Cyano Scrubber Experiment
- Thread starter dg3147
- Start date
elegance coral
They call me EC
This is a horrible method for filtering our water. Please see link I posted earlier.
Here's a quote form that link.
"Nitrogen fixation by cyanobacteria
Cyanobacteria inhabit nearly all illuminated environments on Earth and play key roles in the carbon and nitrogen cycle of the biosphere. In general, cyanobacteria are able to utilize a variety of inorganic and organic sources of combined nitrogen, like nitrate, nitrite, ammonium, urea, or some amino acids. Several cyanobacterial strains are also capable of diazotrophic growth, an ability that may have been present in their last common ancestor in the Archaean.[4] Nitrogen fixation by cyanobacteria in coral reefs can fix twice the amount of nitrogen than on land—around 1.8 kg of nitrogen is fixed per hectare per day. The colonial marine cyanobacterium Trichodesmium is thought to fix nitrogen on such a scale that it accounts for almost half of the nitrogen-fixation in marine systems on a global scale."
Here's a quote form that link.
"Nitrogen fixation by cyanobacteria
Cyanobacteria inhabit nearly all illuminated environments on Earth and play key roles in the carbon and nitrogen cycle of the biosphere. In general, cyanobacteria are able to utilize a variety of inorganic and organic sources of combined nitrogen, like nitrate, nitrite, ammonium, urea, or some amino acids. Several cyanobacterial strains are also capable of diazotrophic growth, an ability that may have been present in their last common ancestor in the Archaean.[4] Nitrogen fixation by cyanobacteria in coral reefs can fix twice the amount of nitrogen than on land—around 1.8 kg of nitrogen is fixed per hectare per day. The colonial marine cyanobacterium Trichodesmium is thought to fix nitrogen on such a scale that it accounts for almost half of the nitrogen-fixation in marine systems on a global scale."
You didn't make your case why this is bad. Sure certain species cyano *can* fix nitrogen it isn't their preference. Fixing nitrogen from the atmosphere takes more energy from getting it from the water. And even if it runs out of easy to get nitrogen and starts fixing nitrogen from the atmosphere it will still be removing phosphates.
This seems no worse than an algae scrubber other than being harder to clean. I wouldn't personally use this approach but I also wouldn't use an ats.
EC, is your concern that cyano will start to uncontrollably fix nitrogen and crash the tank?
Barjam is right. That won't happen. From a basic biological standpoint, ultimately what cyano wants -- what it needs for making amino acids, and thus proteins -- is ammonia. The farther removed the available nitrogen source is from NH3, the more energy-intensive it is for cyano to make use of it. This is because cyano has to reverse nitrification, the familiar NH3 --> NO2 --> NO3 transformations that occur in a cycled biofilter, and each step is driven by specialized enzymes. So nitrate "costs" more to use than nitrite, which in turn requires more energy than ammonia. Nitrogen gas (N2) is the most costly source of nitrogen, so cyano won't use it until nitrates (and nitrites and ammonia, if they're anvailable) are zeroed out. In fact, fixing nitrogen is so energy-intensive that not all species of cyano can do it, and for "normal" cyano that can, it just requires too much energy (and also a lot of iron, which is usually hard to come by in a marine environment) to spin up the machinery until it's actually needed.
At that point, cyano's ability to fix nitrogen becomes an enormous advantage, as it can continue to pull PO4 out of an N-limited system. And crucially, it should keep the system N-limited, as a cyano-based scrubber will want to use any available NO3 to reduce the amount of energy it has to expend on fixing N2.
This would be a better link for criticizing a cyano scrubber...
Yikes! But on the other hand, you'd think that if cyano posed a serious health threat to hobbyists, we'd've noticed by now...
