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Figure 1. Diagram of the marine nitrogen cycle.

There are other methods of fishless cycling being recommended or used however one method being pushed on the internet by "cut & paste", anecdotal websites and forums is the use of ; however this is a recycled idea (which included the use of silversides, frozen shrimp, and even dead feeder fish) and has reappeared on the internet even though it was debunked in the early 1990's!

I do not recommend this method, not because it does not work for cycling, but because it also allow a Saprolegnia infection to get started in your new aquarium (or at the very least; heterotrophic bacteria which is not a desirable nitirfying bacteria as discussed earlier).
Saprolegnia is a mold (often called a fungus) that easily gets a foot hold in decaying nitrogenous matter such as raw shrimp and I have seen this many times in my experiments. Even after the source of Saprolegnia growth is removed, the secondary zoospores which are the primary mode of pathogenic transmission can remain, even after large water changes/vacuumings.
A new tank is the worst time to have a Saprolegnia infection get started as this is when fish are often much less resistant to disease due to the stressor of a new tank environment.

I should note back when this method was making its “rounds” in popularity that it worked fine in many instances and with a 100% water change and vacuuming of gravel can reduce this risk even further, however some risk still remains as per my many tests of pathogens .

Please Reference for further information:

1. List the three major processes involved in the nitrogencycle.

In 2004, a particular gene called the ammonium mono-oxygenase (amoA) was discovered in marine Crenarchaeota, indicating the capacity to oxidize ammonium. The definite and convincing link between this new gene and the ammonium oxidation in archaeabacteria has been recently established in Crenarchaeota, the , which was isolated from the water of aquarium. us is chemoautrophic: as a matter of fact it grows with bicarbonate as the only source of carbon (organic carbon inhibits its growth) and converts NH4+ in NO2- (green line in Figure 4 and Figure 7). Other archaeabacteria have been successively identified with this property and have been named as Ammonium oxidizing archaeabacteria (AOA). An accurate analysis of the AmoA gene in many archaeabacteria has revealed diverse isoforms of this gene, each one is associated to a microorganism which is present in different habitats (with little overlapping, for example, between sediment and water column). Symbiont archaeabacteria have also been identified, like for example the , a symbiont Crenarchaeota with a sponge. Surprisingly, it was observed that this archaeabacteria is not able to produce hydroxylamine as intermediate reaction (see the Nitrosation process in the BOX 2) indicating that ammonium oxidization occurs with a mechanism which is different from that of the classic nitrification. Finally, the most recent studies conclude that the majority of Crenarchaeota are AOA's and AOA's are microorganisms whose presence is numerically predominant in the ocean.

3. Describe the significance of legumes in the global nitrogencycle.

The archaeabacteria, like the bacteria, consist of single cells without nucleus and in the past they were classified as prokaryotes together with the bacteria. Based on the DNA analysis, the archaeabacteria were re-grouped into three phyla: , and . The Euryarchaeota bacteria are the most prominent and they include methane producers and holophiles. The Crenarchaeota bacteria include thermophilic microorganisms, while the Korarchaeota bacteria are less known because only their DNA is recognized but no microorganism has so far been isolated. Originally, it was thought that the archaeabacteria were just inhabitants of a harsh and most hostile environment on the face of the earth. The thermophiles can grow at a temperature higher than 100°C, the psychrophiles are those which grow at temperatures lower than -10°C, while the acidophilus and the alkaliphiles grow in extremely acidic or alkaline environments, respectively. Finally, the halophiles prefer the highly saline environment. Today, we know that archaeabacteria are present in all habitats: for example the Crenarchaeota bacteria are considered ubiquitous components of zooplankton.

are an organism that requires organic substrates to get its carbon for growth and development. Some are strictly aerobic, but many are facultative anaerobes (they can survive in either the presence or absence of oxygen).
Heterotrophic Bacteria are generally found in most over the counter aquarium cycling products (especially "Sludge Removers") due to their portability and quick activity.
Heterotrophs can be either gram-positive (ex: Bacillus) or gram-negative (ex: Pseudomonas) which in the case of Pseudomonas many gram negative aquarium treatments (such as Kanamycin) can be effective against Pseudomonas while not harming true Autotrophic nitrifying bacteria.

Another point is growth (which is why Heterotrophic bacteria are favored for cycling products); nitrifying (Autotrophic) bacteria will double in population every 15-24 hours under optimal growth conditions. Heterotrophic bacteria, on the other hand, can reproduce in as little as 15 minutes to 1 hour.
Unfortunately research has shown that up to one million times more of these heterotrophic bacteria are required to perform a comparable level of ammonia conversion that is attained by true autotrophic nitrifying bacteria, in part due to the fact of Heterotrophic Bacteria to convert many organics into food.

