Specific and global regulation of genes associated with the degradation of aromatic compounds in bacteria.

A large number of bacteria are able to degrade aromatic carbon sources employing different strategies. All these pathways are objects of regulatory control at the level of gene expression. This includes specific control in response to the availability of the respective substrate and in many cases global control responding to other available carbon sources or to the metabolic status of the cell. Here, the regulatory proteins responsible for gene regulation are reviewed in particular in correlation to other proteins with a similar primary structure. Most common is the appearance of regulators of the LysR family; other abundant regulator types are NtrC/XyIR-type proteins, AraC/XyIS-type proteins and the IcIR-type proteins. Almost all of the regulators exert their effects as activators of gene expression with the exception of the GntR-type proteins, which are exclusively described as repressors. Factors involved in individual cases of global regulatory mechanisms are enterobacterial CAP, (p)ppGpp, Crc protein, and direct modification of a specific regulator. However, for most pathways of aromatic compound degradation, the molecular mechanisms causing global regulation are not understood.