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Insect transmitted diseases could be prevented by symbiotic bacteria
Symbiosis is tight, mutualistic (cooperative), relationship between two or more biological species. Most symbiotic relationships last for a life time. Lichen is typical examples of symbiotic organism. It looks like a single species, but is actually composed of fungus and algae that are living in a tight relationship. Algae provide food through photosynthesis, and fungus provides water and mineral material from the ground. This community is obligatory; neither one species would survive without the other one. When symbiosis is facultative, two organisms could live separately, but they prefer symbiosis because their well being will be improved after they join forces. Humans form symbiotic relationships also. Intestinal bacteria are important part of immune system serving as significant defense line against pathogenic microorganisms; other gut bacteria could produce certain vitamins or accelerate digestion…. Symbiotic relationships are old probably as nature itself. Today, using the advantages of modern technology, man is able to directly affect and improve different symbiotic organisms to meet his own needs.

Recently published story describes a man who injured himself while cutting the old crab apple tree (branch impaled between his fingers). Although he properly cleaned the wound, it became infected and painful. He visited a doctor who sampled a liquid from the formed cyst for the bacteriological analysis. That analysis couldn’t determine the strain of infected agent. There were similarities with the already known bacteria but perfect match was missing. Bacterial species living in the gut of the insects, named Sodalis, proved to be its closest relative. Sodalis was discovered in 1999 as simbiont in 17 different insect species (most significant are tsetse fly, weevils, bird lice…). Newly discovered bacterial strain was named HS (shorter version of Human Sodalis). When genomes of Sodalis species living in tsetse fly and grain weevils were compared with the genome of the newly discovered species, it was obvious they are related but some interesting difference were noted. Almost half of the genes of the two well known bacterial species were lost or inactivated compared to genome of the HS species. HS provided new insight in the way symbiotic relationships between insects and bacterial species arise. Pathogenic bacteria species could be collected from the environment and domesticated inside certain insect species. Initially it was believed that spreading of the symbiotic bacteria from one insect species to another is possible via mites and other insects that contain symbiotic bacteria in their guts. Observed changes in the genome of the investigated bacteria offered another theory. Plants and animals derived pathogenic bacteria could be easily collected by the insects from their environment. Their further evolution from pathogenic to symbiotic partner is unique and insect specific. Both species need to find a way to adjust to a newly created community. Bacteria will lose virulent genes and this change will guarantee successful spreading of the future bacteria generation to the insect's offspring (instead from one species to another). They will be well fed thanks to food provided by the insect. In return, bacteria produce vitamin K and amino acids that are beneficial for insect nutrition. Also, bacteria could produce toxins to prevent parasitic wasp to lay eggs or fungi to colonize the insect. Loss of large number of bacterial genes resulted from the change in the lifestyle - genes essential for the classic environmental survival became unimportant. These modifications are beneficial for both species.

Close genetic link between Sodalis species and newly discovered HS species inspired scientists to design new solution against insect transmitted diseases. Tsetse fly is carrying a protozoan, well known inducer of the sleeping sickness. Sodalis species live inside the tsetse fly and can’t be grown in the laboratory, but HS species can. HS species could be genetically modified to fit tsetse fly and at the same time be able to induce killing of the protozoan after they are brought back in tsetse fly. By introducing modified bacteria back to the tsetse fly, insect will still be “equipped” with its valuable simbiont and disease transmission will be prevented through protozoan elimination. Same is planned for aphids that transmit viruses responsible for crop sickness (soybeans, alfalfa, peanuts…).

If this method proves to be successful, completely new chapter in treating insect transmitted diseases will open.
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Symbiotic association reminds me the story “power in unity “which I heard in my childhood.
Our elders use to demonstrate the moral of story "power of unity" by giving us single stick and then use to ask us to break it, which was easy. Later, we tried to break bunch/set of same sticks at a time and then could understood what is the meaning of power in unity and ultimately the moral of story.
I think, bacteria might have heard this story somewhere during their evolution! This is so because today many bacteria are symbiotically associated not only with other microorganisms but also with plants, animals and even humans. In our intestine, many bacteria survive and also helps us in digesting various food. They provid required acidic condition in gut and other enzymes for digestive support etc.
The best example is Genus Lactobacillus. Many bacteria produce vitamins in our body which are vital for our growth and metabolism. These vitamins include Vitamin B2, B12 etc.
The presence of many bacteria in plants helps in fixing atmospheric nitrogen and thus plants can readily utilize atmospheric nitrogen in the form of nitrate. These are especially found in leguminous plants having microorganism with nif gene which expresses and convert nitrogen in to readily utilizable form “nitrate” for plants. In turn bacteria get host and other molecules for their survival within the host.
This is nothing but give and take, the power of symbiotic association which helps such bacteria to become more capable of survival in extreme conditions and in developing resistant to unfavorable conditions as compared to one who live isolated.
Whatever is the life form, whether microorganisms, animals or humans but the moral of story is same for all of them- Symbiosis/ Unity is power!
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What an informative article. Thanks for sharing.
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