I've seen some suggestion that the offending species of cyanobacteria produce toxins when in a planktonic phase, but not in algal mats. This would seem to be a straightforward evolutionary adaptation: in algae blooms, cyano produces toxins to exclude other microorganisms and claim all the available nutrients; in microbial mats, cyano lives symbiotically with algae and other bacteria, so secreting toxins would be self-defeating. However, this is not established science AFAIK.
Barjam is right. That won't happen. From a basic biological standpoint, ultimately what cyano wants -- what it needs for making amino acids, and thus proteins -- is ammonia. The farther removed the available nitrogen source is from NH3, the more energy-intensive it is for cyano to make use of it. This is because cyano has to reverse nitrification, the familiar NH3 --> NO2 --> NO3 transformations that occur in a cycled biofilter, and each step is driven by specialized enzymes. So nitrate "costs" more to use than nitrite, which in turn requires more energy than ammonia. Nitrogen gas (N2) is the most costly source of nitrogen, so cyano won't use it until nitrates (and nitrites and ammonia, if they're anvailable) are zeroed out. In fact, fixing nitrogen is so energy-intensive that not all species of cyano can do it, and for "normal" cyano that can, it just requires too much energy (and also a lot of iron, which is usually hard to come by in a marine environment) to spin up the machinery until it's actually needed.
At that point, cyano's ability to fix nitrogen becomes an enormous advantage, as it can continue to pull PO4 out of an N-limited system. And crucially, it should keep the system N-limited, as a cyano-based scrubber will want to use any available NO3 to reduce the amount of energy it has to expend on fixing N2.
This would be a better link for criticizing a cyano scrubber...
Wikipedia said:
Yikes! But on the other hand, you'd think that if cyano posed a serious health threat to hobbyists, we'd've noticed by now...
I've seen some suggestion that the offending species of cyanobacteria produce toxins when in a planktonic phase, but not in algal mats. This would seem to be a straightforward evolutionary adaptation: in algae blooms, cyano produces toxins to exclude other microorganisms and claim all the available nutrients; in microbial mats, cyano lives symbiotically with algae and other bacteria, so secreting toxins would be self-defeating. However, this is not established science AFAIK.
dg3147
Active member
seems like the point is being missed here. It could be a quick fix to a horrible problem. The balls of screen go in only for a few days to export the cyano. Someone needs to try and duplicate it in there tank. I seemingly cured my tank of it, but it needs to be replicated to be valid.
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coralreefdoc
New member
While this isn't innovative/cutting edge, by any means ... Attempted this with success, both in a wholesale coral/fish facility as well as in a traditional reef system, using 'plastic' eggcrate years ago ... It certainly will provide others, who are less inclined to develop an intelligent/biological solution than to just grab a bottle of chemical(s) marketed to the ignorant.
dg. The perceptive/knowledgable use of 'plastic' screening, with its open/flowing pattern, is a detail/variable in which you've diversified this method nicely :thumbsup:
Cyanoacteria will occur, in some form/location, in most all captive reef systems. Especially those which are not mature and low nutrient balanced/stable ... It's a issue of controlling population density/location, and the methods such as/similar to this one provide an efficient means to that control.
dg. The perceptive/knowledgable use of 'plastic' screening, with its open/flowing pattern, is a detail/variable in which you've diversified this method nicely :thumbsup:
Cyanoacteria will occur, in some form/location, in most all captive reef systems. Especially those which are not mature and low nutrient balanced/stable ... It's a issue of controlling population density/location, and the methods such as/similar to this one provide an efficient means to that control.
elegance coral
They call me EC
There is a balance in nature between nitrogen fixing and denitrification. They can both be viewed as hard work, or energy consuming processes, but they are both equally important to the nitrogen cycle that keeps us all alive. If denitrification exceeded the rate of nitrogen fixing, we would run out of organically bound nitrogen, and we would all die. Cyanobacteria, and their nitrogen fixing capabilities, are the big guns insuring this doesn't happen.
