Bacterial Parcel Service Discovered
Bacteria send letters and parcels to one another. Some of them are love letters, some of them are letter bombs. This amazing packaged system of communication, separate from the mere sending of diffusible chemicals, was described in Nature1 with the title, “Microbiology: Bacterial speech bubbles.” Stephen C. Winans described what is known about bacterial communication:
Many bacteria socialize using diffusible signals. But some of these messages are poorly soluble, so how do they move between bacteria? It seems they can be wrapped up in membrane packages instead. (Emphasis added in all quotes.)
He said that two research studies in the same issue of Nature, one on how bacteria talk to their friends, and another on how they attack their enemies, met in an “unexpected convergence.” One type of parcel, for instance, is “released in bubble-like ‘vesicles’ that also contain antibacterial agents and probably toxins aimed at host tissue cells as well.”
Through this form of packaged communication, a community of microbes engages in “quorum sensing” to detect whether it is alone or surrounded by its own kind or other species. Some genes only turn on when there is a quorum reached. One of these Winans mentioned is bioluminescence – turning on the lights.
The parcels can contain chemicals, proteins, toxins and other molecules in a lipid envelope. The packaging permits delivery of proteins and chemicals that otherwise might be insoluble. Some bacteria have three separate kinds of signal parcels. The packages form lipid bubbles around them as they emerge from the bacterial membrane. These can merge with a friendly neighbor or, depending on the need of the moment, deliver a toxin to an enemy – a package bomb on the scale of bacteria.
To work, the system requires multiple parts: the contents, the packaging, the delivery method, and the response to received parcels. Winans did not speculate on how this system might have evolved, other than to say, “Various groups of bacteria use diffusible chemicals to signal to their own kind, and this method of communication seems to have evolved independently several times.”
1Stephen C. Winans, “Microbiology: Bacterial speech bubbles,” Nature, 437, 330 (15 September 2005) | doi: 10.1038/437330a.
This is an interesting phenomenon that deserves further investigation by science and medicine. Since humans are sometimes targets of the toxins delivered by these vesicles, interrupting or targeting the bacterial UPS might lead to cures for disease. Was this system originally a beneficial delivery service that got co-opted for harm? It seems unlikely that a mindless bacterium could come up with such a complex system of interacting parts once, let alone several times, by an evolutionary process of trial and error.
It’s a stunning thought to envision lowly bacteria with a social life and a coordinated, effective package delivery system. Rather than assuming it arose spontaneously as an opportunistic mechanism for serving the bacterial “self,” perhaps it is best to look at this phenomenon from the vantage point of systems biology (06/15/2005, 06/20/2005). What role might it play in the bigger picture?
“Attacking and killing enemies” is a metaphor with metaphysical baggage (see “Metaphors Bewitch You,” 07/04/2003). Another way of thinking about the “parcel bombs” might be with the give-and-take metaphor of action/reaction, feedback/feedforward, agonist/antagonist – i.e., a sensory mechanism of messages and responses that keeps a larger dynamic system in balance (homeostasis). Such balancing interactions take place at many levels in biology, from interactions between molecules and proteins within the cell all the way up to interactions between higher organisms. If too much of one side causes pain and suffering, that does not preclude the possibility that, in balance, the operation had a beneficial role.
An evolutionist would undoubtedly study this bacterial UPS as a byproduct of selfish genes at work trying to ensure their own survival. A design theorist could continue investigating it with just as much curiosity and enthusiasm, but without the tunnel vision of Darwinian self-centeredness. He or she would ask, in the big picture, what role does it play, and has that role gone awry?