Home - An introduction to the microbial world
Bacteria have certainly been around for millions of years but it is only fairly recently that we have known about their existence.
Much debate had raged for several hundred years as to what caused infectious disease. Some early pioneers such as Girolamo Fracastoro 1478-1553 an Italian physician had proposed in 1546 that epidemic diseases are caused by transferable seed like entities that could transmit infection. Friedrich Gustav Henle 1809-1885 a German physician, along with other less well known scientists and medical practitioners also supported this theory but no proof could be offered. For much of this time the debate had been hampered by the simple inability to see microorganisms. Nearly all microorganisms (bacteria, viruses, protozoa, fungi and algae) cannot beseen with the naked eye, except for some examples, under certain circumstances when the growth becomes so intense that the life form can be seen un aided. Anton van Leeuwenhoek (circa 1685) is thought to be the original discoverer of bacteria. He observed using primitive lens various forms of life that he characteristically described as little animacules. He observed these microscopic forms in diverse environments such as pond water and scrapings from teeth and reported his findings to the scientific community. From his drawings it was also clear that Leeuwenhoek had observed protozoa as well as bacteria in his studies.
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Anton van Leeuwenhoek 1632-1723 |
Soon after Leeuwenhoek's discovery, many investigators tried to classify microorganisms particularly based on their shape, but poor magnification at the time made this very difficult. One interesting concept that prevailed in the 19th Century was that all microscopic forms of life were merely stages in the development of more complicated forms i.e. bacteria developed into fungi. Of course today we know this not to be the case, but approximately 150 years ago almost everything about microorganisms was unknown. The major theory of the time as to where these microorganisms came from focused on spontaneous generation i.e. small life forms could spontaneously arise from non-living matter. Thus, even the idea that maggots spontaneously arose from decaying meat was accepted by many scientists.
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Louis Pasteur 1822-1895 |
Louis Pasteur a French microbiologist and chemist (1822-1895) was the first to prove that microorganisms did not just appear and that they were specific individual life forms.
So it took several hundred years to just arrive at the position whereby bacteria were recognised as individual living creatures along with other microorganisms like the fungi, algae and protozoa and that was just the very beginning. These pioneering scientists had merely touched the surface on the path to understanding the huge diversity and complexity of microbial life. To even begin to understand the world of microorganisms we need to perhaps draw a number of parallels with how we live our own lives.
There are many millions of types of microorganims, particularly bacteria and probably that number again that we haven't even discovered yet. Why so many different types? You will have heard of a few, Pseudomonas, Aeromonas, Nitrosomonas, Nitrobacter. You will also know about how very different these bacteria are. For instance, for the first two you may think of disease and for the second two you may think of nitrification and a healthy pond. Different bacteria have different ways of scraping a living and that's what it is all about. If every bacterium and microscopic life form needed the same things for life, there would be huge competition and poor environmental stability. It's all about finding your niche in life and exploiting it. At the end of the day it's the same for us, people do different jobs, servicing different needs in a community, some jobs are dependent on products from other industries. Bacteria and microorganisms generally are no different, a pond ecosystem is just like a small town each pond inhabitant has a job to do and can use different resources to do a job. In the end everyone benefits so long as the pond environment remains stable.
As we know from the so called 'new pond syndrome' true stability takes time and pond maturity involves far more than just the conversion of ammonia to nitrate. So, back to niches, some bacteria have fully committed themselves to their niche and probably the best and most relevant examples here are Nitrosomonas and Nitrobacter. These bacteria are absolute specialists focusing on just one thing, the conversion of ammonia to nitrite and the conversion of nitrite to nitrate respectively. These two types of bacteria need ammonia or nitrite respectively for survival and they use nothing else for generation of their energy. Hence, they are in perfect balance with the ammonia producing koi carp. With regard to survival they all need each other. Koi cannot tolerate the presence of ammonia or nitrite, Nitrosomonas needs the ammonia but it is sensitive to accumulating nitrite concentrations and Nitrobacter needs Nitrosomonas to supply its nitrite for conversion to relatively low toxicity, safer nitrate, so relieving Nitrosomonas's nitrite sensitivity. Other bacteria have developed specialist systems that allow them to live off unusual sources of 'food' but also keep their options open retaining the capability to swap over if some other source of 'food' becomes available. This makes them more flexible but the disadvantage is that they end up competing with lots of other types of bacteria that can do the same thing. Sometimes in the microbial world it is best to do a few things really well rather than lots of things to an average standard. Nitrosomonas and Nitrobacter have little competition in their restrictive but effective lifestyles. It should also be noted that bacteria and microorganisms do not always act selfishly, that's where the balance in the pond comes from. For instance, as a consequence of one bacterium ensuring its own survival, it often produces 'food' for others.
What this is all saying is that different bacteria can do different things. Of course this comment extends in many directions and includes the ability to cause infection. All bacteria want to survive by any means available and if the bacterium is waterborne and has a means of obtaining life at the expense of a fish, then that is what it will do if it is able to overcome the fish's immune system defences.
A little more about our two koi pond specialists
Nitrosomonas and Nitrobacter are what are known as chemoautotrophs. They get their energy from chemical oxidation of either ammonia or nitrite ('chemo') and they are autotrophs (self feeders). They do not depend on preformed organic matter for life they just use carbon dioxide from the air or the water.
