My short article for Uni on Nitrifying Bacteria


HI all,

A few weeks ago I posted a thread about needing to write a short article for microbiology and wanting to do it on nitrifying bacteria and its importance in an aquarium.

Well, I finally got it written, so I figured I'd post it here as there were several people who expressed an interest in reading it

I've written it for uni, but I think fishlorians may find it interesting, as we all have a passion for fish here I'll include the reference list too. I only had 500 words to play with (plus its due tomorrow, so I needed to finish it asap), but I'm tempted to further research and build on this when UnI slows down a bit (just for the heck of it ) Oh, another thing I'd like to add, big thanks to Kyle for starting up a thread about articles he'd read on nitrfiying bacteria I ended up using on the articles from a link he posted

Nitrifying Bacteria and its Importance in Aquariums

Microorganisms are an essential part of our world. They are present in every ecosystem and are the primary catalysts of nutrient cycles in nature (4). The nitrogen cycle, for example, can only transpire due to the presence of nitrifying bacteria. Madigen (4) defines nitrifying bacteria as being capable of growing chemolithotrophically at the cost of reduced nitrogen compounds. The nitrogen cycle is a two step microbiological process (8) that involves ammonia, NH3, being converted to nitrite, NO2, and then nitrite being converted to nitrate, NO3 (7). This cycle occurs in both aquatic and terrestrial ecosystems. This article will focus primarily on the nitrogen cycle in aquatic ecosystems and the effects on the animal inhabitants, particularly fish species.

As suggested by Ferguson (1), nitrifying bacteria are generally classed as chemolithoautotrophs and include nitrosomona spp. and nitrobacter spp. The nitrosmona bacteria convert NH3 to NO2, while the nitrobacter convert NO2 to NO3. These nitrifying bacteria are obligate aerobes, as they use molecular oxygen in the conversion process. Nitrosomonas are gram-negative short to long rods that are either motile with polar flagella, or non-motile and have peripheral membrane systems (4). Conversely, Nitrobacter are short rods that are occasionally motile with a single subterminal flagellum and reproduce by budding, while their membrane system is arranged as a polar cap (4). Nitrobacter are related to photosynthetic bacteria and also possess intracytoplasmic membranes (5). While there are other genera of nitrifying bacteria, such as nitrosospira and nitrospira, nitrosomona and nitrobacter are the only two that prefer to live in freshwater or marine habitats, while nitrosospira and nitrospira prefer to live in freshwater and marine habitats respectively (4). However, there has been past evidence to suggest that in fact nitrospira may be more prevalent than nictrobater is freshwater systems (2). There are no chemolithotrophs that can completely oxidate NH4 to NO3, which is why these bacteria are often found living in tandem.

The importance of nitrifying bacteria in freshwater and marine ecosystems can also be likened its importance in an aquarium, which is a miniature ecosystem. As Randall (6) states, ammonia is excreted by animals and produced by the decomposition of organisms. Aquatic exposure to ammonia is particularly bad due to its toxicity, unlike terrestrial exposure, it cannot rise to the atmosphere and be destroyed. Ammonia intoxication affects the central nervous system in vertebrates and can result in convulsions, coma and death. Nitrite is also toxic, particularly to fish as the nitrite is taken up from ambient water by the gill epithelium and accumulates to high concentrations (3). Nitrite intoxication leads to problems with chloride, Cl-, uptake which eventuates in cell death. Intoxication also leads to a decrease of O2 in the blood. Jensen (3) also states that transferring intoxicated fish to nitrite-free water can reverse the effects, providing this isn’t initiated at too late a stage.

The effects of ammonia and nitrite intoxication, as Randall (6) and Jensen (3) state, are detrimental to the health of fish. Clearly, basic knowledge about the nitrogen cycle is of upmost important to fish-keepers so that they may ensure that nitrifying bacteria is present in their aquarium through testing ammonia and nitrite levels regularly.

