TAU

TAU Trends in Research

June 1999

How Smart are Bacteria?

A colony of Paenibacillus vortex
Paenibacillus vortex
In the ongoing arms race between scientists and bacteria, bacteria still have the upper hand. For example, they can develop antibiotic resistance at a higher rate than scientists can develop new drugs. To "outsmart" bacteria and other microorganisms, we first have to appreciate how "smart" they really are. Although bacteria were long viewed as simple, largely non-interacting and passive unicellular entities, TAU Prof. Eshel Ben-Jacob (Faculty of Exact Sciences) and his colleagues (in particular, Prof. David Gutnick, Faculty of Life Sciences) have shown that they are actually sentient, interactive organisms, capable of displaying and benefiting from sophisticated collective activity.

Indeed, bacteria possess an unexpectedly broad repertoire of chemical and physical signaling mechanisms which allow them to develop complex spatio-temporal patterns in response to adverse growth conditions, including the effect of exposure to antibiotics. Prof. Ben-Jacob's pioneering work was recently highlighted in a six page, full color photo-essay in Scientific American (October 1998), for the patterns formed by evolving and responding bacterial colonies are as visually beautiful as they are scientifically informative. For example, the preferential uptake of food dyes by different parts of a colony of Bacillus subtilis elegantly illustrates the colony's complex structure in soft agar. Under the stresses induced by harder agar, the bacteria mutate to a longer, swifter moving form that gives rise to assymetric curls. The bacteria meet the challenge of still harder agar, by congregating into tight round rotating circular structures (dots at the end of the branches) which, like circular saws, cut their way through the recalcitrant medium.

A colony of Paenibacillus dendritiformis displays complex spatial patterns in response to stress, here a lack of nutn'ents.
Paenibacillus dendritiformis
Nor does bacterial communication and collaboration stop there. Escherichia coli, and Salmonella typhimurium use attractive chemicals (chemotaxis) to call their peers for aid in detoxificating their environment. Bacillus subtilis, Paenibacillus dendritiformis and Serratia marcescnes cooperatively produce lubrication fluid in which they swim. P. dendritiformis use repulsive chemotactic signaling to report their peers about unfavorable locations. Bacillus circulans and Paenibacillus vortex utilize cell-to-cell physical interactions to respond to external signals. Thus the bacteria can communicate and organize their colonies into multicellular aggregates with new properties. Such aggregates can be viewed as a community or, to a degree, even as a multicellular organism.

In general, the TAU findings underline how bacterial communication and cooperation promote bacterial survival. Of particular interest to us humans, bacteria in organized colonies are generally more resistant to antibiotics than the same bacteria in isolated suspensions. Ben-Jacob and his TAU colleagues have thus proposed a novel strategy to weaken bacteria by impairing their cooperative capabilities, rather than directly attacking individual bacteria.

A colony of Paenibacillus dendritiformis adopts different spapial patterns in response to the stress induced by antibiotics in its medium.
Paenibacillus dendritiformis
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TAU Trends in Research Last modified: June 27, 1999