Nitrosomonas
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Nitrosomonas bacterium |
Nitrosomonas is an organism found in diverse environments ranging from soil, sewage, freshwater and believe it or not, on the surface of buildings, especially in areas with high air pollution. It can tolerate a pH range between 6 and 9 but its ideal pH is 7.8-8.0 and its ideal temperature range 20-30oC. These bacteria are what are known as motile. Motile means that they are able to move under their own power i.e. they can move towards a solid surface.
Anyone that has started off a new filter will know how long it can take to mature to a position where no ammonia or nitrite is detectable in the water. In addition, you are advised not to add too many fish too quickly. Well Nitrosomonas the key converter of ammonia to nitrite is far from lively in its lifestyle. Nitrosomonas needs a source of carbon to grow (to make more of itself) this it can achieve by taking carbon dioxide from the air. This process is energetically demanding. The big problem however, is the amount of ammonia that it needs to convert to nitrite to generate enough energy for life. Nitrosomonas needs lots of ammonia because the conversion of ammonia to nitrite although carried out efficiently by this bacterium produces only low levels of energy. Unfortunately because a lot of this energy is used to obtain carbon dioxide from the air not much is left to use for actual growth. The wheels of life for this bacterium turn very slowly. This poor energy generation means that the creation of a new Nitrosomonas can take several days although generally 15-24 hours under reasonable conditions. Little surprise then that biological filters take weeks or more to mature. For comparison, a Pseudomonas or Aeromonas (potential fish pathogens) can take just a few hours to complete the job of reproduction. Another interesting feature of Nitrosomonas is its sensitivity to light. It really hates light and will cover itself in slime and form clumps with other microbes to avoid it. In addition, these bacteria have the capacity to adhere to surfaces. Makes sense really, if they find themselves in an area that serves their needs why move on? So, lets think about it, a question often asked. Why do the filter bacteria stay in the filter? Well it's a source of essential ammonia, it's dark and they can grab hold and stay. Perfect ! Do they exist in other parts of the pond ? Yes, almost certainly but the filter is an ideal collection point for an organism that would like to attach itself in an ideal oxygenated environment.
Nitrosomonas has also evolved another interested feature. As a true ammonia specialist it needed to devise a strategy for coping when ammonia isn't around. Why did it get into that situation in the first place you might ask ? Well, I guess the answer to that lies several billions of years ago, the beginning of life. Yes, these bacteria have been around for a while. On early earth, ammonia was a very abundant molecule. The development of plants led to the generation of oxygen. Throw in a little carbon dioxide and a few other nutrients and you have potential for growth of Nitrosomonas. Nitrosomonas has evolved a protection system whereby in the absence of ammonia it can slowly shut down its metabolism finally reaching a state of dormancy. Even in this state, one thing remains active, the ability to detect ammonia. This detection system however is also specialised. Nitrosomonas wont reactivate at a sniff of ammonia, no, it needs to know that there is plenty about at high concentration. What would be the point of waking up just to find a little breakfast and nothing for later? Reactivation and deactivation do not happen instantaneously hence, some 'thought' needs to go into the choices to optimise survival chances. The sensitivity of the detection system only allows reactivation at suitable and sustained ammonia concentrations and indeed before it wakes up fully it must adhere to a surface to fix itself in the suitable environment. Reactivation can take several days or even weeks depending on the concentration of ammonia present. Perhaps this goes some way to explaining why adding mature filter media to a new filtration system will kick of a new system far quicker than adding large quantities of liquid filter start bacteria, which are actually unlikely to contain large amounts of Nitrosomonas anyway.
Nitrobacter
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Nitrobacter bacterium |
This bacterium is the other half of the nitrification team in the koi pond. Nitrobacter shares many of Nitrosomonas's features and requirements, except that it is the nitrite to nitrate specialist. Again the amount of energy produced from this conversion is low, hence, like Nitrosomonas, the time required for the bacterium to reproduce itself is many hours. Its ideal pH is a little lower than that for Nitrosomonas at pH 7.3-7.5 but it is still happy at the pH range acceptable to koi 7.0-8.5. Growth temperature preference is also very similar to that for Nitrosomonas. Nitrobacter can also cope with periods of starvation or cold but its survival efficiency is a little lower than Nitrosomonas. For this reason koi ponds recovering from winter may often show spikes of nitrite due to a reduced and recovering Nitrobacter population. This bacterium is also sensitive to light as described above for its nitrification partner and will also produce slime for adhesion to surfaces. Nitrosomonas and Nitrobacter really do come as an evolved package.
One interesting fact about Nitrosomonas and Nitrobacter is that unlike many other bacteria they cannot survive drying. One must therefore question as to whether any dried filter start bacterial preparations actually contain any living cells of these specialist bacteria.
So, we have focused on the two crucial bacteria in the koi pond, however, that is just like spending some time with one or two people from Japan and thinking you know everything about Asia. The microbial world comprises all sorts of microorgansims of different types, sizes, shapes and friendliness. Some shall we say have the benefit of koi in mind, others see koi as a source of nutrient for their own individual struggle for life. The best way to tip the balance in favour of the beneficial bacteria is to keep the pond water low in nutrients. Keep it clean and free from organic waste matter. Nitrosomonas and Nitrobacter don't need organic matter, the potential parasites and fish pathogens do. Don't overfeed your fish !
Copyright Koi Oriental Limited 2005