The fact that a process can be viewed as energy consuming, does not exclude organisms from preforming that process. Competition often drives organisms to preform tasks that on the surface may seem to be a waste of energy. Giraffes spent massive amounts of energy and resources producing those long necks. They did this, and continue to do this, due to competition. Through spending the energy for those long necks, they're able to access resources that are unavailable to many others. Cyanobacteria my need to spend more energy fixing nitrogen, but through this process they are able to access a resource that is unavailable to many others.
In our systems, there is a HUGE amount of competition for ammonia. When we "cycle" a tank, we are culturing massive numbers of organisms that utilize ammonia. The competition for ammonia is so fierce in our systems that the ammonia level in a healthy system never reaches a concentration high enough to be detected by our test kits. Despite the fact that we have fish and other organisms constantly releasing ammonia into our water.
Cyanobacteria have spent Billions of years perfecting the ability to circumvent this competition and tap into a resource where there is little competition. I don't believe it is realistic to expect these organisms to abandon billions of years of evolution simply because its hard work, or because it would be in our benefit if they did.
We have many methods to aid us in maintaining low levels of nitrate and phosphate. Properly maintained mechanical filtration, protein skimming, absorption/adsorption media, water changes, manual detritus removal............ These methods do not run the risk of elevating those substances that we are trying to remove. IMHO, any method that has the potential to raise the nutrients that we work so hard to keep at low levels, would be a horrible method. Cyanobacteria have the potential to cause a rise in nitrate levels. Therefore, IMHO, deliberately culturing these organisms in our systems would be a horrible idea.
The fact that a process can be viewed as energy consuming, does not exclude organisms from preforming that process. Competition often drives organisms to preform tasks that on the surface may seem to be a waste of energy. Giraffes spent massive amounts of energy and resources producing those long necks. They did this, and continue to do this, due to competition. Through spending the energy for those long necks, they're able to access resources that are unavailable to many others. Cyanobacteria my need to spend more energy fixing nitrogen, but through this process they are able to access a resource that is unavailable to many others.
In our systems, there is a HUGE amount of competition for ammonia. When we "cycle" a tank, we are culturing massive numbers of organisms that utilize ammonia. The competition for ammonia is so fierce in our systems that the ammonia level in a healthy system never reaches a concentration high enough to be detected by our test kits. Despite the fact that we have fish and other organisms constantly releasing ammonia into our water.
Cyanobacteria have spent Billions of years perfecting the ability to circumvent this competition and tap into a resource where there is little competition. I don't believe it is realistic to expect these organisms to abandon billions of years of evolution simply because its hard work, or because it would be in our benefit if they did.
We have many methods to aid us in maintaining low levels of nitrate and phosphate. Properly maintained mechanical filtration, protein skimming, absorption/adsorption media, water changes, manual detritus removal............ These methods do not run the risk of elevating those substances that we are trying to remove. IMHO, any method that has the potential to raise the nutrients that we work so hard to keep at low levels, would be a horrible method. Cyanobacteria have the potential to cause a rise in nitrate levels. Therefore, IMHO, deliberately culturing these organisms in our systems would be a horrible idea.
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elegance coral
They call me EC
I appreciate what you're doing here. It is through people posting threads like this, that we all learn, and become better care takers of our pets. So, please don't take my disagreement with this process as anything personal towards you.:beer:
With all due respect, and IMHO, this is not a "quick fix to a horrible problem". It is a horrible attempt to manage the symptoms of a problem. When Cyanobacteria bloom in our systems, it is a symptom of a problem. Fighting the Cyanobacteria itself, isn't addressing the problem that caused it. The problem remains unsolved. This is like taking over the counter medication for the flu. These medications may aid with some of the symptoms, but you will remain ill until the microbes causing your illness have been dealt with.
Cyanobacteria bloom when nutrient level rise high enough to fuel that bloom. The key to eliminating, controlling, and preventing these blooms, is to keep nutrient level below problem causing levels. When something goes wrong, and there is a Cyanobacteria bloom, the cure to the problem is removing the Cyanobacteria itself, and reducing the nutrients that fueled it. The answer is not to provide a better habitat for the bacteria somewhere else in the system.
