tolerance, since microorganisms regain planktonic levels of suscep-
tibility once they leave the biofilm community [43]. Just as QS has
been associated with biofilm formation and some biofilm pheno-
types [44], there is now increasing evidence of different signals and
chemical stimuli being associated with biofilm dispersion [45]. One
example of a dispersant signal iscis-decanoic acid [46]. Other dis-
persion triggers include nitric oxide, altered nutrition, starvation,
and anthranilate (reviewed in [43, 45]). A number of mechanisms
have been proposed including a reduction of the second messenger,
30 ,5^0 -cyclic di-guanylate (c-di-GMP) [47] via phosphodiesterases.Fig. 4Comparison ofC. violaceumwithA. tumefaciensbiosensor activity. (a)
shows reaction ofA. tumefaciensA136 (pCF 218)(pCF 372) [29],A. tumefaciens
KYC55 (pJZ372)(pJZ384)(pJZ410) [30], andC. violaceumCVO26 [11] biosensors
(top streak) to C6-HSL production byC. violaceum31532 (bottom streak)ina
plate bioassay (Subheading3.2.1). (b) shows response of same three biosensor
strains to 3-o-C8-HSL production byA. tumefaciensstrain KYC6 [51]. However,
the 3-o-C8-HSL, produced byA. tumefaciens, can be detected indirectly by
C. violaceum12472 pigmentation inhibition (c, Subheading3.2.2), bioassay10 Starla G. Thornhill and Robert J.C. McLean