1. Ferguson S.J., Richardson D.J., van Spanning R.J.M. 2007. ‘Chapter 14 – Biochemistry and Molecular Biology of Nitrification’, in Bothe H., Ferguson S.J., Newton W.E., Biology of the Nitrogen Cycle, Elsevier, 20-04-2010,|Orightresult|X5?lang=eng&suite=pearl , pgs 209, 216, 218

2. Hovanec T.A., Taylor L.T., Blakis A., Delong E.F. 1998. Nitrospira-Like Bacteria Associated with Nitrite Oxidation in Freshwater Aquaria, Applied and Environmental Microbiology, 64, 1, 258-264

3. Jensen F.B. 2002. Review: Nitrite disrupts multiple physiological functions in aquatic animals, Comparative Biochemistry and Physiology Part A, 135, 9–24

4. Madigen M.T, Martinko J.M, Dunlap P.V, Clark D.P. 2009. Brock Biology of Microorganisms, Pearson-Benajmin Cummings, San Francisco, 402-403; 676

5. Prosser, J.I. 2007. ‘Chapter 15 – The Ecology of Nitrifying Bacteria’ in in Bothe H., Ferguson S.J., Newton W.E., Biology of the Nitrogen Cycle, Elsevier, 20-04-2010,|Orightresult|X5?lang=eng&suite=pearl pgs 235, 241

6. Randall D.J, TsuI T.K.N. 2002. Ammonia toxicity in fish, Marine Pollution Bulletin, 45, 17–23

7. van Spanning R.J.M., Richardson D.J., Ferguson S.J. 2007. ‘Chapter 1 - Introduction to the Biochemistry and Molecular Biology of Denitrification’, in Bothe H., Ferguson S.J., Newton W.E., Biology of the Nitrogen Cycle, Elsevier, 20-04-2010,|Orightresult|X5?lang=eng&suite=pearl , pg 3

8. Zhang Y., Love N., Edwards M. 2009. Nitrification in Drinking Water Systems, Critical Reviews in Environmental Science and Technology, 39, 154

The links are through my university library, so people who aren't a student/lecturer there can't view them. They are required for 'e-books' in my Uni's referencing rules. But you should still be able to find the articles if you wish using the other information


Good Write up
Very well done


Thank you Red


Impressive Rhan.

Too many big words that I don't understand. Now I'm going to have to do more research just so that I know what "motile", "subterminal flagellum", "chemolithotrophs", "obligate aerobes" & "gill epithelium" mean.

I never even finished high school, let alone went to uni. Your too smart for me.


LOL thanks Nutter

Too smart eh, I doubt that I could ever know half as much about plants as you Plants are just.... complicated. I'll stick with my bacteria


Very well done.
Funny, it wasn't the big words that got me, but the little ones (I was trying to figure out what publication "uni" was. ;D It was only when Nutter used the word that I realized what it meant.)


Very nice writeup. You deserve a very high grade!

Thanks for sharing this with all of us.



Oh my gosh... I just got my mark back for my article and I got the highest score out of my class of 50 people!!

15/15 !!!!

I can't believe it! I was hoping for a high mark, but I honestly didn't think I'd get a full score, especially considering this lecturer is a very tough marker.

Wow, I just had to put it out there I might just go do a little dance


Congratulations Rhan.
The high marks are well deserved. Your lecturer obviously knows good work when they see it.

platy ben

Dance away
As much as I didn't understand half of the words! It's a great write up

Great job!!

Hmmm, I'm taking biology next year at 6th form, I hope your still on fishlore


Party time! Congrats Rhan!



Thanks again guys Definetly a pleasant suprise.

Platy Ben: Biology is awesome, it's very hard not to like it I didn't do it in highschool (although I wish I had done it as well as chemistry), so when I had to do it at UnI it was like 'woah!', but the fact it was so interesting made it a great subject


That's awesome, Rhan!

Congratulations and it's very much deserved!


Congrats Rhan! definitely time to dance! arty0049:




great write up! my mind works in very odd ways and I find write ups like this more helpful than the more "watered down" versions. I even understood most of the words! (Having taken college biology classes helps lol)

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