Peace
EC
dg3147
Active member
It's just like using Macro Algae to export phosphates. Once the phosphates drop to reasonabale levels, the algae stops growing. Yes, good husbandry is great --but even prestine tanks run into this issue (when new and with carbon dosing).
Exporting the cyano os no different than sucking it up with a siphon. This was just much more efffective.
Exporting the cyano os no different than sucking it up with a siphon. This was just much more efffective.
coralreefdoc
New member
With all due respect, and IMHO, some people around here simply regurgitate half of the misinformed/trivial nonsense they read from the other misinformed, self proclaiming windbags which came before them already polluted this site with previously.
It's like a stopped/clogged up toilet around here half the time, unfortunately. The sh!t just keeps circling around and around ...
Sometimes one needs to provide the water to flush it !
It's like a stopped/clogged up toilet around here half the time, unfortunately. The sh!t just keeps circling around and around ...
Sometimes one needs to provide the water to flush it !
coralreefdoc said:
Indeed. After I very excitedly mooted the idea of a cyano scrubber on another forum last year, I discovered that the aquaculture industry has been hip to this for years -- you can even buy cyano to seed your system with nowadays. We're clearly well behind the curve, here.
Stuff like this is why marine biologists point at us and laugh.
elegance coral said:
EC, I find your reasoning vague and unconvincing.
As noted by Barjam and myself, fixing N2 is substantially harder work than denitrification, so cyano will avoid it if possible. If it didn't, it would be outcompeted by other algae using the NO3 that the cyano is inexplicably ignoring, and cyano blooms would be uncommon, if not vanishingly rare, outside of tanks where NO3 is zeroed out and fixing N2 is the only game in town. Moreover, if your analysis were correct and cyano pulled potentially dangerous amounts of nitrogen into our systems, cyano would routinely crash any system that lacked an extensive anaerobic zone and a robust population of denitrifying bacteria living there. Which pretty much means that a cyano bloom would put the average FW tank into a death spiral...
And in any event, the point of the exercise is to export the cyano, so even granting for the sake of argument that you're right and cyano poses a risk for eutrophication by bringing additional nitrogen into the system, all that nitrogen would go down the drain when the screen is cleaned. Problem solved.
elegance coral said:
Excellent point. Let's look at this problem more closely. Here's a deconstruction of a cyano bloom that I posted on my local MAS forum a little over a year ago...
begin repost:
I suspect that cyano outbreaks in well-run tanks with extremely low or zero measurable macronutrients are tied to nutrient levels in the substrate rather than the water. Specifically, I suspect that phosphorus accumulation in the substrate is key.
Most hobbyists are aware that cyano can fix its own nitrogen and therefore has a major competitive advantage in low N conditions. But it's more complex than that (...ain't it always?). It's not simply low N but a low N
ratio (less than 16:1) that is advantageous to cyano. There are two ways to drop the N ratio: either reduce N or raise P. Most hobbyists want low-N environments for the good health of our livestock and do everything we can to that end, so that's half the problem right there... The other half is that cyano can raise P by extracting it from the substrate -- or, more accurately, by creating conditions which allow P to diffuse out of the substrate at night.In anoxic (low oxygen) and anaerobic (zero oxygen) water, a fundamental aspect of the water's chemistry changes, permitting nutrients that aren't normally soluble to become so. Under anoxic/anaerobic conditions in the water within the substrate (known as "pore water" or "interstitial water" because it occupies the spaces between the individual grains of sand and silt) the solubility of some nutrients can be such that their concentration can potentially reach hundreds or even thousands of times that measured in the overlying water.*
This is the source of what is colloquially known in the hobby as "the deep sand bed nutrient time bomb": at some point, the concentration of nutrients in the substrate will max out, and it will stop absorbing them. When this nutrient sink suddenly stops working, what appeared to be a balanced system will begin to accumulate nutrients and crash. Calling it a "bomb" is fundamentally misleading: nutrients aren't expelled from the substrate; rather, the substrate simply stops absorbing them. Back In The Day, this was known as "old tank syndrome" among hobbyists. It occurs when the substrate becomes saturated with phosphorus.
