Light-emitting bacteria live in ocean water, but not only there: they also maintain symbiosis and live in insects, light organs in fish and other marine creatures. How and how does man use them?
Dror Bar-Nir
The genus Photorhabdus, from the family Enterobacteriaceae, includes several species of intestinal bacteria symbiotic with soil nematodes, but they do not reproduce in them. The worms infect insects during their life cycle when they enter the digestive system of the insect through the mouth. From the digestive tract, the worms enter the hemolymph system of the insect, then the bacteria are secreted, along with the worm eggs and the bacteria's toxins (which kill the insect within a day or two) and there, in the hemolymph system, they multiply.
The worms cannot complete their life cycle without the bacteria, because the latter inhibit the growth of other bacteria and provide the worm's offspring with food and essential growth factors (mainly by preventing the rotting of the insect and breaking it down into its components). P. luminescens bacteria glow after about 20 hours in the insect's lymphatic system, for about four hours. All the offspring of the worm come out of the insect when they are inhabited by bacteria.
When the bacteria enter human wounds, usually from soil that had insect carcasses, the wounds glow in the dark due to the bacteria growing there as well. Cultivating these bacteria in the wound is not problematic, and it even accelerates the healing of the wound due to the secretion of the antibiotic substances. The first reports we know of the glowing wounds are known from the American Civil War. It is not clear what biological advantage the warning confers on the bacteria and/or their hosts. Other terrestrial luminescent bacteria are found in the carcasses of various animals and in decaying plant matter.
Light organs in fish and squid
Anyone who has visited the underwater observatory in Eilat and entered the dark room has seen points of light running around in the aquariums: these "points of light" are nothing but fish and other marine creatures that have luminescent organs. In these luminescent organs are luminescent bacteria, usually of the species Vibrio (Photobacterium) fischeri and they emit the light.
How do the bacteria get to these organs of light? From these luminous pockets, towards the end of the day, attractants to the bacteria found in the sea water are secreted. The bacteria, which are present in the seawater during the day and do not illuminate, move according to the concentration cascade of the attracting substance, a process known as chemotaxis, and enter the organ of illumination, where they accumulate and multiply.
In 1970, Kenneth Nielson (Nealson) and John Hastings (Hastings) from Harvard University discovered that bacteria isolated from these luminescent organs do not glow regularly. At the beginning of the growth of the bacteria in the test tube (and the illuminant organ) they did not glow at all, and only when a sufficient amount of bacteria accumulated, they began to glow at once.
How do the bacteria "feel" that they are present in sufficient quantity? It turns out that a simple but sophisticated control system is at work here: each bacterium regularly secretes an autoinducer into the environment (autoinducer: in the case of the luminescent bacteria it is a derivative of the amino acid serine). As long as the bacteria are few, the self-stimulator will run in the environment. But in a closed space (such as in the illumination pocket or in a test tube) and when the number of bacteria increases - the concentration of the autoinducer in the solution increases until it penetrates the bacteria, connects to the inactive activator protein of the illumination system, activates it and this causes the activation of the illumination system.
The very activation of the illumination system also includes an excess secretion of the self-inductor, so that its concentration continues to rise and the illumination increases. This phenomenon is called crowd sensing or quorum sensing. Sensing the density by means of a self-inductor was indeed characterized for the first time in these luminous bacteria, but it was followed by more discoveries in many other bacteria, after which the bacteria were "announced", contrary to what was accepted until then, as multicellular organisms.
In the marine animals you can find real advantages for the combination of the host and the bacteria. For example, for the squid Euprymna scolopes, which is a nocturnal predator, the glowing organ "disguises" it from its potential prey below, and the bacteria gain a protected place and nutrients provided by the squid. Other marine luminescent bacteria swim freely and emit light independent of larger animals.
Uses of the lighting system
The light systems of Vibrio fischeri and other bacteria have been introduced into Escherichia coli, other bacteria and even yeast cells and higher eukaryotic organisms. These bacteria emit light continuously as long as there is oxygen and the raw materials of the lighting system. Using such engineered bacteria, it is possible to check the presence of pollutants in drinking water by comparing the degree of illumination in a clean solution compared to the tested solution. A decrease in the intensity of illumination is an indicator of contamination that affects the supply of oxygen and/or the vitality of the bacteria.
Another possibility, the opposite, will cause engineered bacteria, where the lighting system is adapted for this, to emit light due to the presence of toxins and pollutants in the water. The luminescent bacteria phenomenon raises interesting biological questions and also has practical use in research laboratories as well as in the detection of infections.
Dr. Dror Bar-Nir teaches microbiology and cell biology at the Open University. The article was published in the January issue of "Galileo" magazine
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Very interesting article. I don't think the idea of a glacier should be dismissed outright, but caution should be taken in growing a bacterium as a domesticated farm "animal", because it is a species that excretes toxins. If it is possible to implant the lighting system with bacteria that are safe to use, and make sure that no pathogenicity develops, the idea could be applicable. Just as people grow plants at home, it will be possible to convince them to grow bacteria (especially if they light up nicely). Another refinement of the idea would be to feed them food scraps and get rid of the organic waste that way. Furthermore, if it is possible to copy the system that prevents decay, they can be used to preserve corpses (for example, in the creation of stuffed animals).
Glacial, you still need to change their liquid because they produce waste materials and add nutrients and in the meantime when you do that you also dilute the concentration of bacteria...
Why not use it as a natural and cheap light source? I don't know what raw materials they require, but using them as a lighting source that does not require energy investment sounds like a fairly cheap solution.
Very interesting, but it's a shame that they managed to think of using bacteria as a simple indicator.
interesting.