Social behaviour

Politics. The one topic that will get that random stranger’s tongue wagging – wherever it may be. The tea shop. The saloon. The bus stand. And the discussion very often revolves around one theme – corruption. We all lambast the system that feeds us. People don’t pay taxes, they steal, etc. What if I were to tell you that such misdemeanors of social behavior are not restricted to the human species alone? Bacteria also have social behavior. They cooperate with each other. They work together to build a community. But not all of them live in harmony. Some cheat the system. There are counter measures in place to sideline such cheaters. Contrary to traditional thought, bacteria also have such societies and exhibit “human tendencies” of social behavior. A recent paper published in Frontiers of Microbiology suggests just that. The group provides experimental proof that bacteria exhibit such traits and show that such cooperative behavior is essential to some of their functions.
To explain the concept of social cooperation, I would like to draw upon an easy-to-understand parallel in human society. Take into consideration a hypothetical community with a road connecting the 10 families that live there. All of the families donate a certain amount of money to a common fund that is used for the upkeep of the road. Now if one of the families decides to default on their payment (tax), the other 9 will be none the wiser. But once we have a number of people failing to pay up, the road falls into neglect. This can be compared to a biofilm of bacteria where harmonious individuals cooperate with their neighbors, ideally, to establish infection, grow, derive nutrition as well as protect the community from antibiotics. The “tax” paid is in the form of extracellular polymeric substances (EPS) which helps in resilience against antibiotics, adherence to a substratum as well as in protecting the “taxpayers” from the defaulters.
The paper shows that when producers of EPS are grown along with non-producers, the biofilm is weakened and establishment of infection is either unsuccessful or hampered. An important implication for this finding is in medicine. The field of medicine is plagued with the issue of biofilms. Their growth has proved to be harmful to health and also, difficult to disrupt. Biofilm lifestyle of bacteria can cause cystic fibrosis and many dental problems as well. Biofilms also develop on stents and other surgical implants, disturbing their functions. Methods to prevent or cure these growths have proved either ineffective or impractical. However, if we take into account the findings of this paper, biofilms can be disrupted by individuals of their kind. These cells would have to be engineered to act as cheaters of the biofilm community and would be introduced to the infection. According to their experiments, such a method will weaken the biofilm and make it more susceptible to removal through the deployment of antibiotics at the site of infection.
In nature, bacteria prefer living in biofilms (communities) as opposed to a planktonic (free-living) state. These biofilms need to be protected from intrusion much like our homes need to be prevented from being burnt to the floor. We have in place barriers such as walls, gates, etc. Biofilms employ an EPS component called cellulose as their wall against intrusion by cells that do not produce EPS. In this way, they are able to maintain the integrity of their community and the tenacity of the biofilm. Such policing mechanisms to curb the development of cheaters can also be seen in higher animals such as mammals – between cells in an individual as well as between individuals in a community.
It remains to be seen what more can be deduced from these findings. What we do know now is that social behavior is not an advanced characteristic we acquired over the course of evolution. We also know that this cooperative behavior in bacteria helps in their pathogenesis and that tweaking their genetic code can help us fight this menace to the medical fraternity. Let us hope that infiltrating the bacterial social order will help us win the arms race between pathogenic bacteria and humans.
Vishvak Kannan

Reference: Srinandan, C. S., Elango, M., Gnanadhas, D. P., Chakravortty, D., Chakravarthy, S., Elango, M., … Chakravortty, D. (2015). Infiltration of Matrix-Non-producers Weakens the Salmonella Biofilm and Impairs Its Antimicrobial Tolerance and Pathogenicity. Frontiers in Microbiology, 6.

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