The depth below the surface of a tank's substrate (or a DSB) at which oxygen becomes depleted is directly related to the grain size of the substrate. Smaller grain sizes become anaerobic at shallower depths because the grains pack tighter and interstitial spaces are smaller, which restricts the diffusion of oxygen into the substrate, and the exposed surface area per unit volume is greater, so there's more space for bacteria to colonize, and it's bacterial respiration that's consuming the oxygen. At what depth in the substrate this change in water chemistry occurs is also highly dependent on whether or not critters are turning over the sand or mud, but the trend toward finer sand in display tanks facilitates it even in shallow sand beds. (...FYI, that's also how "miracle mud" works. And it's worth noting that some nutrients, including phosphorus, can adhere directly to substrate particles when in soluble form, so substrates with a high surface-area-to-volume ratio -- ie, a small grain size, like fine sand and mud -- make the best nutrient sinks.)
The availability of this reservoir of soluble nutrients not far below the surface of the substrate makes it a biological hot spot. It's an interface between two different environments, analogous to the intertidal zone or the littoral zone of a lake. In the wild, mats of algae and bacteria will often grow in both FW and SW just above the substrate. These communities thrive by maintaining a pocket of anoxic water underneath the mats, allowing nutrients to diffuse up out of the substrate -- though only at night because photosynthesis oxygenates the water, and oxygen makes the nutrients (most notably phosphorus and iron, for those of you playing along at home) insoluble again. FWIW, I suspect that some freshwater aquatic plants can pull off this trick, as well.
Cyano has been a prime mover in the creation of microbial mats for billions of years, and that seems to be what it wants to do in our fish tanks, as well. That's why it doesn't like high flow, and that's why it goes away if you wait it out -- it will eventually deplete the phosphorus in the substrate, lose its competitive advantage over the other algaes in the tank, and die back. And when some critical tipping point is reached as phosphorus accumulates and population density increases, you get another cyano bloom.
--
* What's really going on is that the change in redox potential in anoxic/anaerobic conditions changes what chemical reactions are "profitable" to bacteria -- that is, it changes what reactions bacteria can extract energy from in order to survive and multiply. The highly soluble nutrients that accumulate in the interstitial water are metabolic waste products of the bacteria:
"The prokaryotes (bacteria) comprise the bulk of the biomass and chemical activity in sediments. ... The characteristic vertical nutrient (electron donor and electron acceptor) profiles seen in sediments are produced as a result of microbial activities, with each nutrient a product or reactant of one or more metabolic groups."
SEDIMENT BACTERIA: Who's There, What Are They Doing, and What's New?
Annual Review of Earth and Planetary Sciences
Vol. 25: 403-434 (Volume publication date May 1997)
DOI: 10.1146/annurev.earth.25.1.403
--
And we conclude tonight's lecture with the obvious Q: Okay, Mr. Smarty-Pants, if cyano likes low N
ratios, will raising N make it go away?A: Yes, it probably will. Hardcore saltwater hobbyists may not be aware of this, but there's a management method for FW planted tanks called estimative index dosing which calls for maintaining a low level of N because if you permit the plants to suck all the N out of the water, you open the door to a cyano bloom.
Of course, raising N in an aquarium that isn't densely planted opens the door to a bloom of green algae, so if you're the type who likes to mess with water chemistry, you might try concurrently raising dissolved silicon to encourage a diatom bloom, instead. They'll outcompete green algae for P at high Si
ratios, and pretty much all your friendly neighborhood algae eaters totally heart diatoms. Though on the other hand, diatoms colonize microbial mats and may have a symbiotic relationship with cyano, so this tactic could massively backfire...Back to the drawing board, then.
