Aromatic compounds are the most abundant organic contaminants. However, utilizing these compounds is disruptive to most bacteria. Due to the genetic and metabolic flexibility of bacteria, some microorganisms can use organic contaminants as their sole carbon source. Several TCRSs have been identified to be involved in catabolizing aromatic compounds by inducing and activating the aromatic metabolism pathways. The TodST TCRS of Pseudomonas putida can be induced by different aromatic substrates such as toluene, xylene, benzene, and ethylbenzene. This TCRS modulates the expression of the tod genes, which encode enzymes for the catabolism of these aromatic compounds . The StySR TCRS identified in Pseudomonas sp. strain Y2 activates the expression of the styABCD genes in response to changes in styrene concentration in the environment . Another TCRS, BpdST, potentially controls biphenyl or polychlorobiphenyl degradation in Rhodococcus sp. .