Talk:CH391L/S12/Quorum Sensing

• "Razan Alnahhas 17:22, 30 March 2012 (EDT)":You wrote that QS has been used in synthetic biology as a biosensor for harmful bacteria, so could the QS system that monitors AHL levels be engineered to also respond to high concentrations of AHL by producing an antibiotic to kill the bacteria?
  • Adam Meyer 21:07, 31 March 2012 (EDT):Do you mean to put this QS-antibiotic system into the harmful bacteria or some other detector/killer strain? In the first case, the harmful bacteria would almost certainly just eliminate the system. In the second case, there is this [1].
  • Brian Renda 12:12, 2 April 2012 (EDT): Great find Adam! In my opinion the better approach to a response is to form some type of visibile indicator than a pathogenic shift in microbial populations is occurring, since having an automatic antibiotic response may just foster competition between the two species (not to the benefit of the host, I would imagine) and lead to resistance against that antibiotic. Also, different antibiotics tend to focus on different types of bacteria (with some more broad spectrum than others). What would be really cool is if you tied different AHLs or concentrations to different antibiotics, such that the response strain could initiate a logic driven tiered response to whatever threat it detected.

• Yi Kou 12:24, 1 April 2012 (EDT):I am kind of interested in whether cell membrane permeability of the inducer interferes with the result; the system seems to be easily interrupted by different kinetics of inducer in and out the cell membrane.
  • • Brian Renda 12:54, 2 April 2012 (EDT): The permeability of the inducer definitely is an important characteristic of a QS system. For AHLs, it looks like the length of the acyl-chain has a significant effect on the diffusibility of the signal across the cell membrane. One study in P. aeruginosa [2] found that an efflux pump is needed to effectively export acyl-chains longer than 12 carbons. As for whether they interfere with the systems they are a part of, generally these systems are for communicating within their species and I am not sure how much variability there is in terms of membrane permeability within a population. I would expect the tuning of each system to take into account the membrane kinetics of their autoinducers. In terms of interspecies QS cross talk (engineered or otherwise), it does seem like it would be important to take into account the relative rates of membrane transport of the autoinducers. Perhaps one would need to use a stronger promoter for the larger AHLs if one wanted equivalency to shorter AHLs in terms of signal production, but I haven't found literature to support that yet.

• Jeffrey E. Barrick 18:02, 1 April 2012 (EDT):In some cases, at least, it seems that quorum sensing is used for other purposes than for bacteria to "determine their densities". It may be used to determine how much flow is happening around a little clump of cells ("diffusion sensing" - kind of like testing the wind) [3]. The idea is that throwing out metabolically "cheap" compounds can let you determine whether making more costly things like extracellular siderophores or proteases is worth doing, or whether they would float away too quickly to give you a benefit.
  • • Brian Renda 14:01, 2 April 2012 (EDT):This is a very interesting hypothesis and I think the diffusion and density hypotheses could both be correct. In the paper, Redfield comments on how in a mixed population, the presence of non-cooperative cheaters haven't been reported and that the lack of individual benefit suggests the need for an alternative hypothesis. In a more recent publication however, found that pathogenic QS bacteria do indeed have non-cooperators and their presence decreases the virulence of the infection [4]. Thus individuals that do not cooperate could lead to a lower fitness of a mixed population (of cooperators and non-cooperators), selecting against non-cooperators).

• Jeffrey E. Barrick 18:09, 1 April 2012 (EDT):Not sure what's up with this sentence..."thus allowing only bacteria on the edge of light and dark to to do."
  • • Brian Renda 13:04, 2 April 2012 (EDT):Stutter-typing fixed.

References

1. Saeidi N, Wong CK, Lo TM, Nguyen HX, Ling H, Leong SS, Poh CL, and Chang MW. Engineering microbes to sense and eradicate Pseudomonas aeruginosa, a human pathogen. Mol Syst Biol. 2011 Aug 16;7:521. DOI:10.1038/msb.2011.55 |
2. Pearson JP, Van Delden C, and Iglewski BH. Active efflux and diffusion are involved in transport of Pseudomonas aeruginosa cell-to-cell signals. J Bacteriol. 1999 Feb;181(4):1203-10. DOI:10.1128/JB.181.4.1203-1210.1999 |
3. Redfield RJ. Is quorum sensing a side effect of diffusion sensing?. Trends Microbiol. 2002 Aug;10(8):365-70. DOI:10.1016/s0966-842x(02)02400-9 |
4. Rumbaugh KP, Diggle SP, Watters CM, Ross-Gillespie A, Griffin AS, and West SA. Quorum sensing and the social evolution of bacterial virulence. Curr Biol. 2009 Feb 24;19(4):341-5. DOI:10.1016/j.cub.2009.01.050 |