I'm not a devotee of EI dosing, but I can't help but notice that the goal of that system is to maintain 20-30 ppm N and 1-3 ppm P, and 1-2 ppm P would be close to the magic N
ratio of 16:1 that's the break point between cyano and green algae. Get down below 10:1 and cyano has the edge; get much above 20:1 and green algae has a competitive advantage. But if you stay close to 16:1, neither group of algaes can get ahead of the other. Of course, allowable nutrient concentrations are much lower in a reef tank, but the magic ratio should be the same, as FW algaes are all descended from species that evolved in SW. And note that 16:1 is part of the Redfield ratio of C:N -- 106:16:1.Something to think about, at any rate.
NOTES FOR REEF CENTRAL REPOST: (1) Turns out that your friendly neighborhood algae eaters only heart diatoms if the Si:N ratio is around 1:1 (...the standard "recipe" marine biologists use to trigger diatom blooms for experiments in NSW is an Si:N
ratio of 16:16:1, or an Si:N ratio of 1:1). Given more Si, diatoms will grow thicker and spikier silica armor. Their demand for Si will be saturated at an Si:N ratio of 3:1 (48:16:1 Si:N), and the resulting diatoms will be all but inedible to zooplankton. (2) Also, I think my analysis of EI dosing was wrong in my original post -- I found Mr. Algae's blog when I was Googling for stuff to support what I had written, and I didn't read it closely enough to pick up on the "Buddy Ratio"... Still works, though: EI recommends 5-30 ppm NO3 and 1-3 ppm PO4 to restrict algae growth in FW planted tanks, and the upper ends of those ranges perfectly correspond to the ideal Buddy Ratio of 10:1. Assuming "average" NO3 of 17.5 ppm and 2 ppm PO4, that's a Buddy Ratio of 8.75 -- well within the recommend range. (3) Just to be clear, I do NOT advocate dosing N to fix a cyano bloom in a reef tank, as messing with macronutrients is way too risky IMHO. To err is human, after all... (4) FWIW, I tried to post a detailed explanation of how and why PO4 accumulates in anaerobic sediments as part of an effort to tie together all the information about deep sand beds that's floating around out there, but my thread was immediately deleted without explanation. Shame -- there was some good information in there, and this seemed like the appropriate place to share it./repost
Note, however, that this model doesn't specifically address the OP's cyano bloom, which is in a new system, not a mature one. Here's how cyano blooms work in new reef tanks...
The porous anaerobic interior of LR is a potential PO4 sink, like any anaerobic zone. In the wild, PO4 doesn't accumulate because nutrient levels are normally very low. However, while being cured, the dieback of inverts releases phosphorus, some of which ends up sequestered within the LR as orthophosphate (PO4). When placed in a new system with freshly mixed water and virgin substrate that contains little or no phosphate, some PO4 will leach out of the LR to bring it into chemical equilibrium with the water column. As the tank cycles, bacterial growth will draw down PO4 from the water, which in turn leaches more from the LR to maintain equilibrium.
Because any anaerobic substrate is a potential P sink, cycling a tank will establish new places for phosphorus to hide -- and because nature abhors a vacuum, it very much wants to hide there... This means that the slow flux of PO4 out of the LR will continue even after demand by the bacterial community falls off when the tank is fully cycled. This is the nutrient flux that cyano is exploiting in new tanks.
dg3147, I suspect I can explain why your success with this tactic was so rapid -- that is, why the cyano didn't come back when you lifted it off the substrate by giving it somewhere else to grow -- but doing so would require making reference to information I previously posted in the thread on DSBs and phosphorous sequestration that was deleted. I'm afraid to share any of the information in that thread without the express written consent of the mods, as I have no idea why it was deleted...
coralreefdoc
New member
* Anoxic = Absence of O2; Anaerobic = Low level of O2
dg3147
Active member
The point is no to encourage or seed the tank. Perhaps the term "scrubber" confused my original concept. The point it that, in tanks that grow cyano anyway, add the screen in the DT/fuge and rinse it off every few hours xseveral days. The cyano will be exported and, with the export, the limiting nutrient leaves too. this MIGHT reduce cyano in your over run, dying tank.
