Bacterial Armies Emit Molecular War Cries
The current issue of Discover magazine (September 2010) has an interesting article ("Field Notes" by Dava Sobel, p. 32) about a phenomenon that provides a possible reason for recent trouble I experienced in my fish room.
About two months ago I was building a new tank rank and accidentally knocked out the power to a pump running air to filters in the tanks to an existing rack. By the time I noticed that the pump was disconnected, the fish were showing a great deal of stress. They were huddled at the bank of the tank, shy and breathing rapidly. I plugged the pump back in. Within a few hours all but a handful of tanks seem to have recovered. But the three or four tanks that stayed down got worse the next day.
The sick tanks grew progressively worse, with the guppies refusing to eat and they were motionless at the back of the tank. They began to die. I unsuccessfully treated them with various medications. I began to cull the tanks and bleach them.
All the affected tanks had a strain of Full Red guppies in them. Some of them had outcross strains in them. The outcross strains got sick as well. Eventually by culling the really sick tanks and babying the tanks that showed milder health problems, I was able to get my guppies back on their feet and I was able to save the Full Red strain.
Right now the Full Reds are my indicator strain. If something goes wrong with the quality of water in my tanks, they will be the first strain to show signs of stress. I am already taking steps to outcross them to a stronger strain.
The incident left me wondering what the disease was...and how the Full Reds were able to infect the other guppies in the same tank. I knew that disease organisms are always in my tanks...but what is the trigger that causes them to expand so rapidly as to overwhelm the immune systems of healthy guppies? I had guppies sick and dying within a day of the sudden deterioration of my water conditions. The ammonia might have spiked when the air system shut down, which would explain why the guppies were stressed. But how were the pathogens able to take advantage of this so quickly?
I know that bacteria can double their population in as little as 20 minutes, although some species take much longer. This is why it is a good idea to do a water change on one day and clean the filters the next. The nitrifying bacteria present in the water can quickly and naturally double and redouble their population density in the water. But what about bad bacteria? How do they know that their host (the guppy) is weak and ripe for takeover? Why is a sick guppy in a tank such a dangerous presence in a group of healthy guppies?
Here is the headline from the Discover magazine article: "Bacterial armies emit molecular war cries to stir others of their kind to action."
Apparently certain strains of bacteria produce molecules that are released into the environment are sensed by their own kind using special receptors. The molecules act as signals. When the number of signals is "loud" enough, the bacteria beginning acting as a group, overwhelming the defense system of the host. The guppy overwhelmed with pathogenic bacteria becomes an incubator, releasing more bacteria into the water. Since the life span of most bacteria is only six hours, and newly sick guppies acting as breeding grounds for more bacteria, the bacterial army overruns the entire tank. So quorum sensing is used by bacteria to signal the weakened state of the guppy so that they can mount a successful attack.
The theory is that a genetically weak Full Red guppy's immune system was compromised by the sudden deterioration of the water quality in the tank, giving the bacteria a foothold. The sick guppy acted as a beachhead in the tank for a sudden increase in the numbers of bacteria. Using quorum sensing, the bacteria increased their numbers exponentially. The immune systems of healthy guppies were overwhelmed.
The ability of bacteria to sense their own population density is called "quorum sensing." There is a good article about it on wikipeda (http://en.wikipedia.org/wiki/Quorum_sensing).
Apparently plants can listen to the chatter of a group of bacteria and avoid putting down its roots where bacteria are present in large numbers. Quorum sensing is also found in animals.
I am not sure if it was indeed bacteria that affected my tanks. It could have been another parasite using quorum sensing. However there is a known species of bacteria affecting guppies that uses quorum sensing. It is called Pseudomonas spp. (See the wiki article on Pseudomonas: http://www.guppydesigner.com/index.php/guppy-disease-wiki/120-common-diseases-of-the-guppy/645-pseudomonas-spp.) It is a very common pathogenic bacterium and is present at all times in the tank. It may not be what affected by Full Reds since none of the usual signs of Pseudomonas were present, but the rapidly of the disease outbreak makes me think that it was some kind of bacterial disease using quorum sensing.
Comments
as i recall there is a rule of thumb that most bacterials need only 20 minutes to double population - at normal temperature. ( Nitrobacteria like those in the filter take much longer - some even days. The good ones are slow, sadly ). Mathematically, you can expect to get 2^72 bacterials for each bacteria starting to divide in 24 hours. Pandemic or what ?
Dont know if it needs quorum sensing - ever had Ichthyophthiriu s ? That little bastard was permanently in the tanks but the fish were stong enough not to show any signs. Then a weak one submits to it, showing very much white spots. Days later the tomonts attack the other fish in large numbers so they also get ill.
Maybe its just about the numbers of parasites and bacterials that the fish have to fend off - once these are too much in numbers ( because they multiplied well on one ill fish ) they win.
Any taxing of the fishes immune system can cause an out break of the ever present trouble makers, whether from environmental causes or a new strain of bacteria. We can turn the air and filter off in any of our overpopulated tanks and presto an outbreak occurs no matter how pristine we thought the tank and fish were.
Philip
Your description of yourself as a redneck fish guy too simple to understand the complexities of science has a name. It is called a canard.
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