What Noam Chomsky is to linguistics, Princeton University’s Bonnie Bassler is to bacterial conversations.
Anthropological science has made plain the myriad communication structures utilized by humans, as well as animals—albeit the latter at a less sophisticated level. Would it come as a surprise that bacteria can also communicate? Quorum sensing, one version of bacterial communication, has become an important tool for a deeper understanding of the living world.
Bassler is working to answer questions of bacteria’s importance for cosmetics. The phenomenon called quorum sensing was first found in only a few examples, most notably Vibrio harveyi, but it is now known to be much more extensive.
When a person is infected by harmful bacteria, the body sends a few antibodies to destroy the invaders. As strange as it seems, bacteria know this. No organism could have survived a billion years without some common sense. The bacteria don’t shout, “Here we are!”—they instead ask, “Anybody here?” and lay low. But as more and more bacteria show up, eventually a viable army is assembled and an attack commences. Your body is challenged to handle this invasion and you call in sick.
The questioning (“Anybody here?”) is done by a quorum-sensing molecule. Bacteria are pretty smart little guys, and have developed one language to talk to each other and a different language to talk between species. Bacterial cell communication involves the exchange of chemical signal molecules called autoinducers. Figure 1 shows the V. Harveyi quorum-sensing circuit.
The V. harveyi attracted attention due to its bioluminescence. These bacteria have some basic chemistry similar to the firefly, discussed in a previous column4. The reaction involves luciferin catalyzed by luciferase with ATP as a cofactor. In different organisms, the genes and proteins involved in bioluminescence are unrelated. It may be confusing that the substrates and enzymes, though chemically different, are all referred to as luciferin and luciferase. To avoid confusion they should each be identified with the appropriate organism.
Into the Ocean’s Depths
Bioluminescence is common in the marine environment. It is most prevalent at mid-ocean depths, where it may occur in more than 95% of the individual organisms, and the light emission of luminous organisms exerts a significant influence on marine ecology. Bioluminescence is rare in the terrestrial environment, though firefly displays are among the most spectacular demonstrations of this process.
Autoinducers regulate mRNA production for specific genes in response to population density. Operons are a set of adjacent structural genes in bacteria whose mRNA is synthesized in one piece. V. harveyi have autoinducers LuxN and LuxQ, both transduced with the aid of LuxO through the relay protein LuxU5.
Okay, the details of Lux proteins are complicated and well left to specialists. The important point is that it involves proteins that send and receive signals. The signals are a call to action through the triggering of gene synthesis. Through this process, a single bacterium amazingly becomes part of a large group acting in unison. The news coming from Princeton is that this is pervasive in the bacterial world, not a rare phenomenon, and that it promises great opportunities for medical science.
There’s extensive knowledge of communication within and between cells beyond bacteria and bioluminescent organisms. If there is extensive damage to a cell’s DNA or it needs more collagen, researchers and scientists understand the signaling. Modern treatment cosmetics use these cellular communications to make efficacious products—at least in theory.
The arachidonic cascade3 can be considered a form of communication, signalling irritation involving an acronym-rich region inhabited by IL-1, PGH2 and 15-HPETE. Since preventing or minimizing irritation is an essential goal of skin treatment, understanding the role of each component contributes a vital piece of the puzzle. Given the nature of a cascade, like a chain reaction setting off an atomic bomb, it is best to focus attention at the early components of the process.
The irritation cascade can be manipulated by inserting antagonists to select signaling molecules. Improvement can be measured in changes to mRNA and protein molecules. An efficacious treatment product could be defined as a signal modulator that encourages desired processes or interrupts an undesirable cascade.
Biofilms are perhaps the best known example of behavior by microorganisms that requires communication. A biofilm is held together by a matrix that protects the cells and facilitates communication through biochemical signals. Some biofilms contain water channels that help disperse signaling molecules. One benefit of this environment is increased resistance to detergents, as the dense matrix and outer layer of cells protects the interior of the community. It is also clear that communication in biofilms has importance for cosmetics.
Quorum sensing isn’t going to result in new products for personal care, at least in the near term. But it vividly remind us that communication is a series of connections that begin with cells signaling their mRNA to respond to a need, illustrating that chemical communication evolves into something even more complex, such as human language. It is by recognizing these connections that we understand the living world, in turn fueling creativity in the lab and the marketplace.
- www.pbs.org/wgbh/nova/sciencenow/3401/04.html (Accessed on Jun 4, 2007)
- ME Taga and BL Bassler, Chemical communication among bacteria, Proceedings of the National Academy of Sciences, 100 2, 14549–14554 (Nov 2003)
- S Herman, Arachidonic what?, GCI, 46 (Feb 2000)
- S Herman, Bright idea for cosmetics, GCI, 52 (Aug 2005)
- JA Freeman and BL Bassler, Sequence and function of LuxU: a two-component phosphorelay protein that regulates quorum sensing in Vibrio harveyi, J Bact, 899–906 (Feb 1999)