ROLE OF RHIZOBIA IN THE DEGRADATION OF AROMATIC SUBSTANCES

Rhizobia are confronted by a wide variety of organic substances in soi ls, including aromatic substances released by plants and those of man- made origin. They have developed mechanisms to degrade and mineralize aromatic substances through the activity of oxygenases encoded by the genes present in the chromosome and in plasmid(s). Genes involved in t he synthesis of some of the oxygenases have been identified and charac terized. Glucose and succinate caused repression of phenol utilization . Some of the enzymes involved in aromatic metabolism including the en zymes associated with the uptake of aromatic substances by the cells h ave been identified and characterized. Aromatic substances, in additio n to inducing catabolic genes, also induced the genes required to form active associations with the host plants (legumes).