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. http://doi.org/10.3389/fmicb.2015.01468
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