Cell sacrifices for the common good

Biologists from ETH Zurich, led by Professor Martin Ackermann and Wolf-Dietrich Hardt, collaborated with Michael Doebeli of British Columbia University in Vancouver (CN), describing the random molecular process in Cell division time allows some cells to self-destruct for the common good, thereby improving the condition of the surviving cells.

Survival tactics

Biologists study this bizarre biological concept using salmo-nella pathogenic bacteria. Salmonellae cause very unpleasant, even life-threatening diseases. Salmonella bacteria follow contaminated food into the intestinal tract and infect. Symptoms of vomiting and diarrhea can last for several days.

Usually, salmonellae are difficult to grow in the intestine because they cannot compete with other bacteria. However, this mechanism changes if salmonellae produces an inflammatory reaction, which is diarrhea, which suppresses other bacteria. This reaction occurs when salmonellae penetrates into the intestinal tissue. Once inside, salmonellae is destroyed by the immune system. This in turn creates a contradiction: salmonellae are overwhelmed by other bacteria in the gut, or destroyed when trying to eliminate their competitors.

Ackermann, Hardt and Doebeli said salmonellae found a surprising solution to the conflict. Inside the intestine, salmonellae form two groups. The first group invades tissue, creates inflammation, and dies. The second group waits for the gut until the intestinal microflora stops working, giving them the opportunity to attack. The second group can then freely flourish.

Random process and self-sacrifice

What determines a self-sacrificing salmonella cell, or will it wait and benefit from the sacrifice of other cells? The two groups have identical genes, so genetics do not play any role. Instead, the difference between the two groups is the result of random molecular processes during cell division. Cell components are randomly distributed between two daughter cells, each receiving a different amount. That imbalance can be extended and lead to different attributes of the siblings born asexually.

Salmonell (Salmonella typhimurium) in the intestine of mice.Green bacteria, rat tissue blue and red.(Photo; Bärbel Stecher / Wolf-Dietrich Hardt / ETH Zürich)

In recent years, the effects of random processes on individual cells have been recognized. Research by ETH Zurich scientists reveals a new biological explanation for this phenomenon. The two salmonella phenotypes share the work, with the result that they achieve what a single phenotype cannot accomplish. Basically, this situation differs from conventional explanations and conjectures that these individual phenotypes interact with each other.Self-sacrifice is quite common among pathogenic bacteria , for example, in bacteria that cause diarrhea after antibiotic treatment (clostridia), or pneumonia (streptococcus).

Important findings

Professor Ackerman said: 'Random processes can promote job division in many organisms' . Many bacteria produce toxins for the host body, but only secrete the environment in the host's body if the bacteria sacrifice themselves - it may be the only method to push the toxin out of the cell. . That's why all cells must decide: toxins and dead or without toxins.

He stressed that this study could not be done completely without the cooperation of three groups of experts: Professor Hardt's group specializes in salmonella infection; Doebeli's group includes mathematicians and theoretical biologists, and Professor Ackermann's team focuses on sound phenotype.

Refer:
Ackermann et al.Self-destructive cooperation mediated by phenotypic noise.Nature, 2008;454 (7207): 987 DOI: 10.1038 / nature07067