorous is food.

Some algae and bacteria may use organic phosphate too which makes the issue more complex.

[Nano sapiens]

The biggest contributor of phosphorous is food.


And the biggest store of phosphates likely to be released into the system is the detrital material in the tank.

[Floyd R Turbo]

All responses are much appreciated

Some Pi just sticks to the aragonite surface and is not encased in a growing crystal . In the later case it is accessible to equilibration with the water.
If you take a piece of live rock previously exposed to high PO4.it will leach back PO4 to the water column. If you keep it in water in a curing bin and maintain near 0 PO4 in the water it will stop leaching after one to three weeks.

So it sounds like this is a limited effect as far as non-encased phosphate. Such phosphate should be able to be "pulled out" in a matter of weeks once P=0 is maintained in the water column, by whatever method is available. If this was done in-tank vs curing bin, where there was still livestock/corals/feeding, would this perhaps take longer?

I would assume that in a given situation where there was maintained high pH that some encased crystal/matrix/etc precipitation of P would still be happening in conjunction with non-encased P.

So this might explain a short-term algae growth on rocks due to past excesses of P, and thank you for the insight

They don't isolate the chemistry any more than they cackle

I was unaware that it was known they could not cackle.

some bacterial activity contributes CO2 which may create acidic conditions sufficient to dissolve some of the aragonite. This is likely a a limited activity ,since as soon as a bit of calcium carbonate dissolves it boosts the local pH

I wonder if a symbiotic relationship exists by where the bacteria pulls P out via this short-term mechanism, then the algae somehow takes that up and the process repeats. Some kind of mechanism like this might explain some examples of long-term algae growth on rocks in a system that was poorly maintained for a long time. I've read of examples of over a year of growth that was attributed to 'leeching', and eventually the algae fades away, the conclusion being "all the P was pulled out of the rocks"...this is the type of scenario I'm trying to get to the bottom of...

Some algae and bacteria may use organic phosphate too which makes the issue more complex.

Dang it.

[tmz]

So it sounds like this is a limited effect as far as non-encased phosphate. Such phosphate should be able to be "pulled out" in a matter of weeks once P=0 is maintained in the water column, by whatever method is available. If this was done in-tank vs curing bin, where there was still livestock/corals/feeding, would this perhaps take longer?

It can take at least several months of persistently low PO4 in a tank vs a bin,ime.
Perhaps because:
There is more water to manage.

Foods and wastes(from animals, algae, bacteria , decay etc.)
contribute Pi and dissolved inorganic nitrogen continuously in a living reef. So. there is always some around for the nuisance organisms to grab unless the tank is starved.

More aggressive PO4 removal can be used in a curing vessel(such as lathanum chloride for example ) without concerns about Pi limitation for the desireable organisms like calms and corals macro algaes ,etc..

read of examples of over a year of growth that was attributed to 'leeching', and eventually the algae fades away, the conclusion being "all the P was pulled out I wonder if a symbiotic relationship exists by where the bacteria pulls P out via this short-term mechanism, then the algae somehow takes that up and the process repeats. Some kind of mechanism like this might explain some examples of long-term algae growth on rocks in a system that was poorly maintained for a long time. I've of the rocks"...this is the type of scenario I'm trying to get to the bottom of...


All the Pi would not be "pulled out " of the rock , unless all of the the rock dissolved .

It's possible some at the surface might dissolve in localized high acidic areas whether they are caused by bacteria, other organisms , decaying detritus and or localized stagnation.

I've noticed a very thin layer of what appears to be softer rock from time to time under matted red turf algae for example . I have no idea if the rodophyta algae induces this to get at Pi ,calcium, carbonate or other things it needs ; or, the overall conditions and organisms in the area under it do.


Usually a dribble of kalk paste will a persistent patch of algae( like red turf or bryopsis that doesn't seem to care very much about Pi limitation in the water.

[Floyd R Turbo]

Has anyone heard of the term "bacterial cleaving"? This was the possible method by which bacteria could cause the release of bound phosphate from rock.

The other method, in conjunction with running an algae scrubber, could be that the algae releases alkaline phosphatase in order to 'access' phosphate in the tank. I admit that I only vaguely understand this mechanism, just not enough time to research it - which is why I turn to the chemical geeks. But as I currently understand it, this is a sort of "chemical warfare" type of mechanism

It is also possible that these 2 methods are working with or at least alongside each other.

I'm looking for an answer to this because the scenario of taking a 'dirty' tank and 'cleaning it up' seems to commonly be followed by a bloom of algae on the rocks that eventually goes away, sometimes in weeks, sometimes in months or even a year - but it does go away. The concept of "bound phosphate leeching from the rocks" has been suggested, but that seems too simple - gotta be another mechanism, and if so, there must be a way to speed up the process.

[Osteoclast]

Floyd-R-T

Review the literature with regard to bacterial phosphatases and proteases. Data exist showing phosphate liberation in aqua systems with various gram negative bacteria. The data reveal that cleaving enzymes are produced by many cells and organisms. Bacteria produce many of these enzymes very efficiently. The enzymes are produced with the bacterial cell and released (exocytosed) outside their membranes to cleave various proteins. Many enzymes have been discovered in water born bacteria. Alkaline phosphatases are a good example of what you are looking for and have a fair body of research. Do a couple of google scholar searches and you will get a great amount of info.

[tmz]

Yes, I've heard of it. I mentioned bacteria and algae accessing inorganic phosphate in my earlier post.
Some bacteria may be able to cleave phosphate from organics with phosphatases as can some algae. Thus providing the Pi they need. Don't know how to speed up the process though.

While I think rock leaching is part of nuisance algae infestations on live rock ,I suspect that problem is more about loosely bound PO4 species and not organic phosphate. though it may also involve cleaving organic phosphate on the rock.

The common hypothesis is that organisms produce phosphatases when near starvation for inorganic phosphate ; that's not proven as far as I know. There are acid and alkaline phosphatases with the later being optimally active at pH under 7 and the former in alkaline conditions.

Pi leaching rock can be quickly cured by keeping it in very low PO4 water for a couple of weeks via lanthanum chloride dosing.I don't recommend this as an in tank treatment,though.The curing process may give organics time to breakdown as well.

[Floyd R Turbo]

Thanks guys. tmz I re-read your posts after my last post and saw that, but left as us to see that further info I might get by adding the more specific questions.

I guess what it comes down to is a process that we know happens, but don't fully understand. But, such is the case with many things in this hobby!

[tmz]

We have just begun to look at the surface of the very complex world of organic compunds in sea water and ther effects on a myriad of interactive organisms . There are hundreds of thousands of them ; if not millions . It's not even possible to test total organic C in our tanks , much less specific types. When we think we have an answer to one issue or another it almost always just leads to another question. It's a great journey though.