File:GtaR quorum-sensing system of RcGTAs in R. capsulatus in low cell density (A) and in high cell density (B).jpg

The system consists of GtaI (square), responsible for synthesising C14 and C16-acyl-HSLs (diamonds), and GtaR (circle), which represses the expression of the gtaRI operon. The acyl-HSLs act to bind to GtaR to prevent it from repressing the operon, and they also stimulate RcGTA production. In low cell density (A), there isn’t a sufficient level of acyl-HSLs to stimulate RcGTA production and repress GtaR, and so the gtaRI operon is inhibited leading to low levels of GtaI and GtaR, leading to only a small amount of acyl-HSL production by the bacterium. In high cell density (B), the small amount of acyl-HSLs made by each bacterium accumulates to a high concentration of acyl-HSLs, sufficient enough to repress GtaR. This leads to high levels of GtaI and GtaR, letting the organism produce a high amount of acyl-HSLs causing the concentration of acyl-HSLs to increase more, stimulating RcGTA production [9].