Not exctly.
Anoxic describes water without oxygen . Anaerobic describes bacterial activity in water without free O2 such as denitrification using the O in NO3 or sulfate reduction using the O in SO4.
As noted by Barjam and myself, fixing N2 is substantially harder work than denitrification,
I tend to agree with that assumption to a point but don't know it to be a fact . Not sure how much work it takes to form a few heterocyst and some nitrogenase and whether bacteria would just abandon this function in the presence of N for assimilation.
Do you have data or studies to support your assertion that cyano species capable of fixing nitrogen are in our tanks . If so, is there any proof that they will use organically fixed nitrogen to the exclusion of fixing it? Perhaps one of the laughing biologists you referenced does. Ask one next time you are chortling together.I know a few microbiologists and thy don 't make a hbit of laughing at reef keepers,btw.
The assertion should be proven if made with certainty as you have made it. . Certainly one of the laughers must have examined some cyano in water with fixed nitrogen to see if heterocysts were present.
I tend to agree with that assumption to a point but don't know it to be a fact . Not sure how much work it takes to form a few heterocyst and some nitrogenase and whether bacteria would just abandon this function in the presence of N for assimilation.
Do you have data or studies to support your assertion that cyano species capable of fixing nitrogen are in our tanks . If so, is there any proof that they will use organically fixed nitrogen to the exclusion of fixing it? Perhaps one of the laughing biologists you referenced does. Ask one next time you are chortling together.I know a few microbiologists and thy don 't make a hbit of laughing at reef keepers,btw.
The assertion should be proven if made with certainty as you have made it. . Certainly one of the laughers must have examined some cyano in water with fixed nitrogen to see if heterocysts were present.
coralreefdoc
New member
tmz said:
Given the ubiquity of cyano in both aquatic and terrestrial environments -- not to mention the atmosphere, where sampling has turned up dozens of species of cyano, some adrift at altitudes as high as 10km -- I think the onus is clearly on the skeptics to demonstrate that cyano capable of fixing N is absent. However, as this is obviously impossible, I would be willing to accept a plausible theoretical mechanism for the exclusion of these species, but not others, from marine and FW aquariums.
I am serenely confident that no such mechanism exists on paper, let alone IRL, but I'd love to be proven wrong... My understanding advances most rapidly when I'm confronted with my own errors and forced to rethink or refine my position. That's why I haven't been shy about making myself a target -- I was hoping somebody around here would be able to keep me on my toes, but so far, I'm not having much luck.
Though props to coralreefdoc for catching the anoxic/anaerobic thing. That was helpful.
tmz said:
Yes.
Here's the salient sentence: "Cyanobacteria assimilate ammonium in preference to other nitrogen sources, like nitrate or N2, and utilize combined nitrogen in preference to N2."
And further, "Nitrogen control is a phenomenon that occurs widely among microorganisms and consists of repression of the pathways of assimilation of some nitrogen sources when some other, more easily assimilated source of nitrogen is available to the cells."
tmz said:
There are species of filamentous cyano that can fix N and do not form heterocysts, so that would not be a conclusive assay. But yes, "one of the laughers" addressed this 15 years ago: "An additional interesting observation is that although overexpression of hetR [that's a gene] results in heterocyst development independent of the nitrogen source, only in a medium without combined nitrogen are the heterocysts active in nitrogen fixation."
Next time, Google before you rant.
dg3147 said:
I'll respect your status as the OP and shut it down, if you wish.
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