So it may come as a surprise that many bacteria are actually quite good at this! And new research suggests that we might be able to disrupt that “group communication” in ways that could make agriculture safer without the use of traditional pesticides.
Bacteria, it turns out, emit signaling molecules to “convince” neighboring bacteria to express a gene, and when a sufficient density of these molecules is detected, a positive feedback loop kicks in that gets the laggards on board. This phenomenon, known as quorum sensing1, was first observed in bioluminescent bacteria 40 years ago2, but its importance and applications are still being explored.
For example, once the role of quorum sensing in causing virulent behavior (the ability to cause disease) to be expressed was understood3,4, it raised the very exciting possibility that we might be able to interrupt that communication and thus keep the bacteria dormant rather than virulent (sometimes called “quorum quenching”).5
While walking through the National Science Foundation lobby in Arlington, Virginia the other day, I happened to notice a poster that described an attempt to do exactly that as a sustainable agriculture strategy.6,7
Some bacterial species are agricultural pests, and currently they are controlled with copper derivatives and antibiotics8. Both the copper derivatives and the antibiotics are environmental contaminants, and the use of antibiotics can lead to the development of antibiotic-resistant bacteria.
The basic idea of the research presented on the poster is that use of a synthetic compound (for instance, a halogenated furanone) might allow us to prevent the bacteria from sensing the signaling compounds being emitted by their neighbors.6,7,9 This, in turn, would keep them from becoming virulent, without having to resort to using harsh chemicals to completely wipe out the bacteria!
The technique also provides another option to protect crops as bacteria become increasingly resistant to existing controls. Finally, since quorum sensing has also been documented in fungi, it may be a viable strategy to combat fungal agricultural pests as well.10
This isn’t necessarily a slam dunk for conservation; many of the anti-quorum sensing compounds being studied are potentially toxic11 (although they can also exhibit anti-carcinogenic behavior)12. As such, further study is needed to determine the toxicity, persistence, efficacy, and side effects of these compounds is needed.13
There are also cases of bacteria (e.g. E. coli) directly sensing stress hormones released by their host to express virulence, meaning that shutting down signaling between bacteria alone may not be enough to control virulence in all cases.
Despite the potential risks and challenges, it seems likely that some compounds will be found that at least have less environmental impact than comparable existing pesticides (which have well-documented problems with toxicity and persistence). Simply the fact that we have an entirely new pathway to explore to disrupt these diseases is exciting enough. Now if only we could come up with quorum facilitating compounds that I could spray in the air the next time I find myself stuck in an endless debate…