The use of Heterotrophic Bacteria to cycle an aquarium (or pond) can result in a bio environment that does not contain the necessary Autotrophic nitrifying bacteria to rapidly adapt to changes in bio load either from added fish, wastes, or similar; thus often resulting in sudden spikes in ammonia or nitrites when these Heterotrophic bacteria cycling products are not added in a timely or regular schedule!The other danger is cloudy water.

For this reason products that contain only Heterotrophic Bacteria such as "Hagen Cycle" or even the popular Eco-Complete planted substrate SHOULD BE AVOIDED in some aquariums!

Low pH and Nitrification ;

Nitrification involving AOB & NOB bacteria is different at pH levels of above 7.0 versus below 6.0.

Toxic Ammonia (NH3) changes to ammonium under 6.0 and ammonium (non toxic NH4) switches back to toxic NH3 over 7.0
until the nitrification process re-establishes itself at the higher pH

The cause of this change in the nitrification process is still not clearly understood.

From the above article and quote, I would postulate that a change in Heterotrophic bacteria along with possible Redox Reactions or lack there of (a low pH below 6.0 is very oxidizing with little/no reduction which for this reason alone is not a healthy environment.
As well, Autotrophic bacterial adaptations may be part of this process and why there is an interruption in nitrification from changes in pH and between NH3 & NH4.
Since typical real world aquarium environments invariably are going to contain Heterotrophic bacteria (from fish food waste, etc.) and these tests seemed to lock out these Heterotrophic bacteria (using only ammonium chloride), this bacterium might be part of the cause.

During the nitrification process carbonates are used by the aquarium or pond to counter acids produced during nitrification (or other organic breakdown), however without an adequate KH (even for Amazon River Fish such as Discus or German Rams), subtle or even sudden changes in pH can occur that affects the nitrogen cycle

Keeping a low pH/KH can be a double edged sword where by a simple procedure such as a water change with slightly higher pH water can result in an immediate conversion of ammonium (NH4) to deadly ammonia (NH3) with disastrous results.
This low pH, poor nitrifying environment also easily allows for the growth of pathogenic Fungi/Saprolegnia and a depressed Redox balance.

See References:

These aerial roots contain a nitrogen-fixing cyanobacterial symbiont.

Practical use of Recombinant DNA technology in the synthesis of human insulin requires millions of copies of the bacteria whose plasmid has been combined with the insulin gene in order to yield insulin.

Sixty three nucleotides are required for synthesising the A chain and ninety for the B chain, plus a codon at the end of each chain,signalling the termination of protein synthesis.

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Aquarium Nitrogen Cycle | Cycling Methods | Ammonia …

Recently, new important components of nitrogen cycle, which form the part of the richer and diffused group of micro-organisms in the planet, the archaeabacteria, have been identified. In spite of the group's evolutive line being unclear, the archaeabacteria (Archaea or Archeobacteria) combined with the eukaryotes and with eubacteria, are some of the fundamental domains of the living beings.

Question 165 Bacteria require nitrogen for the synthesis of ..

For SeaChem products to help with you aquariums nitrogen cycle, such as:
to neutralize ammonia & nitrites (as well as chlorine and chloramines), for Nitrate control or to aid in your aquarium cycling or for accidental high decaying organics removal (this product does not take the place of full aquarium cycling)

nitrogen-fixing bacteria | Definition & Types | …

Denitrification is the process by which microorganisms convert nitrate (NO3) to nitrogen gas (N2). In terms of the global nitrogen cycle, denitrification serves to balance nitrogen fixation by removing fixed nitrogen (rather than supplying it) to the biosphere.
Most denitrifying bacteria are heterotrophic (such as Paracoccus denitrificans and various pseudomonads), utilizing organic carbon, hydrogen or hydrogen sulfide as electron donor and nitrate as electron acceptor. The electron donor is oxidized (to CO2, water or sulfate) and nitrate is contemporaneously reduced to dinitrogen gas (N2).
Denitrifying bacteria require a source of reductant (energy) and a source of oxidant (nitrate).

This process can take place in an environment of very limited oxygen by anaerobic bacteria. This process is more common in Marine aquaria and takes place in fine #00 sand, live rock, or “aquarium mud”.
In freshwater aquariums this process often produces potentially dangerous Hydrogen Sulfide, but by maintaining an oxygen level above 1 ppm, this can be avoided. Plants roots are great for maintaining this balance of oxygen in the gravel for proper Nitrate removal by allowing very small amounts of oxygen into the substrate which promotes nitrogen reduction over sulfur reduction (which occurs in substrate with 0 oxygen).

plants require nitrogen in the form of soil ..

The previous description represents a well-known scenario for a long time. In the course of the recent years however, our references concerning the nitrogen cycle have drastically changed to the extent that the principle of closed linear cycle itself is being questioned. This is because new reactions have been discovered and consequently new microorganisms that make the entire nitrogen cycle even more complex and twisted (Figure 4). In the second part of this article, I will try to clarify some important ways which will be inserted within the canonical nitrogen cycle:

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